Seismic wave measuring method, aging rate measuring method, program and data processing device

Abstract

To enable accurate correction of internal time. [Solution] The data processing device 1 has a temperature determination unit 181 that determines the seabed temperature at a position on the seabed where a measuring device is installed that creates measurement data for seismic waves associated with the internal time at which the seismic waves were detected in response to the vibration waves being emitted from the seismic source; a low temperature reduction unit 182 that changes the temperature of an oscillator 41 built into the measuring device located in a location other than seawater to the seabed temperature; a rate measurement unit 183 that measures an aging rate, which is the rate of change over time in the frequency of the oscillator 41, when the temperature of the oscillator 41 built into the measuring device located in a location other than seawater has reached the determined seabed temperature; and a correction unit 188 that corrects the internal time associated with the measurement data based on the aging rate after the measuring device installed on the seabed creates measurement data.

Description

[Technical field]

[0001] The present invention relates to a method for measuring seismic waves, a method for measuring aging rate, and a program. and Data Processing Equipment Place Regarding. [Background technology]

[0002] Since the oscillation frequency of a crystal oscillator changes over time, techniques for adjusting the oscillation frequency are known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-245978 A Summary of the Invention [Problem to be solved by the invention]

[0004] Measuring devices installed on the seafloor that detect seismic waves in response to seismic waves emitted from a seismic source measure the time at which the seismic waves are detected using a built-in oscillator. However, the frequency of the oscillator changes over time due to aging characteristics, so a difference (time drift) occurs between the internal time measured by the oscillator built into the measuring device and absolute time. As a result, the accuracy of analysis of the subseafloor geological structure based on seismic waves decreases.

[0005] One possible method to prevent the analysis accuracy from decreasing is to measure the aging rate, which is the rate at which the oscillator's frequency changes over time, in advance in the air and then correct the internal time. However, the aging rate in the air is different from the aging rate on the ocean floor. This means that even if the aging rate in the air is measured, the internal time cannot be accurately corrected.

[0006] The present invention has been made in consideration of these points, and has an object to enable accurate correction of the internal time. [Means for solving the problem]

[0007] A first aspect of the seismic wave measurement method of the present invention includes a temperature determination step of determining the seabed temperature at a position on the seabed where a measurement device is installed that creates measurement data for seismic waves associated with an internal time at which a seismic wave was detected in response to a vibration wave being emitted from a seismic source; a cooling step of setting the temperature of an oscillator built into the measurement device located in a location other than seawater to the seabed temperature; a rate measurement step of measuring an aging rate, which is the rate of change in frequency of the oscillator over time, when the temperature of the oscillator built into the measurement device located in a location other than seawater has reached the determined seabed temperature; and a correction step of correcting the internal time associated with the measurement data based on the aging rate after the measurement device installed on the seabed has created the measurement data.

[0008] In the seismic wave measurement method, the measurement device located in a location other than seawater may have a temperature change device that changes the temperature of the oscillator, and in the low-temperature reduction step, the temperature of the oscillator may be set to the seabed temperature by controlling the temperature change device so as to change the temperature of the oscillator.

[0009] The seismic wave measurement method may further include a step of releasing the control over the temperature change device after performing the low-temperature step and the rate measurement step, and an installation step of installing the measurement device on the seabed after releasing the control over the temperature change device.

[0010] The seismic wave measurement method may further include an installation step of installing the measurement apparatus on the seabed while maintaining the control over the temperature change device after performing the low temperature step and the rate measurement step.

[0011] The seismic wave measurement method may further include, before the correction step, a time difference determination step of determining the time difference between absolute time and the internal time of the measurement device, and an installation step of installing the measurement device on the seabed, and in the correction step, the internal time associated with the measurement data may be corrected based on the time difference and the aging rate.

[0012] In the correction step, an amount of time drift in the elapsed time from a first internal time, which is the internal time at the time when the time difference is determined, to a second internal time associated with the measurement data, may be determined based on the aging rate, and the second internal time may be corrected based on the determined amount of time drift.

[0013] An aging rate measurement method of a second aspect of the present invention includes a temperature determination step executed by a computer to determine the seabed temperature at a position on the seabed where a measuring device is installed that creates measurement data for seismic waves associated with the internal time at which the seismic waves were detected in response to the vibration waves being emitted from a seismic source, a cooling step to set the temperature of an oscillator built into the measuring device located in a location other than seawater to the seabed temperature, and a rate measurement step to measure an aging rate, which is the rate of change in frequency of the oscillator over time, when the temperature of the oscillator built into the measuring device located in a location other than seawater has reached the determined seabed temperature.

[0014] A third aspect of the program of the present invention causes a processor of an information processing device to function as a temperature determination unit that determines the seabed temperature at a position on the seabed where a measuring device is installed, which creates measurement data of seismic waves associated with the internal time at which the seismic waves were detected in response to the vibration waves being emitted from a seismic source; a low-temperature reduction unit that changes the temperature of an oscillator built into the measuring device located in a location other than seawater to the seabed temperature; and a rate measurement unit that measures an aging rate, which is the rate of change in the frequency of the oscillator over time, when the temperature of the oscillator built into the measuring device located in a location other than seawater has reached the determined seabed temperature.

[0015] A data processing device of a fourth aspect of the present invention has a temperature determination unit that determines the seabed temperature of a position on the seabed where a measuring device is installed that creates measurement data for seismic waves associated with the internal time at which the seismic waves were detected in response to the emission of seismic waves from a seismic source; a low-temperature reduction unit that changes the temperature of an oscillator built into the measuring device located in a location other than seawater to the seabed temperature; a rate measurement unit that measures an aging rate, which is the rate of change in frequency of the oscillator over time, when the temperature of the oscillator built into the measuring device located in a location other than seawater has reached the determined seabed temperature; and a correction unit that corrects the internal time associated with the measurement data based on the aging rate after the measuring device installed on the seabed creates the measurement data.

[0016] The measurement device of the fifth aspect of the present invention includes an oscillator used for measuring the internal time, a temperature change device for changing the temperature of the oscillator, a processor for controlling the temperature change device so that the temperature change device changes the temperature of the oscillator, and a seismic wave measurement unit for creating measurement data of the seismic wave associated with the internal time at which the seismic wave was detected in response to the seismic wave being emitted from a seismic source. The temperature change device may be made of a material that absorbs heat on one surface and releases the absorbed heat on the other surface. Effect of the Invention

[0017] According to the present invention, it is possible to accurately correct the internal time. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an overview of a seismic wave measuring system S. [Diagram 2] FIG. 1 is a diagram showing an example of a temperature change in a conventional oscillator. [Diagram 3] 1 is a diagram showing the relationship between an external device 1, a measuring device 4, and a temperature change device 5 according to a first embodiment. [Figure 4]4 is a flowchart showing the flow of a measurement method according to the first embodiment. [Diagram 5] 5 is a schematic diagram showing a change in temperature of an oscillator while performing the measurement method according to the first embodiment. FIG. [Figure 6] FIG. 13 is a diagram for explaining a procedure for starting up a plurality of measuring devices 4. [Figure 7] 13 is a diagram showing an example of a management table showing the state of each measuring device 4. FIG. [Figure 8] 1 is a diagram showing a configuration of a data processing device 1 according to a first embodiment. [Figure 9] 1 is a graph showing the amount of time drift over time. [Figure 10] FIG. 11 is a diagram showing an example of a flowchart illustrating internal time correction processing according to the embodiment. [Figure 11] 1 is a diagram showing a configuration of a measurement device 4 according to a first embodiment. [Figure 12] 10 is a flowchart showing the flow of a measurement method according to a second embodiment. [Figure 13] FIG. 11 is a schematic diagram showing a change in temperature of an oscillator while a measurement method according to a second embodiment is performed. [Figure 14] FIG. 4 is a diagram showing the configuration of a measurement device 4 according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] First Embodiment [Overview of measurement system S] Fig. 1 is a diagram showing an overview of a measurement system S. The measurement system S is a marine geophysical exploration system for analyzing the sub-seafloor geological structure. In the measurement system S, seismic waves are generated from a seismic source 2 such as an air gun or a sparker, and a data processing device 1 analyzes the sub-seafloor geological structure using the results of measurements of the seismic waves by a number of measuring devices 4 installed on the seabed.

[0020] The measurement system S includes a data processing device 1, a seismic source 2, an optical communication device 3, and a plurality of measurement devices 4. The data processing device 1, the seismic source 2, and the optical communication device 3 are mounted on a ship 100 capable of moving on the ocean. The plurality of measurement devices 4 are installed on the seabed at intervals of at least a predetermined distance.

[0021] The data processing device 1 is, for example, a computer, and acquires measurement data indicating the vibration state of the seabed observed by multiple measuring devices 4 at the timing when seismic waves are emitted, and analyzes the acquired measurement data. That is, the data processing device 1 analyzes the measurement data of seismic waves detected by the measuring devices 4 in response to seismic waves emitted from a seismic source 2 toward the seabed from a ship sailing on the sea during a measurement period. As shown in FIG. 1(a), the data processing device 1 controls the multiple measuring devices 4 by transmitting and receiving acoustic signals, and receives measurement data generated by the multiple measuring devices 4. The data processing device 1 also acquires information indicating absolute time from, for example, a PTP network or a Global Positioning System (GPS).

[0022] The seismic source 2 generates seismic waves during a measurement period. The seismic source 2 generates seismic waves, for example, under the control of the data processing device 1, but may generate seismic waves under the control of a control device different from the data processing device 1 (for example, a computer installed on a ship different from the ship 100).

[0023] The optical communication device 3 acquires measurement data from the measurement device 4 by optically communicating with at least one measurement device 4 under the control of the data processing device 1. The optical communication device 3 emits a first optical signal to the measurement device 4 in the sea, and receives a second optical signal transmitted by the measurement device 4 that has received the first optical signal. The optical communication device 3 is connected to the data processing device 1 by a cable C, and, under the control of the data processing device 1, performs optical communication with the measurement device 4 after diving to a position where optical communication with the measurement device 4 can be performed. The optical communication device 3 moves sequentially to the vicinity of multiple measurement devices 4, and acquires measurement data from the multiple measurement devices 4 sequentially. Note that the measurement system S may have multiple optical communication devices 3, and the multiple optical communication devices 3 may acquire measurement data from the multiple measurement devices 4.

[0024] The measuring device 4 creates measurement data of seismic waves associated with the internal time at which the seismic waves were detected in response to the seismic waves being emitted from the seismic source 2. The measurement data indicates the amount of vibration of the measuring device 4 caused by the seismic waves. The measurement data is data indicating the magnitude of vibration detected by a sensor possessed by the measuring device 4, and is, for example, data including a measurement value generated by sampling a signal output by the sensor every millisecond. The measurement data is associated with the internal time kept by an oscillator inside the measuring device 4. The measuring device 4 transmits the measurement data to the optical communication device 3 by an optical signal.

[0025] Incidentally, the internal time of the measuring device 4 is different from the absolute time because it is measured by an oscillator built into the measuring device 4. Furthermore, due to the aging characteristics of the oscillator of the measuring device 4, the frequency of the oscillator changes over time. As a result, a difference occurs between the internal time that the measuring device 4 associates with the measurement data and the absolute time. If there is a difference between the absolute time and the internal time, it is not possible to determine with high accuracy the relationship between the timing at which the seismic source 2 emitted seismic waves and the timing of the seismic waves indicated by the measurement data, resulting in a problem that the accuracy of the analysis of the sub-sea bottom geological structure based on seismic waves is reduced.

[0026] In order to prevent the analysis accuracy from decreasing, it is possible to correct the internal time by measuring in advance the aging rate, which is the rate of change of the oscillator frequency over time. However, since the oscillator frequency varies depending on the temperature at which it is measured, the aging rate also varies depending on the temperature at which it is measured. Therefore, the aging rate measured in air differs from the aging rate of the oscillator of the measuring device 4 installed on the ocean floor, where the temperature is much lower than that in air. As a result, if the internal time is corrected using the aging rate measured in air, the correction accuracy will be insufficient.

[0027] Fig. 2 is a diagram showing an example of temperature change of a conventional oscillator. The horizontal axis indicates the number of days elapsed, and the vertical axis indicates the temperature of the oscillator. The characters "injected" and "recovered" indicate the time when the measuring device 4 was injected into the sea and the time when it was recovered from the sea, respectively. These points are the same for Figs. 5 and 13 shown later.

[0028] As shown in Figure 2, when measurement device 4 in the air is dropped into the sea, the temperature of the oscillator drops. The aging rate of an oscillator in the air differs from the aging rate of an oscillator that exists on the seabed, where measurement device 4 is installed. As a result, there was a problem in that even if the aging rate of an oscillator in the air was measured, it was not possible to accurately correct the internal time.

[0029] Therefore, in the measurement method according to this embodiment, the temperature of the oscillator built into measurement device 4, which is in the air, is set to the seabed temperature using a temperature change device included in measurement device 4, and the aging rate is measured when the oscillator temperature is at the seabed temperature. By correcting the internal time using the aging rate measured when the oscillator temperature is at the seabed temperature, the accuracy of internal time correction is improved.

[0030] The "ocean bottom temperature" is not limited to the actual temperature of the ocean bottom on which the measuring device 4 is installed, and may be a temperature within a predetermined allowable range from the actual ocean bottom temperature. The "oscillator temperature" may be the temperature on the surface of the measuring device 4, or may be the temperature inside the measuring device 4.

[0031] 3 is a diagram showing the relationship between an external device 1, a measurement device 4, and a temperature change device 5 according to the first embodiment. The external device 1 functions as an external power supply that applies a voltage to the temperature change device 5 via a wiring W to lower the temperature of an oscillator 41 built into the measurement device 4. The external device 1 may be a data processing device 1.

[0032] The temperature change device 5 is installed so as to be in contact with the outer surface of the measuring device 4. The temperature change device 5 is a device that changes the temperature of the oscillator 41, and is, for example, a device that includes a material that absorbs heat on one surface and releases the absorbed heat on the other surface. An example of such a material is a Peltier element. The Peltier element is an element that can switch between a heat absorption surface and a heat dissipation surface by changing the direction of the current flowing through it. Therefore, when the Peltier element is installed so as to be in contact with the outer surface of the measuring device 4, the oscillator 41 can be cooled by controlling the direction of the current flowing through the Peltier element so that the surface in contact with the outer surface becomes the heat absorption surface. The temperature change device 5 may be directly attached to the oscillator 41.

[0033] The temperature change device 5 may be, for example, a blower device that blows cool air from the outside of the measurement device 4 to the inside of the measurement device 4. The temperature change device 5 operates using external power in the air. Below, an overview of the process flow according to the first embodiment will be described with reference to Figs. 4 and 5.

[0034] [Processing flow overview] Fig. 4 is a flowchart showing the flow of the measurement method according to the first embodiment. Fig. 5 is a schematic diagram showing a change in temperature of an oscillator while the measurement method according to the first embodiment is performed. The data processing device 1 identifies the seabed temperature at the seabed installation position, which is the position on the seabed where the measurement device 4 is installed, by acquiring seabed temperature data indicating the seabed temperature at the seabed installation position (S11). The data processing device 1 may identify the seabed temperature at the seabed installation position by accepting a setting of the seabed temperature at the seabed installation position from a user of the measurement system S.

[0035] When the data processing device 1 applies a voltage to the temperature change device 5, the temperature change device 5 lowers the temperature of the oscillator 41 (S12). This causes the temperature of the oscillator 41 to drop to the seabed temperature, as shown in Fig. 5. Note that in Fig. 5, the period during which the temperature change device 5 operates to make the temperature of the oscillator 41 the seabed temperature is shown as the "device operation period". The device operation period is, for example, about one week. The same points apply to Fig. 13 shown later.

[0036] The data processing device 1 receives from the measurement device 4 an oscillation signal output by the oscillator 41 when the temperature of the oscillator 41 is at the seabed temperature, and measures the aging rate of the oscillator 41 at the seabed temperature based on the change in frequency of the oscillation signal over time (S13). For example, the data processing device 1 obtains an average frequency indicating the average value of the oscillation signal frequency in one hour over a period of one week, and measures the aging rate based on the change in the obtained average frequency. By thus bringing the oscillator 41 to the seabed temperature, a highly reliable aging rate can be obtained from the oscillator 41 that exists in the air.

[0037] When the measurement of the aging rate is completed, the data processing device 1 determines the time difference between the absolute time at which the measurement device 4 is inserted into the sea and the internal time of the measurement device 4 at that time (S14). Next, the data processing device 1 stops applying voltage to the temperature change device 5. The temperature change device 5, from which the application of voltage has been stopped, cancels the low temperature setting of the oscillator 41 (S15).

[0038] After the low temperature applied to the oscillator 41 is released, the measurement device 4 is placed on the seabed (S16). As a result, as shown in Fig. 5, the temperature of the oscillator 41, which has reached the seabed temperature in the air, rises once, but when the measurement device 4 is placed on the seabed, the temperature of the oscillator 41 drops again. The measurement device 4 placed on the seabed creates measurement data of the seismic waves associated with the internal time at which the seismic waves were detected in response to the seismic waves being emitted from the seismic source 2 of the ship 100, and transmits the created measurement data to the data processing device 1. The data processing device 1 receives the measurement data (S17).

[0039] The data processing device 1 corrects the internal time associated with the measurement data received in S17 based on the aging rate measured in S13 and the time difference identified in S14 (S18). Specifically, the data processing device 1 determines the amount of time drift in the elapsed time from the internal time of the measurement device 4 at the time the time difference was identified to the internal time to be corrected based on the aging rate measured in S13. The data processing device 1 then corrects the internal time to be corrected associated with the measurement data by adding the time difference identified in S14 and the amount of time drift identified to the internal time to be corrected associated with the measurement data.

[0040] In this way, by setting the oscillator 41 in the air to the seabed temperature, the measurement system S can determine the aging rate of the oscillator 41 in a state where the oscillator 41 is in the air and the measurement device 4 is installed on the seabed. By using the aging rate determined in this way, the measurement system S can improve the accuracy of correction of the internal time associated with the measurement data of seismic waves measured by the measurement device 4 installed on the seabed.

[0041] [Start-up procedure for measuring device 4] Measurements for analyzing the subseafloor geological structure are carried out periodically. For example, measurements are carried out over several days to several weeks once a year. For example, the multiple measuring devices 4 are installed on the seabed when the period for carrying out the measurements arrives, and are retrieved from the seabed when the measurements are completed. However, if multiple measuring devices 4 are installed every time the period for carrying out the measurements arrives, the installation work takes a lot of time, resulting in poor measurement efficiency. Therefore, the measurement system S in this embodiment may be configured to have multiple measuring devices 4 installed in advance on the seabed measure seismic waves during multiple measurement periods spanning multiple years.

[0042] Since the measuring device 4 is battery-powered, if it is installed on the seabed and operated for a long period of time, the battery will be depleted in a short time. Therefore, in the measurement system S, multiple measuring devices 4 may be configured to start at the start of a measurement period and stop measuring operation when the measurement period ends. The measuring device 4 that has stopped measuring operation enters a sleep state in which the oscillator of the measuring device 4 is stopped to reduce power consumption while maintaining the function of receiving an acoustic signal from the data processing device 1. The measuring device 4 has, for example, a measurement state in which measurement is performed, a standby state in which the oscillator is operating and no measurement is being performed, and a sleep state in which the oscillator is stopped and no measurement is being performed.

[0043] 6 and 7 are diagrams for explaining the procedure for starting up multiple measuring devices 4. Fig. 6 shows a schematic diagram of multiple measuring devices 4 viewed from above. The circle (◯) shown in Fig. 6 indicates a measuring device 4 installed on the seabed. The number under the circle is identification information (ID) for identifying the measuring device 4.

[0044] While the ship 100 is moving, the data processing device 1 transmits an acoustic signal including control information to the measuring device 4 within the range that the acoustic signal can reach (for example, the range within the dashed frame in FIG. 6), thereby enabling the measuring device 4 to start a measurement operation. Specifically, the data processing device 1 transmits a start command, a synchronization command, and a recording start command, thereby enabling the measuring device 4 to start a measurement operation. The dashed arrow in FIG. 6 represents a start command, and the solid arrow represents a synchronization command. The data processing device 1 may transmit parameters required for measurement (for example, a sampling interval or a preamplifier gain) to the measuring device 4.

[0045] The start-up command includes a character string corresponding to an instruction to transition the measurement device 4 from a sleep state to a state in which measurements can be made, and the ID of the measurement device 4. The synchronization command includes a character string corresponding to an instruction to request the internal time of the measurement device 4, and the ID of the measurement device 4. The data processing device 1 may transmit a synchronization command including an absolute time recognized by the data processing device 1. In the following description, the process in which the data processing device 1 specifies the relationship between the absolute time and the internal time of the measurement device 4 based on the internal time received from the measurement device 4 by transmitting a synchronization command to the measurement device 4 is referred to as "synchronization." The record start command includes a character string corresponding to an instruction to start recording of measurement data, and the ID of the measurement device 4.

[0046] A measuring device 4 with no letter written in a circle shown in FIG. 6 (for example, a measuring device 4 with an ID of 0606) is in a stopped state. A measuring device 4 with a "W" written in a dashed circle indicates that it has received a startup command and is in the process of starting up. A measuring device 4 with a "W" written in a solid circle indicates that it has completed startup, but synchronization has not yet been completed. A measuring device 4 with an "S" written in a dashed circle indicates that it has received a synchronization command and is in the process of synchronizing. A measuring device 4 with an "S" written in a solid circle indicates that it has completed synchronization.

[0047] Fig. 7 is a diagram showing an example of a management table indicating the state of each measurement device 4. In the management table shown in Fig. 7, the ID of the measurement device 4, information indicating whether or not startup has been completed, information indicating whether or not synchronization has been completed, the previous action (i.e., the action executed immediately before), and the time when the action was executed are associated with each other. As can be seen from the states of the multiple measurement devices 4 in the dashed line area in Fig. 6 and the times in the management table in Fig. 7, the data processing device 1 transmits startup commands and synchronization commands to different measurement devices 4 in a time-division manner.

[0048] Specifically, the data processing device 1 transmits a synchronization command to the already started second measuring device 4 during the period from when the start-up command is transmitted to the first measuring device 4 until the start-up of the first measuring device 4 is completed. By the data processing device 1 sequentially starting up the multiple measuring devices 4 in this manner and then synchronizing them, the multiple measuring devices 4 can be brought into a state in which they can measure in a shorter time than when the start-up command is transmitted to the measuring device 4 and then the measuring device 4 is waited for to start up. Also, the measuring devices 4 can be brought into a state in which they can measure reliably in a shorter time than when a person starts up each measuring device 4.

[0049] Moreover, the data processing device 1 activates the multiple measuring devices 4 while proceeding in a fixed direction. As an example, as shown in Fig. 6, the data processing device 1 transmits an activation command to the multiple measuring devices 4 located ahead of the ship 100, and transmits a synchronization command to the multiple measuring devices 4 after the ship 100 moves to a position ahead of the activated multiple measuring devices 4.

[0050] In this way, the data processing device 1 transmits commands to multiple measuring devices 4 located at the front of the ship 100 on which the data processing device 1 is mounted and capable of receiving acoustic signals, and multiple measuring devices 4 located at the rear of the ship 100 and capable of receiving acoustic signals. By operating in this manner, the data processing device 1 can bring the multiple measuring devices 4 into a state where they can measure in a shorter time than if commands were sent only to the measuring devices 4 located either at the front or the rear of the ship 100.

[0051] Although not shown in Fig. 6 and Fig. 7, the data processing device 1 may transmit a recording start command to the measurement device 4 that has completed synchronization after receiving a response to the synchronization command from the measurement device 4 and completing synchronization. The recording start command may be a command including an instruction to start recording immediately, or may be a command indicating the time to start recording. The data processing device 1 may transmit recording start commands successively to the multiple measurement devices 4 after synchronization of all the measurement devices 4 is completed and before the seismic source generates seismic waves.

[0052] If multiple measuring devices 4 are installed on the seabed every time a measurement is performed, the installation time and cost will be significant. On the other hand, leaving the measuring devices 4 in operation for a long period of time will cause the battery to run out. In the measurement system S, the data processing device 1 sequentially starts up and synchronizes the multiple measuring devices 4 before a measurement period, and when the measurement period ends, the measuring devices 4 go into a sleep state to reduce battery consumption. Because the measurement system S is configured in this way, it is possible to have the multiple measuring devices 4 measure seismic waves efficiently over a long period of time.

[0053] [Configuration of data processing device 1] FIG. 8 is a diagram showing the configuration of the data processing device 1 according to the first embodiment. The data processing device 1 includes a voltage generating unit 10, a position information acquiring unit 11, an acoustic signal transmitting unit 12, an acoustic signal receiving unit 13, a data transmitting / receiving unit 14, an absolute time acquiring unit 15, an external communication unit 16, a storage unit 17, and a control unit 18. The control unit 18 includes a temperature identifying unit 181, a cooling unit 182, a rate measuring unit 183, a seismic source control unit 184, a command creating unit 185, a data acquiring unit 186, a time difference identifying unit 187, and a correction unit 188. Note that some of the functional units of the control unit 18 may be provided in a device other than the data processing device 1. For example, among the control unit 18, the functional units related to seismic control, the functional units related to acoustic communication control, and the functional units related to temperature control may be provided in data processing devices of different ships.

[0054] The voltage generating unit 10 is connected to the temperature changing device 5, and has a circuit that outputs a voltage for lowering the temperature of the temperature changing device 5. The voltage generating unit 10 may be included in an external device other than the data processing device 1. The voltage generating unit 10 starts or stops applying a voltage in response to the control of the low temperature unit 182.

[0055] The position information acquisition unit 11 acquires position information indicating the position of the data processing device 1, i.e., the position of the ship 100 on which the data processing device 1 is mounted. The position information acquisition unit 11 acquires, for example, radio waves received from a GPS satellite as position information, and identifies latitude and longitude based on the acquired position information. The position information acquisition unit 11 notifies the command creation unit 185 of the identified latitude and longitude.

[0056] The acoustic signal transmitting unit 12 is an acoustic communication unit that transmits a first acoustic signal to the measurement device 4. For example, based on the control of the command creating unit 185, the acoustic signal transmitting unit 12 transmits a first acoustic signal including control data (e.g., various commands) input from the command creating unit 185. The acoustic signal transmitting unit 12 transmits the first acoustic signal including a command to the measurement device 4 within a predetermined range from the position of the ship 100 indicated by the position information acquired by the position information acquiring unit 11 by referring to the respective positions of the multiple measurement devices 4 stored in the memory unit 17. The predetermined range is a range in which the measurement device 4 can receive the first acoustic signal transmitted by the acoustic signal transmitting unit 12.

[0057] As an example, the acoustic signal transmitting unit 12 transmits, to each of the multiple measuring devices 4, a first acoustic signal including a startup command that is startup data for starting up the measuring device 4. The acoustic signal transmitting unit 12 transmits the first acoustic signal including a synchronization command indicating absolute time (i.e., a synchronization command including time data) to a measuring device 4 from which the acoustic signal receiving unit 13 has received a second acoustic signal including response data to the startup command.

[0058] Furthermore, the acoustic signal transmitting unit 12 transmits a first acoustic signal including a recording start command, which is recording start data indicating an instruction to start recording of measurement data, to a measuring device 4 from which the acoustic signal receiving unit 13 has received a response to the first acoustic signal including a synchronization command. That is, the acoustic signal transmitting unit 12 transmits the first acoustic signal including the recording start data to the measuring device 4 that has transmitted the response data to the synchronization command.

[0059] The acoustic signal transmitting unit 12 may transmit a recording start command including the ID of one measuring device 4, or may transmit a recording start command including the IDs of multiple measuring devices 4 that have completed synchronization. The acoustic signal transmitting unit 12 may transmit a recording start command including information indicating that the command is intended for all measuring devices 4. By transmitting such a recording start command from the acoustic signal transmitting unit 12, it is possible to cause multiple measuring devices 4 to start recording seismic waves by transmitting the recording start command once, thereby improving measurement efficiency.

[0060] The acoustic signal receiving unit 13 is an acoustic communication unit that receives a second acoustic signal emitted by the measuring device 4 that has received the first acoustic signal. The acoustic signal receiving unit 13 receives, for example, the second acoustic signal indicating the internal time of the measuring device 4. The acoustic signal receiving unit 13 identifies the internal time based on the time data included in the received acoustic signal, and notifies the data acquiring unit 186 of the identified internal time.

[0061] The data transmitter / receiver 14 is a communication interface for transmitting and receiving data to and from the optical communication device 3. The data transmitter / receiver 14 transmits, for example, data input from the data acquisition unit 186 to the optical communication device 3, including an instruction to acquire the internal time from the measurement device 4, and receives time data indicating the internal time acquired by the optical communication device 3 from the measurement device 4.

[0062] The data transmitter / receiver 14 may notify the optical communication device 3 of the absolute time acquired by the absolute time acquisition unit 15, and receive time data in which the internal time is associated with the absolute time at the time when the optical communication device 3 acquired the internal time from the measurement device 4. The data transmitter / receiver 14 receives data indicating the internal time acquired by the optical communication device 3 from the measurement device 4 at a time within a predetermined range from the time when the last measurement is made in the measurement period. The data transmitter / receiver 14 notifies the data acquisition unit 186 of the acquired time data.

[0063] The absolute time acquisition unit 15 acquires the absolute time from, for example, a GPS satellite. The absolute time acquisition unit 15 notifies the acquired absolute time to the time difference specification unit 187. The absolute time acquisition unit 15 may also notify the data transmission / reception unit 14 of the absolute time.

[0064] The external communication unit 16 transmits the measurement results including the measurement data after the internal time has been corrected, which are input from the correction unit 188. The external communication unit 16 may transmit the measurement results to an external computer that executes a process of analyzing the measurement results and identifying the sub-seafloor geological structure, or may transmit the measurement results to another processing unit included in the control unit 18.

[0065] The storage unit 17 has storage media such as a ROM (Read Only Memory), a RAM (Random Access Memory), and an SSD (Solid State Drive). The storage unit 17 stores programs executed by the control unit 18. The storage unit 17 also stores various data for causing the multiple measuring devices 4 to perform measurements. The storage unit 17 stores, for example, the position of each of the multiple measuring devices 4 and identification information of the measuring device 4 in association with each other. Specifically, the storage unit 17 stores the latitude and longitude of the measuring devices 4 in association with the IDs of the multiple measuring devices 4.

[0066] 7. Furthermore, storage unit 17 stores a management table as shown in Fig. 7. Furthermore, storage unit 17 stores a plurality of pieces of measurement data acquired from measurement devices 4 in association with the IDs of the plurality of measurement devices 4. Storage unit 17 stores a plurality of pieces of measurement data in association with the internal time of measurement device 4 at the time the measurement data was generated. Thereafter, when the time corrected from the internal time by correction unit 188 is associated with the measurement data, storage unit 17 stores the measurement data in association with the corrected time.

[0067] The control unit 18 has, for example, a CPU (Central Processing Unit). The control unit 18 executes the programs stored in the storage unit 17 to function as a temperature identification unit 181, a low temperature unit 182, a rate measurement unit 183, a seismic source control unit 184, a command creation unit 185, a data acquisition unit 186, a time difference identification unit 187, and a correction unit 188.

[0068] The temperature specifying unit 181 specifies the seabed temperature at the seabed installation position, which is the position on the seabed where the measurement device 4 is installed. The temperature specifying unit 181 specifies the seabed temperature at the seabed installation position by, for example, acquiring seabed temperature data indicating the seabed temperature at the seabed installation position measured by a drop-type water temperature system dropped from the ship 100. The temperature specifying unit 181 may specify the seabed temperature at the seabed installation position by accepting a setting of the seabed temperature at the seabed installation position from a user of the measurement system S. The temperature specifying unit 181 may refer to a database that records the seabed temperature at each reference position on the seabed, and specify the seabed temperature at the reference position closest to the seabed installation position as the seabed temperature at the seabed installation position. The temperature specifying unit 181 inputs the acquired seabed temperature data to the cooling unit 182.

[0069] The low temperature unit 182 sets the temperature of the oscillator 41 built in the measuring device 4 located in a place other than seawater to the seabed temperature. The low temperature unit 182 sets the temperature of the oscillator 41 to the seabed temperature, for example, by controlling the temperature change device 5 so as to change the temperature of the oscillator 41. The low temperature unit 182 may input a voltage application signal to the voltage generating unit 10 to instruct the voltage generating unit 10 to apply a voltage for controlling the temperature change device 5. When the temperature change device 5 is a Peltier element, the low temperature unit 182 may input a voltage application signal to the voltage generating unit 10 to instruct the voltage generating unit 10 to apply a voltage of a magnitude necessary for the temperature of the oscillator 41 to become the seabed temperature, in order to pass a current in a direction in which the surface of the Peltier element in contact with the measuring device 4 becomes a heat absorbing surface. The voltage generating unit 10 that has received the input of the voltage application signal applies a voltage to the temperature change device 5. The oscillator 41 built in the measuring device 4 may be set to the seabed temperature by storing the measuring device 4 in a freezer whose inside has been set to the seabed temperature for a predetermined period of time.

[0070] The rate measurement unit 183 measures the aging rate of the oscillator 41 when the temperature of the oscillator 41 built into the measurement device 4 located in a place other than seawater becomes a specified seabed temperature. For example, the rate measurement unit 183 receives from the measurement device 4 an oscillation signal output by the oscillator 41 when the temperature of the oscillator 41 becomes the seabed temperature, and measures the aging rate of the oscillator 41 that has become the seabed temperature based on the change in frequency of the oscillation signal over time.

[0071] The rate measurement unit 183 may input measurement completion data indicating that measurement of the aging rate has been completed to the low temperature unit 182. In response to receiving the input of the measurement completion data, the low temperature unit 182 may input a voltage release signal to the voltage generation unit 10 instructing it to stop applying voltage. Upon receiving the input of the voltage release signal, the voltage generation unit 10 stops applying voltage to the temperature change device 5. This releases control over the temperature change device 5. After control over the temperature change device 5 has been released, the measurement apparatus 4 is installed on the seabed.

[0072] The epicenter control unit 184 transmits an instruction to generate a seismic wave to the epicenter 2. The epicenter control unit 184 causes the epicenter 2 to generate a seismic wave, for example, after the acoustic signal transmission unit 12 transmits a first acoustic signal including a recording start command to the plurality of measuring devices 4. The epicenter control unit 184 transmits an instruction to generate a seismic wave to the epicenter 2, for example, after receiving a notification from the data acquisition unit 186 that all measuring devices 4 are ready to perform measurement. The epicenter control unit 184 may cause the epicenter 2 to generate a seismic wave at a predetermined date and time, or may cause the epicenter 2 to generate a seismic wave in response to an instruction from an external device. The data processing device 1 may not have the epicenter control unit 184, and an external control device may function as the epicenter control unit 184.

[0073] The command creation unit 185 creates commands to be transmitted by the acoustic signal transmission unit 12 to the measuring device 4. The command creation unit 185 creates, for example, a startup command, a synchronization command, and a recording start command, and inputs the created commands to the acoustic signal transmission unit 12. When creating a command, the command creation unit 185 selects a measuring device 4 within a predetermined range from the latitude and longitude input from the position information acquisition unit 11 by referring to the latitude and longitude of the positions at which the multiple measuring devices 4 are installed that are stored in the memory unit 17. The command creation unit 185 creates a command including the ID of the selected measuring device 4.

[0074] 6, the command creation unit 185 creates a start-up command for a measuring device 4 in a sleep state among multiple measuring devices 4 within a predetermined range. In response to receiving a notification from the data acquisition unit 186 that a measuring device 4 corresponding to the created start-up command has started up, the command creation unit 185 creates a synchronization command for that measuring device 4. In response to receiving a notification from the data acquisition unit 186 that a measuring device 4 corresponding to the created synchronization command has completed synchronization, the command creation unit 185 creates a recording start command for that measuring device 4.

[0075] When the command creation unit 185 inputs the created command to the acoustic signal transmission unit 12, it updates the "last action" in the management table stored in the storage unit 17. When the command creation unit 185 inputs a start-up command to the acoustic signal transmission unit 12, it sets the "last action" corresponding to the ID of the measuring device 4 included in the start-up command to "starting up". When the command creation unit 185 inputs a synchronization command to the acoustic signal transmission unit 12, it sets the "last action" corresponding to the ID of the measuring device 4 included in the synchronization command to "synchronizing".

[0076] The data acquiring unit 186 acquires various data transmitted from the measuring device 4. The data acquiring unit 186 acquires response data to a command transmitted by the acoustic signal transmitting unit 12 via the acoustic signal receiving unit 13. The data acquiring unit 186 notifies the command creating unit 185 that the response data has been acquired.

[0077] When the data acquiring unit 186 acquires response data, it updates the contents of the "last action" in the management table stored in the storage unit 17. When the data acquiring unit 186 acquires response data indicating, for example, startup, it updates the "last action" corresponding to the ID of the measuring device 4 included in the response data to "startup completed". When the data acquiring unit 186 acquires response data including the internal time of the measuring device 4 transmitted by the measuring device 4 in response to receiving a synchronization command, it updates the "last action" corresponding to the ID of the measuring device 4 included in the response data to "synchronization completed". The data acquiring unit 186 associates the absolute time when the synchronization command was transmitted and the internal time indicated by the response data with the ID of the measuring device 4 and stores them in the storage unit 17.

[0078] When the data acquiring unit 186 acquires response data indicating that the measuring device 4 has started recording, it updates the "last action" corresponding to the ID of the measuring device 4 included in the response data to "start recording." When the data acquiring unit 186 receives response commands to the start recording command from all measuring devices 4, that is, when the "last action" of all measuring devices 4 has become "start recording," it notifies the epicenter control unit 184 that it is possible to start measurement.

[0079] The data acquiring unit 186 may further acquire an emission time, which is the absolute time when the optical communication device 3 emits the first optical signal, and an internal time included in the second optical signal received by the optical communication device 3. The second optical signal is an optical signal transmitted by the measurement device 4 in response to receiving the first optical signal. The data acquiring unit 186 associates the emission time and the internal time with the ID of the measurement device 4, stores them in the storage unit 17, and notifies the time difference identifying unit 187.

[0080] Furthermore, the data acquiring unit 186 acquires measurement data from the measuring device 4 via the data transmitting / receiving unit 14. The data acquiring unit 186 acquires a plurality of pieces of measurement data each indicating a measurement value corresponding to a different time. For example, after the measurement period ends, the data acquiring unit 186 acquires a plurality of pieces of measurement data collected from the measuring device 4 by the optical communication device 3 through optical communication from the data transmitting / receiving unit 14. The data acquiring unit 186 associates the acquired measurement data with the ID of the measuring device 4 and stores it in the storage unit 17, thereby enabling the time difference identifying unit 187 to refer to the measurement data.

[0081] The time difference specifying unit 187 specifies the time difference between the absolute time and the internal time of the measurement device 4. For example, the time difference specifying unit 187 specifies the time difference between the absolute time at the time when the measurement device 4 is submerged in the sea and the internal time of the measurement device 4 at that time. If the internal time of the measurement device 4 is synchronized with the absolute time at the time when the measurement device 4 is submerged in the sea, the time difference will be zero.

[0082] After the measurement device 4 installed on the seabed creates measurement data, the correction unit 188 corrects the internal time associated with the measurement data based on the aging rate measured by the rate measurement unit 183. For example, the correction unit 188 corrects the internal time associated with the measurement data based on the time difference identified by the time difference identification unit 187 and the aging rate measured by the rate measurement unit 183. The correction unit 188 calculates the amount of time drift, which is the difference between the internal time of the measurement device 4 and the absolute time at each point in time after the measurement device 4 starts creating the measurement data, based on the aging rate, and corrects the internal time associated with the measurement data using the time difference and the amount of time drift identified by the time difference identification unit 187.

[0083] The correction unit 188 calculates the amount of time drift based on the aging rate measured by the rate measurement unit 183, using the following formula 1.

number

[0084] The meaning of each term in the formula 1 is as follows: E(t): Time drift amount E0: Time difference at the time when the measuring device 4 is dropped into the sea (t0) a: Aging rate y0: Frequency error at time t0

[0085] The time difference E0 at the time when the measurement device 4 is immersed in the sea can be made zero by synchronizing the internal time of the measurement device 4 with absolute time at the time when the measurement device 4 is immersed in the seabed. y0 is an error from the design value that occurs due to a change in the frequency of the oscillator 41 accompanying a change in temperature caused by the measurement device 4 being immersed in the sea from the air. The method for determining y0 will be described later.

[0086] FIG. 9 is a graph showing the amount of time drift over time. The horizontal axis shows the number of days that have passed since the measurement device 4 was dropped into the sea. The dotted curve shows the time drift calculated using Equation 1 (a=1.68×10 -129 shows the predicted time drift amount (left vertical axis) calculated by the above equation (assuming that y0 is the theoretical time drift amount). The solid curve sloping to the right indicates the theoretical time drift amount (left vertical axis) as a theoretical value. The upward convex parabola indicates the residual error (right vertical axis) which is the difference between the predicted time drift amount and the theoretical time drift amount. The correction unit 188 uses y0 as a fitting parameter to calculate the time drift amount E(t) based on Equation 1. Then, the correction unit 188 specifies y0 at which the residual error between the theoretical time drift amount and the predicted time drift amount at the time (E1 in FIG. 9) when the measurement device 4 is recovered from the sea is minimized.

[0087] 10 is a diagram showing an example of a flowchart illustrating the internal time correction process according to this embodiment. The correction unit 188 identifies a first internal time, which is the internal time at the time when the time difference between absolute time and the internal time of the measurement device 4 is identified. The correction unit 188, for example, identifies the internal time of the measurement device 4 at the time when the time difference (the time difference between absolute time and the internal time of the measurement device 4 at the time when the measurement device 4 is thrown into the sea) as the first internal time (S181). The correction unit 188 identifies a second internal time associated with the measurement data obtained from the measurement device 4 (S182). The second internal time is the internal time to be corrected.

[0088] The correction unit 188 calculates the elapsed time from the first internal time to the second internal time (S183). The correction unit 188 identifies the amount of time drift corresponding to the elapsed time (S184). For example, the correction unit 188 identifies the amount of time drift corresponding to the elapsed time by substituting the elapsed time calculated in S183 for "t" in Equation 1 in which y0 is identified.

[0089] Then, the correction unit 188 corrects the second internal time (internal time to be corrected) associated with the measurement data based on the identified amount of time drift. The correction unit 188 corrects the second internal time (internal time to be corrected) by, for example, adding to the second internal time, which is the internal time to be corrected, the time difference between the absolute time at the time when the measurement device 4 is thrown into the sea and the internal time of the measurement device 4, and the amount of time drift identified in S184 (S185).

[0090] [Configuration of measuring device 4] 11 is a diagram showing the configuration of the measurement device 4 according to the first embodiment. The measurement device 4 has an oscillator 41, a sensor 42, an acoustic signal receiving unit 43, an acoustic signal transmitting unit 44, an optical signal receiving unit 45, an optical signal transmitting unit 46, a storage unit 47, and a control unit 48. The control unit 48 has a seismic wave measuring unit 481 and a data communication unit 482.

[0091] The oscillator 41 generates an oscillation signal used to keep time in the measuring device 4. The oscillator 41 is, for example, a temperature compensated crystal oscillator (TCXO). The TCXO is an oscillator with a built-in temperature compensation circuit for correcting frequency fluctuations caused by temperature changes. Unlike an oven-controlled oscillator (OCXO), the TCXO does not have a thermostatic bath, and therefore, using a TCXO has the advantage that the power required for temperature control of the thermostatic bath is not required. In particular, when there are a large number of measuring devices 4 to be installed on the seabed, preparing a thermostatic bath for each of the oscillators 41 requires a great deal of effort and power, but using a TCXO eliminates such effort and power. The oscillator 41 may be, for example, a chip-scale atomic oscillator.

[0092] The sensor 42 generates a detection signal whose level changes in response to vibration of the measuring device 4. The sensor 42 inputs the detection signal to the seismic wave measuring unit 481.

[0093] The acoustic signal receiving unit 43 receives a first acoustic signal transmitted from the data processing device 1. The acoustic signal receiving unit 43 inputs data such as a command and absolute time contained in the received first acoustic signal to the data communication unit 482. In response to the acoustic signal receiving unit 43 receiving the first acoustic signal, the acoustic signal transmitting unit 44 transmits a second acoustic signal indicating the internal time at which the first acoustic signal was received to the data processing device 1.

[0094] The optical signal receiving unit 45 receives a first optical signal transmitted from the optical communication device 3. The optical signal receiving unit 45 inputs data such as a command and absolute time contained in the received first optical signal to the data communication unit 482. In response to the optical signal receiving unit 45 receiving the first optical signal, the optical signal transmitting unit 46 transmits a second optical signal indicating the internal time at which the first optical signal was received. The optical signal transmitting unit 46 transmits the second optical signal including the internal time input from the data communication unit 482, for example, to the optical communication device 3.

[0095] The storage unit 47 includes storage media such as a ROM, a RAM, and an SSD. The storage unit 47 stores a program executed by the control unit 48. The storage unit 47 also stores measurement data created by the seismic wave measurement unit 481.

[0096] The control unit 48 includes, for example, a CPU. The control unit 48 executes a program stored in the storage unit 47 to function as a seismic wave measurement unit 481 and a data communication unit 482.

[0097] The seismic wave measuring unit 481 creates a plurality of pieces of measurement data associated with the internal time kept based on the oscillator 41. The seismic wave measuring unit 481 creates a plurality of pieces of measurement data indicating the sampled signal levels (i.e., measurement values) by, for example, sampling the detection signal input from the sensor 42 at a predetermined time interval (for example, 1 millisecond intervals). The seismic wave measuring unit 481 stores the plurality of pieces of measurement data in the storage unit 47 in association with the internal time. The seismic wave measuring unit 481 may keep the internal time by counting the oscillation signal input from the oscillator 41, or may identify the internal time based on the data indicating the internal time input from the oscillator 41.

[0098] The data communication unit 482 transmits, via the acoustic signal transmission unit 44, response data to a command included in the first acoustic signal received from the data processing device 1 via the acoustic signal reception unit 43. The data communication unit 482 also transmits, via the optical signal transmission unit 46, response data to a command included in the optical signal received from the optical communication device 3 via the optical signal reception unit 45. When the data communication unit 482 receives a synchronization command, it acquires the internal time at the time when the synchronization command was received from the oscillator 41 or the seismic wave measurement unit 481, and transmits response data including the acquired internal time.

[0099] Furthermore, the data communication unit 482 transmits the plurality of pieces of measurement data created by the seismic wave measurement unit 481 to the optical communication device 3 via the optical signal transmission unit 46. Specifically, the data communication unit 482 transmits the plurality of pieces of measurement data stored in the storage unit 47 in association with the internal time.

[0100] [Effects of measurement system S] As described above, in the measurement system S, by setting the oscillator 41 in the air to the seabed temperature, it is possible to identify the aging rate of the oscillator 41 when the oscillator 41 is in the air and the measurement device 4 is installed on the seabed. By using the aging rate identified in this way, the accuracy of correcting the internal time associated with the measurement data of seismic waves measured by the measurement device 4 installed on the seabed is improved. As a result, it is possible to accurately correct the internal time associated with the measurement data of seismic waves even if an oscillator with normal aging characteristics is used instead of a chip-scale atomic oscillator with relatively good aging characteristics.

[0101] In addition, in the measurement system S, by using a Peltier element or the like as the temperature change device 5 that changes the oscillator 41 present in the air to the seabed temperature, it becomes unnecessary to use an oven-controlled oscillator (OCXO) having a thermostatic bath. As a result, less power is consumed than when the temperature is controlled using an OCXO.

[0102] <Second embodiment> In the first embodiment, the measurement device 4 is installed on the seabed after the low temperature of the oscillator 41 that has reached the seabed temperature in the air is released. However, in this case, as described with reference to FIG. 5, the temperature of the oscillator 41 that has reached the seabed temperature in the air rises once before and after the measurement device 4 is immersed in the sea. For this reason, the frequency of the oscillator 41 may not change according to the aging rate measured at the seabed temperature in the air. As a result, the amount of time drift from the internal time of the measurement device 4 to the internal time to be corrected associated with the measurement data at the time the measurement device 4 is immersed in the sea may slightly differ from the actual amount of time drift.

[0103] Therefore, in the second embodiment, the measurement device 4 is installed on the seabed in a state where the low temperature of the oscillator 41 that has reached the seabed temperature in the air is maintained. The second embodiment differs from the first embodiment mainly in that the measurement device 4 also has a temperature specifying unit 483 and a low temperature unit 484. Below, an overview of the processing flow according to the second embodiment will be described with reference to Figs. 12 and 13.

[0104] [Processing flow overview] Fig. 12 is a flowchart showing the flow of the measurement method according to the second embodiment. Fig. 13 is a schematic diagram showing the change in temperature of the oscillator while the measurement method according to the second embodiment is performed. The data processing device 1 and the measurement device 4 identify the seabed temperature at the position on the seabed where the measurement device 4 is installed (S21).

[0105] The data processing device 1 applies a voltage to the temperature change device 5 via wiring. As a result, the temperature change device 5 cools the oscillator 41 (S22). This causes the temperature of the oscillator 41 to drop to the seabed temperature, as shown in Fig. 13. The processes of measuring the aging rate (S23) and determining the time difference (S24) performed by the data processing device 1 are similar to those in the first embodiment, and therefore will not be described.

[0106] The data processing device 1 stops applying voltage to the temperature change device 5 when the measurement device 4 is dropped into the sea. The temperature change device 5, from which the application of voltage has been stopped, cancels the low-temperature control of the oscillator 41 (S25). Immediately thereafter, the measurement device 4 applies voltage to the temperature change device 5 using a built-in battery. As a result, the temperature change device 5 cools the oscillator 41 (S26).

[0107] By doing so, even before and after the measurement device 4 is thrown into the sea, the oscillator 41 can maintain a low temperature state as shown in FIG. 13 without the temperature increasing as in the first embodiment.

[0108] Next, the measuring device 4 is placed on the seabed with the oscillator 41 maintained at a low temperature (S27). After a predetermined time has elapsed since the measuring device 4 was placed in the sea, the measuring device 4 stops applying voltage to the temperature change device 5. As a result, the low temperature keeping of the oscillator 41 by the battery built into the measuring device 4 is released (S28), but since the oscillator 41 is cooled by seawater, the low temperature state can be maintained even in the sea, as shown in FIG.

[0109] The processes of receiving measurement data (S29) and correcting the internal time (S30) performed by the data processing device 1 are similar to those in the first embodiment, and therefore will not be described.

[0110] In this way, in the second embodiment, the measurement device 4 is installed on the seabed in a state where the oscillator 41, which has reached the seabed temperature in the air, is kept at a low temperature. This causes the frequency of the oscillator 41 to change according to the aging rate measured in the air at the seabed temperature. This makes it possible to obtain a value with higher accuracy than in the first embodiment as the amount of time drift from the internal time of the measurement device 4 at the time the measurement device 4 is inserted into the sea to the internal time to be corrected associated with the measurement data. As a result, it becomes possible to correct the internal time with higher accuracy than in the first embodiment.

[0111] [Configuration of measuring device 4] Fig. 14 is a diagram showing the configuration of a measuring device 4 according to the second embodiment. The measuring device 4 according to the second embodiment differs from the measuring device 4 according to the first embodiment shown in Fig. 11 in that it has a voltage generating unit 40, an operating unit 49, a temperature identifying unit 483, and a low temperature unit 484. The temperature changing device 5 according to the second embodiment also differs from the temperature changing device 5 according to the first embodiment in that the measuring device 4 can operate using a battery built into it even after the measuring device 4 is thrown into the sea.

[0112] The voltage generating unit 40 has a circuit that generates a voltage to be applied to the temperature change device 5. The voltage generating unit 40 generates a voltage based on power supplied from a battery (not shown) that supplies power for operating each unit of the measuring device 4. The voltage generating unit 40 is built into the measuring device 4, and starts or stops applying a voltage in response to the control of the low temperature unit 484.

[0113] Incidentally, the oscillator 41 built into the measuring device 4 is also powered by a battery (not shown). The power required to operate the temperature change device 5 is greater than the power required to operate the oscillator 41. For this reason, if the battery that operates the oscillator 41 and the voltage generating unit 40 that operates the temperature change device 5 are the same, there is a possibility that the power to operate the oscillator 41 will be insufficient. Therefore, it is preferable that the battery that operates the oscillator 41 and the voltage generating unit 40 that operates the temperature change device 5 are different.

[0114] The operation unit 49 is, for example, a touch panel. In response to the user's selection of the "battery activation mode" displayed on the operation unit 49, the operation unit 49 inputs an instruction signal to the low-temperature unit 484 to input a voltage application signal to the voltage generation unit 40 to apply a voltage for controlling the temperature change device 5. The user selects the "battery activation mode" from the operation unit 49, for example, at the time of throwing the measuring device into the sea. Note that the instruction signal input to the low-temperature unit 484 does not have to be input from the operation unit 49. For example, a wireless communication device (remote controller) capable of wireless communication with the measuring device 4 may transmit an instruction signal to the measuring device 4 in response to an operation by the user. Alternatively, a detection unit included in the measuring device 4 may input an instruction signal to the low-temperature unit 484 in response to detection that the wiring of the data processing device 1 has been removed from the temperature change device 5.

[0115] The temperature determining unit 483 determines the seabed temperature at the seabed installation position of the measurement device 4 by the same process as that performed by the temperature determining unit 181 described in the first embodiment. The temperature determining unit 483 inputs the obtained seabed temperature data to the cooling unit 484.

[0116] In response to receiving the instruction signal, the low temperature unit 484 inputs a voltage application signal to the voltage generating unit 40. The voltage generating unit 40, which has received the voltage application signal, applies a voltage to the temperature changing device 5. The temperature changing device 5, which has received the voltage application, lowers the temperature of the oscillator 41. In this way, the measurement apparatus 4 is installed on the seabed while maintaining control over the temperature changing device 5 by the low temperature unit 484.

[0117] After a predetermined time has elapsed since accepting the input of the measurement mode, the low temperature unit 484 inputs a voltage release signal to the voltage generating unit 40 to instruct the voltage generating unit 40 to stop applying voltage for controlling the temperature change device 5. Upon accepting the input of the voltage release signal, the voltage generating unit 40 stops applying voltage to the temperature change device 5.

[0118] The predetermined time is, for example, the time from when the measuring device 4 is thrown into the sea to when the oscillator 41 built into the measuring device 4 installed on the seabed is cooled by seawater. In this way, the voltage generating unit 40 built into the measuring device 4 stops applying voltage to the temperature change device 5 at the stage when the measuring device 4 is cooled by seawater. In this way, it is possible to reduce power consumption by the voltage generating unit 40 compared to the case where the voltage continues to be applied even after the measuring device 4 is cooled by seawater.

[0119] [Effects of measurement system S] As described above, in the measurement system S according to the second embodiment, the measurement device 4 is installed on the seabed in a state where the oscillator 41, which has reached the seabed temperature in the air, is kept at a low temperature. This causes the frequency of the oscillator 41 to change according to the aging rate measured in the air at the seabed temperature. This makes it possible to obtain a value with higher accuracy than in the first embodiment as the amount of time drift from the internal time of the measurement device 4 at the time the measurement device 4 is inserted into the sea to the internal time to be corrected associated with the measurement data. As a result, it becomes possible to correct the internal time with higher accuracy than in the first embodiment.

[0120] [Variations] In the measurement system S described above, an example has been described in which the measurement of the temperature reduction and the aging rate of the oscillator 41 is performed before the measurement device 4 is placed in the sea, but the measurement of the temperature reduction and the aging rate of the oscillator 41 may also be performed after the measurement device 4 installed on the seabed is retrieved.

[0121] In the measurement system S described above, an example in which the control unit 18 of the data processing device 1 has multiple functional units has been described, but some of the multiple functional units may be included in the data processing device 1, and the remaining functional units may be included in one or more data processing devices. In this way, it is possible to reduce the processing load in each data processing device.

[0122] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0123] 1 Data Processing Device 2. Epicenter 3. Optical communication devices 4. Measuring Equipment 5. Temperature change devices 10 Voltage generation section 11 Location information acquisition section 12 Acoustic signal transmitter 13 Acoustic signal receiving unit 14 Data transmission and reception unit 15 Absolute time acquisition section 16 External Communications Department 17 Memory section 18 Control Unit 40 Voltage generation section 41 Oscillator 42 Sensors 43 Acoustic signal receiving unit 44 Acoustic signal transmitter 45 Optical signal receiving section 46 Optical signal transmitter 47 Memory section 48 Control Unit 49 Operation section 100 ships 181 Temperature identification part 182 Low Temperature Section 183 Rate Measurement Unit 184 Seismic Source Control Unit 185 Command Creation Department 186 Data Acquisition Department 187 Time difference identification part 188 Correction section 481 Seismic Wave Measurement Section 482 Data Communications Department 483 Temperature identification part 484 Low Temperature Section

Claims

1. a temperature determination step of determining a seabed temperature at a position on the seabed where a measuring device is installed, the measuring device creating measurement data of the seismic waves associated with an internal time at which the seismic waves were detected in response to the seismic waves being emitted from a seismic source; a cooling step of lowering the temperature of an oscillator built into the measuring device located in a place other than seawater to the seabed temperature; a rate measurement step of measuring an aging rate, which is a rate of change over time of a frequency of the oscillator, when the temperature of the oscillator included in the measurement device located in a place other than seawater becomes the specified seabed temperature; a correction step of correcting the internal time associated with the measurement data based on the aging rate after the measurement device installed on the seabed creates the measurement data; A seismic wave measuring method comprising the steps of:

2. the measurement device, which is present in a location other than seawater, has a temperature change device that changes the temperature of the oscillator; In the cooling step, the temperature of the oscillator is set to the seabed temperature by controlling the temperature change device so as to change the temperature of the oscillator. The seismic wave measuring method according to claim 1 .

3. After performing the low temperature step and the rate measurement step, Releasing the control over the temperature change device; installing the measurement device on the seabed after releasing the control over the temperature change device; Further comprising The seismic wave measuring method according to claim 2.

4. After performing the low temperature step and the rate measurement step, and installing the measurement apparatus on the seabed while maintaining the control over the temperature change device. The seismic wave measuring method according to claim 2.

5. Prior to the correction step, a time difference specifying step of specifying a time difference between an absolute time and an internal time of the measurement device; a step of installing the measurement device on the seabed; and In the correction step, the internal time associated with the measurement data is corrected based on the time difference and the aging rate. The seismic wave measuring method according to claim 1 .

6. in the correction step, an amount of time drift in the elapsed time from a first internal time, which is the internal time at the time point when the time difference was determined, to a second internal time associated with the measurement data is determined based on the aging rate, and the second internal time is corrected based on the determined amount of time drift. The seismic wave measuring method according to claim 5.

7. The computer executes a temperature determination step of determining a seabed temperature at a position on the seabed where a measuring device is installed, the measuring device creating measurement data of the seismic waves associated with an internal time at which the seismic waves were detected in response to the seismic waves being emitted from a seismic source; a cooling step of lowering the temperature of an oscillator built into the measuring device located in a place other than seawater to the seabed temperature; a rate measurement step of measuring an aging rate, which is a rate of change over time of a frequency of the oscillator, when the temperature of the oscillator included in the measurement device located in a place other than seawater becomes the specified seabed temperature; The aging rate measuring method has the following steps.

8. A processor included in the information processing device a temperature determination unit that determines a seabed temperature at a position on the seabed where a measurement device is installed, the measurement device creating measurement data of the seismic wave associated with an internal time at which the seismic wave was detected in response to the seismic wave being emitted from a seismic source; a low-temperature unit that adjusts the temperature of an oscillator built into the measuring device located in a place other than seawater to the seabed temperature; a rate measurement unit that measures an aging rate, which is a rate of change over time in the frequency of the oscillator, when the temperature of the oscillator included in the measurement device that is located in a place other than seawater becomes the specified seabed temperature; and A program to function as a

9. a temperature determination unit that determines a seabed temperature at a position on the seabed where a measurement device is installed, the measurement device creating measurement data of the seismic wave associated with an internal time at which the seismic wave was detected in response to the seismic wave being emitted from a seismic source; a low-temperature unit that adjusts the temperature of an oscillator built into the measuring device located in a place other than seawater to the seabed temperature; a rate measurement unit that measures an aging rate, which is a rate of change over time in the frequency of the oscillator, when the temperature of the oscillator included in the measurement device that is located in a place other than seawater becomes the specified seabed temperature; and a correction unit that corrects the internal time associated with the measurement data based on the aging rate after the measurement device installed on the seabed creates the measurement data; A data processing device having:

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