Measuring equipment

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 emission of seismic waves from an epicenter; 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 the 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 the measurement data.

Description

[Technical Field]

[0001] The present invention relates to a measuring device for measuring seismic waves. [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] Japanese Patent Application Laid-Open No. 2010-245978 Summary of the Invention [Problem to be solved by the invention]

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

[0005] One possible way to prevent a decline in analysis accuracy is to measure the aging rate, which is the rate at which the oscillator's frequency changes over time, in advance in air, and then correct the internal time. However, the aging rate in air differs from that on the seabed. This means that measuring the aging rate in air does not allow for accurate correction of the internal time.

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

[0007] The measuring device of the present invention comprises an oscillator used to measure internal time, a temperature change device that changes the temperature of the oscillator, a processor that controls the temperature change device so that the temperature change device changes the temperature of the oscillator, and a seismic wave measurement unit that creates measurement data of the seismic wave associated with the internal time at which the seismic wave was detected in response to the emission of a seismic wave from a seismic source.

[0008] The temperature change device may be a material that absorbs heat on one side and releases the absorbed heat on the other side.

[0009] The temperature change device may be made of a material whose heat absorption surface and heat radiation surface can be switched by changing the direction of the current flowing through it.

[0010] The temperature change device may be installed so as to be in contact with an outer surface of the measuring device, and the processor may control the direction of the current flowing through the temperature change device so that the surface of the temperature change device in contact with the outer surface of the measuring device becomes a heat absorption surface.

[0011] The measurement apparatus may further include a first generating unit that generates a voltage to be applied to the temperature change device.

[0012] The measuring device may further have an operation unit for a user to operate, and the first generating unit may generate a voltage in response to the user performing an operation on the operation unit to apply a voltage to the temperature change device.

[0013] The first generating unit may generate a voltage in response to a wiring connecting the temperature change device to an external power that generates a voltage to be applied to the temperature change device being removed from the temperature change device.

[0014] The first generating unit may stop applying voltage after a predetermined time has elapsed since starting to apply voltage, which is the time required for the oscillator of the measuring device installed on the seabed to be cooled to the seabed temperature by seawater after the measuring device is submerged in the sea.

[0015] The measurement device may further include a second generating unit that generates a voltage to be applied to the oscillator. [Effects of the Invention]

[0016] The present invention provides the advantage of enabling accurate correction of the internal time. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing an overview of a seismic wave measurement system S. [Figure 2] FIG. 10 is a diagram showing an example of temperature change in a conventional oscillator. [Figure 3] 1 is a diagram showing the relationship between an external device 1, a measurement device 4, and a temperature change device 5 according to a first embodiment. [Figure 4] 3 is a flowchart showing the flow of a measurement method according to the first embodiment. [Figure 5] 5 is a schematic diagram showing a change in the temperature of an oscillator while the measurement method according to the first embodiment is carried out. FIG. [Figure 6] FIG. 10 is a diagram for explaining a procedure for starting up a plurality of measuring devices 4. [Figure 7] 10 is a diagram showing an example of a management table showing the state of each measurement 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] 10 is a graph showing the amount of time drift over time. [Figure 10] FIG. 10 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 the 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. 10 is a schematic diagram showing a change in the 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 INVENTION

[0018] First Embodiment [Overview of Measurement System S] Figure 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 sparker, and a data processing device 1 analyzes the sub-seafloor geological structure using the results of measurements of the seismic waves by multiple measuring devices 4 installed on the seafloor.

[0019] The measurement system S comprises 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.

[0020] The data processing device 1 is, for example, a computer, which acquires measurement data indicating the seismic 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 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 GPS (Global Positioning System).

[0021] The seismic source 2 generates seismic waves during the measurement period. The seismic source 2 generates seismic waves, for example, under the control of the data processing device 1, but may also 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).

[0022] The optical communication device 3 acquires measurement data from at least one measurement device 4 by optically communicating with it under the control of the data processing device 1. The optical communication device 3 emits a first optical signal to the measurement device 4 underwater 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, it dives to a position where it can perform optical communication with the measurement device 4 and then performs optical communication with the measurement device 4. The optical communication device 3 moves sequentially to the vicinity of multiple measurement devices 4 and sequentially acquires measurement data from the multiple measurement devices 4. 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.

[0023] The measuring device 4 generates 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 indicates 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 the 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 via an optical signal.

[0024] Incidentally, the internal time of the measuring device 4 is measured by an oscillator built into the measuring device 4, and is therefore different from absolute time. 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, which leads to a problem of reduced accuracy in analyzing the subseafloor geological structure based on seismic waves.

[0025] One possible method to prevent a decline in analysis accuracy is to calibrate the internal time by measuring in advance the aging rate, which is the rate at which the oscillator frequency changes over time. However, because 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 will differ from the aging rate of the oscillator of the measurement device 4 installed on the seabed, where the temperature is much lower than in air. As a result, if the internal time is calibrated using the aging rate measured in air, the accuracy of the correction will be insufficient.

[0026] Figure 2 is a diagram showing an example of temperature changes in a conventional oscillator. The horizontal axis indicates the number of days that have passed, and the vertical axis indicates the temperature of the oscillator. The words "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 also apply to Figures 5 and 13 shown later.

[0027] As shown in Figure 2, when measurement device 4, which is in the air, is placed in 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 is 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.

[0028] 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 the internal time correction is improved.

[0029] The "ocean bottom temperature" is not limited to the actual temperature of the ocean bottom where the measuring device 4 is installed, but 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 the temperature inside the measuring device 4.

[0030] 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 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.

[0031] 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. A Peltier element is an element that can switch between a heat absorption surface and a heat release 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 attached directly to the oscillator 41.

[0032] The temperature change device 5 may be, for example, a blower device that blows cool air from the outside of the measuring device 4 to the inside of the measuring device 4. The temperature change device 5 operates using external power when in the air. Below, an overview of the processing flow according to the first embodiment will be explained using Figs. 4 and 5.

[0033] [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 changes in the temperature of the oscillator while the measurement method according to the first embodiment is carried out. The data processing device 1 identifies the seabed temperature at the seabed installation position by acquiring seabed temperature data indicating the seabed temperature at the seabed installation position, which is the position on the seabed where the measurement device 4 is installed (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 the user of the measurement system S.

[0034] 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). As a result, as shown in FIG. 5, the temperature of the oscillator 41 drops to the seabed temperature. Note that in FIG. 5, the period during which the temperature change device 5 operates to bring the temperature of the oscillator 41 to the seabed temperature is shown as the "device operation period." The device operation period is, for example, about one week. These points also apply to FIG. 13 shown later.

[0035] The data processing device 1 receives from the measurement device 4 the 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 the frequency of the oscillation signal over time (S13). The data processing device 1, for example, acquires an average frequency indicating the average value of the oscillation signal frequency in one-hour units over a one-week period, and measures the aging rate based on the change in the acquired average frequency. By setting the oscillator 41 at the seabed temperature in this way, it is possible to acquire a highly reliable aging rate from the oscillator 41 that is in the air.

[0036] When the measurement of the aging rate is completed, the data processing device 1 determines 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 (S14). Next, the data processing device 1 stops applying voltage to the temperature change device 5. With the application of voltage stopped, the temperature change device 5 stops the low temperature setting of the oscillator 41 (S15).

[0037] After the low temperature setting for 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).

[0038] 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.

[0039] In this way, by bringing the oscillator 41 in the air to the seabed temperature, the measurement system S can determine 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 determined in this way, the measurement system S can improve 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.

[0040] [Start-up procedure for measuring device 4] Measurements for analyzing subseafloor geological structures are carried out periodically. For example, measurements are carried out over several days to several weeks once a year. For example, multiple measurement devices 4 are installed on the seabed when the measurement period arrives and are retrieved from the seabed once the measurement is completed. However, installing multiple measurement devices 4 every time a measurement period arrives in this manner reduces measurement efficiency because the installation work requires a significant amount of time. Therefore, the measurement system S in this embodiment may be configured to have multiple measurement devices 4 installed on the seabed in advance measure seismic waves over multiple measurement periods spanning multiple years.

[0041] Since the measurement device 4 is battery-powered, if it is installed on the seabed and operates for a long period of time, the battery will be depleted in a short time. Therefore, the measurement system S may be configured so that multiple measurement devices 4 are activated at the start of a measurement period and stop measuring operation when the measurement period ends. The measurement devices 4 that have stopped measuring operation enter a sleep state in which their oscillators are stopped to reduce power consumption while maintaining the function of receiving acoustic signals from the data processing device 1. The measurement device 4 has, for example, a measurement state in which measurement is performed, a standby state in which the oscillator is operating but no measurement is being performed, and a sleep state in which the oscillator is stopped and no measurement is being performed.

[0042] 6 and 7 are diagrams for explaining the procedure for starting up multiple measurement devices 4. FIG. 6 schematically shows the state of multiple measurement devices 4 as viewed from above. The circle (◯) shown in FIG. 6 indicates a measurement device 4 installed on the seabed. The number below the circle is identification information (ID) for identifying the measurement device 4.

[0043] While the ship 100 is moving, the data processing device 1 transmits an acoustic signal containing 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. In FIG. 6, the dashed arrow represents the start command, and the solid arrow represents the synchronization command. The data processing device 1 may also transmit parameters required for measurement (for example, the sampling interval or preamplifier gain) to the measuring device 4.

[0044] The startup command includes a character string corresponding to an instruction to transition the measurement device 4 from a sleep state to a state where it can measure, 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 send a synchronization command including the absolute time recognized by the data processing device 1. In the following description, the process in which the data processing device 1 determines 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 sending a synchronization command to the measurement device 4 is referred to as "synchronization." The recording start command includes a character string corresponding to an instruction to start recording measurement data, and the ID of the measurement device 4.

[0045] A measurement device 4 in Figure 6 that has no letter in the circle (for example, a measurement device 4 with an ID of 0606) is in a stopped state. A measurement device 4 with a "W" in a dashed circle indicates that it has received a startup command and is currently executing startup processing. A measurement device 4 with a "W" in a solid circle indicates that it has completed startup but has not yet completed synchronization. A measurement device 4 with an "S" in a dashed circle indicates that it has received a synchronization command and is currently executing synchronization processing. A measurement device 4 with an "S" in a solid circle indicates that it has completed synchronization.

[0046] Fig. 7 is a diagram showing an example of a management table showing 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 startup has been completed, information indicating whether synchronization has been completed, the previous action (i.e., the action executed immediately before), and the time at which the action was executed are associated with each other. As can be seen from the states of the multiple measurement devices 4 within 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.

[0047] Specifically, the data processing device 1 transmits a synchronization command to the second measuring device 4 that has already started up, during the period from when the data processing device 1 transmits a startup command to the first measuring device 4 until startup of the first measuring device 4 is completed. By having the data processing device 1 sequentially start up and then synchronize the multiple measuring devices 4 in this way, the multiple measuring devices 4 can be brought into a state where they can measure in a shorter time than if the data processing device 1 transmits a startup command to each measuring device 4 and then waits until the measuring device 4 starts up. Furthermore, the measuring devices 4 can be brought into a state where they can measure in a shorter time and more reliably than if a person starts up each measuring device 4.

[0048] Furthermore, 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 activation commands to the multiple measuring devices 4 located ahead of the ship 100, and transmits synchronization commands to the multiple measuring devices 4 after the ship 100 has moved to a position ahead of the activated multiple measuring devices 4.

[0049] In this way, the data processing device 1 transmits commands to a plurality of measuring devices 4 located at the front of the vessel 100 on which the data processing device 1 is mounted and capable of receiving acoustic signals, and a plurality of measuring devices 4 located at the rear of the vessel 100 and capable of receiving acoustic signals. By operating in this manner, the data processing device 1 can bring the plurality of 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 at either the front or rear of the vessel 100.

[0050] 6 and 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 that includes an instruction to start recording immediately, or may be a command that indicates the time to start recording. The data processing device 1 may transmit recording start commands successively to multiple measurement devices 4 after synchronization of all measurement devices 4 is completed and before the seismic source generates seismic waves.

[0051] Installing multiple measuring devices 4 on the seabed every time a measurement is made would require a great deal of installation time and expense. Meanwhile, leaving the measuring devices 4 in operation for long periods of time poses the problem of battery depletion. In the measurement system S, the data processing device 1 sequentially starts and synchronizes multiple measuring devices 4 before a measurement period, and then puts the measuring devices 4 into a sleep state when the measurement period ends to reduce battery consumption. This configuration of the measurement system S allows multiple measuring devices 4 to measure seismic waves efficiently over long periods of time.

[0052] [Configuration of data processing device 1] FIG. 8 is a diagram showing the configuration of a 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 temperature reducing unit 182, a rate measuring unit 183, a hypocenter 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 included in the control unit 18 may be provided in a device other than the data processing device 1. For example, the functional units of the control unit 18 involved in controlling hypocenter generation, the functional units involved in controlling acoustic communication, and the functional units involved in temperature control may each be provided in a data processing device of a different ship.

[0053] 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 accordance with the control of the low temperature changing unit 182.

[0054] 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.

[0055] The acoustic signal transmitting unit 12 is an acoustic communication unit that transmits a first acoustic signal to the measurement device 4. For example, under 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 that is 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 within which the measurement device 4 can receive the first acoustic signal transmitted by the acoustic signal transmitting unit 12.

[0056] 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 each measuring device 4 whose acoustic signal receiving unit 13 has received a second acoustic signal including response data to the startup command.

[0057] 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 measurement data, to a measuring device 4 whose acoustic signal receiving unit 13 has received a response to the first acoustic signal including the synchronization command. That is, the acoustic signal transmitting unit 12 transmits a first acoustic signal including recording start data to a measuring device 4 that has transmitted response data to the synchronization command.

[0058] 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, multiple measuring devices 4 can start recording seismic waves by transmitting the recording start command once, thereby improving measurement efficiency.

[0059] 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 that indicates the internal time of the measuring device 4. The acoustic signal receiving unit 13 determines the internal time based on the time data included in the received acoustic signal, and notifies the data acquiring unit 186 of the determined internal time.

[0060] The data transmitter / receiver 14 is a communication interface for transmitting and receiving data to and from the optical communication device 3. For example, the data transmitter / receiver 14 transmits data input from the data acquisition unit 186 to the optical communication device 3, the data 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.

[0061] 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 may 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, for example, at a time within a predetermined range from the time when the last measurement is made within the measurement period. The data transmitter / receiver 14 notifies the data acquisition unit 186 of the acquired time data.

[0062] 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 identification unit 187. The absolute time acquisition unit 15 may also notify the data transmission / reception unit 14 of the absolute time.

[0063] The external communication unit 16 transmits the measurement results including the measurement data after correcting the internal time, which are input from the correction unit 188. The external communication unit 16 may transmit the measurement results to an external computer that analyzes the measurement results and executes a process to identify the sub-seafloor geological structure, or may transmit the measurement results to another processing unit included in the control unit 18.

[0064] 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 location 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 multiple measuring devices 4 in association with the IDs of the measuring devices 4.

[0065] 7. Furthermore, storage unit 17 stores a management table such as that shown in Fig. 7. Furthermore, storage unit 17 stores a plurality of pieces of measurement data acquired from a plurality of measurement devices 4, in association with the IDs of the measurement devices 4. Storage unit 17 stores the 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 correction unit 188 associates the time corrected from the internal time with the measurement data, storage unit 17 stores the measurement data in association with the corrected time.

[0066] The control unit 18 includes, 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 temperature reduction unit 182, a rate measurement unit 183, a hypocenter control unit 184, a command creation unit 185, a data acquisition unit 186, a time difference identification unit 187, and a correction unit 188.

[0067] 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, for example, by 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 seabed temperature setting for 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.

[0068] The temperature reducing unit 182 adjusts the temperature of the oscillator 41 built into the measuring device 4 located outside of seawater to the seabed temperature. The temperature reducing unit 182 adjusts the temperature of the oscillator 41 to the seabed temperature, for example, by controlling the temperature change device 5 to change the temperature of the oscillator 41. The temperature reducing unit 182 may input a voltage application signal to the voltage generating unit 10 instructing it to apply a voltage to control the temperature change device 5. If the temperature change device 5 is a Peltier element, the temperature reducing unit 182 may input a voltage application signal to the voltage generating unit 10 instructing it to pass a current in a direction such that the surface of the Peltier element in contact with the measuring device 4 becomes a heat absorption surface, and to apply a voltage of a magnitude necessary to adjust the temperature of the oscillator 41 to the seabed temperature. Upon receiving the voltage application signal, the voltage generating unit 10 applies a voltage to the temperature change device 5. The oscillator 41 built into the measuring device 4 may be adjusted to the seabed temperature by storing the measuring device 4 in a freezer whose interior has been adjusted to the seabed temperature for a predetermined period of time.

[0069] 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 location other than seawater reaches 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 reaches the seabed temperature, and measures the aging rate of the oscillator 41 that has reached the seabed temperature based on changes in the frequency of the oscillation signal over time.

[0070] 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 to instruct 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 is released, the measurement apparatus 4 is installed on the seabed.

[0071] The epicenter control unit 184 transmits an instruction to generate seismic waves to the epicenter 2. The epicenter control unit 184 causes the epicenter 2 to generate seismic waves, 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 seismic waves 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 seismic waves at a predetermined date and time, or may cause the epicenter 2 to generate seismic waves 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.

[0072] 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 locations where multiple measuring devices 4 are installed, which are stored in the memory unit 17. The command creation unit 185 creates a command including the ID of the selected measuring device 4.

[0073] As described with reference to Fig. 6, the command creation unit 185 creates a startup command for a measuring device 4 that is in a sleeping 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 startup 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.

[0074] 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."

[0075] The data acquisition unit 186 acquires various types of data transmitted from the measuring device 4. The data acquisition unit 186 acquires response data to the command transmitted by the acoustic signal transmission unit 12 via the acoustic signal reception unit 13. The data acquisition unit 186 notifies the command creation unit 185 that the response data has been acquired.

[0076] When the data acquiring unit 186 acquires response data, it updates the content of the "last action" in the management table stored in the storage unit 17. For example, when the data acquiring unit 186 acquires response data indicating startup, it updates the "last action" corresponding to the ID of the measurement 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 measurement device 4 transmitted by the measurement device 4 in response to receiving a synchronization command, it updates the "last action" corresponding to the ID of the measurement 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 in the response data with the ID of the measurement device 4, and stores them in the storage unit 17.

[0077] 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.

[0078] 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.

[0079] Furthermore, the data acquiring unit 186 acquires measurement data from the measurement device 4 via the data transmitting / receiving unit 14. The data acquiring unit 186 acquires multiple pieces of measurement data each indicating a measurement value corresponding to a different time. For example, after the measurement period has ended, the data acquiring unit 186 acquires multiple pieces of measurement data that the optical communication device 3 has collected from the measurement device 4 via optical communication from the data transmitting / receiving unit 14. The data acquiring unit 186 associates the acquired measurement data with the ID of the measurement device 4 and stores it in the storage unit 17, thereby enabling the time difference identifying unit 187 to refer to the measurement data.

[0080] The time difference determination unit 187 determines the time difference between the absolute time and the internal time of the measurement device 4. For example, the time difference determination unit 187 determines 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.

[0081] 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 absolute time at each time point 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 amount of time drift identified by the time difference identification unit 187.

[0082] 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 equation 1.

number

[0083] The meaning of each term in Equation 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 (time t0) a: Aging rate y0: Frequency error at time t0

[0084] The time difference E0 at the time when the measurement device 4 is dropped into 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 dropped into the seabed. y0 is an error from the design value that occurs when the frequency of the oscillator 41 changes due to a change in temperature caused by the measurement device 4 being dropped from the air into the sea. The method for determining y0 will be described later.

[0085] FIG. 9 is a graph showing the amount of time drift over time. The horizontal axis represents the number of days that have passed since the measurement device 4 was dropped into the sea. The dotted curve represents the time drift calculated using Equation 1 (a = 1.68 × 10 -12 9 shows the predicted time drift (left vertical axis) calculated by the equation (assuming that y0 is the theoretical time drift). The solid curve sloping upward to the right indicates the theoretical time drift (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 and the theoretical time drift. The correction unit 188 calculates the time drift E(t) based on Equation 1 using y0 as a fitting parameter. The correction unit 188 then identifies y0 at which the residual error between the theoretical time drift and the predicted time drift is minimized at the time (E1 in FIG. 9) when the measurement device 4 is recovered from the sea.

[0086] 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. For example, the correction unit 188 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 dropped 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.

[0087] 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.

[0088] The correction unit 188 then 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, which is the internal time to be corrected, by adding, for example, 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 to the second internal time (S185).

[0089] [Configuration of measurement device 4] 11 is a diagram showing the configuration of the measurement device 4 according to the first embodiment. The measurement device 4 includes 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 includes a seismic wave measuring unit 481 and a data communication unit 482.

[0090] The oscillator 41 generates an oscillation signal used to measure the internal time of the measurement device 4. The oscillator 41 may be, for example, a temperature-compensated crystal oscillator (TCXO). A TCXO is an oscillator with a built-in temperature compensation circuit for correcting frequency fluctuations due to temperature changes. Unlike an oven-controlled oscillator (OCXO), a TCXO does not have a thermostatic bath. Therefore, using a TCXO has the advantage of eliminating the power required for temperature control of a thermostatic bath. In particular, if a large number of measurement devices 4 are installed on the seabed, preparing a thermostatic bath for each of the oscillators 41 would require a great deal of effort and power, but using a TCXO eliminates this effort and power. The oscillator 41 may also be, for example, a chip-scale atomic oscillator.

[0091] The sensor 42 generates a detection signal whose level changes in accordance with the vibration of the measuring device 4. The sensor 42 inputs the detection signal to the seismic wave measuring unit 481.

[0092] 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 the 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.

[0093] 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.

[0094] The storage unit 47 has storage media such as a ROM, a RAM, and an SSD. The storage unit 47 stores programs executed by the control unit 48. The storage unit 47 also stores measurement data created by the seismic wave measurement unit 481.

[0095] The control unit 48 includes, for example, a CPU. The control unit 48 executes a program stored in the storage unit 47, thereby functioning as a seismic wave measurement unit 481 and a data communication unit 482.

[0096] The seismic wave measurement unit 481 creates a plurality of measurement data associated with the internal time kept based on the oscillator 41. The seismic wave measurement unit 481 creates a plurality of measurement data indicating the sampled signal level (i.e., measurement value) by, for example, sampling the detection signal input from the sensor 42 at predetermined time intervals (e.g., 1 millisecond intervals). The seismic wave measurement unit 481 stores the plurality of measurement data in association with the internal time in the storage unit 47. Note that the seismic wave measurement unit 481 may keep the internal time by counting the oscillation signal input from the oscillator 41, or may determine the internal time based on data indicating the internal time input from the oscillator 41.

[0097] The data communication unit 482 transmits, via the acoustic signal transmission unit 44, response data to a command contained 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 contained 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 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.

[0098] 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.

[0099] [Effects of Measurement System S] As described above, in the measurement system S, by bringing the oscillator 41 in the air to the seabed temperature, it is possible to determine 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 determined 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, for example, an oscillator with normal aging characteristics is used instead of a chip-scale atomic oscillator with relatively good aging characteristics.

[0100] Furthermore, 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) with a thermostatic bath. As a result, less power is consumed than when temperature control is performed using an OCXO.

[0101] Second Embodiment In the first embodiment, the measurement device 4 is installed on the seabed after the low-temperature setting of the oscillator 41, which has reached the seabed temperature in the air, is stopped. However, in this case, as described with reference to FIG. 5 , the temperature of the oscillator 41, which 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 in the air at the seabed temperature. As a result, the amount of time drift from the internal time of the measurement device 4 at the time the measurement device 4 is immersed in the sea to the internal time to be corrected associated with the measurement data may differ slightly from the actual amount of time drift.

[0102] Therefore, in the second embodiment, the measurement device 4 is installed on the seabed while maintaining the temperature of the oscillator 41, which has reached the seabed temperature in the air. The second embodiment differs from the first embodiment mainly in that the measurement device 4 also has a temperature specifying unit 483 and a temperature reducing unit 484. Below, an overview of the processing flow according to the second embodiment will be explained using Figures 12 and 13.

[0103] [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 carried out. 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).

[0104] 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). As a result, the temperature of the oscillator 41 drops 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 the same as those in the first embodiment, and therefore will not be described here.

[0105] 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).

[0106] By doing so, even before and after the measurement device 4 is thrown into the sea, the oscillator 41 does not increase in temperature as in the first embodiment, and can be maintained in a low-temperature state as shown in FIG.

[0107] 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 battery built into the measuring device 4 stops maintaining the oscillator 41 at a low temperature (S28), but because the oscillator 41 is cooled by seawater, the low-temperature state can be maintained even in the sea, as shown in FIG.

[0108] The processes of receiving measurement data (S29) and correcting the internal time (S30) performed by the data processing device 1 are the same as those in the first embodiment, and therefore will not be described again.

[0109] In this way, in the second embodiment, the measurement device 4 is installed on the seabed while maintaining a low temperature relative to the oscillator 41 that has reached the seabed temperature in the air. This causes the frequency of the oscillator 41 to change in accordance with the aging rate measured in the air at the seabed temperature. This makes it possible to obtain a more accurate value 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 submerged in the sea to the internal time to be corrected that is associated with the measurement data. As a result, it becomes possible to correct the internal time with greater accuracy than in the first embodiment.

[0110] [Configuration of measurement 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 specifying 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 it can operate using a battery built into the measuring device 4 even after the measuring device 4 is thrown into the sea.

[0111] The voltage generating unit 40 has a circuit that generates a voltage to be applied to the temperature changing device 5. The voltage generating unit 40 generates a voltage based on power supplied from a battery (not shown) that supplies power to operate 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 control from the low temperature unit 484.

[0112] 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 powers the oscillator 41 and the voltage generating unit 40 that powers 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 powers the oscillator 41 and the voltage generating unit 40 that powers the temperature change device 5 be different.

[0113] The operation unit 49 is, for example, a touch panel. For example, in response to a user's selection of "battery activation mode" displayed on the operation unit 49, the operation unit 49 inputs an instruction signal to the low-temperature unit 484 instructing the voltage generation unit 40 to input a voltage application signal instructing the voltage generation unit 40 to apply a voltage for controlling the temperature change device 5. For example, the user selects the "battery activation mode" from the operation unit 49 when 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 the instruction signal to the measuring device 4 in response to a user's operation. Alternatively, a detection unit included in the measuring device 4 may input the instruction signal to the low-temperature unit 484 in response to detecting that the wiring of the data processing device 1 has been removed from the temperature change device 5.

[0114] The temperature specifying unit 483 specifies the seabed temperature at the seabed installation position of the measurement device 4 by the same processing as that performed by the temperature specifying unit 181 described in the first embodiment. The temperature specifying unit 483 inputs the acquired seabed temperature data to the cooling unit 484.

[0115] In response to receiving the instruction signal, the low temperature unit 484 inputs a voltage application signal to the voltage generation unit 40. Upon receiving the voltage application signal, the voltage generation unit 40 applies a voltage to the temperature change device 5. Upon receiving the voltage application, the temperature change device 5 low-temperatures the oscillator 41. In this way, the measurement device 4 is installed on the seabed while the low temperature unit 484 maintains control over the temperature change device 5.

[0116] After a predetermined time has elapsed since the temperature reducing unit 484 received the input of the measurement mode, the temperature reducing unit 484 inputs a voltage release signal to the voltage generating unit 40 to instruct the voltage generating unit 40 to stop applying voltage to control the temperature changing device 5. Upon receiving the voltage release signal, the voltage generating unit 40 stops applying voltage to the temperature changing device 5.

[0117] 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 when the measuring device 4 is cooled by seawater. By doing so, it is possible to reduce power consumption by the voltage generating unit 40 compared to when voltage continues to be applied even after the measuring device 4 is cooled by seawater.

[0118] [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 while maintaining the oscillator 41 at a low temperature after reaching the seabed temperature in the air. This causes the frequency of the oscillator 41 to change in accordance with the aging rate measured in the air at the seabed temperature. This makes it possible to obtain a more accurate value 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 submerged in 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 greater accuracy than in the first embodiment.

[0119] [Variations] In the measurement system S described above, an example has been described in which the measurement of the temperature reduction and 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 aging rate of the oscillator 41 may also be performed after the measurement device 4 installed on the seabed is retrieved.

[0120] In the measurement system S described above, an example has been described in which the control unit 18 of the data processing device 1 has multiple functional units, 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 on each data processing device.

[0121] The present invention has been described above using embodiments, but 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 functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0122] 1 Data processing device 2. Epicenter 3 Optical communication equipment 4. Measuring equipment 5 Temperature change devices 10 Voltage generation section 11 Location information acquisition section 12 Acoustic signal transmitter 13 Acoustic signal receiver 14 Data transmission and reception unit 15 Absolute time acquisition unit 16 External Communications Department 17 Memory section 18 Control Unit 40 Voltage generation unit 41 Oscillator 42 sensors 43 Acoustic signal receiver 44 Acoustic signal transmitter 45 Optical signal receiving unit 46 Optical signal transmitter 47 Memory section 48 Control Unit 49 Control 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 Unit 481 Seismic Wave Measurement Unit 482 Data Communications Department 483 Temperature identification part 484 Low Temperature Section

Claims

1. A measuring device installed on the seabed, The measuring device is an oscillator used to keep internal time; a temperature change device that changes the temperature of the oscillator so that the temperature of the oscillator becomes a seabed temperature; a processor for controlling the temperature change device such that the temperature change device changes the temperature of the oscillator to the bottom temperature; a seismic wave measurement unit that generates measurement data of seismic waves associated with an internal time when the seismic waves are detected in response to the seismic waves being emitted from a seismic source; A measuring device having:

2. The temperature change device further includes a first generating unit that generates a voltage to be applied to the temperature change device; the first generating unit stops applying the voltage after a predetermined time has elapsed since starting to apply the voltage, the time being required for the oscillator of the measuring device installed on the seabed to be cooled to the seabed temperature by seawater after the measuring device is thrown into the sea. The measuring device according to claim 1 .

3. The temperature change device is a material that absorbs heat on one side and releases the absorbed heat on the other side.

3. The measuring device according to claim 1 or 2.

4. The temperature change device is made of a material that can switch between a heat absorption surface and a heat radiation surface by changing the direction of the current flowing through it.

3. The measuring device according to claim 1 or 2.

5. the temperature change device is disposed in contact with an outer surface of the measurement apparatus; the processor controls the direction of the current flowing through the temperature change device so that the surface of the temperature change device in contact with the outer surface of the measurement apparatus becomes a heat absorption surface.

5. The measuring device according to claim 4.

6. further comprising an operation unit for a user to perform an operation; the first generating unit generates a voltage in response to the user performing an operation on the operating unit to apply a voltage to the temperature change device; The measuring device according to claim 2 .

7. the first generating unit generates a voltage in response to a wiring connecting an external power that generates a voltage to be applied to the temperature change device and the temperature change device being removed from the temperature change device; The measuring device according to claim 2 .

8. further comprising a second generating unit that generates a voltage to be applied to the oscillator; The measuring device according to claim 2 .

Images