Measuring device

Abstract

To enable accurate correction of the internal time. [Solution] The data processing device 1 includes a temperature determination unit 181 that determines the seabed temperature at the location on the seabed where a measuring device is installed that creates measurement data of seismic waves associated with an internal time in which seismic waves were detected in response to vibration waves being emitted from the source of the earthquake; a temperature reduction unit 182 that lowers the temperature of an oscillator 41 built into a measuring device located outside of seawater to the seabed temperature; a rate measurement unit 183 that measures the aging rate, which is the rate of change in the frequency of the oscillator 41 over time, when the temperature of the oscillator 41 built into the measuring device located outside of 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 has created the measurement data.

Description

Technical Field

[0001] The present invention relates to a measuring device for measuring seismic waves.

Background Art

[0002] Since the transmission frequency of a crystal oscillator changes over time, a technique for adjusting the transmission frequency is known (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A measuring device installed on the seabed that detects seismic waves in response to the generation of seismic waves from a seismic source measures the time when the seismic waves are detected by a built-in oscillator. However, since the frequency of the oscillator changes over time due to aging characteristics, a difference (time drift) occurs between the internal time, which is the time measured by the oscillator built into the measuring device, and the absolute time. As a result, the analysis accuracy of the subsurface geological structure based on seismic waves decreases.

[0005] In order to suppress the decrease in analysis accuracy, a method of correcting the internal time by previously measuring the aging rate, which is the rate of change of the oscillator frequency over time, in air can be considered. However, the value of the aging rate in air is different from the value of the aging rate on the seabed. Therefore, there is a problem that even if the aging rate in air is measured, the internal time cannot be accurately corrected.

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

[0007] The measuring device of the present invention includes an oscillator used for timing 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 of the oscillator changes, and a seismic wave measuring 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 seismic waves from the earthquake source.

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

[0009] The temperature-changing device may be made of a material that allows the heat-absorbing surface and the heat-dissipating surface to be swapped 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 the 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-absorbing surface.

[0011] The measuring device 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 include an operating unit for user operation, and the first generating unit may generate a voltage in response to the user performing an operation on the operating unit to apply a voltage to the temperature change device.

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

[0014] After starting the application of the voltage, after a predetermined time has elapsed from when the measuring device is dropped into the sea until the oscillator of the measuring device installed on the seabed is cooled to the seabed temperature by seawater, the application of the voltage may be stopped.

[0015] The measuring device may further include a second generating unit that generates a voltage applied to the oscillator.

Effect of the Invention

[0016] According to the present invention, there is an effect that the internal time can be accurately corrected.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing an overview of the seismic wave measurement system S. [Figure 2] It is a diagram showing an example of the temperature change of a conventional oscillator. [Figure 3] It is a diagram showing the relationship between the external device 1, the measuring device 4, and the temperature change device 5 according to the first embodiment. [Figure 4] It is a flowchart showing the flow of the measurement method according to the first embodiment. [Figure 5] It is a schematic diagram showing the change in the temperature of the oscillator during the implementation of the measurement method according to the first embodiment. [Figure 6] It is a diagram for explaining the procedure for starting a plurality of measuring devices 4. [Figure 7] It is a diagram showing an example of a management table indicating the state of each measuring device 4. [Figure 8] It is a diagram showing the configuration of the data processing device 1 according to the first embodiment. [Figure 9] It is a graph showing the amount of time drift over time. [Figure 10] It is a diagram showing an example of a flowchart showing the correction process of the internal time according to the present embodiment. [Figure 11] It is a diagram showing the configuration of the measuring device 4 according to the first embodiment. [Figure 12] It is a flowchart showing the flow of the measurement method according to the second embodiment. [Figure 13] It is a schematic diagram showing the change in the temperature of the oscillator during the implementation of the measurement method according to the second embodiment. [Figure 14] It is a diagram showing the configuration of the measuring device 4 according to the second embodiment.

Embodiments for Carrying Out the Invention

[0018] <First Embodiment> [Overview of the Measurement System S] FIG. 1 is a diagram showing an overview of the measurement system S. The measurement system S is an ocean physical exploration system for analyzing the submarine geological structure. In the measurement system S, a seismic wave is generated from a seismic source 2 such as an air gun or a sparker, and the data processing device 1 analyzes the submarine geological structure using the results of the measurement of the seismic wave by a large number of measurement devices 4 installed on the seabed.

[0019] 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 that can move in the ocean. The plurality of measurement devices 4 are installed on the seabed at intervals of a predetermined distance or more.

[0020] The data processing device 1 is, for example, a computer, acquires measurement data indicating the vibration state of the seabed observed by the plurality of measurement devices 4 at the timing when the seismic wave is generated, and analyzes the acquired measurement data. That is, the data processing device 1 analyzes the measurement data of the seismic wave detected by the measurement device 4 in response to the generation of the seismic wave from the seismic source 2 during the measurement period from a ship sailing on the sea toward the seabed. As shown in FIG. 1(a), the data processing device 1 controls the plurality of measurement devices 4 by transmitting and receiving acoustic signals, and receives the measurement data generated by the plurality of measurement devices 4. Further, the data processing device 1 acquires information indicating the absolute time from, for example, a PTP network or GPS (Global Positioning System).

[0021] The seismic source 2 generates vibration waves during the measurement period. The seismic source 2 generates vibration waves based on, for example, the control of the data processing device 1, but it may also generate vibration waves based on the control of a different control device (for example, a computer installed on a ship different from ship 100).

[0022] The optical communication device 3 acquires measurement data from at least one measuring device 4 by communicating optically with it based on the control of the data processing device 1. The optical communication device 3 emits a first optical signal to the measuring device 4 underwater, and receives a second optical signal transmitted by the measuring device 4 that received the first optical signal. The optical communication device 3 is connected to the data processing device 1 by cable C, and after diving to a position where it can communicate optically with the measuring device 4 based on the control of the data processing device 1, it communicates optically with the measuring device 4. The optical communication device 3 moves sequentially to the vicinity of multiple measuring devices 4 and acquires measurement data from multiple measuring devices 4 sequentially. Note that the measurement system S may have multiple optical communication devices 3, and multiple optical communication devices 3 may acquire measurement data from multiple measuring devices 4.

[0023] The measuring device 4 generates seismic wave measurement data associated with the internal time at which it detected seismic waves in response to the emission of seismic waves from the earthquake 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 the sensors of the measuring device 4, and includes, for example, measured values ​​generated by sampling the signal output by the sensors every 1 millisecond. The measurement data is associated with the internal time measured by the oscillator inside the measuring device 4. The measuring device 4 transmits the measurement data to the optical communication device 3 using an optical signal.

[0024] Incidentally, the internal time of the measuring device 4 is the time measured by the oscillator built into the measuring device 4, and therefore differs from the absolute time. Furthermore, due to the aging characteristics of the oscillator in the measuring device 4, the oscillator frequency changes over time. As a result, a difference arises between the internal time associated with the measurement data by the measuring device 4 and the absolute time. When there is a difference between the absolute time and the internal time, it becomes impossible to determine with high accuracy the relationship between the timing when the earthquake source 2 emitted vibration waves and the timing of the seismic waves indicated by the measurement data, which leads to a problem in that the accuracy of the analysis of the subseafloor geological structure based on seismic waves decreases.

[0025] To suppress the decrease in analysis accuracy, one possible method is to correct the internal time by pre-measuring the aging rate, which is the rate of change in the oscillator frequency over time. However, since the oscillator frequency differs depending on the temperature at which it is measured, the aging rate also differs 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 measuring device 4 installed on the seabed, 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 accuracy of the correction will be insufficient.

[0026] Figure 2 shows an example of the temperature change of a conventional oscillator. The horizontal axis represents the number of days elapsed, and the vertical axis represents the oscillator temperature. The words "Deployment" and "Retrieval" indicate the time when the measuring device 4 was deployed into the sea and the time when it was retrieved from the sea, respectively. These points are also the same for Figures 5 and 13, which will be shown later.

[0027] As shown in Figure 2, when the measuring device 4, which is in the air, is submerged in the sea, the oscillator temperature decreases. The aging rate of the oscillator in the air is different from the aging rate of the oscillator located on the seabed where the measuring device 4 is installed. As a result, there was a problem in that accurate correction of the internal time could not be performed even if the aging rate of the oscillator in the air was measured.

[0028] Therefore, in the measurement method according to this embodiment, the temperature change device of the measuring device 4 is used to change the temperature of the oscillator built into the measuring device 4, which is present in the air, to the seabed temperature, and the aging rate is measured when the oscillator temperature is the seabed temperature. By correcting the internal time using the aging rate measured when the oscillator temperature is the seabed temperature, the accuracy of the internal time correction is improved.

[0029] Furthermore, "seabed temperature" is not limited to the actual temperature of the seabed where the measuring device 4 is installed, but may be any temperature within a predetermined allowable range from the actual seabed temperature. Also, "oscillator temperature" may be the temperature on the surface of the measuring device 4 or the temperature inside the measuring device 4.

[0030] Figure 3 shows the relationship between the external device 1, the measuring device 4, and the temperature change device 5 according to the first embodiment. The external device 1 functions as an external power source that applies a voltage to the temperature change device 5 via wiring W to lower the temperature of the oscillator 41 built into the measuring device 4. The external device 1 may also 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 side and releases the absorbed heat on the other side. A Peltier element is an example of such a material. A Peltier element is an element that can swap its heat-absorbing surface and heat-dissipating surface by changing the direction of the current flowing through it. Therefore, if 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-absorbing surface. The temperature change device 5 may also be directly attached to the oscillator 41.

[0032] The temperature change device 5 may be, for example, a blower device that sends cold air from outside the measuring device 4 into the measuring device 4. The temperature change device 5 operates using external power in the air. The outline of the processing flow according to the first embodiment will be described below with reference to Figures 4 and 5.

[0033] [Overview of the processing flow] Figure 4 is a flowchart showing the flow of the measurement method according to the first embodiment. Figure 5 is a schematic diagram showing the change in the oscillator temperature during the measurement method according to the first embodiment. The data processing device 1 identifies the seabed temperature at the seabed installation location by acquiring seabed temperature data indicating the seabed temperature at the seabed installation location, which is the location on the seabed where the measurement device 4 is installed (S11). The data processing device 1 may also identify the seabed temperature at the seabed installation location by receiving a setting for the seabed temperature at the seabed installation location 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 Figure 5, the temperature of the oscillator 41 decreases to seabed temperature. In Figure 5, the period during which the temperature change device 5 operates to lower the temperature of the oscillator 41 to seabed temperature is indicated as the "device operating period." The device operating period is, for example, about one week. These points are also true for Figure 13, which will be shown later.

[0035] The data processing device 1 receives the oscillation signal output by the oscillator 41 from the measuring device 4 when the oscillator 41's temperature is at seabed temperature, and measures the aging rate of the oscillator 41 at seabed temperature based on the change in the frequency of the oscillation signal over time (S13). For example, the data processing device 1 acquires the average frequency, which is the average value of the oscillation signal frequency on an hourly basis, over a week, and measures the aging rate based on the change in the acquired average frequency. By setting the oscillator 41 to seabed temperature in this way, a highly reliable aging rate can be obtained from the oscillator 41 that is in the air.

[0036] Once the aging rate measurement is complete, the data processing device 1 identifies the time difference between the absolute time when the measuring device 4 is submerged in the sea and the internal time of the measuring device 4 at that time (S14). Subsequently, the data processing device 1 stops applying voltage to the temperature change device 5. With the voltage application stopped, the temperature change device 5 releases the cooling of the oscillator 41 (S15).

[0037] After the cooling of the oscillator 41 is released, the measuring device 4 is installed on the seabed (S16). As a result, as shown in Figure 5, the temperature of the oscillator 41, which has reached the seabed temperature in the air, rises temporarily, but once the measuring device 4 is installed on the seabed, the temperature of the oscillator 41 falls again. The measuring device 4 installed on the seabed creates seismic wave measurement data associated with the internal time at which it detected seismic waves in response to the emission of vibration waves from the earthquake 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 identifies the amount of time drift in the elapsed time from the internal time of the measuring 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. Then, the data processing device 1 corrects the internal time to be corrected associated with the measurement data by adding the time difference identified in S14 and the identified amount of time drift to the internal time to be corrected associated with the measurement data.

[0039] In this way, by setting the oscillator 41, which is present in the air, to 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 the correction of the internal time associated with the seismic wave measurement data measured by the measurement device 4 installed on the seabed.

[0040] [Startup procedure for measuring device 4] Measurements for analyzing the subseafloor geological structure are carried out periodically. For example, measurements are carried out annually over a period of several days to several weeks. Multiple measuring devices 4 are installed on the seabed when the measurement period arrives, and retrieved from the seabed when the measurement is completed. However, installing multiple measuring devices 4 each time the measurement period arrives in this way requires a great deal of time for installation work, resulting in poor measurement efficiency. Therefore, the measurement system S in this embodiment may be configured to measure seismic waves using multiple measuring devices 4 that have been pre-installed on the seabed over multiple measurement periods spanning several years.

[0041] Since the measuring device 4 is battery-powered, if it operates while installed on the seabed for a long period of time, the battery will be depleted quickly. Therefore, in the measuring system S, multiple measuring devices 4 may be configured to start up when the measurement period begins, and to stop measuring operations when the measurement period ends. When measuring operations are stopped, the measuring device 4 maintains the function of receiving acoustic signals from the data processing device 1, while stopping the oscillators it has and entering a sleep state to reduce power consumption. The measuring device 4 has, for example, a measurement state in which it performs measurements, a standby state in which the oscillator is operating but no measurements are being performed, and a sleep state in which the oscillator is stopped and no measurements are being performed.

[0042] Figures 6 and 7 illustrate the procedure for activating multiple measuring devices 4. Figure 6 schematically shows multiple measuring devices 4 viewed from above. The circles (〇) in Figure 6 represent measuring devices 4 installed on the seabed. The numbers below the circles are identification information (ID) to identify each measuring device 4.

[0043] The data processing device 1 prepares the measuring device 4 to begin measurement operation by transmitting an acoustic signal containing control information to the measuring device 4 within the range to which the acoustic signal can reach (for example, the area within the dashed frame in Figure 6) while the ship 100 is moving. Specifically, the data processing device 1 prepares the measuring device 4 to begin measurement operation by transmitting a start command, a synchronization command, and a recording start command. In Figure 6, the dashed arrows represent the start command, and the solid arrows represent the synchronization command. The data processing device 1 may also transmit parameters necessary for measurement (for example, sampling interval or preamplifier gain) to the measuring device 4.

[0044] The startup command includes a string corresponding to an instruction to transition the measuring device 4 from sleep state to a measurable state, and the ID of the measuring device 4. The synchronization command includes a string corresponding to an instruction to request the internal time of the measuring device 4, and the ID of the measuring device 4. The data processing device 1 may also send a synchronization command that includes the absolute time recognized by the data processing device 1. In the following description, the process by which the data processing device 1 determines the relationship between the absolute time and the internal time of the measuring device 4 based on the internal time received from the measuring device 4 by sending a synchronization command to the measuring device 4 is referred to as "synchronization". The recording start command includes a string corresponding to an instruction to start recording measurement data, and the ID of the measuring device 4.

[0045] In Figure 6, measuring devices 4 without any letters inside the circle (for example, measuring device 4 with ID 0606) are in a stopped state. Measuring devices 4 with a dashed circle containing "W" indicate that they have received a start command and are in the process of starting up. Measuring devices 4 with a solid circle containing "W" indicate that they have finished starting up but have not yet completed synchronization. Measuring devices 4 with a dashed circle containing "S" indicate that they have received a synchronization command and are in the process of synchronizing. Measuring devices 4 with a solid circle containing "S" indicate that synchronization has been completed.

[0046] Figure 7 shows an example of a management table that indicates the status of each measuring device 4. In the management table shown in Figure 7, the ID of the measuring device 4 is associated with information indicating whether or not startup is complete, information indicating whether or not synchronization is complete, the previous action (i.e., the action performed immediately before), and the time at which that action was performed. As can be seen from the status of the multiple measuring devices 4 within the dashed area in Figure 6 and the time in the management table in Figure 7, the data processing device 1 sends startup commands and synchronization commands to different measuring devices 4 in a time-division multiplexing manner.

[0047] Specifically, the data processing device 1 sends a synchronization command to the already running second measuring device 4 between the time it sends a start command to the first measuring device 4 and the time it takes for the first measuring device 4 to complete its startup. By sequentially starting up and synchronizing multiple measuring devices 4 in this way, the data processing device 1 can make multiple measuring devices 4 ready for measurement in a shorter time than if it were to wait for a measuring device 4 to start up after sending a start command to it. Furthermore, it can make the measuring devices 4 ready for measurement in a shorter time and with greater reliability compared to a person starting each measuring device 4 individually.

[0048] Furthermore, the data processing device 1 activates multiple measuring devices 4 while moving in a constant direction. As an example, as shown in Figure 6, the data processing device 1 sends activation commands to multiple measuring devices 4 located in front of the ship 100, and after the ship 100 has moved to a position ahead of the activated multiple measuring devices 4, it sends synchronization commands to the multiple measuring devices 4.

[0049] In this manner, the data processing device 1 transmits commands to multiple measuring devices 4 located in front of the vessel 100 on which the data processing device 1 is installed and capable of receiving acoustic signals, and to multiple measuring devices 4 located behind the vessel 100 and capable of receiving acoustic signals. By operating in this manner, the data processing device 1 can bring multiple measuring devices 4 into a measurement-ready state in a shorter time compared to when commands are transmitted only to measuring devices 4 located in either the front or rear of the vessel 100.

[0050] Although not shown in Figures 6 and 7, the data processing device 1 may send a recording start command to the synchronized measuring device 4 after receiving a response to the synchronization command from the measuring device 4 and completing the synchronization. The recording start command may be a command that includes an instruction to start recording immediately, or it may be a command that indicates the time to start recording. The data processing device 1 may send recording start commands to multiple measuring devices 4 in succession after the synchronization of all measuring devices 4 is complete and before the earthquake source generates vibration waves.

[0051] Installing numerous measuring devices 4 on the seabed each time a measurement is performed would incur significant time and expense for installation. On the other hand, keeping the measuring devices 4 operational for extended periods would lead to battery depletion. In the measurement system S, before the measurement period begins, the data processing device 1 sequentially starts and synchronizes multiple measuring devices 4, and when the measurement period ends, the measuring devices 4 are put into sleep mode to suppress battery consumption. With the measurement system S configured in this way, it is possible to efficiently measure seismic waves with numerous measuring devices 4 over a long period of time.

[0052] [Configuration of Data Processing Unit 1] Figure 8 shows the configuration of the data processing device 1 according to the first embodiment. The data processing device 1 includes a voltage generation unit 10, a position information acquisition unit 11, an acoustic signal transmission unit 12, an acoustic signal reception unit 13, a data transmission / reception unit 14, an absolute time acquisition unit 15, an external communication unit 16, a storage unit 17, and a control unit 18. The control unit 18 includes a temperature identification unit 181, a low-temperature unit 182, a rate measurement unit 183, an earthquake 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. Note that some of the functional units of the control unit 18 may be provided in devices other than the data processing device 1. For example, the functional units related to earthquake control, acoustic communication control, and temperature control of the control unit 18 may each be provided in data processing devices of other ships.

[0053] The voltage generation unit 10 is connected to the temperature change device 5 and has a circuit that outputs a voltage to lower the temperature of the temperature change device 5. The voltage generation unit 10 may be an external device other than the data processing device 1. The voltage generation unit 10 starts or stops applying voltage in accordance with the control of the cooling unit 182.

[0054] The location information acquisition unit 11 acquires location information indicating the location of the data processing device 1, that is, the location of the ship 100 on which the data processing device 1 is installed. The location information acquisition unit 11 acquires location information, for example, from radio waves received from GPS satellites, and determines the latitude and longitude based on the acquired location information. The location information acquisition unit 11 notifies the command creation unit 185 of the determined latitude and longitude.

[0055] The acoustic signal transmitting unit 12 is an acoustic communication unit that transmits a first acoustic signal to the measuring device 4. The acoustic signal transmitting unit 12 transmits a first acoustic signal that includes control data (e.g., various commands) input from the command creation unit 185, for example, based on the control of the command creation unit 185. The acoustic signal transmitting unit 12 transmits a first acoustic signal including a command to measuring devices 4 that are within a predetermined range from the position of the ship 100 indicated by the position information acquired by the position information acquisition unit 11, by referring to the positions of each of the multiple measuring devices 4 stored in the storage unit 17. The predetermined range is the range in which the measuring 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 a first acoustic signal to each of the multiple measuring devices 4, which includes a startup command, that is startup data for starting up the measuring device 4. The acoustic signal transmitting unit 12 transmits a second acoustic signal, which includes response data to the startup command, to the measuring device 4, which has been received by the acoustic signal receiving unit 13, and transmits a first acoustic signal that includes a synchronization command indicating the absolute time (i.e., a synchronization command including time data).

[0057] Furthermore, the acoustic signal transmitting unit 12 transmits a first acoustic signal, which is recording start data indicating the start of recording of measurement data, to the measuring device 4, whose response to the first acoustic signal, including the synchronization command, has been received by the acoustic signal receiving unit 13. In other words, the acoustic signal transmitting unit 12 transmits a first acoustic signal, which is recording start data, to the measuring device 4, which has transmitted the response data to the synchronization command.

[0058] The acoustic signal transmission unit 12 may send a recording start command that includes the ID of one measuring device 4, or it may send a recording start command that includes the IDs of multiple measuring devices 4 that have completed synchronization. The acoustic signal transmission unit 12 may also send a recording start command that includes information indicating that the command applies to all measuring devices 4. By sending such a recording start command, the acoustic signal transmission unit 12 can start recording vibration waves on multiple measuring devices 4 by sending the recording start command only 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, which has received a first acoustic signal. The acoustic signal receiving unit 13 receives, for example, a second acoustic signal indicating the internal time of the measuring device 4. Based on the time data contained in the received acoustic signal, the acoustic signal receiving unit 13 identifies the internal time and notifies the data acquisition unit 186 of the identified internal time.

[0060] The data transmission / reception unit 14 is a communication interface for sending and receiving data with the optical communication device 3. For example, the data transmission / reception unit 14 transmits data to the optical communication device 3 that includes an instruction to acquire the internal time from the measuring device 4, which is input from the data acquisition unit 186, and the optical communication device 3 receives time data indicating the internal time acquired from the measuring device 4.

[0061] The data transmission / reception unit 14 may notify the optical communication device 3 of the absolute time acquired by the absolute time acquisition unit 15, and the optical communication device 3 may receive time data in which the absolute time and the internal time are associated at the time the internal time was acquired from the measuring device 4. For example, the data transmission / reception unit 14 receives data indicating the internal time acquired by the optical communication device 3 from the measuring device 4 at a predetermined time within a certain range from the time when the last measurement within the measurement period is performed. The data transmission / reception unit 14 notifies the data acquisition unit 186 of the acquired time data.

[0062] The absolute time acquisition unit 15 acquires the absolute time, for example, from GPS satellites. The absolute time acquisition unit 15 notifies the time difference identification unit 187 of the acquired absolute time. 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 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 performs processing to analyze the measurement results and identify the subseafloor geological structure, or it may transmit them to other processing units of the control unit 18.

[0064] The storage unit 17 has storage media such as ROM (Read Only Memory), RAM (Random Access Memory), and 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. For example, the storage unit 17 stores the location of each of the multiple measuring devices 4 in association with the identification information of the measuring device 4. Specifically, the storage unit 17 stores the latitude and longitude of the measuring device 4 in association with the ID of each of the multiple measuring devices 4.

[0065] Furthermore, the storage unit 17 stores a management table as shown in Figure 7. In addition, the storage unit 17 stores multiple measurement data acquired from the multiple measuring devices 4, associated with the IDs of the multiple measuring devices 4. The storage unit 17 stores multiple measurement data associated with the internal time of the measuring device 4 at the time the measurement data was generated. Subsequently, when the time corrected from the internal time by the correction unit 188 is associated with the measurement data, the storage unit 17 stores the measurement data associated with the corrected time.

[0066] The control unit 18 includes, for example, a CPU (Central Processing Unit). By executing a program stored in the memory unit 17, the control unit 18 functions as a temperature determination unit 181, a low-temperature reduction unit 182, a rate measurement unit 183, an earthquake source control unit 184, a command creation unit 185, a data acquisition unit 186, a time difference determination unit 187, and a correction unit 188.

[0067] The temperature determination unit 181 determines the seabed temperature at the seabed installation location, which is the location on the seabed where the measuring device 4 is installed. The temperature determination unit 181 determines the seabed temperature at the seabed installation location by acquiring seabed temperature data, for example, from a drop-type water temperature system dropped from a ship 100. The temperature determination unit 181 may also determine the seabed temperature at the seabed installation location by accepting the setting of the seabed temperature at the seabed installation location from the user of the measurement system S. The temperature determination unit 181 may also refer to a database that records the seabed temperatures of various reference locations on the seabed and determine the seabed temperature of the reference location closest to the seabed installation location as the seabed temperature at the seabed installation location. The temperature determination unit 181 inputs the acquired seabed temperature data to the cooling unit 182.

[0068] The cooling unit 182 lowers the temperature of the oscillator 41, which is built into the measuring device 4 located outside of seawater, to the seabed temperature. The cooling unit 182 lowers the temperature of the oscillator 41 to the seabed temperature by, for example, controlling the temperature change device 5 to change the temperature of the oscillator 41. The cooling unit 182 may also input a voltage application signal to the voltage generation 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 cooling unit 182 may input a voltage application signal to the voltage generation unit 10 instructing it to flow a current in the direction that the surface of the Peltier element in contact with the measuring device 4 becomes the heat-absorbing surface, and to apply a voltage of the magnitude necessary for the temperature of the oscillator 41 to reach the seabed temperature. Upon receiving the voltage application signal, the voltage generation unit 10 applies a voltage to the temperature change device 5. The oscillator 41 built into the measuring device 4 may also be lowered to the seabed temperature by housing the measuring device 4 in a freezer whose interior temperature is the seabed temperature for a predetermined time.

[0069] The rate measurement unit 183 measures the aging rate of the oscillator 41 when the temperature of the oscillator 41, which is built into the measuring device 4 located outside of seawater, reaches a specified seabed temperature. For example, the rate measurement unit 183 receives the oscillation signal output by the oscillator 41 from the measuring device 4 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.

[0070] The rate measurement unit 183 may input measurement completion data to the cooling unit 182, indicating that the aging rate measurement is complete. The cooling unit 182 may, upon receiving the measurement completion data, input a voltage release signal to the voltage generation unit 10, instructing it to stop applying voltage. Upon receiving 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 device 4 is installed on the seabed.

[0071] The seismic source control unit 184 transmits an instruction to the seismic source 2 to generate vibration waves. The seismic source control unit 184 generates vibration waves at the seismic source 2 after, for example, the acoustic signal transmission unit 12 transmits a first acoustic signal including a recording start command to a plurality of measuring devices 4. The seismic source control unit 184 transmits an instruction to the seismic source 2 to generate vibration waves after, for example, receiving notification from the data acquisition unit 186 that all measuring devices 4 are ready to measure. The seismic source control unit 184 may generate vibration waves at the seismic source 2 at a predetermined date and time, or it may generate vibration waves at the seismic source 2 in response to an instruction received from an external device. The data processing device 1 does not have a seismic source control unit 184, and an external control device may function as the seismic source control unit 184.

[0072] The command creation unit 185 creates commands for the acoustic signal transmission unit 12 to transmit to the measuring device 4. For example, the command creation unit 185 creates 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 location 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 storage unit 17. The command creation unit 185 creates a command that includes the ID of the selected measuring device 4.

[0073] As explained with reference to Figure 6, the command creation unit 185 creates a start command for a sleep-state measuring device 4 among a plurality of measuring devices 4 within a predetermined range. When the command creation unit 185 receives notification from the data acquisition unit 186 that the measuring device 4 corresponding to the created start command has been started, it creates a synchronization command for that measuring device 4. When the command creation unit 185 receives notification from the data acquisition unit 186 that the measuring device 4 corresponding to the created synchronization command has completed synchronization, it 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 "previous action" in the management table stored in the storage unit 17. When the command creation unit 185 inputs a startup command to the acoustic signal transmission unit 12, it sets the "previous action" corresponding to the ID of the measuring device 4 included in the startup command to "Starting Up". When the command creation unit 185 inputs a synchronization command to the acoustic signal transmission unit 12, it sets the "previous 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 data transmitted from the measuring device 4. The data acquisition unit 186 acquires response data to commands transmitted by the acoustic signal transmission unit 12 via the acoustic signal receiving unit 13. The data acquisition unit 186 notifies the command creation unit 185 that it has acquired the response data.

[0076] When the data acquisition unit 186 acquires response data, it updates the contents of the "previous action" in the management table stored in the storage unit 17. For example, when the data acquisition unit 186 acquires response data indicating that the device has been started, it updates the "previous action" corresponding to the ID of the measuring device 4 included in the response data to "startup complete". When the data acquisition unit 186 acquires response data that includes the internal time of the measuring device 4, which was transmitted by the measuring device 4 in response to receiving a synchronization command, it updates the "previous action" corresponding to the ID of the measuring device 4 included in the response data to "synchronization complete". The data acquisition unit 186 stores the absolute time when the synchronization command was sent and the internal time indicated by the response data in the storage unit 17, associating them with the ID of the measuring device 4.

[0077] When the data acquisition unit 186 acquires response data indicating that the measuring device 4 has started recording, it updates the "previous action" corresponding to the ID of the measuring device 4 included in the response data to "start recording". When the data acquisition unit 186 receives response commands to the start recording command from all measuring devices 4, that is, when the "previous action" of all measuring devices 4 becomes "start recording", it notifies the seismic source control unit 184 that measurement can be started.

[0078] Furthermore, the data acquisition unit 186 may acquire the emission time, which is the absolute time when the optical communication device 3 emitted the first optical signal, and the 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 measuring device 4 in response to the receipt of the first optical signal. The data acquisition unit 186 stores the emission time and the internal time in the storage unit 17, associating them with the ID of the measuring device 4, and notifies the time difference identification unit 187.

[0079] Furthermore, the data acquisition unit 186 acquires measurement data from the measuring device 4 via the data transmission / reception unit 14. The data acquisition unit 186 acquires multiple measurement data, each representing a measurement value corresponding to a different time. For example, after the measurement period has ended, the data acquisition unit 186 acquires multiple measurement data recovered by the optical communication device 3 from the measuring device 4 via optical communication from the data transmission / reception unit 14. The data acquisition unit 186 stores the acquired measurement data in the storage unit 17, associating it with the ID of the measuring device 4, so that the time difference identification unit 187 can refer to the measurement data.

[0080] The time difference identification unit 187 identifies the time difference between the absolute time and the internal time of the measuring device 4. For example, the time difference identification unit 187 identifies the time difference between the absolute time at the time the measuring device 4 is submerged in the sea and the internal time of the measuring device 4 at that time. If the internal time of the measuring device 4 is synchronized with the absolute time at the time the measuring device 4 is submerged in the sea, the time difference becomes 0.

[0081] 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 after the measurement device 4 installed on the seabed has created the measurement data. 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. Based on the aging rate, 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 since the measurement device 4 started creating the measurement data, and corrects the internal time associated with the measurement data using the time difference identified by the time difference identification unit 187 and the amount of time drift.

[0082] The correction unit 188 calculates the amount of time drift using the following formula 1, based on the aging rate measured by the rate measurement unit 183.

number

[0083] The meaning of each term in Equation 1 is as follows: E(t): Time drift amount E0: Time difference at the point when measuring device 4 is lowered into the sea (time t0) a: Aging rate y0: Frequency error at time t0

[0084] The time difference E0 at the point when the measuring device 4 is lowered into the sea can be reduced to 0 by synchronizing the internal time of the measuring device 4 with absolute time at the point when the measuring device 4 is lowered to the seabed. y0 is the error from the design value caused by the change in the frequency of the oscillator 41 due to the temperature change resulting from the measuring device 4 being lowered from air into the sea. The method for determining y0 will be described later.

[0085] Figure 9 is a graph showing the amount of time drift over time. The horizontal axis represents the number of days elapsed since the measurement device 4 was deployed into the sea. The dotted curve is given by equation 1 (a = 1.68 × 10 -12 The left vertical axis shows the predicted time drift amount calculated by (assuming this is the case). The upward-sloping solid line curve shows the theoretical time drift amount as a theoretical value (left vertical axis). The upward-opening parabola shows 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 and calculates the time drift amount E(t) based on equation 1. The correction unit 188 then identifies the y0 at which the residual error between the theoretical time drift amount and the predicted time drift amount is minimized at the time the measuring device 4 is recovered from the sea (E1 in Figure 9).

[0086] Figure 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 point in time when the time difference between the absolute time and the internal time of the measuring device 4 is identified. For example, the correction unit 188 identifies the internal time of the measuring device 4 at the point in time when the time difference (the time difference between the absolute time and the internal time of the measuring device 4 at the point in time when the measuring device 4 is submerged in 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 measuring 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 into "t" in equation 1 in which y0 is identified.

[0088] The correction unit 188 then corrects the second internal time (the internal time to be corrected) associated with the measurement data based on the identified time drift amount. For example, the correction unit 188 corrects the second internal time, which is the internal time to be corrected, by adding the time difference between the absolute time at the time the measuring device 4 is submerged in the sea and the internal time of the measuring device 4, and the time drift amount identified in S184 (S185).

[0089] [Configuration of measuring device 4] Figure 11 shows the configuration of the measuring device 4 according to the first embodiment. The measuring 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 an earthquake wave measuring unit 481 and a data communication unit 482.

[0090] Oscillator 41 generates an oscillation signal used for timing the internal time in the measuring device 4. Oscillator 41 is, for example, a temperature-compensated crystal oscillator (TCXO). A TCXO is an oscillator that incorporates a temperature compensation circuit to correct frequency fluctuations due to temperature changes. Unlike an oven-controlled oscillator (OCXO), a TCXO does not have an oven, so using a TCXO has the advantage that the power required for temperature control of the oven is not needed. In particular, when there are many measuring devices 4 installed on the seabed, providing an oven for each oscillator 41 would require a great deal of effort and power, but using a TCXO eliminates the need for such effort and power. Note that oscillator 41 may also be, for example, a chip-scale atomic oscillator.

[0091] Sensor 42 generates a detection signal whose level changes in response to vibrations in the measuring device 4. 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 unit 1. The acoustic signal receiving unit 43 inputs the command and absolute time data included 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 unit 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 commands 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, for example, the data communication unit 482, to the optical communication device 3.

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

[0095] The control unit 48 has, for example, a CPU. The control unit 48 functions as the seismic wave measurement unit 481 and the data communication unit 482 by executing a program stored in the memory unit 47.

[0096] The seismic wave measurement unit 481 creates multiple measurement data associated with an internal time measured based on the oscillator 41. The seismic wave measurement unit 481 creates multiple measurement data indicating sampled signal levels (i.e., measured values) by sampling detection signals input from the sensor 42 at predetermined time intervals (e.g., 1-millisecond intervals). The seismic wave measurement unit 481 stores the multiple measurement data in the storage unit 47, associating them with the internal time. The seismic wave measurement unit 481 may measure the internal time by counting the oscillation signals input from the oscillator 41, or it may determine the internal time based on data indicating the internal time input from the oscillator 41.

[0097] The data communication unit 482 transmits response data for commands included in the first acoustic signal received from the data processing device 1 via the acoustic signal receiving unit 43, via the acoustic signal transmitting unit 44. The data communication unit 482 also transmits response data for commands included in the optical signal received from the optical communication device 3 via the optical signal receiving unit 45, via the optical signal transmitting unit 46. When the data communication unit 482 receives a synchronization command, it obtains the internal time at the time the synchronization command was received from the oscillator 41 or the seismic wave measuring unit 481, and transmits response data including the obtained internal time.

[0098] Furthermore, the data communication unit 482 transmits multiple 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 multiple measurement data stored in the storage unit 47, associating them with the internal time.

[0099] [Effects of Measurement System S] As explained above, in the measurement system S, by setting the oscillator 41, which is present in the air, to the seabed temperature, the aging rate of the oscillator 41 can be determined 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 seismic wave measurement data measured by the measurement device 4 installed on the seabed is improved. As a result, even if an oscillator with normal aging characteristics is used instead of a chip-scale atomic oscillator with relatively good aging characteristics, for example, it becomes possible to accurately correct the internal time associated with the seismic wave measurement data.

[0100] Furthermore, in the measurement system S, by using a Peltier element or the like as a temperature change device 5 to adjust the oscillator 41 present in the air to seabed temperature, it becomes unnecessary to use an oscillator with a constant temperature chamber (OCXO). As a result, less power is consumed compared to when temperature control is performed using an OCXO.

[0101] <Second Embodiment> In the first embodiment, the measuring device 4 was installed on the seabed after the cooling of the oscillator 41, which had reached seabed temperature in the air, was released. However, in this case, as explained with reference to Figure 5, the temperature of the oscillator 41, which had reached seabed temperature in the air, temporarily rises before and after the measuring device 4 is introduced into the sea. As a result, the frequency of the oscillator 41 may not change according to the aging rate measured at seabed temperature in the air. Consequently, the amount of time drift from the internal time of the measuring device 4 at the time the measuring device 4 is introduced into the sea to the corrected internal time associated with the measurement data may deviate slightly from the actual amount of time drift.

[0102] Therefore, in the second embodiment, the measuring device 4 is installed on the seabed while maintaining a low temperature relative to the oscillator 41, which has reached seabed temperature in the air. The second embodiment mainly differs from the first embodiment in that the measuring device 4 also has a temperature identification unit 483 and a low-temperature unit 484. The outline of the processing flow according to the second embodiment will be explained below with reference to Figures 12 and 13.

[0103] [Overview of the processing flow] Figure 12 is a flowchart showing the flow of the measurement method according to the second embodiment. Figure 13 is a schematic diagram showing the change in the oscillator temperature during the measurement method according to the second embodiment. The data processing device 1 and the measuring device 4 identify the seabed temperature at the location on the seabed where the measuring 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 lowers the temperature of the oscillator 41 (S22). As a result, as shown in Figure 13, the temperature of the oscillator 41 decreases to seabed temperature. The processes of measuring the aging rate (S23) and identifying the time difference (S24) performed by the data processing device 1 are the same as those in the first embodiment, so their explanation is omitted.

[0105] The data processing device 1 stops applying voltage to the temperature change device 5 when the measuring device 4 is submerged in the sea. The temperature change device 5, having had its voltage removed, releases the cooling of the oscillator 41 (S25). Immediately thereafter, the measuring device 4 applies voltage to the temperature change device 5 using its built-in battery. As a result, the temperature change device 5 cools the oscillator 41 (S26).

[0106] In this way, the oscillator 41 can maintain a low temperature state as shown in Figure 13, without its temperature rising as in the first embodiment, both before and after the measuring device 4 is submerged in the sea.

[0107] Next, the measuring device 4 is installed on the seabed while the oscillator 41 remains at a low temperature (S27). After a predetermined time has elapsed since the measuring device 4 was submerged in the sea, the measuring device 4 stops applying voltage to the temperature change device 5. As a result, the low temperature applied to the oscillator 41 by the battery built into the measuring device 4 is released (S28), but since the oscillator 41 is cooled by seawater, it can maintain a low temperature even in the sea, as shown in Figure 13.

[0108] The processes performed by the data processing device 1 for receiving measurement data (S29) and correcting the internal time (S30) are the same as those in the first embodiment, so a detailed explanation is omitted.

[0109] Thus, in the second embodiment, the measuring device 4 is installed on the seabed while maintaining a low temperature relative to the oscillator 41, which has reached seabed temperature in air. As a result, the frequency of the oscillator 41 changes according to the aging rate measured at seabed temperature in air. Therefore, it is possible to obtain a more accurate value than in the first embodiment as the amount of time drift from the internal time of the measuring device 4 at the time the measuring device 4 is deployed into the sea to the corrected internal time associated with the measurement data. As a result, it is possible to correct the internal time with higher accuracy than in the first embodiment.

[0110] [Configuration of measuring device 4] Figure 14 shows the configuration of the 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 Figure 11 in that it has a voltage generation unit 40, an operation unit 49, a temperature identification unit 483, and a low-temperature unit 484. Furthermore, the temperature change device 5 according to the second embodiment differs from the temperature change device 5 according to the first embodiment in that it can operate using the battery built into the measuring device 4 even after the measuring device 4 has been submerged in the sea.

[0111] The voltage generation unit 40 has a circuit that generates a voltage to be applied to the temperature change device 5. The voltage generation unit 40 generates a voltage based on power supplied from a battery (not shown) that supplies power to operate each part of the measuring device 4. The voltage generation unit 40 is built into the measuring device 4 and starts or stops the application of voltage in accordance with the control of 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. Therefore, if the battery that powers the oscillator 41 and the voltage generator 40 that powers the temperature change device 5 are the same, there is a possibility that the power required to operate the oscillator 41 will be insufficient. For this reason, it is preferable to use different batteries for the oscillator 41 and the voltage generator 40 that powers the temperature change device 5.

[0113] The control unit 49 is, for example, a touch panel. The control unit 49, for example, when the user selects "battery-powered mode" displayed on the control unit 49, inputs an instruction signal to the cooling unit 484 instructing the voltage generation unit 40 to input a voltage application signal instructing it to apply a voltage to control the temperature change device 5. The user selects "battery-powered mode" from the control unit 49 when, for example, the measuring device is submerged in the sea. Note that the instruction signal input to the cooling unit 484 does not have to be input from the control 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 from the user. Alternatively, the detection unit of the measuring device 4 may input an instruction signal to the cooling unit 484 in response to detecting that the wiring of the data processing device 1 has been disconnected from the temperature change device 5.

[0114] The temperature determination unit 483 determines the seabed temperature at the seabed installation location of the measuring device 4 by performing the same processing as the temperature determination unit 181 described in the first embodiment. The temperature determination unit 483 inputs the acquired seabed temperature data to the cooling unit 484.

[0115] The cooling unit 484 inputs a voltage application signal to the voltage generation unit 40 in response to receiving an instruction signal. The voltage generation unit 40, having received the voltage application signal, applies a voltage to the temperature change device 5. The temperature change device 5, having received the applied voltage, lowers the temperature of the oscillator 41. In this way, the measuring device 4 is installed on the seabed while the cooling unit 484 maintains control over the temperature change device 5.

[0116] After a predetermined time has elapsed since receiving the input for the measurement mode, the cooling unit 484 inputs a voltage release signal to the voltage generation unit 40, instructing it to stop applying the voltage used to control the temperature change device 5. Upon receiving the voltage release signal, the voltage generation unit 40 stops applying the voltage to the temperature change device 5.

[0117] The predetermined time is, for example, the time from when the measuring device 4 is submerged in the sea until the oscillator 41 built into the measuring device 4, which is installed on the seabed, is cooled by the 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 the seawater. By doing this, the power consumption of the voltage generating unit 40 can be reduced compared to when voltage is continuously applied even after the measuring device 4 has been cooled by the seawater.

[0118] [Effects of Measurement System S] As described above, in the measurement system S according to the second embodiment, the measuring device 4 is installed on the seabed while maintaining a low temperature relative to the oscillator 41, which has reached seabed temperature in air. As a result, the frequency of the oscillator 41 changes according to the aging rate measured at seabed temperature in air. Therefore, it is 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 measuring device 4 at the time the measuring device 4 is deployed into the sea to the internal time to be corrected associated with the measurement data. As a result, it is possible to correct the internal time with higher accuracy than in the first embodiment.

[0119] [Differentiation] In the measurement system S described above, an example was described in which the low-temperature and aging rate measurements of the oscillator 41 are performed before the measurement device 4 is deployed into the sea. However, the low-temperature and aging rate measurements of the oscillator 41 may also be performed after the measurement device 4 installed on the seabed is recovered.

[0120] In the measurement system S described above, an example was described in which the control unit 18 of the data processing device 1 has multiple functional units. However, the data processing device 1 may have some of the multiple functional units, and the remaining functional units may be handled by one or more data processing devices. This makes it possible to reduce the processing load on each data processing device.

[0121] Although the present invention has been described above using 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 its gist. For example, all or part of the apparatus can be configured by functionally or physically distributing and integrating in 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 combinations are combined with the effects of the original embodiments. [Explanation of Symbols]

[0122] 1 Data Processing Device 2 earthquake epicenters 3. Optical communication device 4. Measuring device 5 Temperature change devices 10 Voltage generation unit 11 Location information acquisition section 12. Acoustic signal transmission section 13. Acoustic signal receiving section 14. Data transmission / 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 receiving section 44 Acoustic signal transmission section 45 Optical signal receiving section 46 Optical signal transmission unit 47 Memory section 48 Control Unit 49 Control section 100 ships 181 Temperature identification part 182 Low-temperature section 183 Rate Measurement Unit 184 Earthquake Source Control Unit 185 Command Creation Section 186 Data Acquisition Unit 187 Time difference identification part 188 Correction section 481 Seismic wave measurement unit 482 Data Communications Department 483 Temperature identification part 484 Low Temperature Section

Claims

1. An oscillator used for timing the internal time, A temperature change device for changing 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, A seismic wave measurement unit creates measurement data of the seismic waves associated with an internal time when seismic waves are detected in response to the emission of seismic waves from the epicenter, A measuring device having the following features.

2. The temperature-changing device is made of a material that absorbs heat on one side and releases the absorbed heat on the other side. The measuring device according to claim 1.

3. The aforementioned temperature-changing device is made of a material that can swap its heat-absorbing surface and heat-dissipating surface by changing the direction of the current flowing through it. The measuring device according to claim 2.

4. The temperature change device is installed so as to be in contact with the outer surface of the measuring device. The processor controls the direction of the current flowing through the temperature change device such that the surface of the temperature change device in contact with the outer surface of the measuring device becomes a heat-absorbing surface. The measuring device according to claim 3.

5. The device further comprises a first generating unit that generates a voltage to be applied to the temperature change device. The measuring device according to claim 1.

6. It further has an operating section for the user to perform operations, 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 5.

7. The first generating unit generates a voltage in response to the external power supply that generates the voltage applied to the temperature change device and the wiring connecting the temperature change device being disconnected from the temperature change device. The measuring device according to claim 5.

8. The first generating unit stops applying the voltage after a predetermined time has elapsed from the start of voltage application until the oscillator of the measuring device installed on the seabed is cooled to seabed temperature by seawater after the measuring device has been submerged in the sea. The measuring device according to claim 5.

9. The system further includes a second generating unit that generates a voltage to be applied to the oscillator. The measuring device according to claim 5.

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