JPH11118961A - Time correction system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce costs and power consumption and at the same time to simply build a system by correcting an error for the clocking result of itself being obtained by a clocking means. SOLUTION: A clock circuit 12 counts time based on a clock signal being provided in an undersea station 10. A CPU 13 corrects the error between the time at a clock circuit 12 and the absolute time. A transducer 15 converts a modulated transmission signal that is inputted by a modem 14 to an acoustic signal S, outputs the acoustic signal S, and converts the acoustic signal A being outputted from an undersea station 20 to a reception signal. A reference time generator 21 generates reference time information being synchronized with the absolute time according to time information from a GPS satellite. A CPU 22 outputs the reference time information as a transmission signal. A transducer 24 converts the modulated transmission signal that is inputted by a modem 23 to the acoustic signal S, and at the same time converts the acoustic signal S from the undersea station 10 to a reception signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time correction system used for time correction of a seafloor seismometer, for example.

[0002]

2. Description of the Related Art Conventionally, in a seafloor seismometer, a clock is corrected immediately before the start of observation by using a high-precision crystal oscillator in order to accurately specify an observation time of a waveform at an observation point. ("High precision digital ocean bottom seismometer MO
Development of OB-24 ”, Journal of the Ocean Acoustics Society, Vol. 24, No. 1,
pp39-47, 1997). In a land-based seismic observation system, in order to improve the time accuracy of a plurality of observation stations, for example, as shown in Japanese Patent Publication No. 60-21500, the oscillator of each observation station (child station) is connected to a transmission cable. It is synchronized with the master station's oscillator.

[0003]

By the way, in the conventional submarine seismometer, the accuracy of the crystal oscillator is at most 5 × 1.
Since it is 0 ^-7 about, the error between the time and the absolute time of the clock in the ocean bottom seismometers in accordance with the observation period becomes longer with the result in cumulative, there has been a problem that it is not possible to grasp the said error. Therefore, it is conceivable to use an ultra-high-precision atomic clock in place of the crystal oscillator. However, this method is not practical because the cost becomes extremely high and the power consumption becomes large. Also, in an earthquake observation system using transmission cables, a large amount of transmission cables is required. In particular, when this system is applied to a seafloor seismometer, an expensive submarine cable must be laid between the seafloor seismometer and the land station. there were. The present invention has been made under such a background, and an object of the present invention is to provide a clock correction system which can reduce cost and power consumption and can easily construct a system.

[0004]

According to a first aspect of the present invention, there is provided a communication means for performing communication between a submarine station and a marine station using an ultrasonic wave as a transmission medium, and a clock provided in the submarine station, A second clocking means provided in the maritime station for clocking absolute time, and a first clocking means provided in the maritime station and transmitted by the communication means. Calculating means for obtaining an error between the clocking result of the clocking means and the absolute time, and outputting information of the error to the first clocking means via the communication means; The clock means corrects the error with respect to its own clock result. The invention according to claim 2 is the clock correction system according to claim 1, wherein the clock correction system is provided in the submarine station,
Oscillating means for generating a clock signal;
The clocking means performs clocking based on the clock signal. The invention according to claim 3 is the clock correction system according to claim 1 or 2, wherein the second clock means clocks the absolute time using a global positioning system. Features.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a clock correction system according to an embodiment of the present invention.
In this figure, reference numeral 10 denotes a submarine station installed on the sea floor, and this submarine station 10 is provided with a seismometer (not shown). In the submarine station 10, an oscillator 11 generates a clock signal. The oscillator 11 has low power consumption and high frequency accuracy.
CXO (temperature compensated crystal oscilato
r: temperature-compensated crystal oscillator) and DTCXO. A clock circuit 12 performs clocking based on the clock signal, and outputs time information as a clocking result. This time information is used in the seismograph.

Reference numeral 13 denotes a CPU (Central Processing Unit) for controlling each part of the apparatus, which outputs various data input from a seismometer or the like as a transmission signal, and also generates an error between the time in the clock circuit 12 and the absolute time. Is corrected. Details of the operation of the CPU 13 will be described later.
Reference numeral 14 denotes a modem having a modulation / demodulation function.
While modulating the input transmission signal, the reception signal input from the transducer 15 is demodulated.

Reference numeral 15 denotes a transceiver, which converts a modulated transmission signal input from the modem 14 into an acoustic signal S as an ultrasonic wave and outputs it, while outputting it from a marine station 20 described later. The converted acoustic signal S is converted into a received signal.
A communication time measuring circuit 16 monitors a communication line between the CPU 13 and the modem 14, and includes a time when a transmission signal is output from the CPU 13 to the modem 14,
4 obtains the time at which the received signal was output from the clock circuit 12 to the CPU 13, and outputs each time information to the CPU 13.

The marine station 20 is installed on a marine vessel or a mooring buoy. Two-way communication is performed between the marine station 20 and the submarine station 10 via an acoustic signal S. In the marine station 20, the reference time 21 generates reference time information synchronized with the absolute time from time information from a GPS (Global Positioning System) satellite (not shown). 22
Is a CPU that controls each unit of the apparatus, and outputs the reference time information as a transmission signal. Details of the operation of the CPU 22 will be described later.

Reference numeral 23 denotes a modem having a modulation / demodulation function, which modulates a transmission signal input from the CPU 22 and demodulates a reception signal input from the transducer 24. The transducer 24 converts the modulated transmission signal input from the modem 23 into an acoustic signal S,
The sound signal S from the submarine station 10 is converted into a received signal. 2
Reference numeral 5 denotes a communication time measuring circuit for monitoring a communication line between the CPU 22 and the modem 23, the time when a transmission signal is output from the CPU 22 to the modem 23,
From the reference time information of the reference time generator 21, and outputs each reference time information to the CPU 22.

Next, the operation of the clock correction system according to the above-described embodiment will be described with reference to FIGS. FIG. 2 is a diagram for explaining the operation of the clock correction system according to one embodiment.
The time axis on the side is the time axis of the reference time generator 21, and the time axis on the submarine station 10 side is the time axis of the clock circuit 12.

At time T0 shown in FIG.
Assuming that a transmission signal is output from the modem 22 to the modem 23,
The transmission signal is modulated by the modem 23 and further converted to an acoustic signal S by the transmitter / receiver 24. Thereby, the acoustic signal S propagates underwater toward the submarine station 10 (see FIG. 2: A). Also, the CPU 2 sends the modem 2
When the transmission signal is output to the communication time measurement circuit 25,
Outputs the reference time information (time T0) of the reference time generator 21 to the CPU 22. Thereby, the CPU 22 recognizes that the acoustic signal S has been transmitted from the transducer 24 to the submarine station 10 at the time T0 (see FIG. 2).

The acoustic signal S propagating underwater to the submarine station 10 is received by the transducer 15 at a time T1 'at which a propagation time τ has elapsed from the time T0 shown in FIG. As a result, the acoustic signal S is converted into a reception signal by the transmitter / receiver 15, demodulated by the modem 14, and then input to the CPU 13. Also, from the modem 14 to C
When a reception signal is output to the PU 13, the communication time measurement circuit 16 outputs time information (time T 1 ′) from the clock circuit 12 to the CPU 13. As a result, the CPU 13 determines that at time T1 ′, the transducer 15 transmits the acoustic signal S from the marine station 20.
Recognizes that the message has been received.

At time T2 ', the CPU 13
Outputs the time information of the time T1 ′ and the time T2 ′ to the modem 14 as a response signal. As a result, the response signal is transmitted as an acoustic signal S to the marine station 20 via the modem 14 and the transducer 15 (see FIG. 2: B). Then, after the acoustic signal S is received by the transmitter / receiver 24 at the time T3 (see FIG. 2), it is input to the CPU 22 as a response signal via the modem 23.

Accordingly, the CPU 22 determines the time T1 'and the time T2' on the submarine station 10 from the response signal.
, The time T when the response signal is output from the modem 23
3, ie, the acoustic signal S (response signal)
Is obtained from the reference time information from the communication time measurement circuit 25. Next, the CPU 22 executes the following (1)
By substituting the times T3, T0, T2 ', and T1' into the equation, the propagation time τ (one-way) of the acoustic signal S from the marine station 20 to the submarine station 10 is obtained. τ = {(T3−T0) − (T2′−T1 ′)} / 2 (1)

Next, the CPU 22 substitutes the time T0 and the propagation time τ into the following equation (2) to obtain a signal reception reference time T1 at the reference time of the marine station 20. T1 = T0 + τ (2) The signal reception reference time T1 is equal to the length of the transceiver 2 of the marine station 20.
The acoustic signal S transmitted from the submarine station 10
5 corresponds to the absolute time.

Next, the CPU 22 obtains an error ΔT in the clock circuit 12 of the submarine station 10 by substituting the signal reception time T1 and the time T1 ′ into the following equation (3). ΔT = T1−T1 ′ (3) The error ΔT is the clocking result of the clock circuit 12 and the clocking of the reference time generator 21. This is the difference from the result (absolute time).

At time T4 shown in FIG.
The PU 22 outputs error information corresponding to the error ΔT obtained from Expression (3) to the modem 23. Thus, the error information is transmitted as an acoustic signal S to the submarine station 10 via the modem 23 and the transducer 24 (FIG. 2:
C).

At time T5 shown in FIG. 2, the acoustic signal S is received by the transmitter / receiver 15, demodulated by the modem 14, and input to the CPU 13 as a received signal. Thereby, the CPU 13 obtains the error information on the error ΔT from the received signal,
Output to Then, the clock circuit 12 corrects the clock result based on the error ΔT. Thus, the clock result of the clock circuit 12 becomes the same as the absolute time.

Here, in general, in the seismic observation, it is required that the error of the observation time is 10 ms or less. From this, when the TCXO is used as the oscillator 11 in the clock correction system according to the above-described embodiment, the clock precision is about 5 × 10 ⁻⁵ , and thus the clock correction is performed every 5 hours by one. By performing the operations a number of times, required clocking accuracy can be obtained.

As described above, according to the clock correction system according to the embodiment of the present invention, the error of the clock circuit 12 is corrected based on the absolute time. Power consumption can be reduced as compared with Therefore, the clock correction system according to one embodiment can be applied to long-term observation by a seafloor seismometer at the seafloor station 10 having a limited power supply capacity.

Further, according to the clock correction system according to the embodiment, the submarine station 10 and the marine station 20
It does not require submarine cables because it communicates with the Internet. Therefore, according to the clock correction system according to the embodiment, it is possible to save the cost and the period of laying the submarine cable, and thus it is possible to perform the earthquake observation in the sea area far from the land at low cost.

[0022]

As described above, according to the present invention,
Since communication is performed between the submarine station and the maritime station using ultrasonic waves as a transmission medium, no submarine cable is required. Therefore, according to the present invention, it is possible to save the cost and the period of laying the submarine cable, and therefore, it is possible to easily perform clock correction in a sea area far from land. Further, according to the present invention, since the clocking result of the first clocking means is corrected based on the absolute time, power consumption can be reduced as compared with the case where an atomic clock is used. it can. Therefore, according to the present invention, the present invention can be applied to long-term observation by a seafloor seismometer in a seafloor station having a limited power supply capacity. According to the second aspect of the present invention, since relatively inexpensive oscillating means is used, the cost can be reduced as compared with the case where an atomic clock is used. According to the third aspect of the present invention, since the absolute time is clocked using the global positioning system, the clock correction can be performed at low cost and with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a clock correction system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of the clock correction system according to the same embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Submarine station 11 Oscillator 12 Clock circuit 13 CPU 15 Transceiver 14 Modem 16 Communication time measurement circuit 20 Marine station 21 Reference time generator 22 CPU 23 Modem 24 Transceiver 25 Communication time measurement circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G01W 1/08 G01W 1/08 G H04L 7/00 H04L 7/00 Z

Claims (3)

[Claims] 1. A communication means for performing communication between a submarine station and a maritime station using an ultrasonic wave as a transmission medium; a first clock means provided in the submarine station for performing clocking; A second clock means for clocking the absolute time; and a clock signal provided by the marine station and transmitted by the communication means and transmitted by the first clock means and the absolute time. Calculating means for obtaining an error and outputting the error information to the first clock means via the communication means, wherein the first clock means performs A clock correction system, wherein the error is corrected. 2. The apparatus according to claim 1, further comprising: an oscillating unit that is provided in the submarine station and generates a clock signal, wherein the first clock unit performs clocking based on the clock signal. 2. The clock correction system according to 1. 3. The clock correction system according to claim 1, wherein the second clock unit clocks the absolute time using a global positioning system.