the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Aug 2024
Research on clock synchronization method of marine controlled source electromagnetic transmitter base on coaxial cable
Abstract. Marine controlled source electromagnetic (MCSEM) method is widely used to reveal the electrical structure of shallow media below the seafloor. It is an indispensable geophysical means in the exploration of marine oil and gas exploration, natural gas hydrates and seafloor geological structures. The transmitter and receiver in electromagnetic detection equipment need to maintain a high temporal consistency, usually using high-stability pulse-per-second (PPS) generated by GPS or BeiDou navigation modules as a synchronization signal. Coaxial cable is a widely used tow cable, so it is necessary to design a clock synchronization method of marine controlled source electromagnetic transmitter using coaxial cable. This paper proposes a method for synchronizing the internal clocks of the transmitter with PPS using ship-borne power supply when coaxial cable is used as tow cable. In this method, the ship-borne high-power supply outputs a high-voltage AC signal that is synchronized with the 400 Hz signal output from GPS; the coaxial cable transmits AC high power electrical energy and control commands; the AC signal transmitted via the coaxial cable is converted into a stable and continuous 1 Hz signal by step-down, waveform shaping and frequency division for synchronizing the internal time pulses of the transmitter. The test result shows that the 1 Hz signal obtained by this method has a deviation of about 504 ns relative to the PPS. This deviation meets the need of MCSEM transmitter for clock synchronization.
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RC1: 'Comment on gi-2024-1', Anonymous Referee #1, 10 Sep 2024
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This research paper explores a clock synchronization method for marine controlled source electromagnetic transmitters using coaxial cable. The authors propose a new method utilizing a ship-borne high-power supply to generate a 400 Hz signal synchronized with GPS signals. This signal is then transmitted to the underwater transmitter via the coaxial cable and converted into a stable 1 Hz square wave signal to synchronize the transmitter's internal clock. The paper discusses the hardware design, signal processing unit, and analysis of clock synchronization deviation, ultimately demonstrating the effectiveness of this method in achieving accurate clock synchronization for marine transmitters.
The presented approach in itself probably has some innovation and new aspects, but mainly since it is a rather special kind of niche technique (although I am no expert on this marine matter). From a more technical standpoint, however, the scientific impact is a mere technical implementation rather than a new radical innovation. Several aspects are rather trivial, like e.g. the description of coaxial cables. The implementation is a rather straight forward technical implementation. The evaluation, especially, leave some aspects to be desired and hence, result in my poor ratings:
- There is no long term evaluation of the synchronization. How did you address/evaluate offset and drift problems?
- Â What happens if there is a short GPS outage?
- Â How does the signal jitter? How does the distribution look-like? From the small number of presented measurements no such information can be reasonably obtained.
Language wise, the paper is readable to some extent, has, however some issues like missing conjunctions or repeated words ("the the", "power power" etc).
Out of curiosity:
- What is an "attitude module" that measures safety-related parameters?
- One image shows GPS coupled to the control chamber and one not (Fig. 2 and Fig. 8). Is it really so that GPS is coupled to the control chamber temporarily before it is submerged? What do you do when there is a short outage when everything is submerged, do you need to pull-in everything that is submerged to restart anew?
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Citation: https://doi.org/10.5194/gi-2024-1-RC1 -
AC1: 'Reply on RC1', Zhibin Ren, 25 Sep 2024
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Dear reviewer,
Thank you very much for taking the time to review our manuscript entitled "Research on clock synchronization method of marine controlled source electromagnetic transmitter base on coaxial cable". We greatly appreciate your valuable comments, which have helped us improve the quality of our paper.
First and foremost, we would like to express our sincere apologies for the delay in responding to your valuable comments. Since September 9th, our team has been engaged in crucial fieldwork at sea, which unfortunately limited our ability to respond until today. We deeply appreciate your patience and understanding.
The responses to your feedback have been included in the attached PDF. Kindly check the attachment.
Your Sincerely,
Zhibin Ren
rzb@email.cugb.edu.cn
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CC1: 'Comment on gi-2024-1', fusheng shi, 03 Dec 2024
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This paper presents a method of clock synchronization using power supply. This method can be applied to the operation of marine controlled source electromagnetic transmitter using coaxial cable. The author has introduced the principle of this method, the hardware design, the implementation process, and the experimental results. The method synchronizes the sine wave output of the power supply with the PPS, transmits it to the underwater equipment via a coaxial cable, and then obtains a 1 Hz synchronization signal through voltage reduction, shaping, and frequency division. The feasibility of this method is proved by experiments. This method is a new approach and it can help to extend the application conditions of the transmitter from optical-electric composite cables to coaxial cables. Some figures in the manuscript are aesthetically pleasing.
However, there are some areas in the manuscript that could be strengthened. I hope my suggestions can help improve the quality of the manuscript and look forward to the updated manuscript.
- The 400Hz synchronous square wave signal is transmitted to the Marine large power supply through RS485. The RS485’s communication rate directly affects the accuracy of the synchronous signal, but this effect has not been analyzed in the article. Please provide additional information on the RS485’s communication rate and analyze its impact on the synchronization accuracy.
- The description of the coaxial cable structure can be streamlined.
- Some parts contain repetitive wording, please revise them.
- In the conclusion part, the positive impact on Marine operations can be a more specific.
Citation: https://doi.org/10.5194/gi-2024-1-CC1 -
AC2: 'Reply on CC1', Zhibin Ren, 13 Dec 2024
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Dear reviewer,
Thank you very much for taking the time to review our manuscript entitled "Research on clock synchronization method of marine controlled source electromagnetic transmitter base on coaxial cable". We greatly appreciate your valuable comments, which have helped us improve the quality of our paper.
Below, we provide detailed responses to each of your comments.
Reviewer Comment 1: The 400Hz synchronous square wave signal is transmitted to the Marine large power supply through RS485. The RS485’s communication rate directly affects the accuracy of the synchronous signal, but this effect has not been analyzed in the article. Please provide additional information on the RS485’s communication rate and analyze its impact on the synchronization accuracy.
Response: Thank you for your feedback on the manuscript on the RS485 communication. Indeed, using RS485 does introduce delays. Generally speaking, the maximum communication rate of RS485 can reach 10 Mbps. In this manuscript, we directly connected the 400Hz signal output from the GPS to the differential input of the RS485. The direction of RS485 is set to unidirectional, so the delay introduced is mainly the input-output delay. Through actual testing, we observed the waveform of the 400 Hz signal before and after RS485 transmission and found that the delay is less than 50 ns. Therefore, we believe that the delay caused by RS485 in the time synchronization method designed in this paper is in the order of tens of nanoseconds.
In Section 3.2, we have added a figure titled "Comparison of PPS before and after RS485 transmission". This figure shows the rising edges of the 400 Hz signals at the input and output of RS485. We have already supplemented the description of this figure in the main text.
Reviewer Comment 2:Â The description of the coaxial cable structure can be streamlined.
Response: Thank you for your feedback on the coaxial cable structure statement. We have re-evaluated the narrative about the coaxial cable structure and concluded that it is redundant. We have already discussed that the coaxial cable consists of only two power lines, as opposed to the hybrid optical cable, in Section 1 "Introduction". Therefore, it is unnecessary to devote a significant amount of space to describing the structure of the coaxial cable. We have removed the original Figure 1 titled "The structure diagram of coaxial cable" and also deleted some parts of the description about the coaxial cable in the first paragraph of Section 2.
Reviewer Comment 3:Â Some parts contain repetitive wording, please revise them.
Response:Â Thank you for your feedback on the language details. We have reviewed the manuscript again and found two repeated words. We have corrected this problem in the manuscript. We have removed repeated "the" (Page 3, line 83 on the original manuscript) and "power" (Page 4, line 115 on the original manuscript). Additionally, we found no space between some numbers and their units. We have reviewed all numbers and units in the manuscript to ensure that there is a space between them. Furthermore, we will continue to revise the manuscript to improve its linguistic clarity and precision.
Reviewer Comment 4:Â In the conclusion part, the positive impact on Marine operations can be a more specific.
Response: The description of the positive impact in the conclusion section of the manuscript is not specific enough. The purpose of the clock synchronization method for the coaxial cable is to enable MCSEM transmitters to operate using coaxial cables. Currently, MCSEM operations have high requirements for vessels, and only some research ships meet these requirements. If the transmitter can be compatible with both coaxial and photoelectric composite cables, it will enable more vessels to have the capability for MCSEM operations, rather than being limited to a few specific ships. We have revised the end part of the Section "Conclusion: to highlight this specific factor of the coaxial cable.
Once again, we sincerely thank you for your thoughtful and constructive feedback. Your insights have greatly contributed to improving our manuscript. We look forward to submitting the updated manuscript to you.
Your Sincerely,
Zhibin Ren
rzb@email.cugb.edu.cn
Â
Citation: https://doi.org/10.5194/gi-2024-1-AC2
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