1. Thank you so much for your careful check, we apologize for the format problems and we revised that.
2. Thank you so much for your careful check, we apologize for the format problems again and that has been corrected.
3. We are grateful for your suggestion. The ship definitely affects wireless communication, and we tried to investigate it but it would take very complicated calculation, which will cause the software to run slowly and prone to errors, so we think the best way is to avoid this impact. As a result, on line 157 on page 9, we can see: ‘As the operation of the ship will interfere with wireless communication, after we release the buoy, the buoy will have a timing of 180 seconds before releasing the probe, as shown in Figure 8. As the expendable instruments are operated in a non-stop way, the ship has gone far within 180 seconds, which will not affect the wireless data transmission. As mentioned in the previous section, our wireless transmission distance can reach 2500 meters, and the ship can not travel beyond 2500 meters within 180 seconds. Therefore, the problem of hull interference with wireless communication is ingeniously solved.’ That is how we solved that problem. This is the best solution we can get after considering performance, method and cost.

1. Thank you for pointing out the calibration related problems. We are sorry that because every component is not exactly the same, such as resistors, capacitors and chips, there are certain differences in resistance, capacitance and performance. Although this difference may be very small, it does exist. Moreover, our magnification is relatively large, which may amplify these differences. Therefore, in order to ensure the accuracy of the measurement results, we need to accurately calibrate each XCP before leaving the factory, and write the parameters on the package of the product for the user to view.
2. We appreciate raising this point. We added the shortcomings of the XCP developed in this paper. For example, our calibration method needs to improvement, and the measurement parameters are not increased. In future, we will improve accuracy, study the effect of increasing the measurement parameters and measurement distance and improve the data transmission mode.

We truly appreciate the time and energy you dedicated in carefully reviewing our manuscript.

Your comments were highly helpful. We really appreciate your attention and comments on our manuscript. Our replies are listed as follows:

1、 We appreciate the reviewer for raising this point. XCP measured the induced electric field generated by the current cutting the geomagnetic field, which is a considerably small signal at a nanovolt level; therefore, if we want to measure accurate current information, we need to have certain requirements for the accuracy and stability of the instrument. The measurement adopts the method of measuring frequency, which needs to generate frequency signals and to compare and simultaneously measure the frequency and phase of multiple signals, including a lot of calculations. This will require a lot of resources; therefore, it is necessary to use the main control chip considering certain resources and performance, which also determines the price of the main control chip. The added modulation and demodulation part of XCP is mainly composed of amplifiers and resistance-capacitors. In this design, four operational amplifiers are used, and four amplifiers are integrated in one chip; therefore, the number of chips added is not large, that is, only two chips are added. In addition, the modulation and demodulation part needs counters. As shown in Figure 6 in this paper, there are two types of chips (CD4046 and CD4040), which are extremely low in cost. In addition, we have also replaced and optimized some other components of the whole system and selected the scheme with the best cost performance. Therefore, the cost of the system is lower.

2、Your suggestion is highly valued, and we express our gratitude for helping us improve our work. The previously developed XCP in the laboratory has been proved its performance. The previous XCP developed in the laboratory has gone through many ocean experiments and has been compared with other mature products (Doppler velocimeter). The results indicated that the XCP has stable performance and performs accurate measurement, which has been reflected in a previous study (Liu, 2017). Therefore, the previous XCP developed in the laboratory has a certain reference value. To better verify the performance of XCP considered in this study, we carried out further experiments comparing with a Nortek Vectrino Profiler Acoustic Doppler Velocimetry according to your suggestions and reflected the experimental results in the paper.

3、 Thank you for pointing out the thermal noise-related problems. In fact, we have considered the noise caused by the resistance of the attenuation circuit. The resistance thermal noise voltage is proportional to the resistance value, bandwidth, and square root of the temperature (Kelvin). In essence, the resistance thermal noise is unavoidable. However, to minimize the noise caused by resistance, we should avoid selecting resistors with larger resistance values. Through actual measurement and experiment, we found that the influence of resistance thermal noise can be ignored. In addition, the reason for designing the attenuation circuit is that an instrument that can generate small signals at the level of nanovolts is not available in the laboratory, and the attenuation network will only be used in the calibration and measurement in the laboratory. In the actual ocean test, originally, the signal is generated at the level of nanovolts; therefore, the attenuation network is not required in the actual ocean application.