Review Reports

Round 1

Reviewer 1 Report

The manuscript reports shipborne gravity measurements with an atomic gravimeter. The authors report series of tests on a lake to evaluate the performance of the gravimeter. Marine gravity measurements with an atomic sensor are rare in the literature and the results presented here are thus very interesting. However, the authors do not give enough details on the instrument, the data processing and the testing protocol to interest fully the community. With these supplementary information and other corrections (see below), I recommend this manuscript for publication.

Line 31 : Reference 2 is not appropriate. It is not a fundamental constant measurement.

Line 44 : Repeated measurement lines and crossing point error analysis are also used.

Line 80 : Important parameters on the atomic gravimeter are missing :

            - The repetition rate of the gravimeter

            - Accuracy and sensitivity in static of the gravimeter

            - detection protocol

            ….

Line 97 :  equation (3) is not at the right place. It should be after line 100.

Line 18 : The vibration correction protocol is not explained. Are the vertical movements of the boat vibrations? This protocol seems very important and has to be described.

Line 110 :No information about the inertial gyrostabilized platetom is given. Is it a commercial product? What is its accuracy?

Line 112 : information about the laser system and the control cabinet or references are missing.

Line 116 : What kind of classical accelerometer is used ? What are its characteristics?

Line 119 : What is cut off frequency of the high pass filter ?

Line 137 : Is the tilt modulation measurement acquired in ship mooring environment ?

Line 142 : What is the acquisition time of the gravity measurements ?

Figure 4, 5, 7, 8 : The vertical axis seems to be the gravity with an arbitrary offset. Since atomic gravimeters perform absolute measurements, the direct value of gravity should be given.

Figure 5 : Have the measured gravity values been filtered ?

Line 154 : More detailed with the CG5 comparison should be given. Where was the CG5 ? On the boat next to the gravimeter or on the ground? Detailed on systematic effects and their correction should be given.

Line 179 What is the diameter of the circle routes ?

Could the authors give some detailed about the accelerations which occurred during this tests. Do the authors expect the same precision with sea trial than lake ?

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

 

1.It is suggested that data should be used to confirm that it is 0.2mGal. 

”To perform a further evaluation on the accuracy of gravity measurement result, a comparison with a high-precision absolute gravity reference value obtained by a relative gravimeter of CG-5 was conducted. an external coincidence accuracy of 0.2 mGal of SAG has been obtained.“

 2. It can be seen from Figure 7 that the total gravity change of the survey line is only 4mGal, and the accuracy of 0.8mGal is not reliable, so it is recommended to adopt the relative error. The same problem Figure 8's 1.2mGal statistics.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This paper reports a shipborne gravity measurement using an atomic gravimeter, it’s performance was evaluated in ship mooring and sailing states. In ship mooring state, the accuracy has been demonstrated to be 0.2 mGal, and the internal consistency reliabilities are evaluated to be 0.8 mGal and 1.2 mGal under the conditions of straight line and circle navigation respectively. The method for testing the performance of SAG on the lake based on modulated Coriolis effect is novel and simple.

The article data is reliable and the writing is smooth. The experimental method is enlightening to peers. I suggest accepting for publication.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors take into account my recommendations and give more details on the instruments, data processing and testing protocol. However there is an inconsistency about gravimeter accuracy that must be addressed before publication (see below). After fixing this problem, I recommend this manuscript for publication

line 23 and line 68 : An accuracy of 0.2 mGal is claimed. However, the systematic effects table give an uncertainty of 0.6 mGal. 0.2 mGal is the difference between CG-5 and SAG. I think it is more appropriate to put 0.6 mGal for accuracy.

Line 108 : I do not understand why the accuracy in static is 10 µGal and the accuracy given in table 1 is 642.9 µGal. The systematic effects listed in the table 1 should be present in static.

line 175 : the term "external coincidence accuracy" may be confusing. I would replace by a difference of 0.2 mGal has been obtained between CG-5 and SAG measurements. What height correction has been taken into account for comparing the gravimeters?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf