Development of a Lightweight Inertial Gravimeter for Use on Board an Autonomous Underwater Vehicle: Measurement Principle, System Design and Sea Trial Mission

Round 1

Reviewer 1 Report

Excellent paper, well writtened and with the origional innovation beyond the state of art, suggest to publish

Author Response

Thank you very much for your very complimentary comments on our article.

Reviewer 2 Report

The authors propose  an innovative instrument which allows to perform dynamic mea2 surements of anomalies of the Earth’s gravity field in the underwater domain.

The system, called  GraviMob (Gravimetry Mobile System), does not require a stabilized platform and is rigidly  attached to the carrier vehicule, in this case an Autonomous Underwater Vehicule (AUV).

The core  of the system consists of triads of accelerometers, thus giving the east, north, vertical components  of the local gravity vector.

They propose also a post-processing algorithm based on a kalman filer

 

They  tested the  instrumental prototype in the Mediterranean Sea during the year 2016.

The results of this comparison are reported in details

This is a very interesting piece.

There is a lot of information useful and encouraging feature applications.

With pure academic spirit I propose the following improvements:

1. The abstract must be rearranged better summarizing the sections (background, methods, results, discussion and conclusions)
2. You say in the intro”As part of our research activities in gravimetry, we are developing an innovative mobile gravity sensor that allows the dynamic measurement of the Earth’s gravity anomalies near seafloor…”. I suggest to be more explicit, for example “ the purpose of the study is to present the design, development and testing…”. You should valorize your idea even if a the end you have a prototype
3. Add a few rows and a flow chart in the methods introducing your organization by paragraphs.
4. In the discussion you cite only a reference “The method for performing such an adjustment has been described theoretically and simulated numerically in Verdun et al. [45].” Are not other study to compare
5. You could also add limitations here in the discussion. All the study have some limitations.
6. Equations are robust and correctly reported and obtained. Check alignment and presentation by worr, for example the (6)

Author Response

Thank you very much for your review and suggestions to improve our article.

Below are the responses to your comments.

Comments n°1 & 2

In line with your recommendations, we have modified the abstract and introduction to clarify the content of the article and its organisation. The changes have been highlighted in the attached version of the article.

Comment n°3

As you recommended, we have added a summary of the article after the introduction.

Comment n°4

In fact, the method of determining the parameters of a Markov model from the covariances of gravity is presented in Jekeli's book [24]. Jekeli uses analytical expressions for the covariance, whereas we have used empirical covariances derived from gravity measurements [45]. The method we have developed has been effectively validated on the analytical covariance models given by Jekeli. We have therefore added the corresponding reference in the article.

Comment n°5

You are right that the Gravimob prototype has some performance limitations. The essential limitations of the system come from the acceleration sensors and the AUV positioning and orientation as recalled in Section 4 (lines 519-521). We have also recalled them in the conclusion of the article.

Comment n°6

Alignment of the equations has been checked and corrected if necessary. Equations 6, 9, 10, 40, A14, A16 have been corrected accordingly.

Author Response File: Author Response.pdf

Reviewer 3 Report

I would like to commend the authors on such exhaustive research. I really have no major objections to the paper. The paper contains all the necessary components, even at times chapters are too long. My personal opinion is that the paper may be more appropriate for the Journal of Marine Science and Engineering, however, the paper can fit into a selected special issue within Remote Sensing. I suggest that the authors make minor "structural" corrections on the paper because they did not follow in total the instructions of the Remote Sensing editorial board in a few places. From the title (Format the title according to the instructions of the journal "Development of a Lightweight Inertial Gravimeter for use on Board an Autonomous Underwater Vehicle: Measurement Principle, System Design and Sea Trial Mission. The title of the paper is appropriate to the content presented"), abstract line 4 Vehicule - “Vehicle” and so on ... Furthermore, if possible, shorten the paper a bit to improve readability.

Author Response

Thank you very much for your very positive comments on our article.

In the revised version, we have corrected the title by adding capitals according to your recommendations. Thank you very much for your vigilance. We have also corrected the remaining typos in the text.

We understand your comment about the long length of some parts of the text, which is explained by our desire to give all the mathematical details of the methods we have developed. We would prefer to keep the text as it is rather than risk losing rigour by reducing the length of some parts of the text, especially the more mathematical ones. I hope you will understand our point of view and thank you in advance.