Underwater Positioning System Based on Drifting Buoys and Acoustic Modems

Round 1

Reviewer 1 Report (New Reviewer)

- The article's main concept(s)

Marine robotics is growing its space on ocean operations. AUVs, ROVs and ASVs are being used as new tools to perform maritime tasks. The maritime environment is harsh, involves pressure and underwater blocks all GPS signals.

Underwater navigation/positioning normally relies on acoustic beacons with LBL, SBL or USBL architecture. AUVs also use sonars or visual cameras/lasers to try to sense and navigate on the seafloor.

This paper presents a solution based on LBL (long baseline) acoustic position system. Each beacon is at the surface with GPS positioning and resends GPS information (position and time) to the underwater vehicle.

AUV can receive messages with GPS information by acoustic modems and estimate its position regarding four surface buoys (triangulation or trilateration methods).

In this case, the authors use drifting buoys with GPS receivers that are resending GPS time/position to the underwater asset. Each message allows the AUV to calculate the distance to the beacon (sound velocity time travel) and receive the information. The authors also present the architecture where each buoy transmit sequentially and the feasibility of the buoy transmission schedule.

 

- Overall Comment

In overall,

 This document shows a reasonable understanding of underwater navigation solutions based on LBL acoustic systems - their key factors. The work has a good theoretical base, using useful references and information of general knowledge.

 

It presents a new and very simple method where the authors use floating drifting buoys with GPS receivers that send GPS time/position by the acoustic modem (LBL) to the underwater vehicle – allowing it to calculate its distance related to each buoy and the buoy GPS position/time.

The manuscript has a simple structure, it is very short for a journal contribution. The idea is very simple. The abstract is very short.

The conclusions resume the paper's contribution and explain common sense knowledge.

Using drifting buoys – constrains the AUV operation. If the AUV is not following the surface current/wind affecting the buoys it will reduce the AUV operation and increase position errors due to the distance to the beacons.

For example, the SIDENAV project (http://www.lsa.isep.ipp.pt/pages/sidenav_home.html) addresses this topic – uses underwater USBL robotic landers for a satellite constellation that gives high precision localization to an underwater mining machine or an AUV, and also localizes all underwater robotic landers with a surface buoy. All the robotic landers have the ability to move and continuously track/follow the underwater asset.

…

 

- Weak and Strong points

Strengths

v  A good resume of underwater acoustic positioning systems regarding LBL;

v  A simple engineering solution – uses surface drifting buoys with relaying GPS info to underwater AUV;

v  .

Weakness

v  Very short Abstract;

v  Small paper for a journal – ideal for a conference;

v  Using drifting buoys will affect the AUV operation;

 

v  …

Author Response

These are the answers to comments of old reviewer 1. Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

This paper presents the underwater positioning system using drifting buoys for AUV positioning. There are some issues as folows:

1. One of the cores of this paper is the “designed third strategy”, namely differential positioning policy. However, some researchers have reported this kind of functional model (Harold T. Vincent II, 2001; Peiliang Xu et al, 2005; Shuang Zhao et al, 2019; Yanhui Cai et al, 2008).

2. There are no any consideration about errors related to sound speed structure, which is one of the most important error sources. Analysis and evaluation about the effect of sound speed errors and time asynchronization on AUV positioning should be presented.

3. Details about the test should be added, such as water depth, fundamental parameters about the hardware equipment, test time span, observation frequency and so on.

4. Observation structure of buoys is vital for positioning performance. How to guarantee drifting buoys not out of control and keep reasonable geometric configuration for AUV location?

Author Response

These are the answers to comments of old reviewer 2. Thank you.

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

An abstract is normally between 150 to 250 words, thus a concise and factual abstract is required to state briefly the purpose of the research, the principal results and the major conclusions. Add some of the most important quantitative results to the abstract. Focus on the advantages of the proposed method with respect to the obtained results. The abstract should be reformulated.

The novelty of the present work should be better stated and justified. The new author's contribution should be justified regarding the previous works in the literature. The literature review should be updated to help readers better understand the subject matter and novelty aspects of this work compared to the more recently published works.

In the Results section You have stated that figures 3 and 4 show the error vs. the receiver speed, when moving along a parallel or a meridian, respectively. It is not quite true: vs. the distance. Elaborate more clearly to what value the error was calculated. This estimated value of distance must be explained (measured to what accuracy because the true value is never known, GNSS measurements also have their accuracies).

Author Response

Here is the responses to reviewer 3. Thank you.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (New Reviewer)

1. The authors should provide a thorough description of the test, particularly regarding the simulation settings and considerations, as no actual experimental work was conducted.

2. This study focuses on utilizing drifting buoys for AUV positioning, which is essentially similar to the sea-surface moving LBL positioning system that has been developed for decades. However, the innovation of this work is not readily apparent. Regarding the positioning model, the authors should extensively reference relevant reports and achievements. Additionally, it would be beneficial to provide photographs or introductions of the necessary parameters for the investigated instruments.

If the aforementioned issues are not addressed, the manuscript cannot be accepted.

Author Response

Kindly read the attached file, thank you.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Reviewer 2 Report

A LBL acoustic repeater system of the GNSS positioning is presented in this manuscript. This reviewer regrets to report that the paper is far off the standard of acceptance as a quality journal paper and should be rejected outright due to the following major deficiencies.
1. Nothing is new about the presented method. The methods presented in this paper are well established technologies

2. Formula 24 in this paper says that when the buoy launching depth is consistent, the position (x, y and z) information of the target cannot be solved by the three equations corresponding to Formula 24. But in fact, according to the model given in the paper, when i and j are not equal and any one of 1, 2 and 3 is taken, only two independent equations can be obtained according to Formula 24, and only two unknowns can be solved. There are problems with the statement from line 239 to line 244 .

3. In Figure 1 and Part 4 (result), the placement spacing between the four buoys is not described, which has a lot to do with the time slot length design in the communication frame structure in Figure 2.

4. The time delay of the underwater targets transmitted by the positioning signals of the four buoys is different, and it is easy to arrive at the same time and cause acceptance failure. This paper does not introduce how the underwater targets receive the positioning signals of the four buoys without collision in the same positioning period.

5. From line 93 to line 99, there are sentences that have nothing to do with this manuscript, which reflects the author's attitude towards this article.

6. Underwater message transmission is the key to the operation of the system proposed in this manuscript. It is suggested to add a description of underwater acoustic communication, such as what modulation mode(DSSS, OFDM, or others) to use and what system parameters are.