Limiting Accuracy of Height Measurement for a Precision Radar Altimeter in a Low Altitude Flying Vehicle above the Sea Surface
Round 1
Reviewer 1 Report
PLease align all figures accorging the text, please improve the numeration equations and add reference to equations in text. From line 118 improve the numeration.
In Fig. 5 change ordinate and abscissa description from russain to english. Line 175 check the formulus (double sign minus).
Author Response
Response to the Reviewers
Original Manuscript ID: remotesensing-1177659
Original Article Title: Limiting Accuracy of Height Measurement for a Precision Radar Altimeter in a Low Altitude Flying Vehicle above the Sea Surface
To: Remote Sensing Editorial Office
Re: Response to reviewers
Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear autors;
The topic of your study is very interesting for sea surface height reconstruction research. However, the mathematical analysis and numerical modeling presented in the draft is not enought in my view. Many mathematical equations are arcane and not readable for readers, the novelty and valuble conclusion in this study is limited. Therefore, I encourage the authors can improve the manuscript with scientific and readable structure, and consider a resubmitted version.
Author Response
Response to the Reviewers
Original Manuscript ID: remotesensing-1177659
Original Article Title: Limiting Accuracy of Height Measurement for a Precision Radar Altimeter in a Low Altitude Flying Vehicle above the Sea Surface
To: Remote Sensing Editorial Office
Re: Response to reviewers
Author Response File: Author Response.docx
Reviewer 3 Report
The presented article is devoted to mathematical analysis and numerical modelling of the estimation of the height measurement error by means of a precision radar altimeter (PRA). The PRA is installed in an aircraft that flies at a low altitude. The theme of the article is the fact that the classical analysis of the characteristics of radio signals, in terms of accuracy of altitude measurement on aircraft flying over solid terrain, cannot be used to measure altitude on aircraft flying at low altitudes above rippled sea level. For a undulating, uneven and changing sea surface, the simulation results, based on a stationary model of the earth's surface, are incorrect. The authors of the article came to the conclusion that even during the flight of the aircraft above the rippled sea surface; it is possible to minimize the error of altitude measurement. At the same time, however, they add that measuring altitude in such conditions has certain limitations for an accurate radar altimeter.
Content shortcomings of the article:
From the point of view of the topic of the article "Limitation of the accuracy of height measurement for RDP ..." and understanding of the physical nature of the issue, Figure 2 is very important for the reader. It can be seen from this figure that the sea level wave shapes the frequency spectrum of the reflected signal from which the instantaneous value of the measured altitude is shaped at the output of the discriminator. This is briefly discussed in sentences (lines 71-74). Figure 2 shows very well the effect of the relative position of the flying vehicle from the sea level on the local backscatter pattern. I consider that the changes in shape and the shifts in the backscatter patterns are so significant that it would be appropriate to give at least one reason for the lawfulness of such a change. E.g. Local dynamic change of the measured altitude during the flight of the vehicle, above the rising wave will create a Doppler increase in the frequency of the reflected signal, which in LFM means a local decrease in the value of the measured altitude.
Figure 2 is divided into two parts 2a) and 2b) for examples of changing the width of the backscatter pattern "??ор". According to the text below the picture, this is the dependence of the LBP on time and sea level profile. The different lower parts of these figures are due to the change in the value of ??ор = (0.1 and 0.34) rad. But the two upper parts of the pictures are drawn exactly the same in terms of the width of the main lobe. It is not possible to judge from the upper parts of the figures what causes the backscatter patterns shown on the lower part to change. Even the massive following text below the picture does not help to explain. There are 6 parameters, of which 2x5 parameters are the same for both images and only one parameter is different. It would be a good idea to edit one of the top of the images. Either show in Figure 2a) a series of narrower backscatter patterns, or in Figure 2b) a series of wider backscatter patterns. In order for the upper parts of Figures 2a), 2b) have a visually better resolution.
Deficiencies in the pictures
- Figure 2 is composed of two parts, these two separate parts of the figure are not marked a) and b) in the article, but the text below Figure 2 is divided into part a) and b),
- in Figure 2a) when the height "Hξ" is shifted to the right, it is not marked "-5m" on the horizontal axis,
- according to the serial number, there are eight figures in the article, in fact there are only seven pictures in the article, there is no picture with the serial number 3 in the article,
- Figure 5 is composed of two parts, these two separate parts of the figure are not marked a) and b) in the article, but the text under Figure 5 is divided into part a) and b),
- in Figure 7 there is no parameter designation on the vertical axis.
Deficiencies in mathematical relationships
a) there are a total of about 20 mathematical relations in the article, which are not arranged in a systematic order, (in the case of twenty relations, some relations also have a three-digit serial number, eg 157),
b) the text of the article requires the writing of extensive mathematical relations, but which do not have the same layout on the pages:
- unequal distribution of the left and right sides of the equation, for comparison of relations (3) and (16),
- unequal distribution of approximately equally long relationships on the page, relationships (16) and (157),
- for one quantity, relations (157) and (168) are divided into three lines, although they can be easily written into two lines,
- imperfect or incomplete record of the relationship, e.g. two consecutive signs "- -" or "+ +" relationship (19),
- unequal methodology of dividing the relationship into two lines:
Methodology 1:
in relation (10) the sign "-" at the end of the 1st line as well as at the beginning of the 2nd line,
in relation (16), the sign "x" at the end of the 1st line and at the beginning of the 2nd line,
Methodology 2:
in relation (101) the sign "+" only at the beginning of the 2nd line,
in relation (168) the sign "-" only at the beginning of the 2nd line.
Author Response
Response to the Reviewers
Original Manuscript ID: remotesensing-1177659
Original Article Title: Limiting Accuracy of Height Measurement for a Precision Radar Altimeter in a Low Altitude Flying Vehicle above the Sea Surface
To: Remote Sensing Editorial Office
Re: Response to reviewers
Author Response File: Author Response.docx
Reviewer 4 Report
This study presents mathematical analysis and numerical modeling for the estimation of measurement errors of height estimation over the sea surface for a precision radar altimeter installed in a low altitude flying vehicle. This paper presents the derivation of the estimation function and the analysis of the limiting accuracy of the height measurement. The results and conclusions are useful. However some elaboration is required.
1. P6, the sentence “The real process of wave formation includes, in addition to wind waves, waves of various nature, among which there are swell waves as well.”, what does it mean? Does the author want to explain?
2. P8, I don't know how to get the result of Figure 7? It is suggested to write down the detailed process, data source, parameters used, etc.
3. P4, The equation (10) is complicated. How to check its correctness? It is suggested to add simulation process.
4. The equation number is confused and there are errors, such as (101) should be (11), (112) should be (12), etc.
5. P3, although equation (1) and (2) are quoted, the significance of important symbols should be added.
6. P8, The unit of ordinate should be marked in Figure 7.
Author Response
Response to the Reviewers
Original Manuscript ID: remotesensing-1177659
Original Article Title: Limiting Accuracy of Height Measurement for a Precision Radar Altimeter in a Low Altitude Flying Vehicle above the Sea Surface
To: Remote Sensing Editorial Office
Re: Response to reviewers
Author Response File: Author Response.docx
Reviewer 5 Report
General comments:
Thanks for giving me the opportunity to review this research paper, I found the findings interesting. This paper studies mathematical analysis and numerical modelling for the estimation of measurement errors of height estimation over the sea surface for a precision radar altimeter installed in a low altitude flying vehicle. I recommend the paper to be published after minor revision.
Major corrections:
- Poor quality figures can impact a reader’s experience and result in an overall negative perception of the journal’s quality. I strongly suggest redrawing all the figures in better quality.
- The authors need to make sure all the parameters used in the formula have been explained and define in the text. For example, most of the parameters have not been defined in formula 2,3. Please check all the formulae and their parameters.
Minor corrections:
- Page 1, Line 20. Define PRA abbreviation (Precision Radar Altimeter) as this is the first time use in the paper.
- Page 2, Figure 1. The figure is adapted from [10]. It needs to be mentioned in the caption of the figure as well. The authors also need to define all the parameters shown in the figure in the caption too.
Author Response
Response to the Reviewers
Original Manuscript ID: remotesensing-1177659
Original Article Title: Limiting Accuracy of Height Measurement for a Precision Radar Altimeter in a Low Altitude Flying Vehicle above the Sea Surface
To: Remote Sensing Editorial Office
Re: Response to reviewers
Author Response File: Author Response.docx
