A Study on Pseudorange Biases in BDS B1I/B3I Signals and the Impacts on Beidou Wide Area Differential Services

Round 1

Reviewer 1 Report

The authors discuss the pseudorange bias due to possible satellite signal distortion. This interesting topic is mainly related to the different configurations with code correlator spacing parameters and correlator algorithms leading to the existence of pseudorange biases for different satellites tracked by different receivers. This phenomenon exists not only for satellite systems such as GPS, but also for the BeiDou system. The paper highlights a method to extract the pseudorange bias using a double-difference approach, and the experimental results show that the positioning accuracy is improved more significantly after eliminating the pseudorange biases. Although it is still difficult to fundamentally address all types of user receivers, this paper provides a proven and valuable solution. So this work has enough materials for publication in Remote Sensing after only some minor changes, which are listed below :

• L64, The launch date of SV19 satellite is wrong, it should be October 21, 1989
• L68, "there is inevitable deformation in satellites that do not have abnormal downlink navigation signals", you mean "do not" or "do" have abnormal?
• L80, "ref.22 and 23", Literature citation errors
• L84 "at the 1.5G band" ->"in the 1.5G frequency bands", "At other bands" -> "In the other bands"
• L91 "determine the algorithm" -> "derive the algorithm"
• L94 "pseudorange biases of BDS B1I and B3I signals" should be "pseudorange biases of BDS B1IB3I ionospheric free combination signals"
• L107,"TEC" should be STEC, the slant total electron content of the ionospheric delay
• Equation (18) and Equation (19) seem to be wrong, please check.
• L145, "station j to satellite i" should be "station I to satellite i". The same spelling mistake as L254, L264
• L159 " One satellite to all monitoring stations has the same error, which is set as the equivalent clock error by the BDS"
• Strictly speaking, this statement is wrong. The satellite orbit error is related to the user's position on the ground, and is not a constant.
• L299, The "OP" in the legend of Figure 8 should be "OS"
• L382, "According to Eq. (18)", should be "According to Eq. (19)"? this statement is confusing.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

It is of great value to study the pseudorange biases in BDS B1I/B3I signals. The authors have made novel contributions in both theory and experiments. I hope the following comments can help improve the manuscript.

1. Methodology and equations

(1) Does “the pseudorange residual” means the observation minus calculation (OMC)? If so, dρ=ρ-s0-…. Thus, in Eq.(5), s and the last term should be moved to left side of the equation, i.e. dρ=(the currently last term)-s=…. The similar case holds for Eq.(12). The authors please have a check, and maybe I am not correct.

(2) Since Eq.(1) and (2) are highly similar, I recommend that Eq.(1) can be removed to avoid repetition. Instead, some concise explanation is still necessary.

(3) In section 2.1, the paragraphs starting with “where” should not indent, since they are logically not new paragraphs.

(4) In the first paragraph of section 2.1, “zero baseline” is mentioned. To be exact, “receivers set at the same position” in the following should be “receivers connected to the same antenna”. I am not sure whether the authors implemented the zero baseline in this way. Please have a check. Anyway, two receivers can never be literally set at the very same position, and maybe a more scientific expression.

(5) The forms of the equations can be more elegant and explicit. To my knowledge, only the variables in equations should be in italic font, while the numbers and texts do not need to be italic. Therefore, the subscripts I and II, which is equivalent to numbers 1 and 2, do not need to be italic. And so are the subscripts “satclk”, “IPP”, “B1I” and “B3I”, etc.. In my opinion, the subscript I is not a wise choice. On one hand, it may confuse the variable name with its value. For example, i (lower case) is a variable name, and 1,2,… are its possible values. In the current Eq.(2), it seems that the subscript I (upper case) is not only the variable name, but also the value. On the other hand, the capital letter I in Eq.(9) and (10) has another meaning. I can understand that the authors may just want to keep consistent with the receiver types (I, II, III, …). Actually, it is not a vital problem, and my advice is for the author’s reference only.

(6) There is no sub- or superscript “j” in either Eq.(12) or (13), while “receiver j” is mentioned in the sentence between the two equation.

(7) In Eq.(18) the second and third minus signs should probably be plus signs. Please have a check.

(8) The right sides of Eq.(19) and (16) are the same, while their left sides are different. Could the authors please have a check or give more explanation on their equivalence? And the superscript in the second line of the left part of Eq.(19) is likely to be 2, not 1. Please have a check.

2. Experiment and results

(1) In section 2.2, it seems that Tables 3-5 are almost corresponding to Figures 3-5. However, only five satellites appear in the three tables, while only two stations appear in the three figures. Could the authors please explain why the five satellites (C20, C24, C33, C37, C45) are selected?

(2) The results shown in Figures 1 and 2 are not relate with those in Tables 3-5 or Figures 3-5, and the reference satellite is altered without explanation. I think the meaning of Figures 1 and 2 are not explicit. I suggest the two figures can be removed, or at least moved behind the current Figure 5. It will be even better to provide some more explanation and discussion on them.

(3) I think the paragraph of Lines 350-356 is also describing Figure 11. It will be better to start the paragraph with “Figure 11” instead of “Table 7”.

(4) The label for the vertical axis of Figure 11 should be something like RMS instead of SPP.

(5) The titles of 3.3 and 3.2 are exactly the same. Actually the process of eliminating the B1I/B3I pseudorange bias is not explicitly introduced. Could the authors give some advice for the users who want to eliminate the bias?

3. Language and format

There are some typos or grammatical errors, please check all through the manuscript and polish the language. For example,

(1) “Beidou System” is not the official name

(2) Line 84: 1.5G à 1.5GHz?

(3) Line 171: open servers (OP), OS?

(4) Line 205: near the other

(5) Line 369: the distance…is close à I and II are close to each other (PS: how close? Quantitative description will be better.)

(6) I think “B1IB3I” is not good, and B1I/B3I might be better

(7) Too many horizontal lines in the tables, erase them as Tables 3-5 or please follow the editor's advice.

Author Response

Please refer to the attachment 

Author Response File: Author Response.docx

Reviewer 3 Report

Dear Authors,

The paper is interesting to read. You have made an interesting contribution to BDS. My only comment is that you should consider more stations.

After a light english editing and perhaps to gain some place, you can gather Figure 1 and 2, and then Figure 3, 4 and 5.

 

Author Response

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Author Response File: Author Response.docx

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.