Assessment of Real-Time GPS/BDS-2/BDS-3 Single-Frequency PPP and INS Tight Integration Using Different RTS Products
Round 1
Reviewer 1 Report
It is of great value to study a real-time PPP/INS tight integration model based on multi-GNSS single-frequency observations, which is a hot topic in the field of multi-sensor fusion navigation and positioning. The method is evaluated by a set of experiment dynamic data that is collected under the GNSS-challenging environments. I have several comments and/or questions concerning the contents and the presentation of the manuscript which may help improve the publication.
1. Could the authors give further explanation on Eq(6)? The symbols d1, d2, f1, f2 have not appeared in the previous equations.
2. The percentages of position differences within a certain level (0.6m or 0.3m, Line 339-342, 423, etc.) are used to measure the positioning accuracy. Could the authors please explain why 0.6 or 0.3 is selected as the threshold? Why not use the RMS or 95% confidence level? Similar cases also occur for the discussion of attitude offsets.
3. The first two photos in Fig. 2 seem meaningless. They can be deleted or else more information could be provided.
4. The language should be checked and improved all through the paper. The typos and/or grammatical errors include but are not limited to the following:
Line 19 & 179：content should be “satisfy”, since content is usually used as an a noun or an adjective
Line 317: it should be “Fig 3. describes the numbers of available satellites…”
Line 455: pitch should be heading?
Author Response
Review response 1 for manuscript remotesensing-1843884
Reviewer #1:
It is of great value to study a real-time PPP/INS tight integration model based on multi-GNSS single-frequency observations, which is a hot topic in the field of multi-sensor fusion navigation and positioning. The method is evaluated by a set of experiment dynamic data that is collected under the GNSS-challenging environments. I have several comments and/or questions concerning the contents and the presentation of the manuscript which may help improve the publication.
- Could the authors give further explanation on Eq (6)? The symbols d1, d2, f1, f2 have not appeared in the previous equations.
Answer: We provided more explanations on Eq. (6) and defined these symbols in the modified manuscript.
- The percentages of position differences within a certain level (0.6m or 0.3m, Line 339-342, 423, etc.) are used to measure the positioning accuracy. Could the authors please explain why 0.6 or 0.3 is selected as the threshold? Why not use the RMS or 95% confidence level? Similar cases also occur for the discussion of attitude offsets.
Answer: In this paper, we have presented the RMS values of position, velocity, and attitude differences. The reason we choose 0.3 as the threshold is that the distribution characters of position differences are more obvious under this condition. RMS can reveal the ensemble positioning accuracy, but positioning difference distributions can reveal more details of positioning performance. And it is similar for velocity and attitude solutions.
- The first two photos in Fig. 2 seem meaningless. They can be deleted or else more information could be provided.
Answer: We have further explained the meanings of corresponding figures in the modified paper.
- The language should be checked and improved all through the paper. The typos and/or grammatical errors include but are not limited to the following:
Line 19 & 179：content should be “satisfy”, since content is usually used as an a noun or an adjective
Line 317: it should be “Fig 3. describes the numbers of available satellites…”
Line 455: pitch should be heading?
Answer: We have checked and corrected the English expressions carefully in the modified paper.
Your comments and suggestions are highly appreciated.
Jie Lv, Zhouzheng Gao, Qiaozhuang Xu, Ruohua Lan, Cheng Yang, and Junhuan Peng.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The proposed contribution investigates a topic of current interest, with the growing success of PPP techniques. In the opinion of the reviewer the topic itself is close yet not perfectly on target with respect to the topics of Remote Sensing journal, but similar articles have been already published, and this evaluation is correctly left to the editor and to the editorial team.
The approach looks correct. The results are original enough, coherent with the discussion, and certainly interesting for reearchers working in the field. However, in order to have a really helpful contribution, some issues, mostly related to the presentation, should be considered:
- In the (quite long) abstract, acronyms of the sources of the used data (CAS, GFZ, WHU) are not clear, and maybe such a detail, as well as the relevant, very detailed results reported as (2) and (3) about the behavior of these data are not needed. The info is included in the paper, but it is not so general to be useful in the abstract itself. In the abstract more general sentences, referring the different performance obtained with different data should be ok, without reporting too many percentages.
- The introduction certainly includes a lot of information and many useful references. Howeve the explanation of the different concepts and steps is not always clear, and the logical sequence is not easy to follow. It is suggested to try to read again and ceheck with a non-author reader in order to verify that the presentation looks clear also to general public.
- The sentence in lines 65-67 "Relatively....each other." is not clear at all and its meanig cannot be understood by this reviewer (an probably by future readers).
- At line 67, a reference about the "new" system BDS3 can be usefully added, as the difference between BDS2 and BDS3 (as systems are named in the text) cannot be clear to all readers.
- line 172: be clear with pseudoranges P1 and P2 and duly state what they are. A reader could think thay belong to two different frequencies (but the paper is about single frequency) or to different systems.
- Line 218: what is the velocity lever arm? which is the difference with the position lever arm?
It should be also possible to improve the language by a check form a third-party reader fluent in English. Some examples of woords that are - in the opinion of this reviewer - not correct: line 55 "In lately yeras" should be "Recently"; line 84 "will be disturbed" should be "will decrease" ; line 177 "to content"(?); and line 215 "conducive"(?). Several other issues can be certainly identified by a fluent reader and then improved.
Reviewer 3 Report
The paper provides an assessment on the real-time tightly coupled integration among GPS, BDS-2, BDS-3 and IMU based on the single frequency observations and the real-time SSR products from three different IGS analysis centers. The authors present the corresponding mathematical models in detail and evaluate the presented methods by a vehicle-borne test data. In general, such a research topic is focused on by the precise positioning and navigation fields (i.e., automatic pilot, seamless positioning indoor and outdoor) and it is a meaningful work. However, to make this paper higher quality, further modifications should be provided according to the suggestions listed below. 1. The ‘tight integration’ is mentioned in the title, but the ‘tightly coupled integration’ is used in the KEYWORDS and the body part of the paper. They should stay the same. 2. Eq. (13), the expression is incorrected while the E < 30, it seems that the square operation is missing. 3. Eq. (14), it is mentioned that ‘ stands for the Doppler observation’, however it cannot be equal to the corresponding expression in at right, because their units are different. 4. Qk is not defined in Eq. (21). 5. Figure 1 could provide more information such as real-time SSR products. 6. The authors need to modify the English writing. 7. “…the percentages of Pitch attitude offsets within 0.5° are 32.99%, 66.32%, and 83.16%...”, it seems that the expressions are not accurate, re-analysis is needed here.
Author Response
Review response 2 for manuscript remotesensing-1843884
Reviewer #2:
The paper provides an assessment on the real-time tightly coupled integration among GPS, BDS-2, BDS-3 and IMU based on the single frequency observations and the real-time SSR products from three different IGS analysis centers. The authors present the corresponding mathematical models in detail and evaluate the presented methods by a vehicle-borne test data. In general, such a research topic is focused on by the precise positioning and navigation fields (i.e., automatic pilot, seamless positioning indoor and outdoor) and it is a meaningful work. However, to make this paper higher quality, further modifications should be provided according to the suggestions listed below.
- The ‘tight integration’ is mentioned in the title, but the ‘tightly coupled integration’ is used in the KEYWORDS and the body part of the paper. They should stay the same.
Answer: We have modified all the expressions in the manuscript in the revised paper.
- Eq. (13), the expression is incorrected while the E < 30, it seems that the square operation is missing.
Answer: We have corrected the description of Eq. (13) in the revised paper.
- Eq. (14), it is mentioned that ‘stands for the Doppler observation’, however it cannot be equal to the corresponding expression in at right, because their units are different.
Answer: We have modified the expression in Eq. (14) in the revised paper.
- Qk is not defined in Eq. (21).
Answer: We have added the definition in the revised paper.
- Figure 1 could provide more information such as real-time SSR products.
Answer: We have modified Figure 1 to provide more information of real-time orbit and clock products in the revised paper.
- The authors need to modify the English writing.
Answer: We have checked descriptions in the whole paper and corrected the corresponding expressions.
- “…the percentages of Pitch attitude offsets within 0.5° are 32.99%, 66.32%, and 83.16%...”, it seems that the expressions are not accurate, re-analysis is needed here.
Answer: We have checked and corrected the inaccurate expressions in the revised paper.
Your comments and suggestions are highly appreciated.
Jie Lv, Zhouzheng Gao, Qiaozhuang Xu, Ruohua Lan, Cheng Yang, and Junhuan Peng.
Author Response File: Author Response.docx
