the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 May 2021
Validation of tropospheric ties at the test setup GNSS co-location site Potsdam
Abstract. Atmospheric ties are theoretically affected by the height differences between antennas at the same site and the meteorological conditions. However, there is often a discrepancy between the expected zenith delay differences and those estimated from geodetic analysis, potentially degrading a combined solution employing atmospheric ties. In order to investigate the possible effects on GNSS atmospheric delay, this study set up an experiment of four co-located GNSS stations of the same type, both antenna and receiver. Specific height differences for each antenna w.r.t the reference antenna are given. One antenna was equipped with a radome at the same height and type as a antenna close to the ground. In addition, a meteorological sensor was used for meteorological data recording. The results show that tropospheric ties from the analytical equation based on meteorological data from GPT3, Numerical Weather Model, and in-situ measurements, and ray-traced tropospheric ties, reduced the bias of zenith delay roughly by 72 %. However, the in-situ tropospheric ties yield the best precision in this study. These results demonstrate, that the instrument effects on GNSS zenith delays were mitigated by using the same instrument. In contrast, the radome causes unexpected bias of GNSS zenith delays in this study. Additionally, multipath effects at low-elevation observations degraded the tropospheric east gradients.
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Interactive discussion
Status: closed
-
RC1: 'Comment on amt-2021-87', Anonymous Referee #3, 14 Aug 2021
General Comments
Four GNSS installations, with the antennas located at different heights, are used to compare the corresponding estimated equivalent zenith propagation delays. The observed offsets in the ZTD agrees with theory together with methods to determine the refractivity in the atmosphere in the layer(s) between the antenna installations.
There are no new findings. All results are predictable. Please excuse a simple example. The study reported in the manuscript is similar to dropping a ball from different heights and using a stop watch and conclude that the longer fall time observed when the ball is dropped from a higher level is in agreement with different models used to predict the value of the acceleration due to gravity.
Although the manuscript is reasonably well structured and parts are also interesting to read I miss new results as already said. Perhaps the authors are aware of this? The last paragraph in the conclusions starts with the sentence: "Further investigation is required as this experiment was conducted only for a short period of about five weeks." I recommend to extend the time series with many months, preferably covering at least one year in order to pin down systematic effects,
to quantify multipath effects (see e.g., King and Watson (2010)), to develop a model for the radome (see e.g., Liu et al. (2019)) and/or calibrate the antenna including the radome (see e.g. Schmid et al., (2016)).King, M. A., and C. S. Watson (2010), Long GPS coordinate time series: Multipath and geometry effects,
J. Geophys. Res., 115, B04403, doi:10.1029/2009JB006543.Liu, J., Li, L., Yong Zuo, Y., Huaming Chen, H., and Shaojie Ni, S. (2019),
Analysis of Performance Degradation Introduced by Radome for High-Precision GNSS Antenna,
Int. J. Antennas Propagat., Article ID 1529656, 13 pages,
https://doi.org/10.1155/2019/1529656.Schmid, R., Dach, R., Collilieux, X., Jäggi, A., Schmitz, M., and Dilssner, F. (2016),
Absolute IGS antenna phase center model igs08.atx: status and potential improvements,
J .Geod., 90:343–364, doi:10.1007/s00190-015-0876-3.
Specific commentsIn the abstract it is stated that the different atmospheric estimates obtained for the antenna with a radome is surprising. This is not consistent with the reference on page 8, line 158, to the IGS guidelines. It is well known that radomes can introduce offsets in atmospheric estimates and depending on the shape of the radome this offset may vary with the elevation cutoff angle used in the analysis.
In Subsection 3 there is a reference to an Appendix. I would certainly prefer to have this simple table with uncertainties directly in Subsection 3.3. Furthermore, the Appendix can be shortened significantly. The table itself is sufficient.
Concerning the data availability I think it shall be made available in an open repository with a doi number. (Who knows the availablility of the contact author some (many) years from now?)
Technical Correctionspage, line 6: a antenna --> an antenna
page 1, lines 6-7: a meteorological sensor was used for meteorological data recording.
--> sensors were used for meteorological data recording.page 1, lines 15-16: "Nowadays" is followed by a reference from 2014?
page 1, line 21: water vapour distribution --> water vapour content
page 5, line 75: What is the meaning of SPKE? Please define!
page 3, line 77: to increasing --> to increase
page 3, lines 78-79: 300 seconds --> 300 s (SI rule)
pages 5-6, Figures 2-3: Fix the axis labels. They cannot be understood.
page 6, Table 1: there is no need to have a resolution of the result at the micrometre level. This shows that the offset correction is so simple so that any one of the methods can be used to achieve the same accuracy.
The resolution of the results presented in Table 4 is also much too high, i.e. not significant.page 7, line 126: "cos" shall not be in an italic font.
page 8: The title "Results" of Section 4 is too general. Results have already been presented in Section 3. Perhaps "Results for the GNSS estimates" is better?
page 8, line 159: This reference appears first in the reference list. Why is not IGS in alphabetical order. It took some time until I found it ...
page 9, Figure 4: Only S0 and S4 can be identified in the graph.
Journal names do not adhere to standards, see e.g. according to: https://www.library.caltech.edu/journal-title-abbreviations
Citation: https://doi.org/10.5194/amt-2021-87-RC1 -
AC2: 'Reply on RC1', Chaiyaporn Kitpracha, 24 Sep 2021
General Comments
Four GNSS installations, with the antennas located at different heights, are used to compare the corresponding estimated equivalent zenith propagation delays. The observed offsets in the ZTD agrees with theory together with methods to determine the refractivity in the atmosphere in the layer(s) between the antenna installations.
There are no new findings. All results are predictable. Please excuse a simple example. The study reported in the manuscript is similar to dropping a ball from different heights and using a stop watch and conclude that the longer fall time observed when the ball is dropped from a higher level is in agreement with different models used to predict the value of the acceleration due to gravity.
Although the manuscript is reasonably well structured and parts are also interesting to read I miss new results as already said. Perhaps the authors are aware of this? The last paragraph in the conclusions starts with the sentence: "Further investigation is required as this experiment was conducted only for a short period of about five weeks." I recommend to extend the time series with many months, preferably covering at least one year in order to pin down systematic effects,
to quantify multipath effects (see e.g., King and Watson (2010)), to develop a model for the radome (see e.g., Liu et al. (2019)) and/or calibrate the antenna including the radome (see e.g. Schmid et al., (2016)).
King, M. A., and C. S. Watson (2010), Long GPS coordinate time series: Multipath and geometry effects,
J. Geophys. Res., 115, B04403, doi:10.1029/2009JB006543.
Liu, J., Li, L., Yong Zuo, Y., Huaming Chen, H., and Shaojie Ni, S. (2019),
Analysis of Performance Degradation Introduced by Radome for High-Precision GNSS Antenna,
Int. J. Antennas Propagat., Article ID 1529656, 13 pages,
https://doi.org/10.1155/2019/1529656.
Schmid, R., Dach, R., Collilieux, X., Jäggi, A., Schmitz, M., and Dilssner, F. (2016),
Absolute IGS antenna phase center model igs08.atx: status and potential improvements,
J .Geod., 90:343–364, doi:10.1007/s00190-015-0876-3.
Response:
First, we would like to thank you for your time reading our manuscript in detail and for your insightful comments. We carefully considered your comments and addressed all your points in the text. Concerning your concern about the novelty of the study, we would like to express our point of view: tropospheric ties are essential information for connecting atmospheric parameters between space geodetic techniques. Over the past few years, local ties (station coordinates differences) have improved estimated station coordinates from space geodetic techniques, which are very important for reference frame derivation. Likewise, tropospheric ties can also improve space geodetic techniques-derived atmospheric parameters, which are essential for climate studies. However, the systematic effects of tropospheric ties need to be addressed. This comes to our motivation in this study. The key of this experiment is the very precise assessment of the quality of tropospheric ties, excluding instrumental effects. Therefore, we applied the same antenna and receiver types with different heights but quasi no horizontal distance. Our experiment can thus be understood as a best-case scenario, where instrumental effects are mitigated. Due to the various heights, multi-pathing affects the antennas in different ways, as clearly demonstrated. The multi-pathing has been found to be much more of a problem for gradients than for zenith delays. All these error sources will have to be considered if tropospheric ties are used for the combination of space geodetic techniques or if GNSS-derived information is to be used in meteorological models. In our next experiment, we will explicitly study the instrumental effects. This work is currently performed. To our knowledge there is no specific study done in this way. Most of the studies use just available instruments, e.g. at Wettzell, which however are dislocated in horizontal direction and are made of different receiver/antenna combinations, so that individual effects on tropospheric parameters can only quantified as a whole but cannot studied in detail. This is the novelty of this study.
Specific comments
In the abstract it is stated that the different atmospheric estimates obtained for the antenna with a radome is surprising. This is not consistent with the reference on page 8, line 158, to the IGS guidelines. It is well known that radomes can introduce offsets in atmospheric estimates and depending on the shape of the radome this offset may vary with the elevation cutoff angle used in the analysis.
Response:
We have edited the sentence in order to avoid misunderstanding.
In Subsection 3 there is a reference to an Appendix. I would certainly prefer to have this simple table with uncertainties directly in Subsection 3.3. Furthermore, the Appendix can be shortened significantly. The table itself is sufficient.
Done
Concerning the data availability I think it shall be made available in an open repository with a doi number. (Who knows the availablility of the contact author some (many) years from now?)
Response:
The data of this experiment is available from GFZ data services (https://doi.org/10.5880/GFZ.1.1.2021.005). We inserted this reference into the manuscript as well.
Technical Corrections
page, line 6: a antenna --> an antenna
Done
page 1, lines 6-7: a meteorological sensor was used for meteorological data recording.
--> sensors were used for meteorological data recording.
Done
page 1, lines 15-16: "Nowadays" is followed by a reference from 2014?
Done
page 1, line 21: water vapour distribution --> water vapour content
Done
page 5, line 75: What is the meaning of SPKE? Please define!
Response:
SPKE: SPECTRA PRECISION conical dome with spike, used with the SPP571908273 antenna; also sold by Aeroantenna and NovAtel (https://semisys.gfz-potsdam.de/semisys/scripts/hardware/radome.php) . We have added an explanation in our manuscript.
page 3, line 77: to increasing --> to increase
Done
page 3, lines 78-79: 300 seconds --> 300 s (SI rule)
Done
pages 5-6, Figures 2-3: Fix the axis labels. They cannot be understood.
Response:
This problem was caused by the journal side during the generation of the preprint version. I have uploaded the correct figure into the author’s comments post on the public discussion page.
page 6, Table 1: there is no need to have a resolution of the result at the micrometre level. This shows that the offset correction is so simple so that any one of the methods can be used to achieve the same accuracy.
The resolution of the results presented in Table 4 is also much too high, i.e. not significant.
Response:
We cannot confirm the second statement of the reviewer. The Potsdam experiment is likely the best-case scenario where the various methods agree exceptionally well. However, at other geographical regions and in particular with larger horizontal/vertical distances involved, the demonstrated methods will most likely differ much more. As we do not show this in this study, we do not mention it in the manuscript.
page 7, line 126: "cos" shall not be in an italic font.
Done
page 8: The title "Results" of Section 4 is too general. Results have already been presented in Section 3. Perhaps "Results for the GNSS estimates" is better?
Response:
We have updated the title of chapter 4 from “Results” to “Comparison of GNSS-derived atmospheric parameters”.
page 8, line 159: This reference appears first in the reference list. Why is not IGS in alphabetical order. It took some time until I found it ...
Response:
We have fixed this issue in our manuscript. Thank you for pointing out this mistake.
page 9, Figure 4: Only S0 and S4 can be identified in the graph.
Response:
We have added the explanation in the caption of this figure in the manuscript.
Journal names do not adhere to standards, see e.g. according to: https://www.library.caltech.edu/journal-title-abbreviations
Response:
We have updated journal abbreviations now following the mentioned standards.
Response:
Thank you for a good recommendation. We implemented all these technical corrections into our manuscript.
Citation: https://doi.org/10.5194/amt-2021-87-AC2
-
AC2: 'Reply on RC1', Chaiyaporn Kitpracha, 24 Sep 2021
- AC1: 'Comment on amt-2021-87', Chaiyaporn Kitpracha, 17 Aug 2021
-
RC2: 'Comment on amt-2021-87', Anonymous Referee #4, 20 Aug 2021
Review of "Validation of tropospheric ties at the test setup GNSS co-location site Potsdam", by Kirpracha, Heinkelmann, Ramatschi,
Balidakis, Mannel and Schuh, AMT-2021-87GENERAL
This is an interesting article on atmospheric ties. The purpose is to find ways to reduce atmospheric delay biases, thereby
improving positioning, which can potentially also improve the global reference frame. The paper is well written, almost ready for publication.In the original pdf fig 2 and 3 lacked proper axis and curve labels. On my request via the editor the correct figures we made available
by the authors. Thanks. They are OK and should substitute the figures in the manuscript uploaded.SPECIFIC
l 6 as a antenna -> as an antennal 10 This sentence is not meaningful.
l 11 It is not unexpected that a radome causes a bias, that has been known for a long time. (But we know that in certain environments snow
that settle on a choke ring antenna can confuse things even more.)l 16 Many met services assimilate GNSS ZTD, but I don't know of services assimilating gradients operationally.
l 18 It takes only pressure to derive ZWD from ZTD. But remember it requires on top the average of the humidity weighted inverse temperature to derive PWV from ZWD. As you don't consider PWV later in your article, maybe you should just avoid mentioning PWV. It only becomes relevant if you start considering for example water vapour radiometers as a source of atmosheric information.
l 82 whether there is any utility in applying -> whether there is any benefit in applying
l 113 A duration of two weeks contrasts the period Jan. 30 to March 7 mentioned in line 82, and the five weeks mentioned in line 208.
l 150 significantly mitigate -> significantly reduceCitation: https://doi.org/10.5194/amt-2021-87-RC2 -
AC3: 'Reply on RC2', Chaiyaporn Kitpracha, 24 Sep 2021
Review of "Validation of tropospheric ties at the test setup GNSS co-location site Potsdam", by Kirpracha, Heinkelmann, Ramatschi, Balidakis, Mannel and Schuh, AMT-2021-87
GENERAL
This is an interesting article on atmospheric ties. The purpose is to find ways to reduce atmospheric delay biases, thereby improving positioning, which can potentially also improve the global reference frame. The paper is well written, almost ready for publication.
In the original pdf fig 2 and 3 lacked proper axis and curve labels. On my request via the editor the correct figures we made available by the authors. Thanks. They are OK and should substitute the figures in the manuscript uploaded.
Response:
We would like to thank you for your time reading our manuscript in detail and for your insightful comments. We carefully considered your comments and addressed all your points in the text.
SPECIFIC COMMENTS
l 6 as a antenna -> as an antenna
Done
l 10 This sentence is not meaningful.
Response:
Thank you. We have rephrased the sentence in our manuscript.
l 11 It is not unexpected that a radome causes a bias, that has been known for a long time. (But we know that in certain environments snow that settle on a choke ring antenna can confuse things even more.)
Response:
Thank you for your comment on this issue. The key of this experiment is the very precise assessment of the quality of tropospheric ties, excluding instrumental effects. Therefore, we applied the same antenna and receiver types with different heights but quasi no horizontal distance. Our experiment can thus be understood as a best-case scenario, where instrumental effects are mitigated. Due to the various heights, multi-pathing, and radome-related effects deteriorate the antennas in different ways, as clearly demonstrated. All these error sources will have to be considered, if tropospheric ties are to be used for the combination of space geodetic techniques or if GNSS-derived information is to be assimilated in meteorological models.
l 16 Many met services assimilate GNSS ZTD, but I don't know of services assimilating gradients operationally.
Response:
We apologize for the misunderstanding. We have rephrased the sentence in our manuscript (line 17).
l 18 It takes only pressure to derive ZWD from ZTD. But remember it requires on top the average of the humidity weighted inverse temperature to derive PWV from ZWD. As you don't consider PWV later in your article, maybe you should just avoid mentioning PWV. It only becomes relevant if you start considering for example water vapour radiometers as a source of atmospheric information.
Response:
Yes, you’re right. We added the dependence of temperature. Nevertheless, we still think it is worth mentioning PWV shortly as it is a quantity that is well known by the meteorological community and thus, improves the readability for those readers of AMT.
l 82 whether there is any utility in applying -> whether there is any benefit in applying
Done
l 113 A duration of two weeks contrasts the period Jan. 30 to March 7 mentioned in line 82, and the five weeks mentioned in line 208.
Done
l 150 significantly mitigate -> significantly reduce
Done
Citation: https://doi.org/10.5194/amt-2021-87-AC3
-
AC3: 'Reply on RC2', Chaiyaporn Kitpracha, 24 Sep 2021
Interactive discussion
Status: closed
-
RC1: 'Comment on amt-2021-87', Anonymous Referee #3, 14 Aug 2021
General Comments
Four GNSS installations, with the antennas located at different heights, are used to compare the corresponding estimated equivalent zenith propagation delays. The observed offsets in the ZTD agrees with theory together with methods to determine the refractivity in the atmosphere in the layer(s) between the antenna installations.
There are no new findings. All results are predictable. Please excuse a simple example. The study reported in the manuscript is similar to dropping a ball from different heights and using a stop watch and conclude that the longer fall time observed when the ball is dropped from a higher level is in agreement with different models used to predict the value of the acceleration due to gravity.
Although the manuscript is reasonably well structured and parts are also interesting to read I miss new results as already said. Perhaps the authors are aware of this? The last paragraph in the conclusions starts with the sentence: "Further investigation is required as this experiment was conducted only for a short period of about five weeks." I recommend to extend the time series with many months, preferably covering at least one year in order to pin down systematic effects,
to quantify multipath effects (see e.g., King and Watson (2010)), to develop a model for the radome (see e.g., Liu et al. (2019)) and/or calibrate the antenna including the radome (see e.g. Schmid et al., (2016)).King, M. A., and C. S. Watson (2010), Long GPS coordinate time series: Multipath and geometry effects,
J. Geophys. Res., 115, B04403, doi:10.1029/2009JB006543.Liu, J., Li, L., Yong Zuo, Y., Huaming Chen, H., and Shaojie Ni, S. (2019),
Analysis of Performance Degradation Introduced by Radome for High-Precision GNSS Antenna,
Int. J. Antennas Propagat., Article ID 1529656, 13 pages,
https://doi.org/10.1155/2019/1529656.Schmid, R., Dach, R., Collilieux, X., Jäggi, A., Schmitz, M., and Dilssner, F. (2016),
Absolute IGS antenna phase center model igs08.atx: status and potential improvements,
J .Geod., 90:343–364, doi:10.1007/s00190-015-0876-3.
Specific commentsIn the abstract it is stated that the different atmospheric estimates obtained for the antenna with a radome is surprising. This is not consistent with the reference on page 8, line 158, to the IGS guidelines. It is well known that radomes can introduce offsets in atmospheric estimates and depending on the shape of the radome this offset may vary with the elevation cutoff angle used in the analysis.
In Subsection 3 there is a reference to an Appendix. I would certainly prefer to have this simple table with uncertainties directly in Subsection 3.3. Furthermore, the Appendix can be shortened significantly. The table itself is sufficient.
Concerning the data availability I think it shall be made available in an open repository with a doi number. (Who knows the availablility of the contact author some (many) years from now?)
Technical Correctionspage, line 6: a antenna --> an antenna
page 1, lines 6-7: a meteorological sensor was used for meteorological data recording.
--> sensors were used for meteorological data recording.page 1, lines 15-16: "Nowadays" is followed by a reference from 2014?
page 1, line 21: water vapour distribution --> water vapour content
page 5, line 75: What is the meaning of SPKE? Please define!
page 3, line 77: to increasing --> to increase
page 3, lines 78-79: 300 seconds --> 300 s (SI rule)
pages 5-6, Figures 2-3: Fix the axis labels. They cannot be understood.
page 6, Table 1: there is no need to have a resolution of the result at the micrometre level. This shows that the offset correction is so simple so that any one of the methods can be used to achieve the same accuracy.
The resolution of the results presented in Table 4 is also much too high, i.e. not significant.page 7, line 126: "cos" shall not be in an italic font.
page 8: The title "Results" of Section 4 is too general. Results have already been presented in Section 3. Perhaps "Results for the GNSS estimates" is better?
page 8, line 159: This reference appears first in the reference list. Why is not IGS in alphabetical order. It took some time until I found it ...
page 9, Figure 4: Only S0 and S4 can be identified in the graph.
Journal names do not adhere to standards, see e.g. according to: https://www.library.caltech.edu/journal-title-abbreviations
Citation: https://doi.org/10.5194/amt-2021-87-RC1 -
AC2: 'Reply on RC1', Chaiyaporn Kitpracha, 24 Sep 2021
General Comments
Four GNSS installations, with the antennas located at different heights, are used to compare the corresponding estimated equivalent zenith propagation delays. The observed offsets in the ZTD agrees with theory together with methods to determine the refractivity in the atmosphere in the layer(s) between the antenna installations.
There are no new findings. All results are predictable. Please excuse a simple example. The study reported in the manuscript is similar to dropping a ball from different heights and using a stop watch and conclude that the longer fall time observed when the ball is dropped from a higher level is in agreement with different models used to predict the value of the acceleration due to gravity.
Although the manuscript is reasonably well structured and parts are also interesting to read I miss new results as already said. Perhaps the authors are aware of this? The last paragraph in the conclusions starts with the sentence: "Further investigation is required as this experiment was conducted only for a short period of about five weeks." I recommend to extend the time series with many months, preferably covering at least one year in order to pin down systematic effects,
to quantify multipath effects (see e.g., King and Watson (2010)), to develop a model for the radome (see e.g., Liu et al. (2019)) and/or calibrate the antenna including the radome (see e.g. Schmid et al., (2016)).
King, M. A., and C. S. Watson (2010), Long GPS coordinate time series: Multipath and geometry effects,
J. Geophys. Res., 115, B04403, doi:10.1029/2009JB006543.
Liu, J., Li, L., Yong Zuo, Y., Huaming Chen, H., and Shaojie Ni, S. (2019),
Analysis of Performance Degradation Introduced by Radome for High-Precision GNSS Antenna,
Int. J. Antennas Propagat., Article ID 1529656, 13 pages,
https://doi.org/10.1155/2019/1529656.
Schmid, R., Dach, R., Collilieux, X., Jäggi, A., Schmitz, M., and Dilssner, F. (2016),
Absolute IGS antenna phase center model igs08.atx: status and potential improvements,
J .Geod., 90:343–364, doi:10.1007/s00190-015-0876-3.
Response:
First, we would like to thank you for your time reading our manuscript in detail and for your insightful comments. We carefully considered your comments and addressed all your points in the text. Concerning your concern about the novelty of the study, we would like to express our point of view: tropospheric ties are essential information for connecting atmospheric parameters between space geodetic techniques. Over the past few years, local ties (station coordinates differences) have improved estimated station coordinates from space geodetic techniques, which are very important for reference frame derivation. Likewise, tropospheric ties can also improve space geodetic techniques-derived atmospheric parameters, which are essential for climate studies. However, the systematic effects of tropospheric ties need to be addressed. This comes to our motivation in this study. The key of this experiment is the very precise assessment of the quality of tropospheric ties, excluding instrumental effects. Therefore, we applied the same antenna and receiver types with different heights but quasi no horizontal distance. Our experiment can thus be understood as a best-case scenario, where instrumental effects are mitigated. Due to the various heights, multi-pathing affects the antennas in different ways, as clearly demonstrated. The multi-pathing has been found to be much more of a problem for gradients than for zenith delays. All these error sources will have to be considered if tropospheric ties are used for the combination of space geodetic techniques or if GNSS-derived information is to be used in meteorological models. In our next experiment, we will explicitly study the instrumental effects. This work is currently performed. To our knowledge there is no specific study done in this way. Most of the studies use just available instruments, e.g. at Wettzell, which however are dislocated in horizontal direction and are made of different receiver/antenna combinations, so that individual effects on tropospheric parameters can only quantified as a whole but cannot studied in detail. This is the novelty of this study.
Specific comments
In the abstract it is stated that the different atmospheric estimates obtained for the antenna with a radome is surprising. This is not consistent with the reference on page 8, line 158, to the IGS guidelines. It is well known that radomes can introduce offsets in atmospheric estimates and depending on the shape of the radome this offset may vary with the elevation cutoff angle used in the analysis.
Response:
We have edited the sentence in order to avoid misunderstanding.
In Subsection 3 there is a reference to an Appendix. I would certainly prefer to have this simple table with uncertainties directly in Subsection 3.3. Furthermore, the Appendix can be shortened significantly. The table itself is sufficient.
Done
Concerning the data availability I think it shall be made available in an open repository with a doi number. (Who knows the availablility of the contact author some (many) years from now?)
Response:
The data of this experiment is available from GFZ data services (https://doi.org/10.5880/GFZ.1.1.2021.005). We inserted this reference into the manuscript as well.
Technical Corrections
page, line 6: a antenna --> an antenna
Done
page 1, lines 6-7: a meteorological sensor was used for meteorological data recording.
--> sensors were used for meteorological data recording.
Done
page 1, lines 15-16: "Nowadays" is followed by a reference from 2014?
Done
page 1, line 21: water vapour distribution --> water vapour content
Done
page 5, line 75: What is the meaning of SPKE? Please define!
Response:
SPKE: SPECTRA PRECISION conical dome with spike, used with the SPP571908273 antenna; also sold by Aeroantenna and NovAtel (https://semisys.gfz-potsdam.de/semisys/scripts/hardware/radome.php) . We have added an explanation in our manuscript.
page 3, line 77: to increasing --> to increase
Done
page 3, lines 78-79: 300 seconds --> 300 s (SI rule)
Done
pages 5-6, Figures 2-3: Fix the axis labels. They cannot be understood.
Response:
This problem was caused by the journal side during the generation of the preprint version. I have uploaded the correct figure into the author’s comments post on the public discussion page.
page 6, Table 1: there is no need to have a resolution of the result at the micrometre level. This shows that the offset correction is so simple so that any one of the methods can be used to achieve the same accuracy.
The resolution of the results presented in Table 4 is also much too high, i.e. not significant.
Response:
We cannot confirm the second statement of the reviewer. The Potsdam experiment is likely the best-case scenario where the various methods agree exceptionally well. However, at other geographical regions and in particular with larger horizontal/vertical distances involved, the demonstrated methods will most likely differ much more. As we do not show this in this study, we do not mention it in the manuscript.
page 7, line 126: "cos" shall not be in an italic font.
Done
page 8: The title "Results" of Section 4 is too general. Results have already been presented in Section 3. Perhaps "Results for the GNSS estimates" is better?
Response:
We have updated the title of chapter 4 from “Results” to “Comparison of GNSS-derived atmospheric parameters”.
page 8, line 159: This reference appears first in the reference list. Why is not IGS in alphabetical order. It took some time until I found it ...
Response:
We have fixed this issue in our manuscript. Thank you for pointing out this mistake.
page 9, Figure 4: Only S0 and S4 can be identified in the graph.
Response:
We have added the explanation in the caption of this figure in the manuscript.
Journal names do not adhere to standards, see e.g. according to: https://www.library.caltech.edu/journal-title-abbreviations
Response:
We have updated journal abbreviations now following the mentioned standards.
Response:
Thank you for a good recommendation. We implemented all these technical corrections into our manuscript.
Citation: https://doi.org/10.5194/amt-2021-87-AC2
-
AC2: 'Reply on RC1', Chaiyaporn Kitpracha, 24 Sep 2021
- AC1: 'Comment on amt-2021-87', Chaiyaporn Kitpracha, 17 Aug 2021
-
RC2: 'Comment on amt-2021-87', Anonymous Referee #4, 20 Aug 2021
Review of "Validation of tropospheric ties at the test setup GNSS co-location site Potsdam", by Kirpracha, Heinkelmann, Ramatschi,
Balidakis, Mannel and Schuh, AMT-2021-87GENERAL
This is an interesting article on atmospheric ties. The purpose is to find ways to reduce atmospheric delay biases, thereby
improving positioning, which can potentially also improve the global reference frame. The paper is well written, almost ready for publication.In the original pdf fig 2 and 3 lacked proper axis and curve labels. On my request via the editor the correct figures we made available
by the authors. Thanks. They are OK and should substitute the figures in the manuscript uploaded.SPECIFIC
l 6 as a antenna -> as an antennal 10 This sentence is not meaningful.
l 11 It is not unexpected that a radome causes a bias, that has been known for a long time. (But we know that in certain environments snow
that settle on a choke ring antenna can confuse things even more.)l 16 Many met services assimilate GNSS ZTD, but I don't know of services assimilating gradients operationally.
l 18 It takes only pressure to derive ZWD from ZTD. But remember it requires on top the average of the humidity weighted inverse temperature to derive PWV from ZWD. As you don't consider PWV later in your article, maybe you should just avoid mentioning PWV. It only becomes relevant if you start considering for example water vapour radiometers as a source of atmosheric information.
l 82 whether there is any utility in applying -> whether there is any benefit in applying
l 113 A duration of two weeks contrasts the period Jan. 30 to March 7 mentioned in line 82, and the five weeks mentioned in line 208.
l 150 significantly mitigate -> significantly reduceCitation: https://doi.org/10.5194/amt-2021-87-RC2 -
AC3: 'Reply on RC2', Chaiyaporn Kitpracha, 24 Sep 2021
Review of "Validation of tropospheric ties at the test setup GNSS co-location site Potsdam", by Kirpracha, Heinkelmann, Ramatschi, Balidakis, Mannel and Schuh, AMT-2021-87
GENERAL
This is an interesting article on atmospheric ties. The purpose is to find ways to reduce atmospheric delay biases, thereby improving positioning, which can potentially also improve the global reference frame. The paper is well written, almost ready for publication.
In the original pdf fig 2 and 3 lacked proper axis and curve labels. On my request via the editor the correct figures we made available by the authors. Thanks. They are OK and should substitute the figures in the manuscript uploaded.
Response:
We would like to thank you for your time reading our manuscript in detail and for your insightful comments. We carefully considered your comments and addressed all your points in the text.
SPECIFIC COMMENTS
l 6 as a antenna -> as an antenna
Done
l 10 This sentence is not meaningful.
Response:
Thank you. We have rephrased the sentence in our manuscript.
l 11 It is not unexpected that a radome causes a bias, that has been known for a long time. (But we know that in certain environments snow that settle on a choke ring antenna can confuse things even more.)
Response:
Thank you for your comment on this issue. The key of this experiment is the very precise assessment of the quality of tropospheric ties, excluding instrumental effects. Therefore, we applied the same antenna and receiver types with different heights but quasi no horizontal distance. Our experiment can thus be understood as a best-case scenario, where instrumental effects are mitigated. Due to the various heights, multi-pathing, and radome-related effects deteriorate the antennas in different ways, as clearly demonstrated. All these error sources will have to be considered, if tropospheric ties are to be used for the combination of space geodetic techniques or if GNSS-derived information is to be assimilated in meteorological models.
l 16 Many met services assimilate GNSS ZTD, but I don't know of services assimilating gradients operationally.
Response:
We apologize for the misunderstanding. We have rephrased the sentence in our manuscript (line 17).
l 18 It takes only pressure to derive ZWD from ZTD. But remember it requires on top the average of the humidity weighted inverse temperature to derive PWV from ZWD. As you don't consider PWV later in your article, maybe you should just avoid mentioning PWV. It only becomes relevant if you start considering for example water vapour radiometers as a source of atmospheric information.
Response:
Yes, you’re right. We added the dependence of temperature. Nevertheless, we still think it is worth mentioning PWV shortly as it is a quantity that is well known by the meteorological community and thus, improves the readability for those readers of AMT.
l 82 whether there is any utility in applying -> whether there is any benefit in applying
Done
l 113 A duration of two weeks contrasts the period Jan. 30 to March 7 mentioned in line 82, and the five weeks mentioned in line 208.
Done
l 150 significantly mitigate -> significantly reduce
Done
Citation: https://doi.org/10.5194/amt-2021-87-AC3
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AC3: 'Reply on RC2', Chaiyaporn Kitpracha, 24 Sep 2021
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