the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Aug 2021
An adaptive echo attenuation correction method for airborne Ka-band precipitation cloud radar based on melting layer
Abstract. In this study, an airborne Ka-band Precipitation Cloud Radar (KPR) is used to carry out a cloud observation experiment.By analyzing the attenuation of the snow echo, it is found that during the snowfall, due to the low liquid water content, the KPR attenuation is small on the detection path, and after preliminary comparative analysis, the maximum attenuation correction value is 0.5 dBZ. According to the echo attenuation analysis of mixed precipitation, the melting layer is found to be the key factor affecting the attenuation correction. This study hereby proposes an adaptive echo attenuation correction method based on the melting layer (AEC), and uses the ground-based S-band radar to extract the echo on the aircraft trajectory to verify the correction results. The results show that the echo attenuation correction value above the melting layer is related to the flight position. The aircraft above the melting layer is dominated by ice particles, with small attenuation correction value, the maximum correction amount of 0.13 dBZ; when the aircraft is at and just below the melting layer, a water film is prone to be on the antenna, which leads to serious attenuation of the KPR detection path, with the attenuation correction value 1~2 dBZ. For the precipitation echo below the melting layer, due to the abundant rain and water vapor content, the KPR attenuation is significant with maximum correction value of about 5 dBZ. Compared with the S-band radar, before attenuation correction, the total mean relative error is 15 %, and the correlation coefficient is 0.82; after correction, the total mean relative error is 6 %, and the correlation coefficient is 0.90, indicating the significant improvement of the KPR data quality.
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Interactive discussion
Status: closed
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RC1: 'Comment on amt-2021-221', Anonymous Referee #1, 26 Aug 2021
The paper presents a method for the attenuation correction of the airborne Ka-band cloud radar. The methodology that has been used is very simple in its roots and I suggest to present it in a simpler way. In most cases a re-read can set the context, but you don’t want to impose additional work on the reader. The scientific significance of the paper could be greatly improved if not only the method itself is presented but also how well it works in a more statistical way. For example, a long term validation of the algorithm over the Rayleigh targets at the cloud top when the aircraft is located below the freezing level. Alternatively a different multifrequency dataset can be used (OLYMPEX, IPHEx are publicaly available). If the presented method is applied to these data the data collocation issue is greately reduced and the low frequency radar can be used as the unattenuated reference for the path integrated attenuation estimates, in particular in case of small precipiattion rates.Â
Major comments:
1. The English usage is fair but inconsistent and difficult to understand at some places. Â The text needs a careful revision for usage and punctuation. I made some comments in the pdf file but these comments are only a fraction of corrections that need to be made.
2. The title. It should reflect more the content of the manuscript. In fact, the paper shows just an application of the attenuation correction to the several precipitation events.
3. The  way the attenuation correction method is presented looks very complicated but in fact it is not. The  whole approch is based on the detection of the freezing level. Below the zero degree isotherm a selected attenuation-reflectivity formula is used based on the reflectivity regime. Above the freezing level a fixed formula is used. The rest of the work is just to integrate the extinction profiles along the propagation path that depends on the airplane altitude.Â
4. The methodology is besed on separating the data into two groups: snow/ice and everything below the melting level. In fact the scattering properties of melting snow are very different from those of rain. Matrosov (2008) showed that the melting layer attenuation is stronger than in rain for the same path and precipitation rate.Â
5. The number of the presented events is unnecesserily large. One case study would be enough to show the algorithm.Â
Technical comments are in the attached *.pdf file
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AC1: 'Reply on RC1', Dongfei ZUO, 21 Sep 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-221/amt-2021-221-AC1-supplement.pdf
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AC1: 'Reply on RC1', Dongfei ZUO, 21 Sep 2021
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RC2: 'Comment on amt-2021-221', Anonymous Referee #2, 27 Aug 2021
The paper proposes an attenuation correction for Ka-band radars.
The paper is way too long and convoluted for the limited amount of information it actually brings to the reader. I do not see any real novelty;Â
also simple messagesÂ
are not really properly conveyed. While there is merit in Ka-band attenuation correction methods, in my opinion this work does not seem to really capture the stateÂ
of the art and does not provide a significant step forward in the field.
Major comments:
1) Snow attenuation: the values of (light) snow attenuation are exteremely low (<0.1 dB). Therefore there is no way to properly validate these results
(miscalibration, volume mismatching, frequency mismatching, etc will produce errors much bigger than such value). So I do not see any valueÂ
in this because no real conclusions can be achieved. In convection ice of course can start producing significant attenuation at KaÂ
but this is not addressed by this paper in any way.2) The overall design of the methodology is very weak. By definition the volumes of the S-band ground based and the Ka-band radar can be very different.
In particular the vertical resolution of the S-band can be very coarse. Not sure what kind of interpolation you used in your figuresÂ
for the S-band but really I do not see this as a viable methodology to assess an attenuation correction. Much better to use multi-frequencyÂ
matched beam aircraft or ground based radars which are available. There is also no mention of cross-calibration between the S and the Ka-band radar (which should beÂ
a key aspect).
 3) Not sure I have fully understood how the attenuation in rain works (it seems the authors are using the same coefficients as in ice, item 5 at page 6?Â
Of course it is well known that rain is attenuating much more than ice. Also the authors do not compute any enhancement of attenuation due to theÂ
melting layer (a lot of work has been done on this topic also at Ka band). So really I do no see any value of this apart saying that rain will produceÂ
some attenuation that must be accounted for (as everybody in the field knows).4) There is no mention at all of the fact that S-band and Ka band unattenuatedÂ
reflectivities are not generally the same, due to non-Rayleigh effects. Discussion of the impact of such assumption should be provided.Â
Other comments:
English needs extensive revision.Â
Attenuation is measured in dB not dBZ.
For your k-Z relationship you should provide units for k and Z.Citation: https://doi.org/10.5194/amt-2021-221-RC2 -
AC2: 'Reply on RC2', Dongfei ZUO, 21 Sep 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-221/amt-2021-221-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Dongfei ZUO, 21 Sep 2021
Interactive discussion
Status: closed
-
RC1: 'Comment on amt-2021-221', Anonymous Referee #1, 26 Aug 2021
The paper presents a method for the attenuation correction of the airborne Ka-band cloud radar. The methodology that has been used is very simple in its roots and I suggest to present it in a simpler way. In most cases a re-read can set the context, but you don’t want to impose additional work on the reader. The scientific significance of the paper could be greatly improved if not only the method itself is presented but also how well it works in a more statistical way. For example, a long term validation of the algorithm over the Rayleigh targets at the cloud top when the aircraft is located below the freezing level. Alternatively a different multifrequency dataset can be used (OLYMPEX, IPHEx are publicaly available). If the presented method is applied to these data the data collocation issue is greately reduced and the low frequency radar can be used as the unattenuated reference for the path integrated attenuation estimates, in particular in case of small precipiattion rates.Â
Major comments:
1. The English usage is fair but inconsistent and difficult to understand at some places. Â The text needs a careful revision for usage and punctuation. I made some comments in the pdf file but these comments are only a fraction of corrections that need to be made.
2. The title. It should reflect more the content of the manuscript. In fact, the paper shows just an application of the attenuation correction to the several precipitation events.
3. The  way the attenuation correction method is presented looks very complicated but in fact it is not. The  whole approch is based on the detection of the freezing level. Below the zero degree isotherm a selected attenuation-reflectivity formula is used based on the reflectivity regime. Above the freezing level a fixed formula is used. The rest of the work is just to integrate the extinction profiles along the propagation path that depends on the airplane altitude.Â
4. The methodology is besed on separating the data into two groups: snow/ice and everything below the melting level. In fact the scattering properties of melting snow are very different from those of rain. Matrosov (2008) showed that the melting layer attenuation is stronger than in rain for the same path and precipitation rate.Â
5. The number of the presented events is unnecesserily large. One case study would be enough to show the algorithm.Â
Technical comments are in the attached *.pdf file
-
AC1: 'Reply on RC1', Dongfei ZUO, 21 Sep 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-221/amt-2021-221-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Dongfei ZUO, 21 Sep 2021
-
RC2: 'Comment on amt-2021-221', Anonymous Referee #2, 27 Aug 2021
The paper proposes an attenuation correction for Ka-band radars.
The paper is way too long and convoluted for the limited amount of information it actually brings to the reader. I do not see any real novelty;Â
also simple messagesÂ
are not really properly conveyed. While there is merit in Ka-band attenuation correction methods, in my opinion this work does not seem to really capture the stateÂ
of the art and does not provide a significant step forward in the field.
Major comments:
1) Snow attenuation: the values of (light) snow attenuation are exteremely low (<0.1 dB). Therefore there is no way to properly validate these results
(miscalibration, volume mismatching, frequency mismatching, etc will produce errors much bigger than such value). So I do not see any valueÂ
in this because no real conclusions can be achieved. In convection ice of course can start producing significant attenuation at KaÂ
but this is not addressed by this paper in any way.2) The overall design of the methodology is very weak. By definition the volumes of the S-band ground based and the Ka-band radar can be very different.
In particular the vertical resolution of the S-band can be very coarse. Not sure what kind of interpolation you used in your figuresÂ
for the S-band but really I do not see this as a viable methodology to assess an attenuation correction. Much better to use multi-frequencyÂ
matched beam aircraft or ground based radars which are available. There is also no mention of cross-calibration between the S and the Ka-band radar (which should beÂ
a key aspect).
 3) Not sure I have fully understood how the attenuation in rain works (it seems the authors are using the same coefficients as in ice, item 5 at page 6?Â
Of course it is well known that rain is attenuating much more than ice. Also the authors do not compute any enhancement of attenuation due to theÂ
melting layer (a lot of work has been done on this topic also at Ka band). So really I do no see any value of this apart saying that rain will produceÂ
some attenuation that must be accounted for (as everybody in the field knows).4) There is no mention at all of the fact that S-band and Ka band unattenuatedÂ
reflectivities are not generally the same, due to non-Rayleigh effects. Discussion of the impact of such assumption should be provided.Â
Other comments:
English needs extensive revision.Â
Attenuation is measured in dB not dBZ.
For your k-Z relationship you should provide units for k and Z.Citation: https://doi.org/10.5194/amt-2021-221-RC2 -
AC2: 'Reply on RC2', Dongfei ZUO, 21 Sep 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-221/amt-2021-221-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Dongfei ZUO, 21 Sep 2021
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