the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Feb 2025
Improved hydrometeor detection near the Earth’s surface by a conically scanning spaceborne W-band radar
Abstract. The Earth’s strong radar surface return limits the detection of clouds and precipitation in the lowest part of the atmosphere by nadir-pointing spaceborne radars such as CloudSat and EarthCARE. The strength of the Earth’s surface radar return is significantly reduced at non-zero incidence angles. The WIVERN 94 GHz radar, currently undergoing Phase A studies by ESA, employs a 3-meter antenna and conical radar sampling at high incidence angles. Here, the benefits of the narrow field of view and the reduction in the Earth’s surface return for studying clouds and precipitation in the lowest kilometers of the atmosphere are quantified. The WIVERN radar is expected to improve the signal (hydrometeors) to clutter (surface return) ratio over ice-free ocean surfaces and marginally worsen it over land and sea ice. The impact of these findings on the detection of light rainfall and snowfall near the Earth’s surface is discussed.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2025-416', Anonymous Referee #1, 31 Mar 2025
The submitted manuscript addresses the use of a conically-scanned radar for spaceborne measurements of precipitation. The concept underlies a radar instrument called WIVERN that may be developed and launched over the next decade, so continued analysis of the WIVERN instrument seems quite relevant to this publication’s readers. Previous publications on the topic of WIVERN include an overview of the design (2018), and various related aspects, including a radar simulator, effects of clutter in orography, impacts of channel cross-talk, effects of mispointing, and radar signal processing. The manuscript under consideration addresses clutter but appears to be covering new territory, relative to previous publications. It introduces the clutter problem and provides several related equations. It then shows two case studies of precipitation with clutter effects for CloudSat, EarthCARE, and for WIVERN. The discussion is generally clear and gives a balanced treatment of WIVERN’s capabilities as compared with nadir-looking spaceborne radars. I think it can be a valuable addition to the literature, but I do have some questions and comments that should be addressed.
Questions and Comments for the Authors:
- There are a number of other WIVERN publications that are not cited. It would be good to confirm that all clutter-related papers are referenced and that this paper explains its novelty relative to those.
- Around line 50, the advantages of conically-scanned W-band radar are noted, but it might be reasonable to list some disadvantages, in particular the large attenuation that needs to be removed when viewing liquid precipitation.
- I think the equations developed in Section 2.1 need better motivation, especially the use of the Gaussian antenna. It appears that the WIVERN calculations use a calculated pattern. Is the Gaussian used for CloudSat and EarthCARE? Is (7) the clutter reflectivity being plotted in Figure 2?
- Do the results in Figure 2 represent the total clutter, from all pulses that could arrive simultaneous with the atmospheric pulse, or only from the pulse illuminating the atmosphere? If only the latter, I would be concerned that the clutter estimate is not complete.
- Around line 125, it could be pointed out that even at the 14 m/s windspeed, the clutter appears small enough that it would be below the thermal noise for WIVERN.
- Line 193, the text could mention the land/ocean contrast that can be seen in Figure 7.
- Line 206: The text points out a thicker clutter signal when flying over land. This is related to the total clutter level and its profile, as well as the color table being used for the image. It might be clearer to mention the level and the 3-dB width.
- Figure 8 compares the simulated WIVERN and CloudSat data. What are the vertical resolutions (not slant range) in the two cases?
- The smaller figure format used for the Labrador case might also work for the west coast case. The larger figures for that case are easier to read but also require a lot of moving around to see both text and figures, when reading.
- I think the text for the snowfall case could be expanded to give more explanation for what is seen. Is the main difference (better detection down to the ground for snowfall) related to the lack of strong attenuation?
- The statistical analysis in 3.2 could also provide a better explanation. In particular, line 247 notes that the “results clearly highlight”. It would be good to point out the particular results in detail, explaining the choice of the definition of DeltaZ and explaining the significance of the plots. This explanation would also help with understanding of the results in Section 3.3. What was the reason for using the SCR=5 dB height?
- Line 255 – in what sense is the WIVERN sampling improved? Is this related to the wide swath, which is, indeed, a nice feature?Minor edits:
- Line 27, the parentheses make reading the sentence difficult. Please consider revising.
- Consider removing paragraph breaks at lines 32, 45, 57, 117, 308.
- Figure 1, please add the angles used in Section 2.1.Citation: https://doi.org/10.5194/egusphere-2025-416-RC1 -
RC2: 'Comment on egusphere-2025-416', Anonymous Referee #2, 09 Apr 2025
The submitted manuscript focuses on detecting precipitation measurements using a conical scanning satellite radar. It is based on the WIVERN radar instrument, which has been developed over the past few years and could be further developed and launched in the next decade. The manuscript compares the conical scans to those of a nadir-directed radar.
The present manuscript addresses WIVERN's reduced ocean surface clutter and, therefore, the increase of precipitation detection compared to nadir-looking satellite missions. In the first part of the manuscript, the equations that underlie the simulations analysed later are introduced and listed. These equations are then applied to case studies of precipitation with clutter effects for CloudSat, EarthCARE, and WIVERN. The discussion provides a comprehensive overview of the advantages of WIVERN over nadir-view radars. This insight is exciting and enriches the existing literature.
Nevertheless, I still have some questions and comments about the submitted manuscript, which I will outline below.
- In general, one could emphasise in the introduction that this refers to reduced clutter over oceans rather than over land. For non-experts, this might give the impression that an increased detection of kidney strike is generally expected worldwide. However, that is not the case, is it?
- I suggest adding a flowchart or a sketch that illustrates all the angles and areas mentioned in the introduction of the formulas. Alternatively, could you add this information to Figure 1? In Equation 1, the incidence angle is yindicated, but in Figure, is S from Equation 1 the darker blue circle in Figure 1?
- Figure 2: Why is the black dotted line not in the legend?
- The text would generally benefit from more precise labelling of the figures. Particularly in the case study and statistical analysis section, many small and large plots are combined into a single figure. Numbering them with a), b), etc., would greatly enhance the text's readability. This approach allows figures to be recognised more quickly, helping the reader locate the correct figure faster.
- Section 3, line 141: Which lookup tables were used precisely? Are there any references? Likewise, for the calculation of the gas absorption (line 143)
- Section 3 includes numerous illustrations. To enhance information extraction from them, the text requires additional explanations or more detailed descriptions of the figures, making it easier for readers to understand and access the information the writer intends to convey. For non-experts, the statistical information is otherwise quite challenging to grasp. A suggestion could be to summarise the data and reduce the number of illustrations to help manage the overwhelming amount of information.
Citation: https://doi.org/10.5194/egusphere-2025-416-RC2
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