the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Jun 2025
Evaluation of the EarthCARE Cloud Profiling Radar (CPR) Doppler velocity measurements using surface-based observations
Abstract. The Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) mission was launched on May 28, 2024. One of the most exciting new measurement capabilities of the EarthCARE mission is the CPR Doppler velocity measurement. The availability of Doppler measurements from space will offer a unique opportunity for the collection of a global dataset of vertical motions in clouds and precipitation. An important step in realizing this opportunity is to evaluate the CPR Doppler velocity measurements against those collected by surface-based observatories. Validation with two high-latitude surface-based Doppler radar observatories demonstrates that the CPR Level-2 Doppler velocities exhibit minimal biases (within a few cm/s), especially in ice clouds. Even in low-level mixed-phase clouds, the CPR’s Doppler velocity measurements provide reliable values, although careful consideration is needed for specific limitations such as vertical smoothing effects due to the radar’s pulse length. Despite the inherent challenges associated with space-based Doppler measurements, these results suggest strong potential for the EarthCARE mission to provide unprecedented global climatological insights into hydrometeor sedimentation velocities.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-2697', Alain Protat, 29 Jul 2025
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RC2: 'Comment on egusphere-2025-2697', Anonymous Referee #2, 06 Aug 2025
This manuscript provides an evaluation of the EarthCARE Doppler product using data from two vertically pointing surface radars, one in the Arctic and the second in Antarctica. The EarthCARE Cloud Profiling Radar (CPR) is a spaceborne W-band radar that measures the W-band reflectivity of clouds and precipitation, like its predecessor, the NASA CloudSat radar. The larger antenna used on the EarthCARE CPR provides improved horizontal resolution and sensitivity; however, it also allows the measurement of Doppler velocity for the first time for a spaceborne atmospheric radar. Hence, validating the EarthCARE CPR velocity measurements is timely. The methodology for the evaluation makes use of a recently developed CPR simulator, which allows the surface-based radar data to be converted to CPR-like data with error bars. These results are then directly comparable with the CPR data. As noted, the work is timely and should be of interest to readers. I think the manuscript is well-written; the reported analysis is well-described. I am curious if the authors plan to extend this study to other situations, like convective systems. I have some minor comments below.
Comments:
Line 41 – the comparison with CloudSat indicates better resolution. Should this be better horizontal resolution? The vertical seems to be 500 m for both.
Sections 2.1 and 2.2.1 – these sections spend quite a bit of space on the sedimentation velocity. However, line 110 notes that “validation is conducted only from the perspective of the Doppler velocity best estimate.” I'm not clear on this - does this mean that the comparisons are on the observed Doppler including both air motion and SVBE? If the study is just on the measured Doppler, then I’m puzzled by the space devoted to the sedimentation velocity. Please clarify. If sedimentation velocity is not really used in the comparison, I would shorten its mention to a couple of sentences.
Line 130 – the horizontal velocity is assumed to be 9 m/s. Where does this come from?
Line 139 – I understand that we don’t want to include more noise than necessary. However, I think maybe more detail would help convince the reader that the correct thermal and speckle noise levels are being used in the simulation.
Line 165 - can't things change quite a bit in three hours? I would think yes in the mid-latitudes but I'm not sure about the arctic. Is the difference in the times somehow included in the surface error bars?
Line 181 - are these offsets then applied to the surface-based radar data prior to running through the simulator?
Figure 2 and text starting around line 266 – I think there is a possibility of misinterpreting the bias correction. Specifically, the term “EarthCARE + e_p” could be interpreted as adding e_p to the EarthCARE observation, which would be the corrected EarthCARE. The caption does clarify that (b) and (f) are the EarthCARE before pointing correction. However, the authors might want to consider calling the uncorrected “EarthCARE” and the corrected “EarthCARE – bias” or EarthCARE – e_p”.
Citation: https://doi.org/10.5194/egusphere-2025-2697-RC2
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