| 25 Mar 2026
Observation modes of EarthCARE/CPR with different Doppler measurement accuracy: Evaluation of their applicability
Abstract. An accurate characterization of cloud vertical motion is essential for understanding cloud microphysical and dynamical processes. The Cloud Profiling Radar (CPR) onboard the Earth Cloud Aerosol and Radiation Explorer (EarthCARE) satellite, launched in May 2024, enables the first global measurements of Doppler velocity from space. The CPR operates in three observation modes—16-km, 18-km, and 20-km modes—each characterized by a distinct pulse repetition frequency (PRF), which determines the Doppler velocity data quality, the maximum observable altitude, and the likelihood of spurious high-altitude echoes known as mirror images. This study quantitatively evaluates the applicability of these three modes using actual CPR observations, focusing on these three aspects. The standard deviation (STD) of Doppler velocity, used as an indicator of measurement noise, indicated that the 16-km and 18-km modes provide more accurate Doppler measurements than the 20-km mode, with comparable STD values between the former two. Clouds above 16 km were primarily observed between 0° and 40° latitude, while clouds exceeding 18 km were rare, suggesting that the 18-km or 20-km modes are suitable for observation in these regions. The risk of overlap between genuine cloud echoes and mirror images at high altitudes was highest in the 16-km and 18-km modes but was largely confined to low-latitude regions (approximately 0°–40°). Accordingly, without considering mirror image-related risks, the 16-km mode is preferable at latitudes above 40°, where high clouds are infrequent and Doppler measurement accuracy is highest. In contrast, the 18-km mode provides an optimal balance between Doppler accuracy and vertical coverage at lower latitudes. It should be noted, however, that high-PRF modes inherently increase the likelihood of mirror image contamination. These results demonstrate, for the first time using actual EarthCARE observations, trade-offs among Doppler measurement accuracy, observation height, and spurious echo contamination across CPR operational modes. Future work should involve continuous assessments of the balance between Doppler accuracy and mirror image contamination to determine the optimal implementation of each mode as a function of latitude.
Competing interests: At least one of the (co-)authors serves as editor for the special issue to which this paper belongs.
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