Performance and data processing of Cloudsat's Cloud Profiling Radar in the first year in orbit

The Cloud Profiling Radar (CPR) for the CloudSat Mission is the first-ever spaceborne millimeter-wave radar dedicated to the understanding of cloud and light-rain physics and meteorology, and their roles in global climate and energy and hydrology cycles. CPR is a 94-GHz nadir-looking radar that measures power backscattered by clouds as a function of distance from the radar. These measurements provide along-track vertical profiles of cloud structure at 500 m vertical resolution and 1.4 km horizontal resolution. Such a data set is expected to provide crucial input to the studies of cloud physics, radiation budget, and water distribution in the atmosphere, and to numerical weather prediction models.

In the first 6 months of flight operations, the CPR performance has met or exceeded all key science requirements: the radar's minimum detectable reflectivity ranges from -30 dBZ to -31 dBZ depending on the observed scene; analyses of the monthly CPR calibration and early under-flight validation data indicate that CPR radiometric accuracy is well within the pre-launch budget of 1.8 dB. CPR system gain, transmit power, and other system parameters have been stable and do not show any discernible sign of degradation. A more accurate long-term radiometric stability estimate will be available when at least one full yearly cycle is completed and when more results from validation campaigns are analyzed. CPR nadir pointing has been verified through analysis of specular ocean returns and by alignment with a high-resolution topographic map. Range resolution has been verified by comparing the in-flight ocean surface response to pre-launch point target response tests. A CPR clutter removal algorithm has been developed and it achieves 10 dB or better surface clutter rejection ratio, and thus, limits the clutter-contaminated region to only the lowest 500 m (i.e., within the surface range bin) on the CPR vertical profiling measurements.

This paper will summarize the CPR system calibration results, instrument performance and status of L1B processing after the first 12 months of flight operations.

The research described in this paper was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.