Articles

To gain a better understanding of precipitation processes and to assess and refine the physical assumptions that go into the GPM algorithms, the ground validation team makes field measurements of specific parameters that describe the physical characteristics and variability of rainfall, including rainfall intensity, distribution, particle shape and precipitation type. Ground validation uses specific ground instrumentation infrastructure developed to observe, quantify and document the physical properties of precipitation. These instruments include: The NASA NPOL radar A research grade S-band...

Integrated hydrologic validation assesses GPM precipitation products by considering how the accuracy of rainfall products being input into hydrological and land-surface modeling affects model outputs. The end goals are to evaluate satellite precipitation measurements for their impacts and utility, and to provide guidance to algorithms that turn satellite retrievals into meaningful estimates of precipitation. The integrated hydrologic modeling process provides a vehicle to evaluate precipitation inputs over a given hydrological basin (watershed) where the surface inputs (land cover, soil type)...

Physical validation activities collect targeted datasets that describe precipitation physics: the size, type, shape and number of raindrops throughout the air column from the cloud to the ground. Scientists use ground validation measurements to evaluate specific assumptions or hypotheses related to the physical behavior of precipitation, and the manner in which those characteristics are, or are not, well represented in a given retrieval algorithm. The goal of this validation process is to improve and fully develop physically-based precipitation retrieval algorithms. These algorithms are the...

In addition to the PMM satellites, TRMM and GPM, roughly a dozen other satellites carry precipitation-relevant sensors. The goal of multi-satellite algorithms is to use “all” of the available quasi-global precipitation estimates computed from this international constellation of satellites to create a High-Resolution Precipitation Product with complete coverage over the chosen domain and period of record (currently 50°N-50°S, 1998-present). Estimates based on microwave and combined radar/radiometer input data have higher quality due to the physically direct relationships that exist between...

Precipitation radiometers provide additional degrees of freedom for interpreting rain and snow in clouds through the use of multiple passive frequencies (9 for TRMM and 13 for GPM). Brightness temperatures at each frequency are a measure of everything in their field of view. These frequencies from the low (10 GHz) end to the high (183 GHz) end transition from being sensitive to liquid rain drops to being sensitive to the snow and ice particles. So, simplifying, when there is liquid rain in the cloud column, the low frequency channels will respond; when there is snow the high frequency channels...