- Related Research Areas
The dual-wavelength Precipitation Radar (DPR) that will be flown on the Global Precipitation Mission (GPM) satellite will be the first dual-wavelength weather radar in space. One of the major challenges is to design algorithms with the goal of obtaining robust and accurate estimates of rain rate and equivalent liquid water contents of snow and rain. The approach proposed is to obtain information on the particle size distribution (PSD) which can be used to estimate rain rate and water content. The basic equations take the form of integral equations that can be expressed as coupled backward recursion relations for two parameters of the PSD. These relations require constraints of path-integrated attenuations (PIA) that are derived either from the surface return or from the measured radar reflectivity factors just above the surface. One of the keys to an efficient implementation of the method is the construction of tables that link the characteristic size parameter of the distribution to various extinction and backscattering integrals as a function of temperature, mass density and mixed-phase parameterizations. Although the solution to the dual-wavelength retrieval can be shown to be unique if certain conditions are satisfied, more generally, multiple solutions, i.e., multiple profiles of the PSD parameters, will satisfy the measured data. For the radar-only solution, the mean and error variance of the estimates can be obtained by generating solutions for various profiles of cloud liquid water and water vapor as well as for different parameterizations of the mixed phase region and values of the shape parameter in the gamma size distribution. These multiple solutions also can be used in the radar-radiometer algorithms by converting each microphysical solution, consistent with the radar data, to radiances at the GPM microwave imager (GMI) frequencies and selecting that solution that minimizes the differences between the measured and inferred radiances. The method will be tested using several approaches including the use of airborne dual-wavelength radar data and the use of model data in conjunction with a radar simulator. Model data will also be used to determine typical ranges of cloud water profiles for stratiform and convective rain types as well as to assist in the development of look-up tables appropriate for the mixed phase region in convective storms.
Project PI: Robert Meneghini/NASA Goddard Space Flight Center
NASA/GSFC Mail Code 613.1 Greenbelt, MD 20771
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