Ground Validation of the GPM-DPR Observations and Precipitation Product from Ground Radar Network

In February 2014 the National Aeronautics and Space Administration (NASA) and Japan Aerospace Exploration Agency (JAXA) launched the Global Precipitation Measurement (GPM) mission core satellite as a joint venture. The Dual – Frequency Precipitation Radar (DPR), onboard the GPM core observatory, is space-borne precipitation radar, deployed to succeed the successful Tropical Rainfall Measurement Mission (TRMM) satellite's precipitation radar (PR). It works at both frequency bands of Ku (13.6 GHz) and Ka (35.5 GHz). The new Ka band channel measurements will be able to improve the radar's threshold for detecting precipitation like light rain and snow [1]. It will also allow the DPR to provide more accurate information on particle size distribution that can be obtained from non-Rayleigh scattering effects at this high frequency. Thus the dual frequency observations will not only enable the DPR in estimating the precipitation phase transition height or melting layer more accurately but it will also help in providing better rainfall estimates as compared to its predecessor, TRMM-PR.

This paper presents ground validation of satellite products with simultaneous dual-polarization ground radars. Careful comparison is made after volume matching the ground and space borne radar observations and the comparison results are presented from multiple ground radar locations in the continental United States. Direct comparison on a point-by-point basis can be very challenging due to a difference in geometric alignment & resolution volumes between the space based and ground based radar. In addition, difference in operating frequencies leading to different attenuation levels can also introduce errors. In order to mitigate these difficulties volume matching has been done between the GPM-DPR and NEXRAD reflectivity & rainfall rate estimate before proceeding with any kind of comparison. Volume matched reflectivity from both the radar shows good agreement with each other. Volume matched rainfall rate estimate from DPR product [2] is also made to compare with that of the ground radar. Algorithm developed by Cifelli et al. [3] has been used to retrieve GR rainfall rate estimate. The comparisons show excellent agreement and the results are presented.