Cross Validation of TEMPEST-D and RainCube Observations Over Precipitation Systems

Abstract

This paper presents cross-validation of nearly simultaneous observations between the Temporal Experiment for Storms and Tropical Systems<b>&#x00A0;-</b>Demonstration<b>&#x00A0;(</b>TEMPEST-D) and RainCube (Radar in a CubeSat) satellite microwave sensors over precipitation systems. RainCube senses the atmosphere using a Ka-band nadir-pointing radar, and TEMPEST-D senses using multi-frequency millimeter-wave radiometers. Nine precipitation systems were used in this cross-validation study. Occurring over nearly a two-year period, these storms were scattered over many regions of the world from the Tropics to the mid-latitudes. A shift correction algorithm was developed to remove the uncertainty between the two sensors&#x0027; observations due to the time difference and the storm motion between the two instrument overpasses. Correlation coefficients were calculated between self-normalized, inverted RainCube cumulative reflectivity and self-normalized TEMPEST-D brightness temperatures. As expected, these correlation coefficients are consistently higher for the four TEMPEST-D high-frequency channels than for the single low-frequency channel. The shift correction algorithm improved the average correlation coefficient by 19&#x0025; for the four high-frequency channels and by 58&#x0025; for the single low-frequency channel. The average correlation coefficient after shift correction is 0.76 for TEMPEST-D&#x0027;s four high-frequency channels and 0.54 for the single low-frequency channel. The comparisons demonstrated high consistency between the TEMPEST-D and RainCube observations, even though the two microwave sensors&#x0027; fundamental physics is different; one is passive, and the other is active.