Novel ExpliSyT method to Correct Dynamic Measurements from Spaceborne Doppler Cloud Profiling Radars

Spaceborne Doppler profiling radars (SDPR) are among the leading instruments considered by space agencies to study atmospheric dynamics. For instance, the European and Japan space agencies are developing the Earth Cloud Aerosol Radiation Explorer (EarthCARE) mission, which will carry the first spaceborne Doppler profiling radar [1,2], while NASA is currently developing the Atmosphere Observing System mission, with a constellation of Doppler radars [3]. 

However, operating an SDPR from low-Earth Orbit (LEO) is challenging due to the large instantaneous speed of the spacecraft (V_SAT ~7200 m/s), which affects velocity measurements by broadening the Doppler spectrum that is being measured. Three major error sources that are caused by this spectral broadening are 1) Non-Uniform BeamFilling (NUBF) biases, 2) prohibitive broadening of the measured spectral widths, and 3) a noisiness of the velocity and width measurements [4,5].

In this presentation we will discuss a novel method that we have developed to overcome NUBF and spectral broadening errors that affect SDPR measurements. This method, coined the ExpliSyT approach, is based on the explicit hierarchical representation of the various Doppler moments. For instance, it allows to correct for the broadening of the measured spectral width (second-order Doppler moment), using the measured mean velocity (first-order Doppler moment) and reflectivity factor (zeroth-order Doppler moment). The resulting corrections enable accuracte retrievals of the full spectrum, which in turns enables a higher-order Doppler characterization of atmospheric dynamics. 

The method will be illustrated with simulations of EarthCARE’s radar, and of a notional Displaced Phase Center Antenna (DPCA) configuration developed at JPL [6]. The DPCA configuration uses a pair of collimated antennas to reduce the severity of the spacecraft-induced fading. 

REFERENCES:
[1] A.J. Illingworth et al., “The EarthCARE satellite: The next step forward in global measurements of clouds, aerosols, precipitation, and radiation,” Bull. Amer. Meteorol. Soc., vol. 96, no. 8, pp. 1311–1332, 2015.
[2] H. Kumagai, H. Kuroiwa, S. Kobayashi, and T. Orikasa, “Cloud profiling radar for EarthCARE mission,” Proc. SPIE, vol. 4894, pp. 118–125, Apr. 2003.
[3] https://aos.gsfc.nasa.gov/
[4] R. Meneghini and T. Kozu, Spaceborne Weather Radar. Boston, MA, USA: Artech House, 1990.
[5] P. Kollias, S. Tanelli, A. Battaglia, and A. Tatarevic, “Evaluation of EarthCARE cloud profiling radar Doppler velocity measurements in particle sedimentation regimes,” J. Atmos. Ocean. Technol., vol. 31, no. 2, pp. 366–386, Feb. 2014.
[6] S. L. Durden, P. R. Siqueira, and S. Tanelli, “On the use of multi-antenna radars for spaceborne Doppler precipitation measurements,” IEEE Geoscience and Remote Sensing Letters, vol. 4, no. 1, pp. 181–183, 2007.