Cross-calibration of millimeter spaceborne radars through orbital intersections

Conically scanning Ka and W band atmospheric radars (e.g. the radars in the Tomorrow.IO constellation and the WIVERN (WInd VElocity Radar Nephoscope) radar) will be introduced in the global satellite observing system. Traditional calibration methods pointing at sea surface at about 12 degrees incidence angle are not feasible for such systems. Therefore, the development of new methodologies for calibrating these systems is needed. This thesis demonstrate the effectiveness of calibrating spaceborne conically scanning radars using cross-calibration with other spaceborne radar working on the same band and orbiting around Earth in the same period of time (e.g. the Ka-band GPM radar or the W-band radars planned for the NASA AOS missions) as reference. Ice clouds at low temperatures are not prone to appreciable attenuation, so they are used as natural targets for cross-calibrating the systems. The orbits of satellites have been propagated and the position of the radar antenna boresight has been computed. The radars' ground-track intersections have been found for different intersection criteria defined by cross-over withing a certain time and withing a given distance. The climatology of calibrating clouds has been studied using the CloudSat CPR and GPM KaPR dataset, respectively for the W-band and the Ka-band, in order to find the global distribution of the frequency of calibrating clouds. Then the ground-track intersection and the climatology of clouds have been merged in order to obtain the number and the global distribution of the calibration points. The CloudSat and GPM datasets have been further exploited to analyze the statistical correlation between the reflectivity probability distribution function of the calibrating clouds for different distance at which the clouds are sampled in order to find the optimal intersection criterion, which optimizes the calibration precision and maximizes the time needed to achieve it. Results for different combinations of orbits and satellites are presented in the thesis.