Ground calibration of an Orbiting Spacecraft Transmitter

The SeaWinds Calibration Ground Station (CGS) is a novel Ku-band receiving station that supports the June 1999-launched JPL/NASA SeaWinds scatterometer radar which measures the near-surface wind speeds over 90% of the ice-free oceans. The CGS purpose is to measure very accurately the radar pulse timing, frequency and amplitude characteristics in order to monitor independently the radar and spacecraft platform performance over the course of the mission. These data are critical to maintaining or improving the quality of the end-data product. Results are presented which show the ability to measure spacecraft pulse timing to microsecond detail, spacecraft attitude to better than 0.1 degrees, and output amplitude that will in future work allow estimation of the spacecraft on-orbit antenna pattern. These efforts will improve registration of the scatterometer-derived wind map to the Earth's coordinate system and provide an independent assessment of the instrument quality over the life of the mission.