Cross-polarized C-band from IWRAP in Winter 2015
During January and February of 2015, the STAR Ocean Winds Science Team performed a series of flight experiments over the North Atlantic Ocean with the NOAA WP-3D N42RF. Using the Imaging Wind and Rain Airborne Profiler (IWRAP), developed and maintained by the University of Massachusetts Amherst (UMass), in conjunction with an antenna on loan from the European Space Agency (ESA), experiments were designed to sample the cross-polarized ocean surface NRCS at various wind speeds, azimuth angles with respect to wind direction, and incidence angles. Though some observations occurred above 30 m s-1, the majority fell between 8 m s-1 and 20 m s-1.
While both C- and Ku-band antennas are usually configured for conical scans, for the Winter 2015 experiment the C-band antenna spinning system was disabled. Its polarization switch was configured to measure VV-, HH-, VH-, and HV-polarizations by toggling rapidly between pairs of co- and cross-polarizations. The C-band antenna was mounted in the aircraft nadir direction, with the side of the antenna with the higher gain on the right side of the aircraft. Since the antenna was not scanned in azimuth, the WP-3D aircraft performed 360° orbits towards the left (i.e., negative roll angle) in order to obtain NRCS measurements at incidence angles from 20° to 60°. At absolute roll angles of less than 50°, two 360° orbits were performed back-to-back; at absolute roll angles of 50° and 60°, three orbits were performed. In total, over 130 orbits were performed at roll angles ranging from -25° to -60°.
Below are links to NetCDF files containing data from these orbits at each of the four polarizations sampled. NRCS is averaged into 64 azimuth bins (with respect to North) and 1° incidence angle bins. No corrections have been performed (e.g., for polarization mixing) except for applying a constant offset to match CMOD5.h over in situ measurement points and general antenna pattern corrections. Orbits were separated into individual elements though they may have been performed immediately after one another at the same nominal incidence angle.