Intermediate results of the NORDSEE experiment

The purpose of this report is to summarize the data collected during January 1984 from the Nordsee Tower in Germany. Brief descriptions of the system used and the experiment are given in section 2.0. Angular responses of the scattering coefficient are discussed in Section 3.0. The apparent ripple spectra calculated from backscatter measurements are presented in section 4.0, and the modulation transfer functions (MTFs) calculated from this data set are given in Section 5.0. Section 6.0 presents some general conclusions. A modified version of the University of Kansas helicopter-borne spectrometer (HELOSCAT) was used to acquire backscatter data during this experiment. Internal (relative) calibration of the system was accomplished by measuring the signal from a delay line switched in place of the antenna before and after each data run. External (absolute) calibration was performed by measuring the power received from a target of known radar cross-section a metal sphere with a diameter of 20 cm). Normally a Luneberg lens (which has a much higher cross-section than the metal sphere) is used for external calibration, but it was not possible to use the Luneberg lens during this experiment because of logistics problems. The main emphasis of these measurements was on long data sets at a few fixed azimuth angles (generally upwind, downwind or crosswind) and incidence angles with VV-polarization at 5.3, 10 and 15 GHz. During aircraft overflights, measurements were made at 5.3 GHz at a fixed azimuth angle and the same incidence angle used by the systems in the aircraft.