This paper focuses on the spatially varying backscattering signature of an area of refrozen brash ice observed by a ship based scatterometer. The measurements were carried out as part of the Baltic Experiment for ERS-1 in 1994. The scatterometer was operated at 5.4 GHz at different incidence angles and polarizations. By analysing the scatterometer data over azimuth scans, it was found that the backscattering variabilities are not only due to fading but also contain a textural component. Surface height profiles were measured using a laser. The observed ice surface roughness was nonstationary over the measurement area. The ice surface can be approximated by adjacent patches of stationary roughness with patch dimensions of about 4.5 m. From the roughness spectra of different stationary patches, two roughness classes can be distinguished. The implications of estimating the roughness parameters from relatively short profile lengths is discussed and the effect on theoretical predictions of the backscattering coefficient is investigated. The texture variance is evaluated theoretically on the basis of the simulated backscattering coefficients of the two observed roughness classes and is found to compare with the scatterometer data.

The effect of inhomogeneous roughness on radar backscattering from slightly deformed sea ice

In the summer of 1991, the backscattering from various background surfaces were measured at 94 GHz. A frequency modulated radar was mounted in a skylift and the backscattering coefficients at HH and VV were estimated at different angles of incidence. The test surfaces included bare sand and soil surfaces, an asphalt road and lawn. Soil-moisture was sampled and surface roughness profiles were recorded using a laser profiler. In the analysis of the data, the measured backscattering coefficients were compared with predictions from different kinds of scattering models, such as the geometric optics and physical optics approximations, the field perturbation approximation and the integral equation model (IEM). Comparisons were also made with Lambert scattering and approximative solutions for fractal surfaces. The vegetation measurements were compared with predictions using a cloud model of dielectric discs. The results of the radar measurements showed that all the tested soil and sand surfaces generated incoherent scattering at 94 GHz with a weak dependence on the angle of incidence. An exception was the asphalt surface, however, and detailed comparisons with different scattering models were carried out using the autocorrelation function of the measured surface profile as input. The best agreement between measured and predicted scattering coefficients was obtained using the IEM-model. >

K.-G. Johnsson

Papers

Comparison of measured and predicted scattering coefficients at 94 GHz