A method for the analysis of spatial statistics in multifrequency polarimetric Synthetic Aperture Radar (SAR) data is presented. The objective is to extract the intrinsic variability of the target by removing the variability from other sources. Three sources which contribute to the spatial variability in the returned power from a distributed target are modelled, they are (1) image speckle, (2) system noise, and (3) the intrinsic spatial variability of the target or texture. Speckle and system noise are modelled based on an understanding of the physics of the SAR imaging and processing systems. Texture is modelled as a random variable which modulates the mean returned power from a distributed target. An image model which accounts for all three sources of variability is presented. The presence of texture is shown to increase the image variance-to-mean square ratio and to introduce deviations of the image a u toco variance function from the expected SAR system response. Two textural parameters, the standard deviation of texture and its autocovariance coefficient, are examined. This statistical approach is illustrated using sea-ice SAR imagery acquired by the Jet Propulsion Laboratory three-frequency polarimetric airborne SAR. Textural modulation of the signal has been detected in the imagery. Results show that for different sea-ice types the spatial statistics seem to vary more across frequency than across polarization and the observed differences increase in magnitude with decreasing frequency. The results also suggest the potential of this approach for discrimination of various sea-ice types and open water in single frequency, single polarization SAR data. Correlation of the spatial statistics to field measurements will be important for the verification of these observations. © 1993 Taylor & Francis Group, LLC.

A more detailed characterization of the apparent thin ice types in the multifrequency, multipolarization synthetic aperture radar (SAR) dataset acquired during a campaign for validation of the DMSP SSM/I radiometer ice products is given. The emphasis is on providing a more detailed characterization of the signatures of apparent thin ice types observed in this data and the utility of these signatures for ice type classification purposes. The statistical characteristics of these signatures and their dependence on system calibration are summarized. Implications of these observations for sea ice scattering models are briefly discussed.

The first known fully polarimetric airborne synthetic aperture radar (SAR) data set of sea ice is introduced. The full Stokes matrix information generated from C, L, and P band data characterize the scattering behavior of different ice types. Polarization ratios and phase differences between linear copolarized returns are used for discrimination between particular image features and mechanisms are suggested for the observed polarimetric characteristics. Results indicate that combinations of frequency and polarization enhance current capability to distinguish ice of different properties using single frequency, fixed polarization microwave radar. -from Authors

During two different overflights (by the JPL radar polarimeter) of the Bonanza Creek Experimental Forest, the environmental conditions changed significantly with temperatures ranging from unseasonably warm (1 to 9°C) to well below freezing (-8 to -15°C), and the moisture content of the snow and trees changed from a liquid to a frozen state. Preliminary investigations have focused on the characterization of the radiometric and polarimetric signatures of the data. Significant changes (up to 6 dB in certain forest stands) were observed in the L-band radar cross sections. Features extracted from the Stokes matrices of the same stands from the thawed and frozen days also suggest the relative contribution of the different scattering mechanisms to the radar return. Comparison of the diffuse component and variance of the H-V phase (white spruce, for example) indicates a relatively higher contribution from diffuse scatterers on the thawed day than on the frozen day. These results indicate that the contribution of scattering from the crown is responsible for this appreciable increase in backscatter. Some of these preliminary L-band and P-band observations are presented.

We have determined the effect of pressure P on the resistance and superconducting transition temperature Tc of RBa2Cu3Ox (R=Gd,Er,andYb) and compare our results to those obtained on high-quality YBa2Cu3Ox. The transition temperature, which is 90 K or greater at ambient pressure for all four compounds, is enhanced by pressure in each at rates between 0.09 and 0.19 K/kbar. Interestingly, the presence of a localized moment in the rare-earth compounds appears to have no influence on the pressure response. From the positive dTcdP we infer a positive change in the thermal expansion upon entering the superconducting state. © 1987 The American Physical Society.