Abstraet. We performed experiments to collect radar backscatter data at K. (13-4GHz) and C bands (5'3GHz) over simulated sea ice at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) during the 1990 and 1992 winter seasons. These experiments were conducted over bare saline ice grown in an indoor tank and an outdoor pond facility. The radar data were calibrated using a complex vector calibration scheme to reduce systematic efTects. In conjunction with the radar measurements we measured ice physical properties.These measurements demonstrate that the dominant backscatter mechanism for bare saline ice is surface scattering. Both the copolarizcd and cross-polarized measurements compare favourably with the predictions of surface scattering models at two frequencies.During the 1992 indoor tank experiment we applied four successive layers of snow (about 2·5 ern each) to the saline ice sheet after the ice thickness had reached about 12cm. The backscatter at normal incidence dropped by 15dB and the backscatter at 45' increased by II dB with the introduction of the first snow layer. The application of three more layers, each of approximately 2·5 cm depth. did not alter the radar signature significantly. By modelling and direct observation we found that the initial change in the signature was caused by a roughening of the surface at the snow-ice interface and the change in dielectric contrast at the snow-icc interface.

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A wireless vibratory strain sensing system, which consists of a passive wireless sensor and a dynamic wireless interrogator, is presented in this paper. The wireless sensor utilizes a microstrip patch antenna as the strain sensing element since its resonant frequency is a function of the tensile strain it experiences. A dynamic wireless interrogator that is based on the principle of Frequency Modulated Continuous Wave (FMCW) radar and permits real-time monitoring of the antenna resonant frequency was designed and validated. The principle of operation of the dynamic wireless sensing system was first described, followed by the description of the design and implementation of the antenna-sensor node as well as the wireless interrogator. After calibrating the antenna-sensor response using static tensile tests, vibratory tensile tests were carried out by subjecting the test specimen to sinusoidal tensile loading at different frequencies.Antenna strain sensing accuracy was evaluated by comparing the strain readings from the antenna-sensor and the reference foil strain gauge. It reveals that the antenna-based strain sensing system has good dynamic strain tracking ability.Index Terms-dynamic interrogation; FMCW; real-time digital data processing; structural health monitoring; vibration sensing; wireless antenna sensor 1530-437X (c)

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