Use of a variance estimator for interferometer angle accuracy

For radar applications requiring angle measurements on ground clutter over a large range swath or large elevation-angle extent, the single-pulse clutter-to-noise power ratio can be small due to low intercept grazing angles or low reflectivity. An approach is presented for using multiple returns to derive an angle variance estimate as a direct measure of data validity, rather than an amplitude threshold to better detect the presence of angle glint prior to angle estimation. The variance estimator can be used to detect the presence of spatially distributed interference returns such as those from a rain cloud. Results of a Monte Carlo signal simulation are presented to demonstrate the expected angle accuracy performance when the variance estimator is used in a phase interferometer radar. These results are compared to angle accuracy estimates based on an amplitude discriminant. Small integration sample size and degradation due to thermal noise, clutter, and glint are considered. The results are applicable to measurements in either azimuth or elevation angle and to discrete targets with Swerling-I amplitude fluctuation