Dot and Segment Feature Analysis and Parameter Inversion of a Curved and Graded Bay Bridge From UAVSAR Imagery

When NASA/JPL UAVSAR imaged the curved and graded Coronado Bridge over San Diego Bay, CA, USA, it was shown as three separate features consisting of dots, short curved segments, and a continuously curved segment on the L-band images. Coupled with the images acquired in the opposite look directions toward the bridge, we analyzed the features, attributed the cause for the unidentifiable direct surface backscatter from the bridge roadway, and assessed the azimuth angle effects linked to the features. A two-step procedure was then articulated to resolve the azimuth angle effect on the decomposition of the quad-pol SAR imagery where orientated man-made objects and trees existed. Next, an algorithm using the single polarization data to estimate the curved and graded bridge height and width was developed. With reference to the Lidar-derived heights and the constant bridge width, we evaluated the algorithm using the difference values of 26 samples. L-HH and L-VV results of two UAVSAR datasets were obtained. Of the bridge height or width, the overall mean and one standard deviation values of the differences were ≤3.7 m and ≤2.8 m, respectively. The values were smaller than the azimuth and ground-range resolutions (5 m × 5 m) of the SAR datasets. Thus, the estimated bridge height and width should be acceptable. Finally, we studied the applicability of the algorithm to ALOS/PALSAR datasets of different data acquisition modes.