Relative-Height Image Generation from Long-Range Airborne Streak-Tube Imaging LiDAR for Wide-Area Building- Structure...

Wide-area building-structure mapping from long-range airborne LiDAR requires image products that can represent building footprints, roof-height variations, and structural discontinuities with low computational latency. Airborne streak-tube imaging LiDAR (ASTIL) records a spatial-temporal echo image for each laser pulse, where the detector row corresponds to the fan-beam spatial angle, the detector column encodes echo arrival time, and the frame sequence represents the scanning process. This row-column-frame topology makes it possible to generate image-domain structural products directly from raw streak-tube echo sequences. In this paper, a relative-height image generation method is proposed for long-range ASTIL. The method constructs slant-range matrices from raw echo images, suppresses row-wise ground-related range trends, maps the residuals into relative-height values, and generates scan-geometry-calibrated swath-level relative-height images using lightweight calibration rather than rigorous point-wise POS/IMU trajectory reconstruction. Airborne experiments at 2 km, 3 km, and 6 km flight heights show that the proposed workflow can generate relative-height images with spatial sampling intervals of 0.30 m, 0.45 m, and 0.90 m, respectively, within a 0.5 s acquisition window. The generated cropped image products occupy less than 0.3% of the raw streak-image sequence volume, reflecting a compact image-domain representation for rapid preliminary mapping rather than lossless data compression. Building-scale comparisons with UAV LiDAR reference data indicate that the generated images preserve the main building footprints, boundary orientations, and roof-height discontinuities. For nine flat-roof targets, the mean absolute roof-to-ground height errors range from 0.24 m to 0.30 m across the three flight heights. These results suggest that ASTIL relative-height imaging can provide an efficient image-domain representation for wide-area building-structure mapping under long-range airborne observation conditions.