Airborne Laser Scanning for calibration and validation of inshore satellite altimetry: A proof of concept

Recent developments in satellite altimetry are leading to improved spatial resolution, allowing applications in the coastal zone and over inland waters. Validation of these sensors near the shore remains a challenge, since the process of upscaling from single point measurements (gauges or GPS buoys) to the radar altimetry footprint is a source of uncertainty. Meanwhile, Airborne Laser Scanning (LIDAR) has been proven capable of delivering accurate water surface heights rapidly over large areas. Here, we show a proof of concept by comparing airborne LIDAR heights over Lake Balaton, Hungary with near-concurrent Envisat and Jason-2 altimeter heights and water level gauge data. The accuracy of LIDAR heights was improved by strip adjustment and absolute georeferencing to ground control points; waveform retracking improved the accuracy of altimetry data. LIDAR heights were averaged within the outlines of the altimetry footprints. Bias is measured for LIDAR and altimetry with respect to gauge heights, and standard deviation of heights measures the vertical dispersion of footprints within one track. Results show standard deviation of heights is in the order of millimeters for LIDAR and 40-50cm for altimetry and bias with respect to gauge heights is 5cm for LIDAR compared to 40cm for altimetry. We conclude that LIDAR may be used for calibration and validation of high resolution satellite radar altimetry over inland waters.