Radiometric Calibration of Full-waveform Small-footprint Airborne Laser Scanners

Small-footprint airborne laser scanners (ALS) are lidar instruments originally developed for topographic mapping. In recent years ALS sensors are increasingly used also in other applications (forest mapping, building extraction, power line modelling, etc.) and their technical capabilities are steadily improving. While the first ALS systems only allowed determining the range from the sensor to the target, current ALS sensors also record the amplitude of the backscattered echoes (peak power of the received echo), or even the complete echo waveform. To fully utilise the potential of the echo amplitude and waveform measurements in applications, it is necessary to perform a radiometric calibration. The calibration process involves the definition of the physical quantities describing the backscattering properties of objects and the development of practical calibration techniques. These issues are currently addressed by an EuroSDR (http://www.eurosdr.net/) project which aims at developing ALS calibration standards. This paper reviews the definition of common scattering (reflectance) parameters and concludes that in the case of small-footprint airborne laser scanning, the cross section σ [m] and the backscattering coefficient γ [mm], which is defined as the cross section normalised with the crosssection of the beam hitting the larget, are the preferred quantities for describing the scattering properties. Hence, either σ or γ should be used in the calibration. Also, some results of converting full-waveform data acquired with the RIEGL LMS-Q560 to cross section data over urban and rural test sites in Austria are shown. * Corresponding author