Laser pointing and characterization parameter determination methods based on laser profile arrays of ICESat/GALS

Satellite laser altimeter data are used for polar ice sheet elevation mapping, vegetation mapping, etc. Data quality mainly depends on complex relationships among several factors in the path of laser transmission and on illuminated surfaces, including clouds, atmospheric aerosol, satellite pointing, laser energy, topography, footprint size, shape and orientation. The precise pointing of the transmitted laser pulse is critical for improving the horizontal accuracy of the footprint on the ground. Thus, we extracted the centroid of the laser profile array (LPA) image of ICESat/GLAS by 1/e² maximum energy distribution method. The results show that the accuracy of extraction of the LPA's centroid improved by 0.3 pixel, and the relative positioning accuracy improved by 0.11 pixel. The fast Fourier transform and Fourier series fitting of the LPA centroid has been implemented to detect the periodic change and analyze the model regularity. The results show that the centroid of the LPA undergoes four periodic changes: 1.83 × 10^-4, 3.36 × 10^-4, 5.19 × 10^-4, and 6.71 × 10^-4Hz. The correlation of fit is a good indicator (R²=0.86) and accurate up to 0.4 arcsec (approximately 0.13 pixel). Finally, we extract and estimate the LPA characteristic parameters (eccentricity, orientation, total intensity, and major axis) in different campaigns. We observe that the results obtained by the 1/e²maximum energy distribution are only approximate.