REMOTE-SENSING OF THE EARTHS SURFACE WITH AN AIRBORNE POLARIZED LASER

A new remote sensing instrument, the Airborne Laser Polarization Sensor (ALPS), makes the first multispectral radiometric and polarization measurements of the Earth's surface using a polarized laser light source. Results from data flights taken over boreal forests in Maine at two wavelengths (using a Nd:YAG laser source: 1060 nm and 532 nm) show distinct depolarization signatures for three broadleaf and five coniferous tree species. A statistically significant increase in depolarization is found to correlate with increasing leaf surface roughness for the broadleaf species in the near-infrared. With the exception of spruce, the dominant species in the boreal forest, conifers had no clear depolarization variations between species at that wavelength. The mean depolarization by conifers was distinctively lower, however, than that measured for the broadleaf species. The conifers did exhibit distinct depolarization signatures at 532 nm, while the broadleaf species had no apparent species dependent depolarization variations at that wavelength. Measurements made over nonforest ground cover had a large dynamic range in depolarization values at both wavelengths. The ALPS system employees twelve photo-multiplier tube detectors configurable to measure desired parameters such as the total backscatter and the polarization state, including the azimuthal angle and ellipticity, at different ultraviolet to near-infrared wavelengths simultaneously. Measurements of the azimuth and ellipticity of the backscatter polarization were variable and no specific conclusions have yet been drawn.