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Abstract:The objective of this study was to determine whether leaf area index (LAI) in temperate mixed forests is best estimated using multiple-return airborne laser scanning (lidar) data or dual-band, single-pass interferometric synthetic aperture radar data (from GeoSAR) alone, or both in combination. In situ measurements of LAI were made using the LiCor LAI-2000 Plant Canopy Analyzer on 61 plots (21 hardwood, 36 pine, 4 mixed pine hardwood; stand age ranging from 12-164 years; mean height ranging from 0.4 to 41.2 m) in the Appomattox-Buckingham State Forest, Virginia, USA. Lidar distributional metrics were calculated for all returns and for ten one meter deep crown density slices (a new metric), five above and five below the mode of the vegetation returns for each plot. GeoSAR metrics were calculated from the X-band backscatter coefficients (four looks) as well as both X-and P-band interferometric heights and magnitudes for each plot. Lidar metrics alone explained 69% of the variability in LAI, while GeoSAR metrics alone explained 52%. However, combining the lidar and GeoSAR metrics increased the R 2 to 0.77 with a CV-RMSE of 0.42.This study indicates the clear potential for X-band backscatter and interferometric height (both now available from spaceborne sensors), when combined with small-footprint lidar data, to improve LAI estimation in temperate mixed forests.

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GeoSAR is a single pass, dual frequency (X-band and P-band) interferometric mapping radar designed to map both top vegetation canopies and the terrain beneath the canopy. This system was developed from 1998-2003 as a joint effort of NASA JPL and EarthData under sponsorship of DARPA and NGA. The system is flown on a G-II aircraft and maps 10-12 km swaths simultaneously on both sides of the aircraft to generate high quality DEMs and imagery at both X-band and P-band. The system was later augmented with a nadir-pointing lidar profiler system to generate highly accurate control points that can be used in generating large area mosaics. Over the last 5 years the field of polarimetric interferometry has shown great utility in mapping the top of canopies and the underlying terrain with a great deal of accuracy at both L-band and P-band. This paper discusses an upgrade of the GeoSAR dual-pol (HH, HV) P-band interferometer to a fully polarimetric interferometer (HH, HV, VH, VV). We present both hardware and processor changes to the GeoSAR system needed for fully polarimetric interferometric operation.

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