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.
ABSTRACT. P-band interferometric synthetic aperture radar (InSAR) data at 5 m resolution from Kahiltna Glacier, the largest glacier in the Alaska Range, Alaska, USA, show pronounced spatial variation in penetration depth, P . We obtained P by differencing X-and P-band digital elevation models. P varied significantly over the glacier, but it was possible to distinguish representative zones. In the accumulation area, P decreased with decreasing elevation from 18 AE 3 m in the percolation zone to 10 AE 4 m in the wet snow zone. In the central portion of the ablation area, a location free of debris and crevasses, we identified a zone of very high P (34 AE 4 m) which decreased at lower elevations (23 AE 3 m in bare ice and 5-10 m in debris-covered ice). We observe that the spatial configuration of P is consistent with the expected thermal regime of each zone: P is high in areas where cold firn/ice likely occurs (i.e. percolation zone and upper ablation area) and low in areas where temperate surface firn/ice likely exists (wet snow zone and lower ablation area). We suggest that the very high P observed in the upper ablation area is due to the presence of a cold surface layer.
The GeoSAR single-pass P-band and X-band IFSAR system was employed 09 April 2012 to acquire ice data over the city of Barrow, Alaska, extending into the Chukchi Sea to the west and the Beaufort Sea to the northeast. The acquisition covered two back-to-back flights obtaining high quality singlepass interferometric X-band and P-band data. Some of the Pband data was collected in fully polarimetric mode. Ground control was established by two geographically separated dualband corner reflectors. Nadir looking lidar profiler data was acquired over the majority of the project. The acquisition was timed to be temporally coincident with airborne electromagnetic (AEM) ice thickness measurements. Sea ice in the region surveyed was primarily composed of first year ice around 1.8 m thick, though multiyear ice was also observed and ice thicknesses >20m were measured over pressure ridges. P-band imagery disclosed a rich network of ridges with high brightness compared with X-band. Owing to the much greater penetration at P-band than X-band the volumetric decorrelation differs significantly between X-band and P-band that could be potentially exploited to improve ice-type classification. P-band penetration was assessed by simplistic differencing of the Xband and P-band digital elevation models (DEMs) after thresholding based on height error. Preliminary observations indicate surface penetration has been observed; however further analysis is required to determine the relationship between Xband-P-band elevation differences and ice penetration. Acquiring data from a lower altitude with improved SNR and enhanced interferometric sensitivity will benefit measurements.
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