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Remote Sens. 2015, 7(4), 4442-4472; doi:10.3390/rs70404442

L-Band SAR Backscatter Related to Forest Cover, Height and Aboveground Biomass at Multiple Spatial Scales across Denmark

1
Department of GeoScience and Natural Resource Management, University of Copenhagen, ØsterVoldgade 10, DK-1350, Copenhagen, Denmark
2
School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JN, UK
3
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
*
Author to whom correspondence should be addressed.
Academic Editors: Nicolas Baghdadi and Prasad S. Thenkabail
Received: 8 February 2015 / Revised: 23 March 2015 / Accepted: 3 April 2015 / Published: 14 April 2015
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Abstract

Mapping forest aboveground biomass (AGB) using satellite data is an important task, particularly for reporting of carbon stocks and changes under climate change legislation. It is known that AGB can be mapped using synthetic aperture radar (SAR), but relationships between AGB and radar backscatter may be confounded by variations in biophysical forest structure (density, height or cover fraction) and differences in the resolution of satellite and ground data. Here, we attempt to quantify the effect of these factors by relating L-band ALOS PALSAR HV backscatter and unique country-wide LiDAR-derived maps of vegetation penetrability, height and AGB over Denmark at different spatial scales (50 m to 500 m). Trends in the relations indicate that, first, AGB retrieval accuracy from SAR improves most in mapping at 100-m scale instead of 50 m, and improvements are negligible beyond 250 m. Relative errors (bias and root mean squared error) decrease particularly for high AGB values (\(>\)110 Mg ha\(^{-1}\)) at coarse scales, and hence, coarse-scale mapping (\(\ge\)150 m) may be most suited for areas with high AGB. Second, SAR backscatter and a LiDAR-derived measure of fractional forest cover were found to have a strong linear relation (R\(^2\) = 0.79 at 250-m scale). In areas of high fractional forest cover, there is a slight decline in backscatter as AGB increases, indicating signal attenuation. The two results demonstrate that accounting for spatial scale and variations in forest structure, such as cover fraction, will greatly benefit establishing adequate plot-sizes for SAR calibration and the accuracy of derived AGB maps. View Full-Text
Keywords: ALOS PALSAR; airborne LiDAR; canopy density; aboveground biomass; mapping scale; non-linear modeling; vegetation interception ratio ALOS PALSAR; airborne LiDAR; canopy density; aboveground biomass; mapping scale; non-linear modeling; vegetation interception ratio
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Joshi, N.P.; Mitchard, E.T.A.; Schumacher, J.; Johannsen, V.K.; Saatchi, S.; Fensholt, R. L-Band SAR Backscatter Related to Forest Cover, Height and Aboveground Biomass at Multiple Spatial Scales across Denmark. Remote Sens. 2015, 7, 4442-4472.

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