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

Remote Sensing

Neha P. Joshi²  Edward T. A. Mitchard³  Johannes Schumacher²  Vivian K. Johannsen²  Sassan Saatchi¹  Rasmus Fensholt²  Nicolas Baghdadi⁴ 

[1] Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA; E-Mail:;Department of GeoScience and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK-1350, Copenhagen, Denmark; E-Mails:;School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JN, UK; E-Mail:Department of GeoScience and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK-1350, Copenhagen, Denmark;

关键词: ALOS PALSAR;    airborne LiDAR;    canopy density;    aboveground biomass;    mapping scale;    non-linear modeling;    vegetation interception ratio;   

DOI  :  10.3390/rs70404442

来源: mdpi

【 摘 要 】

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 (≥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 (R² = 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.

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland