Airborne S-band SAR for forest biophysical retrieval in temperate mixed forests of the UK
Ramesh K. Ningthoujam (University of Leicester)
Heiko Balzter (University of Leicester)
Kevin Tansey (University of Leicester)
Keith Morrison (Cranfield University)
Sarah C.M. Johnson (University of Leicester)
France Gerard (Centre for Ecology and Hydrology)
Charles George (Centre for Ecology and Hydrology)
Yadvinder Malhi (University of Oxford)
Geoff Burbidge (Airbus)
Sam Doody (Airbus)
Nick Veck (Satellite Applications Catapult)
Gary M. Llewellyn (Airborne Research and Survey Facility)
Thomas Blythe (Leigh Woods Office)
Pedro Rodriguez-Veiga (University of Leicester)
Sybrand van Beijma (Airbus)
Bernard Spies (University of Leicester)
Chloe Barnes (University of Leicester)
Marc Padilla-Parellada (University of Leicester)
James E.M. Wheeler (University of Leicester)
Valentin Louis (University of Leicester)
Tom Potter (University of Leicester)
Alexander Edwards-Smith (Cranfield University)
J. Polo Bermejo (TU Delft - Water Resources)
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Abstract
Radar backscatter from forest canopies is related to forest cover, canopy structure and aboveground biomass (AGB). The S-band frequency (3.1-3.3 GHz) lies between the longer L-band (1-2 GHz) and the shorter C-band (5-6 GHz) and has been insufficiently studied for forest applications due to limited data availability. In anticipation of the British built NovaSAR-S satellite mission, this study evaluates the benefits of polarimetric S-band SAR for forest biophysical properties. To understand the scattering mechanisms in forest canopies at S-band the Michigan Microwave Canopy Scattering (MIMICS-I) radiative transfer model was used. S-band backscatter was found to have high sensitivity to the forest canopy characteristics across all polarisations and incidence angles. This sensitivity originates from ground/trunk interaction as the dominant scattering mechanism related to broadleaved species for co-polarised mode and specific incidence angles. The study was carried out in the temperate mixed forest at Savernake Forest and Wytham Woods in southern England, where airborne S-band SAR imagery and field data are available from the recent AirSAR campaign. Field data from the test sites revealed wide ranges of forest parameters, including average canopy height (6-23 m), diameter at breast-height (7-42 cm), basal area (0.2-56 m2/ha), stem density (20-350 trees/ha) and woody biomass density (31-520 t/ha). S-band backscatter-biomass relationships suggest increasing backscatter sensitivity to forest AGB with least error between 90.63 and 99.39 t/ha and coefficient of determination (r2) between 0.42 and 0.47 for the co-polarised channel at 0.25 ha resolution. The conclusion is that S-band SAR data such as from NovaSAR-S is suitable for monitoring forest aboveground biomass less than 100 t/ha at 25 m resolution in low to medium incidence angle range.
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