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Airborne S-Band SAR for Forest Biophysical Retrieval in Temperate Mixed Forests of the UK

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posted on 2016-12-01, 15:19 authored by Ramesh K. Ningthoujam, Heiko Balzter, Kevin Tansey, K. Morrison, Sarah C. M. Johnson, F. Gerard, C. George, Y. Malhi, G. Burbidge, S. Doody, N. Veck, G. M. Llewellyn, T. Blythe, Pedro Rodriguez-Veiga, S. van Beijma, Bernard Spies, Chloe Barnes, Marc Padilla-Parellada, James E. M. Wheeler, Valentin Louis, Tom Potter, A. Edwards-Smith, J. P. Bermejo
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.

Funding

The authors acknowledge the AirSAR data from Airbus Defence and Space, Natural Environment Research Council Airborne Research & Survey Facility and Satellite Applications Catapult (Project Code: AS 14/24) to Heiko Balzter, Kevin Tansey, Ramesh K. Ningthoujam, Keith Morrison and Sarah C.M. Johnson, and GIS database from Forestry Commission (Bristol and Savernake, UK). Professor Leland Pierce from the Radiation Lab, The University of Michigan (United States of America) is highly appreciated for providing the MIMICS-I code. The invaluable Environmental Change Network plot database for Wytham Woods being shared by Ms Lorna Sherrin from Centre for Ecology & Hydrology (CEH) is also appreciated. Heiko Balzter was supported by the Royal Society Wolfson Research Merit Award, 2011/R3 and the NERC National Centre for Earth Observation.

History

Citation

Remote Sensing, 2016, 8(7), 609;

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Geography/GIS and Remote Sensing

Version

  • VoR (Version of Record)

Published in

Remote Sensing

Publisher

MDPI

issn

2072-4292

eissn

2072-4292

Acceptance date

2016-07-19

Available date

2016-12-01

Publisher version

http://www.mdpi.com/2072-4292/8/7/609

Language

en

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