Airborne S-band SAR for forest biophysical retrieval in temperate mixed forests of the UK

Ramesh K. Ningthoujam*, Heiko Balzter, Kevin Tansey, Keith Morrison, Sarah C.M. Johnson, France Gerard, Charles George, Yadvinder Malhi, Geoff Burbidge, Sam Doody, Nick Veck, Gary M. Llewellyn, Thomas Blythe, Pedro Rodriguez-Veiga, Sybrand van Beijma, Bernard Spies, Chloe Barnes, Marc Padilla-Parellada, James E.M. Wheeler, Valentin LouisTom Potter, Alexander Edwards-Smith, Jaime Polo Bermejo

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

29 Citations (Scopus)
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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.

Original languageEnglish
Article number609
JournalRemote Sensing
Volume8
Issue number7
DOIs
Publication statusPublished - 1 Jul 2016

Keywords

  • Aboveground biomass
  • MIMICS-I model
  • S-band SAR
  • Savernake Forest
  • Wytham Woods

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