TY - JOUR
T1 - Toward structural assessment of semi-arid African savannahs and woodlands
T2 - The potential of multitemporal polarimetric RADARSAT-2 fine beam images
AU - Mathieu, Renaud
AU - Naidoo, Laven
AU - Cho, Moses A.
AU - Leblon, Brigitte
AU - Main, Russell
AU - Wessels, Konrad
AU - Asner, Gregory P.
AU - Buckley, Joseph
AU - Van Aardt, Jan
AU - Erasmus, Barend F.N.
AU - Smit, Izak P.J.
N1 - Funding Information:
We acknowledge the Council for Scientific and Industrial Research, Department of Science and Technology, South Africa (grant agreement DST/CON 0119/2010 , Earth Observation Application Development in Support of SAEOS), the European Union's Seventh Framework Programme (FP7/2007-2013, grant agreement no. 282621 , AGRICAB) for funding this research. The 12 RADARSAT-2 scenes were provided by MacDonald Dettwiler and Associates Ltd. — Geospatial Services Inc. (MDA GSI), the Canadian Space Agency (CSA), and the Natural Resources Canada's Centre for Remote Sensing (CCRS) through the Science and Operational Applications Research (SOAR) programme. The Carnegie Airborne Observatory is made possible by the Gordon and Betty Moore Foundation , the Grantham Foundation for the Protection of the Environment , Avatar Alliance Foundation , W. M. Keck Foundation , the Margaret A. Cargill Foundation , Mary Anne Nyburg Baker and G. Leonard Baker Jr. , and William R. Hearst III . Application of the CAO data in South Africa is made possible by the Andrew Mellon Foundation , Grantham Foundation for the Protection of the Environment , and the endowment of the Carnegie Institution for Science . LiDAR and hyperspectral data were processed by T. Kennedy-Bowdoin, D. Knapp, J. Jacobson and R. Emerson at the Carnegie Institution for Science. The authors further acknowledge SANParks, Sabi Sands Game Reserve (Michael Grover), and Bushbuckridge local authorities and personnel for facilitating access to their lands, sharing field expertise, and the logistical support provided.
PY - 2013/11
Y1 - 2013/11
N2 - Woody vegetation structure affects wildlife habitat selection and species diversity for a wide range of taxa, and at a variety of scales. Indicators of woody structure can indicate the spatio-temporal variability of biodiversity, species occurrence and assemblages. Woody cover is the simplest and most widely used structural metric. Combined with the vegetation height, it provides a volumetric indicator, which is more informative, and is simple to calculate. We therefore assessed the utility of multitemporal polarimetric RADARSAT-2 C-band imagery to map measures of woody volumetric indices in Lowveld savannahs, in the vicinity of the Kruger National Park, South Africa. RADARSAT-2 Quad-Pol fine beam images were acquired at three key phenological stages of the seasonal savannah cycle: i) wet (summer), ii) dry (winter), and iii) end of wet (autumn). Multi-polarized band intensities (C-HH, C-HV, and C-VV, with V=vertical and H=horizontal) and polarimetric decomposition variables (Freeman-Durden, Cloude-Pottier, and Van Zyl) were derived from the SAR images and used to predict structural metrics (woody canopy cover, cylindrical woody volume, and woody canopy volume, see definition in Section3.3) derived from 1.1m LiDAR strips acquired across the study area, and coinciding with 12% of the SAR dataset. The best single relationship (R2=0.66) was obtained between the cross-polarized HV intensity band and the total canopy volume (TCV). In terms of the seasonality, the best results were obtained using the SAR imagery from the dry season when most woody plants have lost their leaves and the grass-soil layer was dry. Validation outputs of best predictive models for TCV, at the individual season level, yielded an R2 of 0.67, a Standard Error of Prediction (SEP) of 39%, and consisted of the SAR parameters: C-HH, C-HV, C-VV, and Freeman-Durden decomposition parameters. At the multi-seasonal level, the best predictive models for TCV yielded an R2 of 0.75, a SEP of 35%, and comprised of the same variables but for all three seasons. The C-band SAR data thus provided encouraging results in open, semi-arid savannahs and hint at larger area structural assessments than is possible with LiDAR sensors alone. The combined use of C-band and L-band (ALOS-Palsar 2) should also be investigated.
AB - Woody vegetation structure affects wildlife habitat selection and species diversity for a wide range of taxa, and at a variety of scales. Indicators of woody structure can indicate the spatio-temporal variability of biodiversity, species occurrence and assemblages. Woody cover is the simplest and most widely used structural metric. Combined with the vegetation height, it provides a volumetric indicator, which is more informative, and is simple to calculate. We therefore assessed the utility of multitemporal polarimetric RADARSAT-2 C-band imagery to map measures of woody volumetric indices in Lowveld savannahs, in the vicinity of the Kruger National Park, South Africa. RADARSAT-2 Quad-Pol fine beam images were acquired at three key phenological stages of the seasonal savannah cycle: i) wet (summer), ii) dry (winter), and iii) end of wet (autumn). Multi-polarized band intensities (C-HH, C-HV, and C-VV, with V=vertical and H=horizontal) and polarimetric decomposition variables (Freeman-Durden, Cloude-Pottier, and Van Zyl) were derived from the SAR images and used to predict structural metrics (woody canopy cover, cylindrical woody volume, and woody canopy volume, see definition in Section3.3) derived from 1.1m LiDAR strips acquired across the study area, and coinciding with 12% of the SAR dataset. The best single relationship (R2=0.66) was obtained between the cross-polarized HV intensity band and the total canopy volume (TCV). In terms of the seasonality, the best results were obtained using the SAR imagery from the dry season when most woody plants have lost their leaves and the grass-soil layer was dry. Validation outputs of best predictive models for TCV, at the individual season level, yielded an R2 of 0.67, a Standard Error of Prediction (SEP) of 39%, and consisted of the SAR parameters: C-HH, C-HV, C-VV, and Freeman-Durden decomposition parameters. At the multi-seasonal level, the best predictive models for TCV yielded an R2 of 0.75, a SEP of 35%, and comprised of the same variables but for all three seasons. The C-band SAR data thus provided encouraging results in open, semi-arid savannahs and hint at larger area structural assessments than is possible with LiDAR sensors alone. The combined use of C-band and L-band (ALOS-Palsar 2) should also be investigated.
KW - LIDAR
KW - Polarimetry
KW - SAR
KW - Savannah
KW - Structure
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U2 - 10.1016/j.rse.2013.07.011
DO - 10.1016/j.rse.2013.07.011
M3 - Article
AN - SCOPUS:84883036949
SN - 0034-4257
VL - 138
SP - 215
EP - 231
JO - Remote Sensing of Environment
JF - Remote Sensing of Environment
ER -