Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud

Spatially-explicit maps of aboveground biomass are essential for calculating the losses and gains in forest carbon at a regional to national level. The production of such maps across wide areas will become increasingly necessary as international efforts to protect primary forests, such as the REDD+...

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Main Authors: E. T. A. Mitchard, S. S. Saatchi, L. J. T. White, K. A. Abernethy, K. J. Jeffery, S. L. Lewis, M. Collins, M. A. Lefsky, M. E. Leal, I. H. Woodhouse, P. Meir
Format: Article
Language:English
Published: Copernicus Publications 2012-01-01
Series:Biogeosciences
Online Access:http://www.biogeosciences.net/9/179/2012/bg-9-179-2012.pdf
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spelling doaj-c189ff9b7b214ba58bce91c578c7c0b72020-11-24T23:28:07ZengCopernicus PublicationsBiogeosciences1726-41701726-41892012-01-019117919110.5194/bg-9-179-2012Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloudE. T. A. Mitchard0S. S. Saatchi1L. J. T. White2K. A. Abernethy3K. J. Jeffery4S. L. Lewis5M. Collins6M. A. Lefsky7M. E. Leal8I. H. Woodhouse9P. Meir10School of GeoSciences, University of Edinburgh, EH8 9XP, UKJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USAAgence Nationale des Parcs Nationaux, Libreville, GabonSchool of Natural Sciences, University of Stirling, Stirling, FK9 4LA, UKAgence Nationale des Parcs Nationaux, Libreville, GabonEarth and Biosphere Institute, School of Geography, University of Leeds, UKGrantham Research Institute on Climate Change and the Environment, London School of Economics, London, UKNatural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado, USAMissouri Botanical Garden, St. Louis, Missouri, USASchool of GeoSciences, University of Edinburgh, EH8 9XP, UKSchool of GeoSciences, University of Edinburgh, EH8 9XP, UKSpatially-explicit maps of aboveground biomass are essential for calculating the losses and gains in forest carbon at a regional to national level. The production of such maps across wide areas will become increasingly necessary as international efforts to protect primary forests, such as the REDD+ (Reducing Emissions from Deforestation and forest Degradation) mechanism, come into effect, alongside their use for management and research more generally. However, mapping biomass over high-biomass tropical forest is challenging as (1) direct regressions with optical and radar data saturate, (2) much of the tropics is persistently cloud-covered, reducing the availability of optical data, (3) many regions include steep topography, making the use of radar data complex, (5) while LiDAR data does not suffer from saturation, expensive aircraft-derived data are necessary for complete coverage. <br></br> We present a solution to the problems, using a combination of terrain-corrected L-band radar data (ALOS PALSAR), spaceborne LiDAR data (ICESat GLAS) and ground-based data. We map Gabon's Lopé National Park (5000 km<sup>2</sup>) because it includes a range of vegetation types from savanna to closed-canopy tropical forest, is topographically complex, has no recent contiguous cloud-free high-resolution optical data, and the dense forest is above the saturation point for radar. Our 100 m resolution biomass map is derived from fusing spaceborne LiDAR (7142 ICESat GLAS footprints), 96 ground-based plots (average size 0.8 ha) and an unsupervised classification of terrain-corrected ALOS PALSAR radar data, from which we derive the aboveground biomass stocks of the park to be 78 Tg C (173 Mg C ha<sup>−1</sup>). This value is consistent with our field data average of 181 Mg C ha<sup>−1</sup>, from the field plots measured in 2009 covering a total of 78 ha, and which are independent as they were not used for the GLAS-biomass estimation. We estimate an uncertainty of &pm;25% on our carbon stock value for the park. This error term includes uncertainties resulting from the use of a generic tropical allometric equation, the use of GLAS data to estimate Lorey's height, and the necessity of separating the landscape into distinct classes. <br></br> As there is currently no spaceborne LiDAR satellite in operation (GLAS data is available for 2003–2009 only), this methodology is not suitable for change-detection. This research underlines the need for new satellite LiDAR data to provide the potential for biomass-change estimates, although this need will not be met before 2015.http://www.biogeosciences.net/9/179/2012/bg-9-179-2012.pdf
collection DOAJ
language English
format Article
sources DOAJ
author E. T. A. Mitchard
S. S. Saatchi
L. J. T. White
K. A. Abernethy
K. J. Jeffery
S. L. Lewis
M. Collins
M. A. Lefsky
M. E. Leal
I. H. Woodhouse
P. Meir
spellingShingle E. T. A. Mitchard
S. S. Saatchi
L. J. T. White
K. A. Abernethy
K. J. Jeffery
S. L. Lewis
M. Collins
M. A. Lefsky
M. E. Leal
I. H. Woodhouse
P. Meir
Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud
Biogeosciences
author_facet E. T. A. Mitchard
S. S. Saatchi
L. J. T. White
K. A. Abernethy
K. J. Jeffery
S. L. Lewis
M. Collins
M. A. Lefsky
M. E. Leal
I. H. Woodhouse
P. Meir
author_sort E. T. A. Mitchard
title Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud
title_short Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud
title_full Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud
title_fullStr Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud
title_full_unstemmed Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud
title_sort mapping tropical forest biomass with radar and spaceborne lidar in lopé national park, gabon: overcoming problems of high biomass and persistent cloud
publisher Copernicus Publications
series Biogeosciences
issn 1726-4170
1726-4189
publishDate 2012-01-01
description Spatially-explicit maps of aboveground biomass are essential for calculating the losses and gains in forest carbon at a regional to national level. The production of such maps across wide areas will become increasingly necessary as international efforts to protect primary forests, such as the REDD+ (Reducing Emissions from Deforestation and forest Degradation) mechanism, come into effect, alongside their use for management and research more generally. However, mapping biomass over high-biomass tropical forest is challenging as (1) direct regressions with optical and radar data saturate, (2) much of the tropics is persistently cloud-covered, reducing the availability of optical data, (3) many regions include steep topography, making the use of radar data complex, (5) while LiDAR data does not suffer from saturation, expensive aircraft-derived data are necessary for complete coverage. <br></br> We present a solution to the problems, using a combination of terrain-corrected L-band radar data (ALOS PALSAR), spaceborne LiDAR data (ICESat GLAS) and ground-based data. We map Gabon's Lopé National Park (5000 km<sup>2</sup>) because it includes a range of vegetation types from savanna to closed-canopy tropical forest, is topographically complex, has no recent contiguous cloud-free high-resolution optical data, and the dense forest is above the saturation point for radar. Our 100 m resolution biomass map is derived from fusing spaceborne LiDAR (7142 ICESat GLAS footprints), 96 ground-based plots (average size 0.8 ha) and an unsupervised classification of terrain-corrected ALOS PALSAR radar data, from which we derive the aboveground biomass stocks of the park to be 78 Tg C (173 Mg C ha<sup>−1</sup>). This value is consistent with our field data average of 181 Mg C ha<sup>−1</sup>, from the field plots measured in 2009 covering a total of 78 ha, and which are independent as they were not used for the GLAS-biomass estimation. We estimate an uncertainty of &pm;25% on our carbon stock value for the park. This error term includes uncertainties resulting from the use of a generic tropical allometric equation, the use of GLAS data to estimate Lorey's height, and the necessity of separating the landscape into distinct classes. <br></br> As there is currently no spaceborne LiDAR satellite in operation (GLAS data is available for 2003–2009 only), this methodology is not suitable for change-detection. This research underlines the need for new satellite LiDAR data to provide the potential for biomass-change estimates, although this need will not be met before 2015.
url http://www.biogeosciences.net/9/179/2012/bg-9-179-2012.pdf
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