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| Titel |
Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud |
| VerfasserIn |
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 |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 1 ; Nr. 9, no. 1 (2012-01-10), S.179-191 |
| Datensatznummer |
250006658
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| Publikation (Nr.) |
 copernicus.org/bg-9-179-2012.pdf |
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| Zusammenfassung |
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.
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 km2) 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−1).
This value is consistent with our field data average of 181 Mg C ha−1,
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 ±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.
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. |
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