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| Titel |
Towards ground-truthing of spaceborne estimates of above-ground life biomass and leaf area index in tropical rain forests |
| VerfasserIn |
P. Köhler, A. Huth |
| 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 ; 7, no. 8 ; Nr. 7, no. 8 (2010-08-25), S.2531-2543 |
| Datensatznummer |
250004937
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| Publikation (Nr.) |
 copernicus.org/bg-7-2531-2010.pdf |
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| Zusammenfassung |
| The canopy height h of forests is a key variable which can be obtained
using air- or spaceborne remote sensing techniques such as radar
interferometry or LIDAR. If new allometric relationships between canopy
height and the biomass stored in the vegetation can be established this would
offer the possibility for a global monitoring of the above-ground carbon
content on land. In the absence of adequate field data we use simulation
results of a tropical rain forest growth model to propose what degree of
information might be generated from canopy height and thus to enable
ground-truthing of potential future satellite observations. We here analyse
the correlation between canopy height in a tropical rain forest with other
structural characteristics, such as above-ground life biomass (AGB) (and
thus carbon content of vegetation) and leaf area index (LAI) and identify
how correlation and uncertainty vary for two different spatial scales. The
process-based forest growth model FORMIND2.0 was applied to simulate
(a) undisturbed forest growth and (b) a wide range of possible disturbance
regimes typically for local tree logging conditions for a tropical rain
forest site on Borneo (Sabah, Malaysia) in South-East Asia. In both
undisturbed and disturbed forests AGB can be expressed as a power-law
function of canopy height h (AGB = a · hb) with an r2 ~ 60%
if data are analysed in a spatial resolution of 20 m × 20 m (0.04 ha, also called plot size).
The correlation coefficient of the regression is becoming significant
better in the disturbed forest sites (r2 = 91%) if data are analysed
hectare wide. There seems to exist no functional dependency between LAI and
canopy height, but there is also a linear correlation (r2 ~ 60%)
between AGB and the area fraction of gaps in which the canopy is highly
disturbed. A reasonable agreement of our results with observations is
obtained from a comparison of the simulations with permanent sampling plot
(PSP) data from the same region and with the large-scale forest inventory in
Lambir. We conclude that the spaceborne remote sensing techniques such as
LIDAR and radar interferometry have the potential to quantify the carbon
contained in the vegetation, although this calculation contains due to the
heterogeneity of the forest landscape structural uncertainties which restrict
future applications to spatial averages of about one hectare in size. The
uncertainties in AGB for a given canopy height are here 20–40% (95%
confidence level) corresponding to a standard deviation of less than ± 10%. This uncertainty on the 1 ha-scale is much smaller than in
the analysis of 0.04 ha-scale data. At this small scale (0.04 ha) AGB can
only be calculated out of canopy height with an uncertainty which is at least
of the magnitude of the signal itself due to the natural spatial
heterogeneity of these forests. |
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