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| Titel |
Estimation of vegetation parameters such as Leaf Area Index from polarimetric SAR data |
| VerfasserIn |
Marina Hetz, Dan G. Blumberg, Stanley R. Rotman |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038903
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| Zusammenfassung |
| This work presents the analysis of the capability to use the radar backscatter coefficient in
semi-arid zones to estimate the vegetation crown in terms of Leaf Area Index (LAI).
The research area is characterized by the presence of a pine forest with shrubs as
an underlying vegetation layer (understory), olive trees, natural grove areas and
eucalyptus trees. The research area was imaged by an airborne RADAR system in
L-band during February 2009. The imagery includes multi-look radar images. All
the images were fully polarized i.e., HH, VV, HV polarizations. For this research
we used the central azimuth angle (113Ë ). We measured LAI using the ÎT Sun
Scan Canopy Analysis System. Verification was done by analytic calculations and
digital methods for the leaf’s and needle’s surface area. In addition, we estimated the
radar extinction coefficient of the vegetation volume by comparing point calibration
targets (trihedral corner reflectors with 150cm side length) within and without the
canopy. The radar extinction in co- polarized images was ~26dB and ~24dB for
pines and olives respectively, compared to the same calibration target outside the
vegetation.
We used smaller trihedral corner reflectors (41cm side length) and covered them with
vegetation to measure the correlation between vegetation density, LAI and radar backscatter
coefficient for pines and olives under known conditions.
An inverse correlation between the radar backscatter coefficient of the trihedral corner
reflectors covered by olive branches and the LAI of those branches was observed. The
correlation between LAI and the optical transmittance was derived using the Beer-Lambert
law. In addition, comparing this law’s principle to the principle of the radar backscatter
coefficient production, we derived the equation that connects between the radar backscatter
coefficient and LAI.
After extracting the radar backscatter coefficient of forested areas, all the vegetation
parameters were used as inputs for the MIMICS model that simulates the radar
backscatter coefficient of pines. The model results show a backscatter of -18dB in HV
polarization which is 13dB higher than the mean pines backscatter in the radar
images, whereas the co-polarized images revealed a backscatter of -10dB which
is 23dB higher than the actual backscatter value deriver from the radar images.
Therefore, next step in the research will incorporate other vegetation parameters and
attempt to understand the discrepancies between the simulation and the actual data. |
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