Ph.D Thesis | |
Ph.D Student | Chang Jisung |
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Subject | Shrublands Biomass Mapping by Integrating Polarimetric SAR Data and Multi-Spectral Data |
Department | Department of Civil and Environmental Engineering | Supervisor | PROF. Maxim Shoshany |
Full Thesis text | ![]() |
The south-eastern Mediterranean is a
hot-spot of climate change and desertification. Further warming and drying of
this region until the end of this century is predicted with potential of
yielding significant deterioration of ecosystems around the Mediterranean
Basin. Shrublands consist a primary element of these ecosystems and their
resilience to climate change. High topographic, lithologic, and soil
variability combined with natural and anthropogenic influences resulted in high
spatio-temporal heterogeneity. Extracting information about shrublands
response to climate change is difficult in such complex environments. The use
of sensor systems that are sensitive to vegetation and soil properties in areas
of varying habitat conditions is instrumental for this purpose. Numerous
optical remote sensing studies were carried out aiming at mapping the Mediterranean
and arid environments and the changes they undergo. Limitations on the
information content of optical sensor data regarding biomass are well
recognized by researchers in this field. Radar L-band systems with
quad-polarization measurements (HH, VV, HV and VH) have the potential of
extraction of volumetric information by remote sensing, however, experience in
the use of polarimetric radar in highly heterogeneous landscapes is quite
limited. Full polarimetric L-band PALSAR data facilitated one of the first
empirical assessments of the relationships between radar polarization
properties (RPPs) and ecological pattern properties (EPPs) in the desert fringe
shrublands of the South-Eastern Mediterranean Basin. Correlations between radar
parameters (polarized backscattering intensities, their ratios, entropy, and
degrees of polarization) and remotely sensed ecological parameters (shrub
cover, edge parameter, average shrub height, and biomass information) were
analyzed for 52 least-disturbed sites along a climatic gradient between
semi-arid and arid zones in the south-eastern Mediterranean. The degree of
horizontal polarization (DOHP) was the RPP that was most highly correlated with
all EPPs, while NDVIR biomass (NDVI multiplied by relative rainfall) was the
EPP most highly correlated with all RPPs. Integrating NDVI with DOHP
facilitated one of the first attempts to map shrublands across the whole
Mediterranean Basin. Principle Component Analysis of NDVI and DOHP
combinations indicated that DOHP has significant contribution for the
discrimination between land cover types. Comparison of NDVI and DOP combination
classes with existing Global Land Cover data bases created using remote sensing
techniques, revealed that they agree regarding forest extents, while there is
very limited information regarding shrublands in the global databases. NDVI and
DOHP showed potential for mapping shrublands and for separating between
desertified and vegetated surfaces. A new polarimetric radar vegetation index
(PRVI) utilizing the degree of polarization and the cross-polarized
backscattering coefficient, based on the theoretical volume scattering model
and a semi-empirical model is proposed. The accuracy of the model was examined
in semi-arid natural areas having high geodiversity, representing wide desert
fringe zones around the world. It shows good agreement with the biomass data
extracted using NDVI and rainfall data and it performed better than other radar
parameters. Assessment of the PRVI based biomass estimation with allometric
data from 67 sites across the desert fringe zone indicated moderate performance
with Root Mean Square Deviation of 0.33 Kg/.