TY  - JOUR
AU  - Jagdhuber, Thomas
AU  - Montzka, Carsten
AU  - Lopez-Martinez, Carlos
AU  - Baur, Martin J.
AU  - Link, Moritz
AU  - Piles, Maria
AU  - Das, Narendra Narayan
AU  - Jonard, Francois
TI  - Estimation of Vegetation Structure Parameters From SMAP Radar Intensity Observations
JO  - IEEE transactions on geoscience and remote sensing
VL  - 59
IS  - 1
SN  - 1558-0644
CY  - New York, NY
PB  - IEEE78494
M1  - FZJ-2021-01237
SP  - 151-167
PY  - 2021
AB  - In this article, we present a multipolarimetric estimation approach for two model-based vegetation structure parameters (shape A and orientation distribution ψ of the main canopy elements). The approach is based on a reduced observation set of three incoherent (no phase information) polarimetric backscatter intensities (|S HH | 2 , |S HV | 2 , and |S VV | 2 ) combined with a two-parameter (A P and ψ) discrete scatterer model of vegetation. The objective is to understand whether this confined set of observations contains enough information to estimate the two vegetation structure parameters from the L-band radar signals. In order to disentangle soil and vegetation scattering influences on these signals and ultimately perform a vegetation only retrieval of vegetation shape A and orientation distribution ψ, we use the subpixel spatial heterogeneity expressed by the covariation of co- and cross-polarized backscatter Γ PP-PQ of the neighboring cells and assume it is indicative for the amount of a vegetation-only co-to-cross-polarized backscatter ratio μ PP-PQ . The ratio-based retrieval approach enables a relative (no absolute backscatter) estimation of the vegetation structure parameters which is more robust compared to retrievals with absolute terms. The application of the developed algorithm on global L-band Soil Moisture Active Passive (SMAP) radar data acquired from April to July 2015 indicates the potential and limitations of estimating these two parameters when no fully polarimetric data are available. A focus study on six different regions of interest, spanning land cover from barren land to tropical rainforest, shows a steady increase in orientation distribution toward randomly oriented volumes and a continuous decrease in shape arriving at dipoles for tropical vegetation. A comparison with independent data sets of vegetation height and above-ground biomass confirms this consistent and meaningful retrieval of A P and ψ. 
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000603079000012
DO  - DOI:10.1109/TGRS.2020.2991252
UR  - https://juser.fz-juelich.de/record/890906
ER  -