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Estimation Of Forest Parameters Using Polarimetric Multi-frequency Sar Data
Abstract
The analysis of polarimetric SAR observations acquired by the JPL polarimetric multi frequency (P-, L- and C-band) SAR during the MAESTRO-1 campaign has continued. We study the Flevoland test site, which extends over two scenes of mainly forested areas and one scene of agricultural areas. The data type studied is the high resolution complex one look product. Natural extended targets have been used to correct for cross-talk and phase errors, and co-channel imbalance is removed by using trihedral reflector responses. Additional field measurements have provided us with a larger amount of ground data. 'we have measured the basal area and the mean stand height of over one hundred stands of mainly poplar, ash, pine and spruce. The correlations between radar backscattering and the measured parameters generally increase with increasing wavelength. The correlation is however strongly species dependent.
... Leckie is with the Pacific Forestry Center, Victoria BC Canada Historically, SAR researchers have held a pessimistic view as to the value of C-band SAR for forest applications [20], [2], [6]. The reason is that C-band radiation does not penetrate as far into the forest canopy as the longer wavelength L and P-band [21]. The longer wavelength signals will have backscatter contributions from the canopy and also from the branches and trunk which provide more information about the structure of the tree than canopy scatter alone [21]. ...
... The reason is that C-band radiation does not penetrate as far into the forest canopy as the longer wavelength L and P-band [21]. The longer wavelength signals will have backscatter contributions from the canopy and also from the branches and trunk which provide more information about the structure of the tree than canopy scatter alone [21]. Furthermore, it has been demonstrated that when linear polarized σ 0 measurements are used, biomass estimation is only valid up to a certain point (the saturation point) [2], [22]. ...
We have applied a non-parametric classifier (k nearest neighbour) to two calibrated orthogonal passes of airborne polarimetric synthetic aperture radar (POLSAR) image data over boreal forest for the purpose of discriminating canopy tree species of predefined stands. We found that a single classifier based on a single feature space (i.e. one set of POLSAR variables for all species) was less accurate than a hierarchical two-stage classifier that used different POLSAR variables for each species. We designed a two-stage classifier that first grouped stands into broad classes: pine, spruce and deciduous, and then classified each sample within the broad classes into individual species. We found that the most effective feature spaces had two or three dimensions. The two-stage classifier attained overall accuracies of between 60% and 75%.We provide a first use of an equivalency test applied to remote-sensing classification. We use Lloyd's test of equivalency to find equivalent classifiers and thus infer informative POLSAR variables. The POLSAR variables that were most informative varied between the two passes and between the various elements of the hierarchical classifier. For the initial three-class classifier the most informative POLSAR variables were the two circular polarization ratios, several of Touzi's Stokes vector variables, HHVV coherence, several texture measures such as the variance of several scattering coefficients and the order parameter of the K-distribution and characteristics of the polarization signature pedestal. These results demonstrate that C-band POLSAR has great potential for mapping boreal forest cover either on its own or in concert with other geospatial data.
... The three-band (C, L, and P) polarimetric AIRSAR sensor has been used in Green, 1998; Kasischke et al., 1991 Kasischke et al., , 1995 Moghaddam et al., 1994; Ranson & Sun, 1997). The strongest correlation between SAR backscatter and forest biomass has been reported in P-band and the weakest in Cband (e.g., Beaudoin et al., 1992; Dobson et al., 1992; Israelsson et al., 1992; Rauste et al., 1992; Skriver & Gudmandsen, 1992). A spaceborne P-band SAR will not be available in the foreseeable future even though it has been proposed (e.g., Rignot et al., 1995). ...
Multi-temporal JERS SAR data were studied for forest biomass mapping. The study site was located in South-eastern Finland in Ruokolahti. Pre-processing of JERS SAR data included ortho-rectification and radiometric normalization of topographic effects.In single-date regression analysis between backscatter amplitude and stem volume, summer scenes from July to October produced correlation coefficients (r) between 0.63 and 0.81. Backscatter level and the slope of the (linear) regression line were stable from scene to scene. Winter scenes acquired in very cold and dry winter conditions had a very low correlation. One winter scene acquired in conditions where snow is not completely frozen produced a correlation coefficient similar to summer scenes.Multivariate regression analysis with a 6-date JERS SAR dataset produced correlation coefficient of 0.85. A combined JERS–optical regression analysis improved the correlation coefficient to 0.89 and also alleviated the saturation, which affects both SAR and optical data.The stability of the regression results in summer scenes suggests that a simple constant model could be used in wide-area forest biomass mapping if accuracy requirements are low and if biomass estimates are aggregated to large areal units.
Polarimetry has the potential to greatly enhance the capabilities of visible and near-IR remote sensing systems. For remote sensing of the oceans, the passive polarimetric signal is a complicated function of solar angle and viewing geometry, along with the confounding effects of the atmosphere. The atmospheric polarization signal becomes dominant as the sensor altitude increases, and this can lead to complications with ground truth measurements. The purpose of this study is to investigate the combined effects of solar and viewing geometries and sensor altitude to determine a strategy for polarimetric remote sensing of the oceans. A polarimetric radiative transfer code is used to model the nature of polarized light in a coupled atmosphere-ocean system. Viewing geometries are examined to find the look angles and azimuth angles relative to the sun that provide the maximum information about the ocean. The effect of sensor altitude is shown for different aerosol and hydrosol types and concentrations. Finally, the complications of ground truth measurements will be discussed.
The Michigan Microwave Canopy Scattering model (MIMICS) is based on a first-order solution of the radiative-transfer equation for a tree canopy comprising a crown layer, a trunk layer and a rough-surface ground boundary. The crown layer is modelled in terms of distributions of dielectric cylinders (representing needles and/or branches) and discs (representing leaves), and the trunks are treated as dielectric cylinders of uniform diameter. This report describes MIMICS I, which pertains to tree canopies with horizontally continuous (closed) crowns. The model, which is intended for use in the 0·5-10GHz region at angles greater than 10 from normal incidence, is formulated in terms of a 4 × 4 Stokes-like transformation matrix from which the backscattering coefficient can be computed for any transmit/receive polarization configuration.
A scattering model for defoliated vegetation is developed by treating a layer of defoliated vegetation as a collection of randomly oriented dielectric cylinders of finite length over an irregular ground surface. Both polarized and depolarized backscattering are computed and their behavior versus the volume fraction, the incidence angle, the frequency, the angular distribution and the cylinder size are illustrated. It is found that both the angular distribution and the cylinder size have significant effects on the backscattered signal. The present theory is compared with measurements from defoliated vegetations.
A technique that uses the radar return from natural targets and at
least one trihedral corner reflector to calibrate compressed
polarimetric radar data is described. Calibration for relative
amplitude, relative phase, absolute amplitude, and system crosstalk is
addressed. The crosstalk calibration method is based on the theoretical
result that for natural targets with azimuthal symmetry the copolarized
and crosspolarized components of the scattering matrix are uncorrelated,
and the method does not require any external calibration targets to be
deployed before imaging. Because compressed data are used, one is forced
to model the transmitting and receiving systems as reciprocal. Even
though the inferred transmit and receive matrices are not each simply
related to the physical transmitter and receiver, the true Stokes matrix
for each pixel in an image can be accurately determined by this
approach. The method is illustrated by estimating the crosstalk
parameters of the NASA/JPL aircraft for different types of terrain and
for two frequencies. For the C -band system, the crosstalk is
less than -20 dB for all ranges in the images. The crosstalk of the
L -band system is a function of range, however, and may be as
poor as -10 dB in the near range, leading to a noticeable distortion of
the polarization signatures