Polarimetric Interferometry Research Articles

Vertical structure of vegetated land surfaces from interferometric and polarimetric radar

This paper describes the estimation of parameters characterizing the vertical structure of vegetated land surfaces, from combined interferometric and polarimetric radar data. Physical models expressing radar observations in terms of parameters describing vegetated land surfaces are the foundation for parameter estimation techniques. Defining a general complex cross correlation enables the unified development of models for interferometry and polarimetry, including polarimetric interferometry. Three simple physical models in this paper express this complex cross correlation in terms of vegetation parameters: (1) a randomly oriented volume, (2) a randomly oriented volume with a ground return, and (3) an oriented volume. For the first two models the parameters include vegetation height, extinction coefficient, underlying topography, and another parameter depending on ground electrical properties and roughness. For the oriented volume, additional parameters depend on the refractivity, extinction coefficients, and backscattering characteristics of waves propagating along eigenpolarizations of the vegetation volume. The above models show that the interferometric cross‐correlation amplitude and the polarimetric {HHHH/VVVV} ratio both change by about 1% per meter of vegetation height change, for experimental conditions typical of airborne and spaceborne interferometric radars. These vertical‐structure sensitivities prompt a parameter estimation demonstration with two‐baseline TOPSAR interferometric and zero‐baseline polarimetric data from the Boreal Ecosystem‐Atmosphere Study (BOREAS) Southern Study Area in Prince Albert National Park, Saskatchewan, Canada. The demonstrations show the feasibility of measuring vegetation height to better than 4.2 m, underlying topography to better than 6.5 m, and the ratio of ground‐to‐volume power to better than 10%, using interferometry and polarimetry, coupled with parameter‐constraining assumptions, concerning the degree of surface roughness. This paper suggests that single‐baseline and multibaseline fully polarimetric interferometry have the potential to obviate the need for such assumptions, thereby making parameter estimation more robust, accurate, and realistic.

Effect of Medium Symmetries On Parameter Estimation With Polarimetric Interferometry

The addition of interferometric backscattering pairs to the conventional polarimetric synthetic aperture radar (SAR) data over forests and other vegetated areas increases the dimensionality of the data space, in principle enabling the estimation of a larger number of parameters. In this paper, the effect of medium symmetries on the number of independent interferometric measurements is studied. Reflection, rotation, and azimuthal symmetries are considered. In each case, the number of independent elements of the interferometric covariance matrix is derived, which puts an inherent limit on the number of scatterer parameters that can be estimated using single-baseline polarimetric interferometry.

The structure of oriented vegetation from polarimetric interferometry

Polarimetric radar interferometry is much more sensitive to the distribution of oriented objects in a vegetated land surface than either polarimetry or interferometry alone. This paper shows that single-baseline polarimetric interferometry can be used to estimate the heights of oriented-vegetation volumes and underlying topography, while at least two baselines are needed for randomly oriented volumes. Single-baseline, calculated vegetation-height accuracies are in the range of 2-8 m for reasonable levels of vegetation orientation in forest canopies.

A polarimetric interferometry-based optical fibre pressure sensor with potential application to flow measurement

The force/pressure induced birefringence in an ordinary single mode optical fibre has been investigated as a possible element for a differential pressure flow sensor. The relative sensitivities of coated and uncoated fibres at various temperatures have been measured using polarimetric interferometry. The sensitivity of an uncoated sensing fibre was found to be increased by 18% over that of the coated fibre. Results are presented showing good linearity and acceptable stability in measurements over the temperature range 20°C to 95°C, and application to flow sensing are discussed.