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Popular SummaryFaraday rotation is a change in the polarization vector of electromagnetic radiation that occurs as the waves propagate from the Earth surface through the ionosphere to a spaceborne sensor. This change can cause errors in monitoring parameters at the surface such as soil moisture and sea surface salinity and it is an important consideration for radiometers on future missions in space such as NASA's Aquarius mission and ESA's SMOS mission. Two prominent strategies for compensating for Faraday rotation are using a sum of the signal at two polarizations and using the correlation between the signals at the two polarizations. These strategies work for an idealized antenna. This paper evaluates the strategies in the context of realistic antennas such as will be built for the Aquarius radiometer. Realistic antennas will make small differences that need to be included in planning for retrieval algorithms in future missions. AbstractThe influence of the pattern of the receive antenna on Faraday rotation is examined in the context of passive remote sensing of soil moisture and ocean salinity at L-band. Faraday rotation is an important consideration for radiometers on future missions in space such as SMOS and Aquarius. Using the radiometer on Aquarius as an example, it is shown that while I = Tv + Th is independent of Faraday rotation to first order, it has rotation dependence when realistic antenna patterns are included in the analysis. Also, it is shown that using the 3rd Stokes parameter to measure the rotation angle can yield a result biased by as much as one degree by purely geometrical issues associated with the finite width of the main beam.

Abstract-This work is intended to investigate the accuracy of modelling simple cylindrical vegetation structures for microwave remote sensing applications. Plane wave scattering by dielectric cylinders of finite length and circular cross section is examined. Cylinders with a radius that varies linearly along the cylinder length -hereafter referred to as tapered cylinders -are also considered. Exact expressions for the scattering cross section do not exist for those objects. Numerical methods can provide accurate results, but they are computationally intensive and therefore less suitable when calculations on a large number of scatterers of different sizes and orientations are necessary. In this paper the scattering cross section of finite cylinders is computed by physical optics methods, which are faster and often employed in microwave vegetation models. Tapered cylinders are modelled by a number of coaxial finite cylinders stacked on top of each other. To check the validity of the results, the problems are also solved numerically by the moment method. For cases often encountered in vegetation studies, the results of the application of the approximate analytical methods are then compared with the corresponding numerical solution. For both constantradius and tapered cylindrical structures, a good agreement with the numerical solution is found in the region of the main scattering lobe, which is the one of interest when considering complex media such as vegetation canopies. However, the accuracy of the approximate solutions decreases as the angle of the incident wave approaches the end-on angle.