Title :
The Interaction Between Faraday Rotation and System Effects in Synthetic Aperture Radar Measurements of Backscatter and Biomass
Author :
Shaun Quegan ; Lomas, Mark R.
Author_Institution :
Sch. of Math. & Stat., Univ. of Sheffield, Sheffield, UK
Abstract :
For long-wavelength space-based radars, such as the P-band radar on the recently selected European Space Agency BIOMASS mission, system distortions (crosstalk and channel imbalance), Faraday rotation, and system noise all combine to degrade the measurements. A first-order analysis of these effects on the measurements of the polarimetric scattering matrix is used to derive differentiable expressions for the errors in the polarimetric backscattering coefficients in the presence of Faraday rotation. Both the amplitudes and phases of the distortion terms are shown to be important in determining the errors and their maximum values. Exact simulations confirm the accuracy and predictions of the first-order analysis. Under an assumed power-law relation between σhv and the biomass, the system distortions and noise are converted into biomass estimation errors, and it is shown that the magnitude of the deviation of the channel imbalance from unity must be 4-5 dB less than the crosstalk, or it will dominate the error in the biomass. For uncalibrated data and midrange values of biomass, the crosstalk must be less than -24 dB if the maximum possible error in the biomass is to be within 20% of its true value. A less stringent condition applies if the amplitudes and phases of the distortion terms are considered random since errors near the maximum possible are very unlikely. For lower values of the biomass, the noise becomes increasingly important because the σhv signal-to-noise ratio is smaller.
Keywords :
Faraday effect; backscatter; geophysical techniques; synthetic aperture radar; European space agency BIOMASS mission; P-band radar; backscatter synthetic aperture radar measurement; biomass estimation error; biomass synthetic aperture radar measurement; channel imbalance deviation magnitude; distortion term amplitude; distortion term phase; faraday rotation; first-order analysis; long-wavelength space-based radar; polarimetric backscattering coefficient; polarimetric scattering matrix measurement; power-law relation; signal-to-noise ratio; stringent condition; system distortion; Backscatter; Biomass; Crosstalk; Distortion measurement; Faraday effect; Noise; Scattering; Biomass; Faraday rotation; calibration; long-wavelength radar; polarimetric measurements; system distortion;
Journal_Title :
Geoscience and Remote Sensing, IEEE Transactions on
DOI :
10.1109/TGRS.2015.2395138