POLINSAR at Low Frequency and Ionospheric Effects
Pascale Dubois-Fernandez(1), Anthony Freeman(2), sebastien Angelliaume(1), My-Linh Truong-Loi(1) and Eric Pottier(3)
(1) ONERA, BA 701, 13661 SALON AIR CEDEX, France
(2) JPL, California, Institute of Technology, Pasadena, United States
(3) IETR CNRS 6164, Université de Rennes 1, Université de Rennes 1, Rennes, France
Global warning is now known to be the major environmental issue mankind will have to face in the next decade. Monitoring
of vegetation and biomass is clearly an essential piece of information required at all levels ranging from the scientific studies
to understand and forecast, to the political actors and government leaders responsible for drafting remediation policies and
evaluating their impact.
Microwave remote sensing with the low-frequency SAR technique can provide a useful characterization of forest (spatial
coverage, species, density, height…) at a global scale, relying on the all-weather imaging capabilities of SAR linked with the
significant penetration of the low-frequency EM wave in the canopy.
The published techniques for forest characterization from low frequency SAR data include radiometry inversion, polarimetric
inversion based on the anisotropy parameters and PolInSAR Random Volume Over Ground inversion . In this paper, we
will more specifically concentrate on the PolInSAR technique and the impact of ionospheric effect on this inversion.
PolInSAR at low frequency can be envisioned with two radar platforms flying in formation or as a repeat pass mission. The
second alternative is more plausible given the cost and the size of a low frequency SAR instrument. However the two cases
will be discussed in the paper.
Among the challenges, the following questions need to be addressed:
· What is the impact of ionosphere and Faraday rotation on the PolInSAR inversion results?
· Is it necessary to correct the data prior to applying the inversion and what is the highest Faraday rotation for which a
correction is not necessary?
· What is the effect of loss of interferometric coherence and could this be compensated for?
· Can the technique provide an estimation of the Faraday rotation or the differential Faraday rotation?
· How does ionospheric and calibration effects interact?
· What are the implications on a compact polarimetry mode of operation?
· Are Faraday rotation-derived estimates of TEC accurate enough to correct for differential phase offsets caused by
e.g. phase delay?