Radar interferometric phase errors induced by Faraday rotation
- Simon Zwieback,
- Franz Meyer
Franz Meyer
University of Alaska Fairbanks, University of Alaska Fairbanks
Author ProfileAbstract
Ionospheric Faraday rotation distorts satellite radar observations of
the Earth's surface. While its impact on radiometric observables is well
understood, the errors in repeat-pass InSAR observations and hence in
deformation analysis are largely unknown. Because Faraday rotation
cannot rigorously be compensated for in non-quad-pol systems, it is
imperative to determine the magnitude and nature of the deformation
errors. Focusing on distributed targets at L-band, we assess the errors
for a range of land covers using airborne observations with simulated
Faraday rotation. We find that the deformation error may reach 2 mm in
the co-pol channels over a solar cycle. It can exceed 5 mm for intense
solar maxima. The cross-pol channel is more susceptible to severe
errors. We identify the leakage of polarimetric phase contributions into
the interferometric phase as a dominant error source. The polarimetric
scattering characteristics induce a systematic dependence of the
Faraday-induced deformation errors on land cover and topography. Also
their temporal characteristics, with pronounced seasonal and
quasi-decadal variability, predispose these systematic errors to be
misinterpreted as deformation. While the relatively small magnitude of
1-2 mm is of limited concern in many applications, the persistence on
semi- to multi-annual time scales compels attention when long-term
deformation is to be estimated with millimetric accuracy. Phase errors
induced by uncompensated Faraday rotation constitute a non-negligible
source of bias in interferometric deformation measurements.