Reducing ionospheric electron density errors in satellite radar interferometry applications

Abstract

It has been demonstrated that ionospheric electron density disturbances can influence multi-pass satellite radar interferometry (SRI). This has been observed to occur near the magnetic poles, particularly during strong magnetic disturbances. Ionospheric disturbances most clearly appear in interferometric synthetic aperture radar (InSAR) as a kilometre-scale modulation in the azimuth pixel shift needed for optimal registration of the interferometric pair. This modulation (also known as "azimuth streaks") also affects the InSAR phase, and consequently such SRI applications as digital elevation model (DEM) generation and displacement measurement, and may appear as "streaks" in the coherence map. The effect is worse for L-band systems (e.g., Japanese Earth resources satellite 1 (JERS-1) and Phased array type L-band synthetic aperture radar (PALSAR)), but can be significant even at C band (e.g., European remote sensing satellites ERS-1/2 and RADARSAT I and II). The influence of ionospheric effects on interferogram phase can often be predicted, and the magnitude can be estimated, by an inspection of a map of the shift in azimuth position for optimal registration obtained using the "speckle tracking" technique. For DEM generation, the ionospheric phase contribution can be approximated, and removed from the interferogram phase, by the scaled and filtered integral of this azimuth shift map. For displacement-measurement applications, appropriate filtering of the distinct patterns of the azimuth streaks is the only resort.