Interferometric Coherence Analysis of the Everglades Wetlands, South Florida

Abstract

Interferometric synthetic aperture radar (InSAR) observations of wetlands reveal spatially detailed measurements of water-level changes and quantitative images of flow dynamics. However, lateral variability of wetland vegetation results in a heterogeneous scattering medium, which can affect interferometric coherence levels and can even limit the applicability of the technique. Here, we analyze coherence variations in Southern Florida, which consist of various wetland vegetation types, including sawgrass, graminoid, cypress, mixed shrubs, and mangrove marsh. We use JERS-1, ERS-1/2, ENVISAT, and RADARSAT-1 data, to investigate the effect of acquisition parameters and temporal baseline (time span between acquisitions) on the coherence level in the various wetland vegetation environments. The main findings of our coherence analysis are as follows: (1) Woody wetlands, such as cypress and mixed shrubs swamps, have higher coherence levels than herbaceous wetlands of sawgrass and graminoid (cattail) in all SAR data types; (2) the coherence level of C-band data is strongly dependent on temporal baseline, whereas the coherence level of L-band data depends mainly on perpendicular baseline, but to some degree also on temporal baseline; (3) backscatter from JERS-1 and RADARSAT-1 is correlated with coherence in four wetland vegetation types (sawgrass, cypress, mixed shrubs, and mangrove), but ERS backscatter has no relation to coherence, except over sawgrass marsh. Finally, our study clearly indicates that high resolution, HH polarization, and small incidence angle observations are most suitable for wetland InSAR applications.