Evaluation and comparison of hyperspectral imagery for mapping surface symptoms of dryland salinity

Abstract

Hyperspectral images from three sensors are compared for their ability to discriminate and map selected symptoms of salinity in a dryland agricultural area in southern Australia. Airborne HyMap and satellite Hyperion imagery were acquired in the late dry season to maximize the discrimination of saline soils and perennial, halophytic vegetation, whereas airborne Compact Airborne Spectrographic Imager (CASI) imagery was acquired in late spring to capture senescence of annual, halophytic grasses. The evaluation of imagery included comparisons of spectral resolution, spectral range, spatial resolution and landscape seasonality. Salinity symptoms were also characterized using field spectra collected with an ASD FieldspecPro spectrometer. Image-derived spectra were used to map salinity symptoms using partial spectral unmixing techniques. Salinity symptom maps were compared with independent mapping of soils and salinity from aerial photography and Landsat imagery. Saltpans were discriminated using the gypsum 1750 nm absorption feature, whereas full-wavelength image spectra were necessary to map the halophytic plants. HyMap imagery produced the most accurate maps of samphire and saltpans, identifying substantial saline areas covered with samphire that had not been delineated in previous aerial photo-interpretation. The study demonstrates that hyperspectral imagery can improve discrimination of vegetation and mineral indicators of surface salinity and has the potential to improve traditional soil and salinity mapping based on multispectral satellite imagery and aerial photo-interpretation.