Spectral properties of cyanobacterial soil crusts, implications for using remote sensing data in aeolian erosion models

Kevin White, Ian Davenport
The University of Reading, Reading, UK

Biological soil crusts are thought to have a significant effect in protecting surfaces from aeolian erosion. Several methods have been proposed to estimate the cover of biological soil crusts from remote sensing data, and these can be used in landscape-scale aeolian erosion models in a similar way to vegetation cover estimates. Analysis of spectral reflectance data of cyanobacterial soil crusts made in southwest Queensland demonstrate that our ability to detect their presence, and estimate their cover, is dependent on whether photosynthesis is taking place at the soil surface, and this is strongly limited by insolation. High levels of solar radiation typical of clear sky conditions cause the surface photosynthesis to decrease rapidly. These results suggest that successful remotely-sensed estimation of cyanobacterial soil crust cover is only possible under a limited set of environmental conditions; surface photosynthesis is only detectable under low solar irradiance (i.e. under thick cloud cover), when orbital remote sensing data of the surface cannot be acquired. These data have implications for use of remote sensing products for monitoring cyanobacterial soil crusts at landscape scale for modelling and monitoring purposes; current methods are likely to significantly underestimate actual cyanobacterial crust cover in southwest Queensland.