Characterising soil moisture in transport corridor environments using airborne LIDAR and CASI data

Much of the world's transport networks are located on cutting and embankment earthworks. In the UK, many of these earthwork structures were constructed in the mid-19th century and are susceptible to slope instability. Instability in transport corridors tends to be triggered by an increase in pore water pressure, which is directly influenced by an increase in soil moisture. This study explores the integration of high spatial resolution airborne (1 m) LIght Detection And Ranging (LIDAR) and Compact Airborne Spectrographic Imager (CASI) imagery to characterize soil moisture distribution for a transport corridor near Haltwhistle, UK. The distribution of soil moisture is estimated using these sensors through techniques that are relatively unaffected by, or make use of, the presence of vegetation, unlike other techniques using thermal, shortwave and microwave sensors. Terrain analysis calculations of potential solar radiation and a topographic wetness index were applied to a DEM interpolated from the LIDAR point data. The CASI imagery was used to map Ellenberg moisture indicator values using partial least squares regression. Individually, the remotely sensed metrics were found to have poor correlations with observed soil moisture. However, improvements could be made using an integrated model which demonstrated a correlation coefficient of 0·68. The resulting integrated model showed soil moisture content to increase on north-facing earthworks and towards the toe of earthwork slopes. Concentrations of moisture were also predicted in cuttings where water is contributed from areas surrounding the earthworks. Copyright © 2011 John Wiley & Sons, Ltd.