The influence of surface and interstitial moisture on the spectral characteristics of intertidal sediments: implications for airborne image acquisition and processing

Intertidal sediment distribution is an important factor in the understanding of estuarine ecological, morphological and pollution processes. Airborne remote sensing is identified as a cost-effective tool that may be used to provide accurate synoptic maps of estuarine sediment distributions. However, prior to the collection and analysis of airborne imagery, spectral characterization of intertidal sediments is fundamental. Through a series of in situ and laboratory reflectance (0.35-2.5 m) experiments the spectral complexity of the Ribble Estuary, UK, intertidal sediments has been investigated. Positive relationships between Daedalus Airborne Thematic Mapper band 9 and band 10 simulated reflectance and percentage sand of intertidal sediments have been identified in the field (r² = 0.51 and r² = 0.61). These associations are sensitive to the interstitial and surface moisture conditions of the intertidal environment and, consequently, temporally unstable. Laboratory experiments demonstrated that interstitial moisture influences the spectral contrast between sediments of contrasting grain size, consequently determining the ability to map sediment domains through remote sensing. As a result, it is recommended that airborne imagery be collected of intertidal areas after a prolonged period of exposure to summer drying conditions. This ensures that the spectral influence of moisture is minimized and the spectral contrast between sediments of different grain size is maximized.