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 understandin g of estuarine ecological, morphological and pollution processes. Airborne remote sensing is identified as a cost-effective tool that may be used to p rovide accurate synoptic maps of estuarine sediment distributions. However, prior to the collection and analysis of airborne imagery, spectral charact erization of intertidal sediments is fundamental. Through a series of in si tu and laboratory reflectance (0.35-2.5 mu m) experiments the spectral comp lexity of the Ribble Estuary, UK, intertidal sediments has been investigate d. Positive relationships between Daedalus Airborne Thematic Mapper band 9 and band 10 simulated reflectance and percentage sand of intertidal sedimen ts have been identified in the field (r(2) = 0.51 and r(2) = 0.61). These associations are sensitive to the interstitial and surface moisture c onditions of the intertidal environment and, consequently, temporally unsta ble. Laboratory experiments demonstrated that interstitial moisture influen ces the spectral contrast between sediments of contrasting grain size, cons equently determining the ability to map sediment domains through remote sen sing. As a result, it is recommended that airborne imagery be collected of intertidal areas after a prolonged period of exposure to summer drying cond itions. This ensures that the spectral influence of moisture is minimized a nd the spectral contrast between sediments of different grain size is maxim ized.