Multispectral remote sensing of shallow water bathymetry: Ground truth accuracy and interference

High resolution airborne digital multispectral and photographic imagery were flown over selected sections of the Horsefly River between 1993 and 1998. The airborne digital imagery was recorded using Sony XC7500 progressive scan cameras with optical filtration in green, red and NIR spectral bands. The photographic imagery included daylight and tungsten colour reversal film and Kodak 2443 IR Aerochrome and EIR colour infrared films. The imagery was flown using the SFU aircraft and camera system in conjunction with detailed ground truth from targeted and surveyed sites. SSC, turbidity and water depth were the principal parameters but substrate and water surface conditions were also considered. Results indicate a high and consistently variable degree of correspondence between the remote sensing of shallow water depth determinations, under relatively clear water conditions (<25mg/l). There was, however, increasing inaccuracy in water depth determinations corresponding to the higher range of these SSC levels (15 - 25mg/l). Above a critical threshold of approximately 25mg/l, there was no significant bottom reflection signal and SSC estimates could be made without bottom reflection considerations. Accuracy was dependent upon reduced water surface reflectance (relatively calm conditions without cloud reflection or shadow), transect selections over spawning gravels (maintaining relative constancy for bottom reflection due to substrate) and determined levels of accuracy for photogrammetric positioning of water depth transects and depth measurement.