Retrieving river attributes from remotely sensed data: an experimental evaluation based on field spectroscopy at the outdoor stream lab

This paper summarizes experiments conducted at the Outdoor Stream Lab to gain insight on the relationships between a channel's spectral characteristics and the river attributes of interest to scientists and managers. Improved understanding of these connections would advance the application of remote sensing to fluvial systems. Motivated by this objective, we examined the following: (i) interactions among local hydraulics, water surface roughness and surface reflectance; and (ii) the influence of periphyton development and streambed disturbance on bottom reflectance. These experiments could thus lead to novel methods for inferring flow velocity and substrate type, respectively, from passive optical image data. Our initial results indicate the following: (i) water surface reflectance can compromise spectrally based depth retrieval by reducing the range of useful wavelengths and weakening correlations between band ratios and depth, implying that removing the surface‐reflected component of the total radiance could facilitate bathymetric mapping; (ii) water surface roughness was influenced by local hydraulics and was positively correlated with water surface reflectance, suggesting that observations of surface reflectance could be used to infer flow velocities; (iii) substrate spectral characteristics were influenced by the degree of periphyton development, implying that algal biomass might be estimated from remotely sensed data; and (iv) similarly, bottom reflectance differed significantly for intact versus disturbed substrates, suggesting that areas of streambed disturbance might be identified via remote sensing. Future work will focus on further elucidating connections between surface reflectance, water surface texture and flow velocity, and developing quantitative relationships between bottom reflectance, periphyton abundance and the degree of streambed disturbance. Copyright © 2013 John Wiley & Sons, Ltd.