Quantifying Riverine Surface Velocities Using Thermal Infrared PIV

With the exception of river width, remotely obtaining riverine properties such as velocity, discharge and depth is difficult. The use of remote sensing techniques to estimate river velocity requires observation of surface texture. Unfortunately, many river environments do not exhibit texture that can be seen by the naked eye nor recorded with standard RGB imagery. Long wave infrared (thermal) imagers are capable of quantifying small true or apparent (usually based on variations in emissivity) temperature variations on the river surface that are advected with the current. A field study was conducted from May 24-28, 2010 in the Wolf River in Harrison County, Mississippi in order to investigate the application of thermal imagery to infer riverine surface currents. Over 20 hours of thermal imagery were captured during daylight and nighttime hours in addition to standard RGB imagery. Imagery is geo-rectified to the riverine surface and velocities are quantified using particle image velocimetry (PIV). The PIV technique identifies similar patterns of intensity between images and quantifies the spatial distance between the patterns. Horizontal velocity vectors are derived using these distances and the image sampling interval (7.5 Hz). Mean, in situ surface velocities were obtained using 6 electro-magnetic current meters deployed from a floating platform that was repositioned numerous times during the study. Image-derived velocities and validation by comparison with surface velocities obtained from the current meters will be presented.