Evaluation of Bias in Moving-Boat Discharge Measurements using an Acoustic Doppler Current Profiler with a Global Positioning System

摘要

Negative bias in discharge measurements made with an acoustic Doppler current profiler (ADCP) can be caused by the movement of sediment on or near the streambed. The integration of a global positioning system (GPS) to track the movement of the ADCP can be used to avoid the systematic bias associated with a moving bed. More than 500 discharge measurement transects and 63 discharge measurements (which consist of the average of at least 2 transects in opposite directions) with GPS data were collected at sites with no moving bed to compare GPS and bottom track referenced discharges. Although the data indicated some statistical bias depending on site conditions and type of GPS data used, these biases were typically about 0.5% or less. An assessment of differential correction sources was hampered by not having data collected with a range of different correction sources and different GPS receivers at the same sites. Despite this limitation, the data indicate that the use of Wide Area Augmentation System (WAAS) corrected positional data is acceptable for discharge measurements using GGA as the boat velocity reference. The discharge data based on GPS-referenced boat velocities from the VTG data string, which does not require differential correction, were comparable to the discharges based on GPS-referenced boat velocities from the differentially corrected GGA data string.