Acoustic Doppler Current Profiler Velocity and Relative Backscatter Anomaly Error Analysis and Error Propagation

Five acoustic Doppler current profilers (ADCPs) were moored to the bottom on the northern Gulf of Mexico shelf from early November 2015 through mid-April 2016. The acoustic backscatter and vertical velocity profiles were used to qualitatively estimate zooplankton concentrations and their vertical velocities during diel vertical migrations. Error analysis and error propagation was performed for the vertical velocities and for each term of the backscatter anomaly equation at the five mooring locations. Four of the ADCPs were 300 kHz Teledyne Workhorse Sentinel measuring continuously every 12 seconds. Another was a 600 kHz ADCP measuring hourly bursts of 10 min at 1 Hz. The vertical velocity errors for hourly averages were of the order of the vertical velocity magnitudes and slightly higher at the bursting ADCP location. However, daily and monthly averaging lowered the vertical velocity errors by at least one order of magnitude. The errors associated with the relative backscatter anomalies were broken down by each relevant term of the backscatter equation. As the errors propagated through the equation and the averaging, the error magnitudes were at least one order of magnitude smaller than the relevant variations. Errors at least one order of magnitude smaller than the signals of interest confirm that the observed diel signals were valid.