Towing Basin Speed Calibration of Acoustic Doppler Current Profiling Instruments

Abstract

With new development in technologies, proliferation of manufacturers, and expanded applications of acoustic Doppler current profiling instruments, the need for proper sensor test procedures becomes increasingly important. This report documents a towing basin speed measurement verification procedure that NOS has adopted for the past decade and a summary of verification results of forty-one cases consisting of twenty-nine individual sensors. These sensors include fourteen RD Instruments acoustic Doppler current profiler (ADCP) units (seven 600 and seven 1200 KHz units) and fifteen SonTek acoustic Doppler profiler (ADP) units (three 500 and twelve 1500 KHz units). Some of these sensors were tested repeatedly on different dates prior to deployment. Tow carriage speeds varied from 5 cm/s to 200 cm/s and were used as references for comparison. The speed differences between sensor readings and carriage references are expressed in terms of mean, standard deviation, and percentage of reference speed. Overall, RDI ADCPs have smaller mean speed differences and standard deviations compared with SonTek ADPs of similar frequencies. There is a larger sensor-to-sensor variation among SonTek units, especially among the 500 KHz ADPs. Except for the SonTek 500 KHz units, the standard deviation and percentage error of the tested sensors were close to manufacturer's specifications. Small zero offsets, on the order of 1 cm/s for ADCPs, 2 cm/s for 1500 KHz ADPs, and 5 cm/s for 500 KHz ADPs, were measured. The test results of both sensor types repeat well over time. To aid in the discussing of test procedure and results, a brief review of related ADCP and ADP design and operational parameters are also included in this report.

Practical aspects of ADCP data use for quantification of mean river flow characteristics; Part II: fixed-vessel measurements

“…Water measurements with ADCP in this water column area are inherently contaminated by side-lobe effects, and consequently discarded. The full significance and usage of the bed-motion velocity need, however, further clarifications in the light of experimental evidence gathered by Shih et al [17]. Shih reports on tests conducted in tow tanks where at zero velocity for the bottom and probe, ADCP sensors of various configurations indicate about 4-5 cm/s velocity readings.…”

Mid-water current aided localization for autonomous underwater vehicles

“…Table 2 summarizes the parameter values used in the 6DOF simulation. In the subsequent simulation, the measurement cell bias magnitudes are constrained to zero within 1 cm/s (2σ), in alignment with the RDI specification (Gordon (1996)) and the calibration report on the RDI ADCP (Shih et al (2000)), which contains maximum biases of ∼1 cm/s. The biases change with time in a correlated fashion (which accounts for changing depth during descent), simulating the bias effects described in section 3.2.1.…”

“…Within the oceanographic community, AUVs are used for tasks such as seafloor mapping (e.g., Caress et al (2012); Kelley et al (2005)), habitat monitoring (e.g., Williams et al (2012)), optical surveys (e.g., Singh et al (2004a)), high-resolution magnetic surveys (Tivey et al (1998)), climate change research (Schofield et al (2010)) and localizing hydrothermal and hydrocarbon plumes (German et al (2008) and Camilli et al (2010), respectively). An advantage of AUVs over other ocean observation methods is the potential for reduced costs (i.e., decreased dependence on manned surface vessels) as well as increased mission duration -especially as long-range AUVs mature (Hobson et al (2012);Furlong et al (2012)) and longer duration missions (on the order of weeks or months) increasingly become a reality.…”

Ornl Adcp Post-Processing Guide and Matlab Algorithms for MHK Site Flow and Turbulence Analysis

“…The accuracy of the ADCP in predicting velocity has been benchmarked against standard stream gauging techniques (e.g., current meter, ADV, towing basin), and most results show agreement within 5% (Shih et al 2000;Oberg 2002;Mueller 2003;Oberg & Mueller 2007;Gunawan et al 2008). ADCPs have been used to characterize mean velocity and turbulence intensity in rivers (Lemmin & Rolland 1997;Barua & Rahman 1998;Muste et al 2004a;Muste et al 2004b;Le Coz et al 2007;Stone and Hotchkiss 2007;Gunawan et al 2010a), oceans/tidal channels (Lohrmann et al 1990;Stacey et al 1999;Cheng et al 2000;Luznik et al 2007;Epler et al 2010;Thomson et al 2010) and laboratories (Nystrom et al 2007).…”