Robert G. Williams

Laboratory and field measurements with a broad band ADCP

A 1200 kHz Broad Band Acoustic Doppler Current Profiler (BBADCP) from RD Instruments was tested in 1992 to determine its applicability to National Ocean Service programs. A series of tow carriage tests was performed at the David Taylor Research Center and comparisons made with standard narrow band ADCP systems. Field tests were performed in the Patuxent River towing the BBADCP in a modified catamaran. The intent is to use the system to perform high resolution current transects from ships of opportunity in coastal waters and estuaries. These tests determined the maximum water track range and tested bottom tracking to depths of 40 meters. Comparisons were performed with a bottom-mounted 1200 kHz narrow band ADCP by anchoring the catamaran 50 meters down river from the platform. The results showed disturbing differences that cannot be adequately explained. Data are presented showing the results of laboratory and field tests and plans are discussed for future tests.<<ETX>>

Development of a Real Time Measurement System for Charleston Harbour

The National Ocean Service of NOAA has developed and deployed a real-time current measuring system for verification of the accuracy of the NOAA tidal current table for Charleston Harbor. An RD Instruments acoustic Doppler current profiler on the bottom of Charleston Harbor is hard wired to a Coastal Climate weather station. The weather station transmits both the weather data and the current profiler data to a shore station for telephone interrogation from Rookville, Maryland. Although there have been several engineering evaluations of acoustic Doppler current measuring systems, this is the first application of the technology to NOS operational programs. The paper will discuss the development, integration and performance of the system as well as techniques used to assure the quality of data.

Field experiment with an ocean surface current sensing microwave radar

There has long been a need for an automated, remote current mapping instrument for use in harbours, bays and estuaries. To meet this need, a dual frequency (Delta-K) X-band microwave radar is being developed by Quadrant Engineering for the National Ocean Service (NOS). It differs from other commercially available surface current sensing radars in that it offers a much finer current resolution cell (100 m/spl times/100 m) than HF/VHF radars, good velocity resolution (1-5 cm/sec) and can automatically transmit multiple frequencies (frequency agility) to adapt to varying surface wave conditions. This paper describes NOS needs, the basic principle and system parameters of Delta-K radar, and a field experiment conducted in January 8-9, 1997 at Newark Bay, New Jersey. The goal of the experiment was to demonstrate the feasibility of the radar system in measuring the surface currents in a harbor environment. Ocean surface conditions varied from rough to calm during the two-day period. The experiment showed that the Delta-K system provided good current signals in the harbor environment under two very different surface conditions. In-situ current measurements consisted of those from a Price current meter, surface drifters, and a bottom-mounted Acoustic Doppler Current Profiler (ADCP). The currents measured by Delta-K radar appear to be reasonable in both magnitude and its spatial distribution. However, because of the uncertainties of the in-situ observations, no quantitative comparison was attempted.

Intercomparison Between Towed And Stationary Acoustic Doppler Current Profilers

This paper discusses the use of a towed acoustic Doppler current profiler (ADCP) for the purpose of evaluating in situ current meters. Data are presented from comparison tests between a towed and bottom-mounted ADCP. Velocity contours parallel and transverse to the main navigation channel under the Sunshine Skyway Bridge (SSB) in Tampa, Florida from a 600 KHz towed ADCP are compared to bottom-mounted current profiles from a 1200 KHz ADCP placed under the SSB. Data are presented to show instrument differences which are a combiination of random and systematic error. The study finds that the bottom-mounted ADCP is measuring current speeds accurately and is in the optimal location to report maximum channel currents under the SSB. The present location of the bottom-mounted ADCP under the SSB in the middle of the main navigation channel reports velocities accurate to 5 cmls. This metho+ is considered a viable technique for evaluating the reliability of moored or bottom-mounted units.