CODAR intercomparison: Delaware Bay 1984

Abstract

During the fall of 1984 surface current measurements were made by means of a Coastal Ocean Dynamics Application Radar (CODAR) in the Delaware Bay during the National Ocean Service's (NOS) Delaware River and Bay Project. This project included a survey of the circulation of the estuary, operation of a real-time numerical circulation model, and real-time instrumentation. The purpose of the CODAR operation in Delaware Bay was to quantify how CODAR could contribute to NOAA's circulation survey operation. The cost, planning, and operation of the project was jointly shared by NOS and the U.S. Army Corps of Engineers (COE). In this study CODAR measurements were compared with Remote Acoustic Doppler system (RADS) measurements and with a Vector Measuring Current Meter (VMCM) that was situated near the RADS site. Ten days of concurrent data starting on October 16, 1984, were used in this study. The intercomparison of the results is qualified by the inherent nature of comparing entirely different measurement systems. The horizontal spatial averages for CODAR were on the order of 1,000 times that of RADS. The temporal sampling was different between the RADS and CODAR because the two CODAR sites did not operate simultaneously. The CODAR sites were operated sequentially for 45 minutes yielding an time of 1.5 hours, thereby biasing the total measurement. By going to a two-frequency system and sampling simultaneously from both sites, differences in temporal sampling can be eliminated. The differences caused by horizontal averaging are not as easily overcome. The major observations of the performance of CODAR are given below: 1. CODAR functioned without major interruption from October 15, 1984, through November 6, 1984. 2. CODAR surface current maps revealed mesoseale features such as eddies and fronts. 3. The threshold velocity for CODAR was 10cm/s. 4. Radial components of velocity would be useful for system diagnosis and oceanographic applications. 5. CODAR is suitable for mapping the flow patterns in estuaries the size of Delaware Bay and larger. 6. CODAR, RADS, and VMCM showed general agreement in the along-channel direction especially during spring tide. 7. The resolution of CODAR was finer than the along-channel length scale. 8. The semidiurnal tidal component of all three devices were within 5cm/s and 30 degrees of phase. 9. The average bias between RADS and CODAR was 12cm/s in the along-channel component of flow. 10. The uncertainty in phase in the along-channel direction might be due to the non-simultaneity of the CODAR averaging period. 11. Cross-channel flow comparisons were inconclusive due to the low signal to noise ratio in the flow and due to the large resolution scale of CODAR when compared to the short cross-channel flow scales.