Showing papers by "National Ocean Service published in 1983"

System Design And Performance Factors For Airborne Laser Hydrography

Abstract: Methods are being sought to improve the efficiency of shallow-water hydrography. Reductions in cost, manpower, and data collection time are desired. Studies have indicated that airborne laser hydrography has the potential to provide five-fold reductions in cost and manpower requirements over conventional launch-based sonar systems, while at the same time increasing productivity and adding rapid response reconaissance capability. Analyses have shown that typical penetration depths are adequate in many coastal waters where extensive survey requirements now exist. The critical performance factor is depth measurement accuracy. Airborne laser hydrography is prone to a number of depth measurement error sources whose net magnitude could exceed standards if not carefully constrained by restricting system design and operational parameters. The interrelationships and compromises among these parameters necessary to meet operational requirements and goals are discussed in detail.

Sea-Truth Experiments On Acoustic Doppler Current Profiling Systems

Abstract: Two experiments were conducted in the summer of 1982 with "off-the-shelf" AMETEK-Straza DCP4400 acoustic Doppler current profiling systems. The first experiment compared a bottom-mounted upward-looking 300 kHz system against moored current measuring systems. Conductivity-temperature-depth (CTD) profiles, water samples, and meteorological data were collected to augment the current measurements and aid in the interpretation of the acoustic Doppler measurements. The second experiment involved real-time comparisons between the downward-looking 115 kHz acoustic profiling system installed on the NOAA Ship RESEARCHER and current measurements made with an EG&G - Vector Measuring Current Meter (VMCM) lowered from the ship while on station off the coast of Florida. This paper presents the results from both experiments along with a discussion on the performance of the AMETEK-Straza DCP4400 systems.

Comparison of offshore wave measurements

Abstract: Preliminary results of a comparison between several wave measurement systems used during the Atlantic Remote Sensing Land Ocean Experiment (ARSLOE) are presented. Measurements in the offshore region 12-40 km offshore, taken during a storm that occurred October 23-26, 1980, are compared. Disagreement between significant waveheights resulting from the different measurement systems in some cases are larger than can be explained by random variability.

A framework for the laboratory testing of Eulerian current measuring devices

Abstract: THE DEVELOPMENT of testing techniques and procedures required to understand the performance of devices used to measure water currents has proven to be one of the most difficult and challenging tasks that the oceanographic community faces. It has long been recognized that some type of controllable relative water motion was a necessary element in the process of determining the accuracy of a current meter. A widely accepted solution is the towing tank where a current meter fastened to a moving carriage is moved through "still" water. A simple measurement of carriage speed over the ground compared to the current meter's flow measurement gives an indication of the accuracy of the device. Although this approach satisfied many, a sense that this technique was not sufficient spawned a few short-lived attempts at simulating time-varying flow conditions and developing deterministic models (transfer functions) for the response of inertial transducers. In addition, mathematical modeling of the motion of buoy moorings was attempted by a variety of investigators. In the late 1960's and early 1970's, the response of a current meter to the complex time-varying ocean environment became a major issue within the oceanographic community. It was clear that this information could not be obtained by simple steady-flow tow tank testing and that either dynamic controllable techniques must be developed or our ability to characterize the measurement environment must be improved.

Accuracy characteristics of the electronics of waverider buoys used in the ARSLOE

Abstract: During the Atlantic Remote Sensing Land Ocean Experiment (ARSLOE), October-November, 1980, a large number of meteorological and oceanographic instruments, especially wave-measurement instruments, were deployed in the ocean near the Army Corps of Engineers Pier, Duck, NC. About nine Waverider buoys were deployed in an approximately rectangular pattern, about 30 km wide by 40 km seaward. The Waveriders were an accepted reference for study of other wave-measurement instrument systems. Almost all of the Waverider buoys were calibrated on the rotating-arm facility of the NOAA, Engineering Support Office. Pre- and post-deployment calibrations formed the basis for tables and equations for correction of the Waverider measurements. The calibrations discussed here established that the Waveriders were measuring lower than specification, averaging about 5 percent low (10 percent for variance spectra coefficients.) Corrections for effects of fluctuations in water temperature on Waverider sensitivity were required and are provided. The manufacturer's modification to prevent future drift in sensitivity is also described.