Lidar Sensor for Measuring Directional-Spectral Characteristics of Water Waves
CORP OF ENGINEERS MOBILE AL JOINT AIRBORNE LIDAR BATHYMETRY TECHNICAL CENTER OF EXPERTISE
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Conventional in situ wave gages, like the pressure gage and current meter PUV and the directional wave gage DWG, cannot satisfy all water-wave measurement requirements in the coastal zone. Specifically, new measurement technologies are required to allow for wave measurement within navigation channels and near navigation structures where bottom-mounted gages are not easily deployed or may themselves become hazards to navigation. Bottom mounted wave gages do not directly measure the elevation of the water surface. Instead, these measurements approximate water surface elevation based on other hydrodynamic processes. The results can be faulty if these processes are different than assumed during analysis. In December 1999, a non-intrusive directional lidar wave gage LWG was tested. The LWG uses lidar technology to directly measure water surface elevation. So unlike bottom mounted gages, the surface elevation measurement from the LWG is independent of other hydrodynamic processes. The prototype LWG consists of four rangefinders, a compass, and an inclinometer. Each rangefinder collected water surface elevation time series at a rate of 10 Hz. The laser footprints were positioned to form an approximate 1-m square. The compass and inclinometer allowed for accurate positioning of the footprints on the water surface. Throughout the field test, ground truth was collected concurrently with the LWG data using a PUV mounted directly beneath the LWG. Directional-spectral wave characteristics determined from the LWG time series using standard Fourier analysis procedures match well with PUV results. This paper discusses the technology on which the LWG is based and presents the preliminary results from the field test of the prototype sensor.
- Physical and Dynamic Oceanography
- Infrared Detection and Detectors