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Measurement of Antenna Patterns for Oceanographic Radars Using Aerial DronesAbstract
A new method is described employing small drone aircraft for antenna pattern measurements (APMs) of high-frequency (HF) oceanographic radars used for observing ocean surface currents. Previous studies have shown that accurate surface current measurements using HF radar require APMs. The APMs provide directional calibration of the receive antennas for direction-finding radars. In the absence of APMs, so-called ideal antenna patterns are assumed and these can differ substantially from measured patterns. Typically, APMs are obtained using small research vessels carrying radio signal sources or transponders in circular arcs around individual radar sites. This procedure is expensive because it requires seagoing technicians, a vessel, and other equipment necessary to support small-boat operations. Furthermore, adverse sea conditions and obstacles in the water can limit the ability of small vessels to conduct APMs. In contrast, it is shown that drone aircraft can successfully conduct APMs at much lower cost and in a broader range of sea states with comparable accuracy. Drone-based patterns can extend farther shoreward, since they are not affected by the surfzone, and thereby expand the range of bearings over which APMs are determined. This simplified process for obtaining APMs can lead to more frequent calibrations and improved surface current measurements.
Abstract
A new method is described employing small drone aircraft for antenna pattern measurements (APMs) of high-frequency (HF) oceanographic radars used for observing ocean surface currents. Previous studies have shown that accurate surface current measurements using HF radar require APMs. The APMs provide directional calibration of the receive antennas for direction-finding radars. In the absence of APMs, so-called ideal antenna patterns are assumed and these can differ substantially from measured patterns. Typically, APMs are obtained using small research vessels carrying radio signal sources or transponders in circular arcs around individual radar sites. This procedure is expensive because it requires seagoing technicians, a vessel, and other equipment necessary to support small-boat operations. Furthermore, adverse sea conditions and obstacles in the water can limit the ability of small vessels to conduct APMs. In contrast, it is shown that drone aircraft can successfully conduct APMs at much lower cost and in a broader range of sea states with comparable accuracy. Drone-based patterns can extend farther shoreward, since they are not affected by the surfzone, and thereby expand the range of bearings over which APMs are determined. This simplified process for obtaining APMs can lead to more frequent calibrations and improved surface current measurements.
Abstract
The design, calibration, and deployment of a buoy and gas-capture assembly for measuring bubbling gas flux in oceans and lakes are described. The assembly collects gas in a chamber while continuously measuring the position of the gas–water interface that forms as gas accumulates. Interface position is determined from the differential pressure between the chamber and ambient seawater. A spar buoy provides flotation and stability to reduce vertical motion from surface waves. The gas-collection assembly and spar, referred to as a flux buoy, is suitable for deployment from small boats under conditions of light wind and small waves. The flux buoy is being used to determine the spatial distribution of natural hydrocarbon seepage off the south-central California coast. Hydrocarbon seepage from continental shelves may be an important source of atmospheric methane.
Abstract
The design, calibration, and deployment of a buoy and gas-capture assembly for measuring bubbling gas flux in oceans and lakes are described. The assembly collects gas in a chamber while continuously measuring the position of the gas–water interface that forms as gas accumulates. Interface position is determined from the differential pressure between the chamber and ambient seawater. A spar buoy provides flotation and stability to reduce vertical motion from surface waves. The gas-collection assembly and spar, referred to as a flux buoy, is suitable for deployment from small boats under conditions of light wind and small waves. The flux buoy is being used to determine the spatial distribution of natural hydrocarbon seepage off the south-central California coast. Hydrocarbon seepage from continental shelves may be an important source of atmospheric methane.
