Radar and infrared propagation drastically depend on the meteorological and oceanographic conditions. Concerning a joint sea trial of German research institutes at the Baltic Sea 2001, FWG was responsible for the environmental characterization of the marine boundary layer. In-situ measurements included recordings of atmospheric properties and sea surface parameters. They were studied by two multi-sensor buoys, on board a vessel and with radiosondes. Pressure, air temperature and humidity were measured from the sea surface to 1 km altitude. The free drifting buoys which have been constructed at FWG offer the opportunity to gain unperturbed, time resolved information about environmental parameters up to 5 m above sea level. Based on the in-situ measurements refractivity profiles can be calculated. With the help of the vertical refractivity gradient and the air sea temperature difference, conditions for radar and infrared propagation are determined. Further experimental results include wind speed and direction, wave height, rain rate and other important parameters. Taking advantage of the parabolic equation model radar propagation is calculated numerically. In conclusion, the experimental results and calculations underline the importance of the environmental characterization of the marine boundary layer with high temporal and spatial resolution.
The performance of radar sensors operating within the marine boundary layer is severely influenced by the actual atmospheric conditions, the sea surface and the geometry between radar and reflection point. Propagation models are in existence, which cope with the varying environment and allow a performance prediction for sensors in different radar bands. To assess the propagation within different layers simultaneously at X-, Ka- and W-band an experiment was performed using the experimental three frequency radar MEMPHIS operating against point targets at different heights above sea, carried on a naval vessel, which moved on outbound and inbound courses to ranges well beyond horizon. In-situ measurements included recordings of atmospheric properties and sea surface parameters. Based upon the environmental measurements, refractivity profiles were calculated. With the help of the vertical refractivity gradient and the air sea temperature difference, conditions for the radar propagation were determined.The experimental results were used to validate respective simulations with the parabolic equation model TERPEM. In conclusion, the experimental results and calculations underline the importance of the environmental characterization of the marine boundary layer with high temporal and spatial resolution.This paper describes the experimental approach and gives representative results for measurement and simulation
The rock 'n' roll phaco technique we describe does not require nucleus chopping or cracking. In this easy-to-learn technique, the lens nucleus is fragmented from both sides, which seems to be an advantage in very soft nuclei.
Radar propagation near the sea surface depends on meteorological conditions and sea surface roughness. Often strong gradients of humidity and temperature can be observed close to the air-water interface leading to abnormal propagation effects such as ducting. For shipborne radars operating at frequencies above L-band, the evaporation duct is the dominant propagation mechanism affecting the maximum detection range of horizon-search radars. Ducting can also increase sea clutter return within and beyond the normal horizon, and surface-based ducts can enhance land clutter return from extended ranges.During sea trials in the Skagerrak and the Baltic Sea in 2003 and 2004, FWG was responsible for environmental characterization of the boundary layer. In-situ measurements included recordings of atmospheric and sea surface parameters. Investigations with multi-sensor buoys and with radiosondes were performed on board the German research vessel PLANET respectively on FGS HELMSAND. The drift buoys developed by FWG provided unperturbed, time resolved information on air-sea interaction processes. In addition to meteorological parameters sea state, sea surface roughness, and sea surface temperature were measured. Refractivity profiles were determined based on data sets gathered by measurements of pressure, humidity and temperature from the sea surface up to 1 km altitude.Simultaneously to atmospheric measurements radar propagation investigations were performed by FGAN-FHR (Research Institute for High Frequency Physics and Radar Techniques). PLANET, FGS STOLLERGRUND were illuminated by a radar operating at X-, Ka- and W-band. The radar system was located at the land-based test site Hirtshals, Denmark during the trials in 2003 and at the land-based test site Surendorf, Germany during the experiment in 2004. Radar propagation characteristics at X-band were measured on board the ships with two omnidirectional antennas mounted in two different altitudes above sea surface. Results of refractivity variability in the marine boundary layer are presented in conjunction with radar propagation data and model outputs
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