Communications: directive radio wave systems and devices (e.g. – Radar for meteorological use
Patent
1993-11-08
1995-11-21
Pihulic, Daniel T.
Communications: directive radio wave systems and devices (e.g.,
Radar for meteorological use
342192, G01S 1395
Patent
active
054691680
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a scheme for obtaining oceanographic and meteorological information from high frequency radio waves scattered from the sea surface. Such waves may have been generated by a skywave radar facility or they may be transmissions of opportunity radiated by HF broadcasters or other sources, man-made or natural.
Reliable measurements of the ocean wave fields, on a large scale, are costly and difficult to obtain. Observations over an entire region, at high spatial resolution, are currently beyond the capabilities of all but two techniques. One is satellite-born sensors and the other is high frequency (HF) skywave radar or Over-the-Horizon Radar (OTHR). If high temporal resolution is also a requirement then OTHR is the only sensor currently available.
Unlike the traditional ground-based radars, which can only see as far as the horizon, an OTHR can make surface observations up to 4000 km away, sometimes further, unconstrained by the earth's curvature. This is made possible by the existence of a radio-reflective layer in the Earth's upper atmosphere--the ionosphere--which extends from about 100 to over 300 km above the Earth's surface.
The OTHR concept is straightforward. A signal is beamed obliquely upwards from a transmitter and reflected down from the ionosphere to illuminate an area of interest; the echoes from the Earth's surface and any targets present travel by a similar path back to a receiver which is usually separated from the transmitter. Notwithstanding the simplicity of the concept, successful exploitation relies on a detailed understanding of the ionosphere, which changes with geographic location, time of day, season of year, sunspot activity and other influences. The coverage of an OTHR is potentially severally million square kilometers for a single installation.
Implicit in OTHR echoes from the sea surface is information about the amplitude, frequency and direction of travel of the wind-generated water waves, which have wavelengths comparable to HF radar wavelengths and thus provide a basis for resonant scattering processes. This continuum of gravity waves can be represented under most conditions by a directional wave spectrum, S(k), that is, a superposition of sinusoidal waves satisfying the deep water dispersion relation. Weak nonlinear interactions between these fundamental waves produce small amounts of additional waves which need not satisfy the dispersion relation. As the wave field is generated primarily by the winds above the surface, determination of the wave conditions enables inferences to be drawn about the wind field which produced them.
SUMMARY OF THE INVENTION
It is an objective of this invention to provide a scheme for the automatic extraction of oceanographic and meteorological information from HF radio waves scattered from the sea surface.
There is a growing demand for high quality oceanographic information by a host of agencies, whose interests range from theoretical studies of the transport of energy and momentum across the air-sea interface to the needs of engineers designing offshore structures. Some of these users require near real-time information and forecasts, as for ship routing, tropical cyclone tracking, and scheduling of off-loading activities at oil drilling platforms. There is also a continuing need for synoptic monitoring of sea conditions to provide calibration information for the radar itself. These tasks have the common need to look in a particular place at a particular time, though to be consistent with the resolution of the radar and wave development times, a time margin of two or three hours usually suffices to maintain a globally consistent `real-time` picture.
At the other extreme, there is keen interest in the accumulation of regional wave climatologies and measurements of large scale events such as the summer monsoon, which may contribute to global environmental research. In this case, the decision of where and when to gather data is relatively unconstrained and the radar can await the occurrence of goo
REFERENCES:
patent: 4053886 (1977-10-01), Wright et al.
T. M. Georges et al: "An Opportunity for Long-Distance Oceanographic and eorological Monitoring using Over-the-Horizon Defense Radars"; Bulletin American Meteorological Society; pp. 1739-1745.
Abstract--INSF--WO6--M2649 D/48.
Australian Patent Application No. PK6899, Jun. 27, 1991.
Madden, J. M., "The Adaptive Suppression of Interference in HF Ground Wave Radar", Radar International Conference Oct. 19-21, 1987, pp. 98-102.
Anderson, S. J., Radar International Conference, Oct. 19-21, 1987, pp. 609-612.
Anderson, S. J., "Adaptive Remote Sensing with HF Skywave Radar", IEE Proceedings, Apr. 2, 1992, pp. 182-192.
Pihulic Daniel T.
The Commonwealth of Australia, c/o The Secretary, Department of
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