Communications: directive radio wave systems and devices (e.g. – Ship collision avoidance
Patent
1996-01-17
1998-09-08
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
Ship collision avoidance
342 21, 342 23, G01S 1366
Patent
active
058051015
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for determining the position of a radar target extending over several resolution cells. More particularly, the invention relates to a position-determining process of the type wherein echo signals reflected from resolution cells are mixed in the baseband so that an amplitude-modulated signal of the radar target is generated; in the baseband, at least for all resolution cells to be associated with a radar target the amplitude values are determined; and the position of the radar target is determined from the size of the amplitude values and/or their distribution in the area defined by the resolution cell.
The term "resolution cell" used in the present patent application is intended to cover the terms "radar resolution cell" as well as "area resolution cell". A radar resolution cell identifies the spatial resolution of a radar installation. A radar resolution cell is a design-dependent constant of the radar installation. In an area resolution cell, several radar resolution cells are combined as needed. Therefore, an area resolution cell is considerably larger in its spatial extension than a radar resolution cell.
The invention relates in particular to the determination of the position of a large-surface radar target such as, for example, an oceangoing freight ship or passenger ship. Such radar targets comprise several resolution cells, for example, a few hundred, when such a radar target moves past a radar set at a relatively small distance and/or when the radar set has a high spatial resolution. This condition exists, for example, in the (radar) monitoring of harbor access routes and/or shipping routes. There, it is necessary, for example, to determine and to track the position of one or several ships as accurately as possible with a stationary radar set, which ships generally have little maneuverability because of their size, so that, for example, compliance with a predetermined route can be checked and/or advance warning of a possible collision can be given.
Such target surfaces, for example, a ship having a length of approximately 200 m, due to their design, e.g., the superstructures and/or the freight, may have a plurality of radar reflectors. A moving ship also generates bow waves as well as stern waves (stern sea) which also reflect radar waves and thus change the extension of the actual radar target, the ship. A particularly disturbing effect on the determination of the target position results from reflections which are generated on the ship itself and which melt into the useful echoes. Furthermore, a radar installation may also create apparent radar targets, for example, due to the so-called minor lobes of the radar antenna, which apparent radar targets can also move along with the actual radar target, the ship.
If, for such a (radar) situation, the position of a (radar) target surface, for example, the ship, is now intended to be determined accurately solely on the basis of the radar information, for example, by way of the spatial resolution capacity possible per se of the radar installation of, for example, one tenth of the length of the ship, it is first necessary to find a characteristic (radar) reference point for the desired radar target, the ship, and to then track the position of the reference point continuously in time.
In this context, one might consider selecting for this (radar) reference point the reflector with the largest (radar) echo amplitude. But this method fails in a disadvantageous manner if several equivalent reflectors and/or apparent reflectors are arranged so as to be closely adjacent to one another.
For a large-surface radar target, which is comprised of several actual and/or apparent individual targets, one might consider selecting and tracking a surface center point or surface center of gravity of the radar target as a characteristic reference point by way of an averaging and/or integration method. A reference point determined in this manner can also greatly change its position in a disadvantageous manner and t
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R. Klepko: "Automatic ship image extraction from synthetic aperture radar imagery". In: IGARSS '90 Conference Proceedings, vol. 1, May 20, 1990, Maryland, pp. 691-694.
J. Maaloe: "Classification of Ships using an Incoherent marine radar". In: Radar-82 International Conference, Oct. 18, 1982, London, UK, pp. 274-277.
Bodenmueller Edeltraud
Vogel Siegfried
Daimler-Benz Aerospace AG
Sotomayor John B.
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