Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Patent
1993-06-24
1995-02-14
Issing, Gregory C.
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
342450, G01S 302
Patent
active
053899369
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of, and system for, direction finding, and more particularly to a triangulation processing apparatus for analysing clusters of bearings taken of distant sources by an array of direction finding stations.
BACKGROUND ART
Methods of direction finding include calculating a fix confidence score for each source of radiation detected by direction finding stations in known separated locations, which stations each produce a set of bearings of the sources each detects, each bearing having an error predetermined for the associated station, and a triangulation process being used to fix the position of the sources. Object location by triangulation is well known in civil applications.
The invention may be applied, for example, to the monitoring of ship movements by coastguards. Radars or radios carried by ships may be distinguishable from one another by reason of the differences in source parameters such as frequency of the radar or radio signal, or the modulation characteristics such as pulse length, pulse repetition frequency or even pulse shape. Thus it may be possible to associate a combination of bearings taken one each from the direction finding stations as being from one particular source with a high degree of confidence on the basis of parameter match alone. Also a combination of bearings may appear to converge on one position but there may be no parameter match, in which event the existence of a source at such a position can be discounted.
However, the sources may match in parameter values and be indistinguishable. This is likely in the case of mass produced shipborne radars. In this event the sets of bearings provided by the direction finding stations need to be analysed on a geometrical basis to establish a confidence level for each apparent convergence of a set of bearings on a source. In practice a parameter match confidence level or score will be combined with a geometrical confidence level, or score, to provide an overall confidence level for any apparent source.
DISCLOSURE OF INVENTION
According to one aspect of the present invention there is provided a method of calculating a fix confidence score for each source of radiation detected by direction finding stations in known separated locations, which stations each produce a set of bearings of the sources each detects, each bearing having an error predetermined for the associated station, and a triangulation process being used to fix the position of the sources, characterised in that there are at least three direction finding stations, in that each fix confidence score is formed for a combination of bearings taken one each from the respective stations, in that one bearing of each of the combinations is taken in turn as a spoke directed at a source, in that the triangulation process generates a bar of intersection points along the spoke for each other bearing of the combination, each bar corresponding to the error of each other bearing, in that the number of overlaps between pairs of bars along the spoke is totalled to give a spoke score, and in that the spoke scores for all spokes of the combination are summed to form the fix confidence score for a source which may be associated with the combination.
According to a second aspect of the present invention there is provided a triangulation processing apparatus for use in a direction finding system, the apparatus being characterised by having at least three inputs for connection to respective means for deriving bearing information, which information is subject to error, fix confidence scoring means for forming a fix confidence score for a combination of items of bearing information taken one from each of the inputs, said fix confidence scoring means being configured to treat one item of bearing information of each of the combinations as a spoke directed at a source of radiation and to generate a bar of intersection points along the spoke for each other item of bearing information of the combination, each bar corresponding to the magnitude of the error o
REFERENCES:
patent: 4806936 (1989-02-01), Williams et al.
patent: 5045860 (1991-09-01), Hodson
Issing Gregory C.
Thorn EMI Electronics Limited
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