1. Field of the Invention
The present invention relates to a system for determining the position of at least one target emitting radiation, comprising:
two passive sighting devices, sensitive to said radiation, disposed at a distance from each other and movable in rotation about a substantially vertical common axis, PA1 means for measuring the intensity of the radiation received by each of the sighting devices along a sighting line scanning a substantially vertical sighting plane, common to the two sighting devices, PA1 means for extracting,in response to the intensities measured, the values of the elevation angles of said target relative to the two sighting devices, and PA1 means for computing, in response to the values of the elevation angles, the distance of said target by triangulation in said substantially vertical common sighting plane. PA1 each of the two sighting devices comprises its own means for measuring the intensity of the radiation received, its own drive means for driving it in rotation about said common axis and its own means for measuring its bearing angle, and PA1 means are provided for controlling said means driving in rotation about said common axis, in response to the values of the bearing angles measured, and arranged so that said bearing angles are equal.
Such a system is used on the ground or on board a ship, for example, for monitoring and, as required, designating to a weapons system the targets which menace the site where said system is set up or the ship on board which it is embarked.
2. Description of the Prior Art
A system of the above defined type is already known, described in the British patent application No. 2 070 877. In this system, the two sighting devices are mechanically coupled and mounted on the same turret which is rotatable about a vertical axis. A single device is provided for measuring the intensity of the radiation received, which serves for each of the sighting devices, as well as a single device for rotating the turret.
This system has the drawback of limited accuracy in determining the distance of the target, because the distance between the two sighting devices is also limited, both for mechanical and optical reasons. It is in fact well known that the accuracy of a triangulation system is related to the value of the distance of its base, here the distance between the two sighting devices.
Now, in the known system, it is not possible to increase this distance, for the hollow mechanical structure which supports the upper sighting device becomes too high and too heavy and difficult to drive. In addition, because the optical path of the ray which penetrates through the lower sighting device must be of the same length as the optical path of the ray which penetrates through the upper sighting device, problems arise if the distance between the two sighting devices is too great.
Furthermore, and still for mechanical reasons, it is not possible, in sighting devices, to use lenses having too large a diameter which increase the weight of the rotary mechanical assembly and introduce an imbalance, at least in the case of the upper sighting device.
In addition, the known system involves the use of a semi-reflecting mirror which introduces a measured energy loss, thus reducing the sensitivity correspondingly. Moreover, in the known system, the height of the field common to each of the sighting devices is smaller than that of the field of each of these devices.
Finally, with this known system it is not possible to determine the distances of several sources present at the same time in the sighting plane.