Radiant energy – Ionic separation or analysis – Static field-type ion path-bending selecting means
Patent
1984-12-12
1986-12-02
Henry, Jon W.
Radiant energy
Ionic separation or analysis
Static field-type ion path-bending selecting means
350500, 250235, G02B 718, G02B 2610
Patent
active
046260633
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention concerns the control of rotating mirrors, such as those used to produce images of regions of land, or to derive information about such regions of land, by sequentially scanning strips of land from an aircraft. It is especially concerned with the decoupling between a rotating mirror and a fixed, associated telescope or other information receiving apparatus.
The present invention was developed primarily for use in an airborne multi-band spectral analyser (of the type used, for example, for thermal imaging), but the invention may be used for other purposes--such as in photographic surveys. In view of the history of its development, the application of the invention to multi-band spectral analysis will be given particular reference in the following description.
BACKGROUND ART
With the establishment of satellites--such as the LANDSAT satellite--there has been an increased recognition of the value of making observations of the earth's surface using equipment which employs thermal imaging techniques. Already, thermal imaging has been proposed for water pollution studies, forest fire detection and damage assessment, location of underground springs, obtaining an inventory of forest, mountain and agricultural lands, monitoring the ripening of wheat and other crops, and observing fishery and tidal movements. More recently, it has been appreciated that further information can be obtained using multi-band spectral analysis (that is, the technique of simultaneously observing an object in several regions of the electromagnetic spectrum), especially if that analysis can be performed on images obtained from low-level aircraft observations.
It is well known that low-flying aircraft often experience substantial turbulence. Consequently, if observations are to be made from low-flying aircraft (especially from light aircraft) using a scanning arrangement such as a rotating mirror, and maximum information is to be obtained from those observations, then perturbations of the scanning process due to roll, pitch and yaw of the aircraft must be compensated.
When making observations from a large aircraft, the effects of roll, pitch and yaw have been eliminated or substantially reduced by mounting the equipment carried in the aircraft on a stabilised platform. However, the use of a stabilised platform in a light aircraft imposes a substantial weight burden and also (because it is necessary to maintain stabilising gyroscopes in action) a substantial power burden.
DISCLOSURE OF THE PRESENT INVENTION
It is an object of the present invention to provide an arrangement for mounting a scanning mirror in an aircraft with a telescope and/or associated analysis equipment, which is responsive to variations in the aircraft's flight to provide compensation for roll, pitch and yaw perturbations of the aircraft's straight and level flight, without the power usage and weight penalties of a stabilised platform.
This objective is achieved by using (a) a novel optical decoupling between the rotating (scanning) mirror and the telescope and/or associated analysis equipment, and (b) stabilisation of the scanning mirror.
According to a first--and preferred--aspect of the present invention, the decoupling is achieved using a "nodding" motion of the rotating mirror, to which an inertial system has been coupled to compensate for pitch and yaw of an aircraft.
According to a second aspect of the present invention, the decoupling is obtained using an elliptical mirror arrangement, and the pitch and yaw stabilisation is provided by coupling an inertial system to a rotating mirror which is mounted on gimbals.
In each case, compensation for roll of an aircraft is achieved by varying the time at which the sampling commences during rotation of the scanning mirror.
In the case of the "nodding" mirror arrangement, the present invention provides for the mounting of the rotating or scanning mirror on a shaft which can move within a hollow region of an outer, larger shaft. The precise location of the inner shaft is controlled by a combi
REFERENCES:
patent: 3580150 (1971-05-01), Watson
A. A. Babayev, "Gyro-Optical Azimuthal Instrument", Soviet Jour. of Optical Tech., vol. 35, No. 5, Sep.-Oct., 1968, pp. 636-639.
A. C. O. Gibb et al, "A Line of Sight . . . ", Jour. of Electrical & Electronics Eng., Australia, vol. 1, No. 1, Mar. 1981.
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