Stabilized terrain optical position sensor

#The present invention relates to information display systems for aircraft guidance and more particularly to such a system for presenting sufficient information to a helicopter pilot to enable him to check the area for obstacles and to hover over a selected ground location.

#At the present time a pilot, during the day and if the day is clear, can visually recognize objects on the ground or land features. He may then maneuver his helicopter and hover over a target object or feature by visually aligning his helicopter with other ground features and watching his altimeter. The accuracy of his hovering maneuver depends on his own skill and the availability of visible terrain features. A skilled helicopter pilot can, for example, hover and descend directly over an injured person who is to be evacuated and can maintain a hover position within 15 feet of a selected ground feature.

#The presence of fog, smoke or nighttime operation presents an entirely different problem to a pilot who wishes to locate a certain ground position and accurately hover over that position. The problem is less serious if the area is lighted, for example, by flares or spotlights, or if the night is illuminated by bright moonlight or if the helicopter is equipped with a spotlight and the pilot is able to use it. However, there are occasions, particularly in military combat situations, where lights cannot be used without revealing the presence, to the enemy, of the helicopter (in the case of a helicopter spotlight or flare) or the presence of ground personnel (in the case of ground lighting). Such nighttime and hidden operations may be required, for example, to evacuate a pilot shot down behind enemy lines, to supply an isolated outpost in the possible presence of enemy troops, or to attack enemy tanks or other enemy forces under cover of darkness.

#Other objectives and features of the present invention will be apparent from the detailed description which follows and which provides the inventor's best mode of practicing the said invention, the detailed description being taken in conjunction with the accompanying drawings.

#In the drawings:

#FIG. 1 is a block schematic diagram of the system of the present invention;

#As shown in FIG. 1, the entire system is mounted within an aircraft and includes a mirror 10 which is automatically positioned within the viewing angle of the image camera 11 under control of the pilot 60. The image camera 11 may be of various types, for example, it may be a forward looking infra-red optical system which converts the infra-red radiation present at night to a visible form. Alternatively, camera 11 may be a low light level television camera which may operate at night by the low level light obtained from starlight or moonlight or the camera 11 may be a normal television camera which operates under daylight conditions or using a search light. The camera 11 is fixedly mounted on the aircraft and the aircraft would generally be a helicopter capable of a hovering operation. The camera 11 is connected to an electronics shaping circuit 12 which, in the case of the forward looking infrared camera, will convert the incoming signals from camera 11 to an output which is in the form of conventional video signals. The video signals from the electronic shaping circuit 12 are transmitted by a video cable 13 to a video combiner 14. The video combiner 14 may be a mixer which combines two different video signals so that they may be both portrayed on the television monitor screen as a superimposed picture. A suitable video combiner is available from Dynair Company of California.

#The video signal from the video combiner 14 is transmitted by video cable 15 to the image inverter 16. The image inverter 16 functions to correct the image inversion of the fore-aft downlooking presentation caused by the mirror and to place the image which would otherwise be at the top portion of the television monitor and re-position it to the bottom portion of the television monitor and similarly to re-position the image which would be otherwise at the bottom portion, for example, the bottom 40%, of the television monitor and re-position is so that it is at the top portion of the television monitor. The image inverter 16 is required because the mirror 10 inverts the reflected image and would otherwise place the ground portion of the image at the top of the television monitoring screen. The helicopter pilot, however, is habituated to seeing the ground at the bottom of his view, the horizon next, and the sky area at the top. The image inverter 16 preferably is an electronic system which alters the vertical raster, i.e., the order of the vertical scan. Instead of starting from the top and progressing from the top downward, the vertical scan may start at the bottom, go to the center, and then skip to the top and go from the top to the center. The image inverter 16 will provide, consequently, this conventional type of image on the television monitor 18, to which it is connected by video cable 17.

#The television monitor 18 may be a conventional television monitor available from various manufacturers, such as RCA Corporation of New Jersey or Conrac Corporation. In addition to the image of the scene in front of the aircraft (which is produced by the lower 20.degree. of the viewing angle of camera 11) and the image of the scene beneath the aircraft (which is produced by the camera 11 viewing the scene reflected from the mirror 10) the television monitor 18 at the bottom portion of its screen also presents a set of active symbols representing flight information. This set of active electronically generated symbols representing flight information is obtained from instrumentation which would normally be in the aircraft for flying purposes, although, alternatively, additional instruments may be used to provide certain active symbols. By "active symbols" is meant that the visual symbol is produced on the screen by the TV gun and is seen as moving, for example, becomes longer or moves position, in proportion to the element represented by the symbol. Preferably, the information provided by the symbols includes the rate of climb, which may be obtained from the instantaneous vertical speed indicator; the altitude, which may be obtained from an altitude radar; the acceleration in the horizontal direction, which may be obtained from an attitude gyroscope; and the velocity and direction of velocity, which may be obtained, for example, from a doppler velocity radar or from the image motion sensor system 30 shown in FIG. 1.