FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1950
1950 - 0291.PDF
February 195° 195 f The parabolic aerial of thevAirborne Profile-Recorder Js shown mounted in the fuselage of a E&ekfeeed Hudson. — GROUND PROFILES — Recorded by Radar Altimeter: Successful New Survey Technique FOUR years ago, the Canadian Department of Minesand Resources initiated a programme of research intothe practicability of using an airborne instrumentation to assist in obtaining ground elevation information for use in topographical mapping. Early experiments with the existing APN-i radio alti- meter proved that special instruments were required if reasonable accuracy was to be achieved. The National Research Council of Canada solved the problem by design- ing a precision radar altimeter for measuring terrain- clearance beneath an aircraft—an instrument capable of recording ground profiles to limits of plus or minus 10ft when flying at a speed of 200 m.p.h. Development of a similar instrument for commercial use was undertaken by the Photographic Survey Corporation, Ltd., of Toronto, and the present P.S.C. Airborne Profile-recorder is the product of lengthy research and operational experience. The equipment is basically an electronic altimeter -utiliz- ing a radar beam projected downwards from the airborne installation to measure the actual clearance between the aircraft and the ground. It produces an. elevation profile of the ground in the form of a continuous record of such measurements taken in continuous sequence as the air- craft flies along the line to be surveyed. The operating principle, briefly, is that a radar aerial mounted beneath the aircraft directs micro-wave radiations vertically down- ward to the ground, while a graphic recorder on the receiv- ing side of the radar set makes a continuous record of the terrain-clearance on a moving tape. Correlation of the record with the ground track is accomplished by syn- chronized vertical photography. The instant of taking a photograph is recorded by an auxiliary pen in the margin Component unitsfh ngus,der, the receiver and indicator, andthe datum stabil- izer; (below) theinverter and trans- mitter. of the radar record, thereby identifying that point on the record with the ground position indicated by the centre point on the photograph. A continuous record of radar readings gives an inverted picture of the ground profile when the altitude of the aircraft is used for reference, but when the record is related to sea level it becomes a scale drawing of the ground profile. Since the height of the aircraft above sea level (measured by a normal sensitive altimeter) is taken as the reference datum for the ground clearance readings and as, by the use of this altimeter alone it is impossible to maintain an exact constant height, a method of stabilizing the reference datum is necessary. For this purpose an electronic datum stabilizer has been developed, incorporating a small, sensitive aneroid which produces an electric current pro- portional to height changes without mechanically loading the aneroid. This current is fed simultaneously with the radar signal to the same recording meter in such a manner that it compensates for deviations from level flight. This type of equipment should be particularly useful in reconnaissance work during the selection of routes for power, oil or railway lines, and particularly for providing accurate ground-elevation information to be used in con- junction with existing methods of map construction. The P.S.C. Airborne Profile-recorder is available for commercial distribution or for hire; and it may be built to the customer's specifications of size and accuracy. Where the volume of work is not great enough to warrant the purchase of an instrument the Photographic Survey Corporation offers a complete service which includes flying, reduction and interpretation of the radar record and topo- graphical mapping on a contract basis. To test the accuracy of the equipment a strip of ground was chosen (shown below) which had previously been well surveyed by existingmethods. The radar record is seen superimposed on the previously surveyed points ; accuracy along the actual flight-line was within the specified, tolerance of the instrument. The numbers refer to photographs for correlation of the radar record and the ground track. Rectified /^RR. Profile Mop Data Profile
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
