Aerial surveying system

An aerial survey method to determine ground contours establishes a reference plane to which all contour measurements are referred. The reference plane intersects a rotating beam optical radar unit which includes a receiving antenna. The antenna receives signal waves emanating from the aircraft to measure the relative height of the aircraft with respect to the reference plane. A survey track along the ground for the aircraft is determined and the position of the aircraft along the track is continuously measured. The aircraft is flown continuously along the track and repeated altitude measurements of the aircraft are made. The relative height of the aircraft with respect to the reference plane, the altitude of the aircraft above the ground and the position of the aircraft along the survey track are correlated to determine the ground contours.

The invention relates to an improved system for aerial surveying. 
In another respect, the invention relates to an aerial surveying system 
comprising components which are utilized to establish an imaginary 
horizontal reference plane, the reference plane being used to determine 
ground contours. 
In a more specific respect, the invention relates to an aerial surveying 
system which utilizes electromagnetic transmission and receiving devices 
to establish an imaginary horizontal reference plane from which ground 
contours are determined. 
In a further important respect, the invention relates to an aerial 
surveying system which utilizes optical radar to define the horizontal 
reference plane from which ground contours are determined. 
Aerial surveying techniques utilizing ground based equipment are well known 
in the art. U.S. Pat. No. 3,918,172 and Australian patent No. 1,399,441 
each disclose a laser-assisted assisted helicopter surveying system in 
which a laser beam is used to mark the hover position of a helicopter and 
telemetry is then used to locate both the helicopter and the laser source. 
Conventional surveying techniques are utilized in conjunction with the 
hovering position of the helicopter as a reference. 
The patents to Alpers U.S. Pat. No. 3,213,451 and to Lustig U.S. Pat. No. 
3,191,170 are basically radar systems, though Lustig makes use of a 
compensated barometric altimeter by which he attempts to maintain the 
aircraft at a constant reference altitude during the course of the 
aircraft's flight. 
Suzaki U.S. Pat. No. 3,817,620 combines triangulation and transmit times to 
determine the location of both an aircraft and undetermined earth 
locations with respect to known earth locations. 
In Pat. No. 3,743,418, Heflinger obtains a contour map comprised of light 
and dark contour lines. He illuminates the ground with pulses of light. He 
views the reflected light through a shutter synchronized to the light 
pulses. Reflected light is admitted or rejected at the shutter dependent 
upon the round-trip transit time of the light. The accuracy of this 
contour plot will depend upon the control of the pilot in maintaining 
altitude and, unless other equipment is added, the pilot will have no 
knowledge of the actual elevation of his contour lines. 
U.S. Pat. No. 3,918,172 to Moreau discloses an aerial survey method 
employing four different systems--a microwave system to measure distance 
from a known reference point, a strobetheodolite system to measure 
azimuth, a laser-mirror system to locate the aircraft above a known point 
on the ground and an infrared reflector or a plumb bob system to measure 
the height of the aircraft above the known point. Moreau does not disclose 
a method in which the aircraft is continuously moved along a survey track 
while making continuous instantaneous measurements of ground elevation. 
Rather, Moreau must first locate a point on the ground utilizing the 
microwave and strobe systems, then place ground-located equipment at the 
point of measurement, and then make the elevation measurement and then 
repeat the entire process of point selection and location, placement of 
ground-located equipment at the point selected and make the ground 
elevation measurement. 
Accordingly, it would be highly desirable to provide an imp-oved aerial 
surveying system in which an aircraft continuously moves along a survey 
track while making continuous instantaneous measurements of ground 
elevation. 
It is, therefore, an object of the present invention to provide an improved 
aerial surveying system. 
A further object of the invention is to provide ground-based equipment 
which will coordinate with airborne equipment to correlate aircraft 
altimeter readings and spacial locations to define a horizontal reference 
plane in space. 
Another object of the invention is to utilize ground-based optical radar to 
obtain instantaneous slant range and elevation angle data for an aircraft, 
the data being utilized to establish a horizontal reference plane to which 
altimeter measurements are referred to determine ground contours. 
Still another object of the invention is to provide an aerial surveying 
system which is economical to manufacture and yet highly accurate and 
simple to use.

Briefly, in accordance with my invention, I provide an improved aerial 
surveying method for determining ground contours. The method comprises the 
steps of collecting data by positioning a radar unit at a known point on 
the ground; defining an imaginary reference plane with respect to the 
radar unit; establishing a survey track for an aircraft along the ground 
and continuously moving the aircraft along the track, the aircraft 
including an altimeter for measuring the height of the aircraft above the 
ground; simultaneously continuously determining the position of the 
aircraft at selected times T.sub.1, T.sub.2, T.sub.3. . . T.sub.n as the 
aircraft continuously moves along the survey track, utilizing the radar 
unit to measure the range and elevation of the aircraft with respect to 
the radar unit at the selected instants in time T.sub.1, T.sub.2, T.sub.3. 
. . T.sub.n as the aircraft continuously moves along the track, and 
utilizing the altimeter to determine the height of the aircraft above the 
ground at the selected times T.sub.1, T.sub.2, T.sub.3. . . T.sub.n and, 
correlating the range, elevation, position and height of the aircraft 
above the ground at each of the selected instants in time T.sub.1, 
T.sub.2, T.sub.3. . . T.sub.n to determine the distance from the reference 
plane to the ground for the location of the aircraft at each of the 
instants in time; and developing ground contours from the reference plane 
to ground distances calculated by correlating the range, elevation, 
position and height of the aircraft above the ground at each of the 
selected instants in time T.sub.1, T.sub.2, T.sub.3. . . T.sub.n. 
The invention is particularly useful in those instances in which the ground 
contours are such that the established horizontal reference plane and 
certain ground features intersect. In such an instance, a line of sight 
along said horizontal reference plane would frequently be impossible 
between the aircraft and the equipment used to generate the horizontal 
reference plane. My improved method of aerial surveying utilizes a ground 
based optical radar in correlation with a transponder mounted on the 
aircraft to obtain the slant range and elevation angle of the aircraft. 
The slant range and elevation angle are used to establish the aircraft's 
position above or below the designated horizontal reference plane. 
Altimeter measurements are made and synchronized to transponder activation 
as the radar beam is intercepted by the transponder. The location of the 
aircraft is simultaneously tracked and recorded by a radio base line 
position determining system, by triangulation using rotating laser beams, 
or by the optical radar unit itself. When rotating laser beams are 
employed, the beams are modulated, both for identification and to prevent 
interference from other laser units in the vicinity. Correlation of the 
altimeter measurements and the aircraft's elevation with respect to the 
reference plane is then accomplished to determine ground contours with 
respect to said reference plane. 
Turning now to the drawings, which depict the presently preferred 
embodiment of the invention for the purpose of illustrating the practice 
thereof and not by way of limitation of the scope of the invention, FIG. 1 
illustrates the presently preferred embodiment of the invention including 
optical or line-of-sight radar 14 equipped with tracking antenna 16. An 
imaginary horizontal reference plane, indicated by line P in FIG. 3, is 
defined as the plane swept by the beam of antenna 16 if the beam were a 
narrow pencil beam and the antenna were rotated at a zero elevation angle. 
During normal operation of the system of FIG. 1 antenna 16 is normally 
rotated or maintained at an elevation angle greater than zero and has a 
fan-shaped beam which diverges as it travels away from radar unit 14. 
Radar 14 permits the determination of the longitude and latitude of 
helicopter 11 at any instant T.sub.1, T.sub.2, T.sub.3 . . . T.sub.n in 
time. Baseline triangulation or other prior art techniques may also be 
utilized to determine the position of aircraft 11 at a given instant in 
time. 
Aircraft 11 is equipped with transponder 15 which receives and is 
responsive to signals emitted by optical radar 14. Transponder 15, acting 
in cooperation with radar 14, permits the determination of the slant range 
or distance R from antenna 16 to aircraft 11 at a particular instant 
T.sub.1, T.sub.2, T.sub.3 . . . T.sub.n in time. Many existing radars have 
the capability to determine slant range R without the use of transponder 
15. The look angle BAC of antenna 16 is equivalent to the azimuth or 
elevation angle of aircraft 11. 
Aircraft 11 makes an altitude measurement BD at each instant in time 
T.sub.1, T.sub.2, T.sub.3 . . . T.sub.n transponder 15 is interrogated by 
radar 14 and slant range R and angle BAC are determined. Since Triangle 
BAC is a right triangle, knowing the hypotenuse R and angle BAC of the 
triangle enables the trigonometic calculation of side BC of the triangle 
to be made for each position of the helicopter. Subtracting the distance 
BC of aircraft 11 above imaginary reference plane P from altitude BD of 
aircraft 11 at a particular instant in time T.sub.n gives the height CD of 
reference plane P above the ground for the position of aircraft 11 at that 
instant in time T.sub.n. 
In operation of the system, a survey track is established for the section 
of land to be surveyed. While an aircraft flies along the survey track 
instantaneous elevation readings BD are continuously taken by an altimeter 
aboard the aircraft at selected times T.sub.1, T.sub.2, T.sub.3 . . . 
T.sub.n. At each instant in time T.sub.n radar unit 16 and transponder 15 
are utilized to determine the range R, elevation angle BAC and bearing of 
aircraft 11. As earlier described, this data is correlated to determine 
the distance CD from the ground to reference Plane P at the position of 
helicopter 11 at each instant in time T.sub.1, T.sub.2, T.sub.3 . . . 
T.sub.n. 
Baseline triangulation techniques, illustrated in FIG. 2, are well known in 
the prior art and may also be employed to provide the instantaneous 
location of the aircraft along the survey track. In baseline triangulation 
at least two angle-determining devices 13 are located a known distance 
apart along an established baseline L. With the baseline distance known 
and the line-of-sight angular dispositions alpha and beta determined, 
trigonometry is utilized to determine the location of aircraft 11 Modern 
electronic positioning systems provide the means to quickly, easily and 
inexpensively permit a pilot to determine exactly where to start on a 
survey track, to maintain his course, and to establish exactly where he 
left his designated survey track if he should have to interrupt his survey 
flight to refuel. 
The Mini-Ranger (.TM.) III position-determining system by Motorola 
Incorporated of Scottsdale, Ariz. is an electronic baseline triangulation 
positioning system of the type noted above. The lightweight, low power 
Mini-Ranger system uses a small receiver/transmitter installed in the 
aircraft. This receiver/transmitter works with two or more portable 
battery-operated reference stations located at known points near the 
survey site. The system measures distances to the unattended reference 
stations, automatically computes the location of the aircraft, and then 
outputs course error data to the pilot on an indicator which allows 
accurate steering control and correction. In operation, a pilot can 
quickly establish and readily follow a survey flight pattern suited to the 
area to be covered. He can also, when necessary, leave the track and later 
readily return to the exact point at which he departed from the track. 
What I have described is the technique and apparatus for establishing a 
horizontal reference plane with reference to which aerial surveying 
measurements may be made so as to determine ground contours in the survey 
area. It should be noted that with reciprocal devices, the decision to 
place a piece of equipment either on the aircraft or on the ground is a 
matter determined by the preferences of the designer. 
Although I have used the term "horizontal reference plane" in explaining 
the presently preferred embodiment and best mode of the invention, such 
usage should not be considered a limitation of the invention. Instances 
could arise in which it would be advisable that the imaginary reference 
plane be established at an angle with respect to a true horizontal plane. 
Similarly, the plane, since it is imaginary, could be positioned above or 
below radar unit 16. Final contour readings would then have to be 
corrected to account for the effects of tilting or otherwise repositioning 
the reference plane. 
The innovative concept, however, remains the same: a continuously moving 
aircraft is instantaneously located at times T.sub.1, T.sub.2, T.sub.3 . . 
. T.sub.n with respect to the established reference plane. The altitude of 
the aircraft above the ground at each of the instants in time T.sub.1, 
T.sub.2, T.sub.3 . . . T.sub.n is correlated with its position BC with 
respect to the reference plane to determine the distance from the ground 
to the reference plane for the position of the aircraft at each instant in 
time T.sub.1, T.sub.2, T.sub.3 . . . T.sub.n. When an on-board aircraft 
altimeter is utilized to determine the aircraft's altitude above the 
ground, an accurate laser altimeter is preferred. 
FIG. 3 further depicts the interrelationship of radar unit 14; antenna 16 
of unit 14; circuitry 21 for calculating range, bearing and elevation 
angle of aircraft 11; transponder 15 of aircraft 11; altimeter 22; and 
correlation apparatus 23.