2. Improvement of aircraft control
On a worldwide scale, aerial photogrammetry is predominant
ly carried out in small aircraft with visual navigation to
follow the given photographic flight routes, while 1arger
airplanes with instrumental navigation are mainly used for
electronic surveying systems, such as scanners and side-
looking radar. This is due partly to the recording prin
ciple and partly to the ratio between the investment re
quired for the aircraft and that for its instrumentation.
It is well known that the high prime costs of an automatic
precision navigation system pay off rapidly, thanks to its
outstandig qualitative and economic advantages. This can be
substantiated by the fact that exact route navigation and
stability of the flying attitude reduce side lap and thus
the number of flight strips. In addition, expensive repeat
flights can be minimized.
An advanced navigation system has to serve two fundamental
tasks in airborne remote sensing, viz.
- ensure highly precise and reliable fligth at reasonable
costs, and
- supply the data of exterior orientation (station coordi
nates, flying attitude angles) for the on-line control
of imaging system and their synchronous recording by
that system on the remote sensing data carriers.
According to INTERFLUG investigations, the first problem
requires the following accuracies of exterior orientation
for a block of exposures, concerning the path of fligth
along a route relative to its middle line or concerning the
mean attitude angles and the routes of a block of
exposures relative to each other:
- Relative on-line position accuracy (depending on flying
height h :
Planimetry Ax , Ay = n • 15 m; h < 2 km : n = 1
Elevation Az = n * 20 m; h = 2.. 4km : n = 2
etc .
- Dynamic on-line angle variation at any flying height:
angular velocity about each of the three axes (pitch,
roll , yaw) < 0.2°/s
- Relative on-line accuracy of attitude at any flying
height: (pitch angle, roll angle, yaw angle) < 0,5°
for photographic and matrix camera, and < 0,2° for line
scanners and side—looking radar
The position accuracy can be materialized by the aircraft
alone, while fine stabilization down to the residual values
mentioned above is possible, after prestabilization by a
flight regulation system, by means of a platform /4/ with
dynamic attitude stabilization for the respective sensing
system.
A navigation system meeting such demands might be a
satellite-aided global positioning and navigation system,
such as GLONASS (USSR) or GPS-NAVSTAR (USA). This is
expected to essentially improve the quality and economy of
remote sensing and particularly its photogrammetric branch.
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