A PRECISE POSITIONING/ATTITUDE SYSTEM IN SUPPORT OF AIRBORNE REMOTE SENSING
K.P. Schwarz, M.A. Chapman, M.E. Cannon, P. Gong, D. Cosandier
Department of Geomatics Engineering, The University of Calgary
2500 University Drive NW, Calgary, AB, Canada T2N 1N4
iphie Tel. (403) 220- 7377 Fax: (403) 284-1980
ISPRS, Commission II, WGII/1 - Session 2
KEY WORDS: Precise position and attitude system, geo-referencing, INS/GPS integration, pushbroom scanner, CCD frame
imager, SAR, calibration of airborne sensors
it en
part ABSTRACT
e VOI
on ce Research in airborne remote sensing at The University of Calgary has as one of its goals the development of a precise
positioning and attitude system that can be used with a variety of airborne sensors and will ultimately eliminate the need for
ground control for georeferencing. In this paper, accuracy requirements for such a system are discussed, different sensor
: configurations are described, and results of the U of C prototype development are analyzed. Applications can be subdivided
ative into three major groups: those where precise positioning is the major requirement, such as photogrammetric applications;
ne de those where both position and attitude are required with high accuracy, such as pushbroom imaging applications; and those
niner where accurate velocity estimation for motion compensation is also needed, as in radargrammetric applications. Sensor
ition configurations for different applications will be discussed and first results of airborne tests will be briefly reviewed.
GPS
nnant 1. INTRODUCTION The current system covers a large range of possible
e de applications and will have specific advantages in
ne de Airborne remote sensing considerably extends the applications of digital remote sensors, such as pushbroom
r en capabilities of satellite remote sensing in terms of scanners and CCD frame images.
resolution and operational planning. Where satellite remote
nent. ; : : :
dis sensing at best achieves accuracies of 10 -15 m, airborne
LS1on remote sensing has the potential of achieving accuracies at 2. ACCURACY REQUIREMENTS FOR
n de the decimeter level in position. Whereas the usefulness of DIFFERENT APPLICATION AREAS
-ypes satellite remote sensing is often restricted by the images
ilyse available for a certain area and the extent of the intervening ^ Airborne remote sensing in its classical form of airborne
juipé cloud coverage, there are no such limitations in airborne photogrammetry has been widely used for cartographic
remote sensing. It is, therefore, possible to optimize the mapping at all scales and currently is the only system used
required result by adapting the operational conditions to the for high accuracy applications. Its major drawback is that
task at hand. the data collection process is film-based and not digital.
: More recently, other airborne remote sensing devices, such
The inherent accuracy and flexibility of airborne remote as pushbroom scanners, have been extensively used in those
sensing is currently not used because the standard method of agricultural and forestry applications where accuracy
georeferencing airborne images by available ground control requirements are not that stringent. With the ongoing
limits not only the accuracy, but also often puts operational ^ improvement of scanning systems and linear array systems,
constraints on a specific flight mission. The objective of a fully digital system with onboard exterior orientation,
the research currently conducted at The University of Calgary suitable for a wide range of applications, seems to be within
is o remove these constraints and to replace the indirect reach. To define the design parameters of such a system, user
method of georeferencing by ground control by a direct requirements will first be discussed.
method of georeferencing from the aircraft. In other words,
the exterior orientation of each image will be determined in
real-time by onboard sensors and not in post mission by
interpolation between available ground control. The fact
that the method is in principle independent of available
ground control has obvious economic advantages,
especially in areas with poor or sparse control. The fact that
position and attitude are available in real time is of no
immediate advantage in current applications but may be of
importance in the future.
In high precision photogrammetric applications such as
highway planning, large engineering projects, and cadastral
applications, positional accuracies of 10 cm or less are
required. In such applications, non-standard photographic
overlaps of 80 % longitudinal and 60 % lateral are often
employed to increase the image per object point ratio.
Typical accuracy requirements at photo scales of 1:3 000 to
1:6 000 are 5-10 cm in position and 15-30 arcseconds in
attitude. External attitude is not needed when a
photogrammetric block adjustment approach is applied. In
those cases, the geometric strength of interlocking bundles
can be used to eliminate the attitude requirement.
In this paper, requirements for an airborne system of this
type are presented in four points. First, the accuracies
required in different application areas are discussed. Second,
the performance of currently available remote sensing
devices are reviewed. Third, the georeferencing problem is
briefly presented, i.e. the transformation of the airborne
measurements to ground level. Fourth, the implementation
of the georeferencing problem by currently available
position and attitude sensors is analysed. Finally, some
possible sensor configurations are studied and first results of
à prototype system, developed at the U of C, are presented.
Map accuracy is a function of map scale, thickness of printed
lines, and positional accuracy of lines and points on the map
sheet. The thinnest line that 1s legible on maps is about
0.05 mm. This high accuracy is impossible to achieve in
the map compilation process which adds to the error budget
through generalization, project transformation, information
transfer, fine drawing, printing, etc. Typical values for the
191
