Michael Breuer
GEOMETRIC CORRECTION OF AIRBORNE WHISKBROOM SCANNER IMAGERY
USING HYBRID AUXILIARY DATA
Michael BREUER, Jörg ALBERTZ
Technical University Berlin, Germany
Department Photogrammetry and Cartography
michael @fpk.tu-berlin.de
albertz@fpk.tu-berlin.de
Working Group III/1
KEY WORDS: Airborne Scanner, Geometry, Geometric Correction, Multispectral, Orthoimage, Rectification
ABSTRACT
This paper proposes the main aspects that must be considered for the development of a general concept for the
geometric correction of airborne whiskbroom scanner imagery making use of hybrid auxiliary data. This may be the
three-dimensional coordinates defining the sensor's position, the angles of the line-of-sight rays according to the axes of
the three-dimensional reference system, a digital elevation model, the availability of orthoimages that can be used as a
reference, interior orientation parameters and last but not least ground control information. All these information has to
be treated in its specific accuracy context. The aim is to respond to the needs of a user who wants to get the best
geometric correction results. The general concept for the geometric correction of whiskbroom scanner imagery regards
all auxiliary information that can theoretically be available. This development is based on practical cases where airborne
whiskbroom imagery has been captured. The concept tries to classify the reachable accuracy levels due to the given
auxiliary data in a particular case.
1 INTRODUCTION
There is an increasing demand on hyperspectral data for geological applications and environmental monitoring
(Mulders and Jordens, 1993). Most of the sensors capture the electromagnetic spectrum in bands from the visible light
up to the far infrared. During the past years the number of bands was increased due to the technical progress, reaching
up to 200 or more spectral channels (Kramer, 1996). It is essential that the data of each spectral band are captured to
each other maintaining stable radiometric properties. In comparison with the pushbroom concept the radiometric
calibration is easier with the whiskbroom concept. Besides the spectral sensitivity range of most pushbroom scanners is
limited to 0,3-1,2 jum. To cover a strip along a straight flight track a rotating mirror or prism moves the instantaneous
field of view (IFOV) cross to the flight track (Binnenkade, 1993). The capturing process can mathematically be
described as a time variant function that defines the orientation of the line-of-sight rays due to a three-dimensional
coordinate system at each moment of observation.
Hyperspectral sensors making use of the whiskbroom concept are operated both from spaceborne and airborne
platforms. The latter are flexibler in operation and often adjustable to special needs (Nieuwenhuis, 1993). The treatment
of the spaceborne imagery is relatively easy because of a stable flight path, attitude and smaller scales of the imagery. In
this case geometric correction can be achieved by means of two-dimensional polynomial functions. However, in
airborne applications the sensor movements are complexer due to irregular and high frequent aircraft motions. To
overcome the related problems airborne sensors are mounted on stabilized platforms. But even such platforms cannot
compensate all of the disturbances. Another effect results directly from the whiskbroom concept. Because the ray-of-
sight rotates across the flight direction around the sensor's projection center each pixel is projected onto some part of a
circle around the projection center (cylindrical projection). This effect is known as panoramic distortion. Additional
distortions result from the topographic relief of the terrain. Therefore geometric correction requires a Digital Elevation
Model (DEM). Thus, if hyperspectral data has to be transformed into a specific geographic reference system (which is
normally the case in practical use) this can only be attained in comprehensive postprocessing operation.
This geometric correction problem has been subject to research for more than thirty years (Albertz, 1998). The problem
is mathematically well described. The geometric correction of the image data can easily be achieved if the sensor
position and attitude can be measured with high precision by using an inertial navigation system (INS) in combination
with a global positioning system (GPS) receiver (Lithopoulos, 1999). However, reality is sometimes far away from this
ideal situation, and many problems remain in practical applications. Even if high precision sensor position and attitude
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 93
