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THE DPA-SENSOR SYSTEM FOR TOPOGRAPHIC AND THEMATIC MAPPING
Michael Hahn, Dirk Stallmann, Christian Státter
Institute of Photogrammetry
Stuttgart University
D-70049 Stuttgart / Germany
Franz Müller
Daimler-Benz Aerospace AG
Dynamics Systems
D-81663 Munich / Germany
ISPRS Commission ll, Working Group 1
KEY WORDS: Real-time mapping, digital data collection, DPA - Digital Photogrammetric Assembly, integrated sensor sys-
tem, topographic and thematic mapping
ABSTRACT
The Digital Photogrammetric Assembly (DPA) is an integrated airborne sensor system for real-time data collection. The
camera module consists of three panchromatic line arrays for stereo imaging and four line arrays for multispectral imag-
ing. For georeferencing the system is provided with an INS and can be synchronized with a GPS sensor. This paper is
concerned with the evaluation of the DPA with respect to its potential and efficiency for topographic and thematic mapping.
We focus on the photogrammetric tasks of georeferencing and image rectification and present results obtained by multi-
spectral image analysis. Some expectations on future investigations into 3D reconstruction using context supplied by the
multispectral data will be given in the outlook.
1. INTRODUCTION
For several years increasing interest of research institutions
and private companies in utilizing mobile mapping systems
for digital data collection can be observed. Highly attrac-
tive are those systems because they aim at fast collection
of digital data, for example, for input into Geographic Infor-
mation Systems (GIS). The systems are designed to be put
on landborne and airborne platforms. Common to all sys-
tems is that at least two types of sensors are integrated:
one for positioning and one for imaging. In the case of
landborne systems this is a selection of GPS (Global Posi-
tioning System), INS (Inertial Navigation System), odome-
ter, digital and analog video, radar, imaging laser and other
sensors. Mostly used imaging sensors of the airborne sys-
tems are CCD line and frame cameras, laser scanners and
radar which are combined with GPS and INS for continu-
ous absolute positioning and for determination of absolute
or relative attitudes of the platform.
With respect to economic aspects inquiry of users is on ver-
satility and cost effectiveness of those systems. Very high
are the requirements on the data collection technologies
for massive database production. At present the most im-
portant application fields for the landborne systems are in-
ventory of highways, railroads and monitoring of utilities.
The airborne systems focus on the cartographic market.
Here is a wide spectrum of all kind of interpretative applica-
tions. Photogrammetric 3D restitution techniques can used
for supporting topographic and thematic mapping of high
spatial resolution and accuracy. Depending of the multi-
spectral component of those sensors application fields like
vegetation mapping, environmental monitoring and geology
are more and more connected to photogrammetry.
The DPA is a line array (pushbroom) scanner system devel-
oped for airborne application. Today a considerable number
141
of pushbroom scanner systems exist. Examples are the
e Compact Airborne Spectrographic Imager (CASI) of
Itres Research Ltd., Calgary, Canada (Kramer, 1994)
e Multi-detector Electro-optical Imaging Sensor (MEIS)
build by MacDonald Dettwiler and Associates of Van-
couver, Canada, for the Canada Centre of Remote
Sensing (Gibson, 1994)
e Wide Angle Airborne Camera (WAAC) of the Ger-
man Aerospace Research Establishment DLR — In-
stitute of Space Sensor Technology, Berlin, Germany
(Eckardt, 1995)
e Three-Line Scanner (TLS) build by Core Co. Ltd.,
Tokyo, Japan (Murai et al., 1995)
In this scanners at least three or more CCD arrays are
mounted on the focal plane. In the CASI this is technically
solved by a frame transfer CCD. With each array a line im-
age of the scene below is recorded. The aircraft motion
provides the scanning in the forward direction.
CASI and MEIS are commercially available multispectral
instruments. CASI has 288 spectral detector lines of 512
pixel per line which cover the visible and near infrared spec-
trum. In spectral and spatial recording mode this gives
39 and 15 bands, respectively. In addition to the imaging
mode, the CASI can also operate as a multi-point spec-
trometer. The MEIS imager covers a similar spectral range
but with 8 spectral channels of 1024 output pixels each. By
adding external mirrors to two of the channels a forward-
looking and an aft-looking channel can be created which
provides single-pass stereo coverage.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
