DMC PRACTICAL EXPERIENCE AND ACCURACY ASSESSMENT
M. Madani', C. Dörstel”, C. Heipke*, K. Jacobsen?
'Z/1 Imaging Corporation, Alabama, USA
27/1 Imaging GmbH, Aalen, Germany
? Hanover University
E-mail: msmadani@ziimaging.com, c.dorstel@ziimaging.de, heipke@ipi.uni-hannover.de, jacobsen@ipi.uni-hannover.de
Commission II, ICWG 2-4
KEY WORDS: Digital Aerial Camera, Automatic, Triangulation, Bundle, Processing Workflow, Empirical Accuracy Estimates
ABSTRACT:
Accuracy of digital image data is expected to be better or at least the same as for analogue images. Since Z/I introduced its Digital
Mapping Camera (DMC) into the market in early 2003, multiple projects have successfully been flown by different customers. The
processing steps from data post processing to the final product generation are described. Investigations revealed a geometric
accuracy which was at least similar and sometimes better than that usually achieved with analogue cameras under similar conditions.
This result has been achieved despite the smaller base-to-height ratio of the DMC and is explained by the higher image coordinate
accuracy resulting from a better radiometric quality of the digital image, and in particular by a better system geometry (flatness of
the image plane, no film shrinkage, etc.) Taken user comments into account, the photogrammetric workflow using DMC imagery is
discussed, and some experience with generating DTM and creating orthophotos is reported.
1. INTRODUCTION
Aerial cameras have been successfully used around the world
for many decades. During the past two decades, the mapping
sciences have progressively moved toward digital mapping,
making use of multidisciplinary developments in the field of
geomatics. The new Digital Mapping Camera (DMC),
manufactured by Z/I Imaging Corporation, represents one of the
latest developmental steps in this long history. The DMC adds
digital capabilities to existing image capture technology.
Because today's airborne camera systems are complex, the new
DMC is more than simply the exchange of film for silicon. For
this reason, several issues, such as data transfer rates, image
postprocessing, colour fusion, calibration, image archiving, and
image data management, have to be addressed.
The DMC is based on Charge Coupled Device (CCD) frame
(matrix) sensor technology, which provides a very high interior
geometric stability. The camera is designed to perform under
various light conditions within a wide range of exposure times.
Features such as electronic Forward Motion Compensation
(FMC) and 12-bit-per-pixel radiometric resolution for each of
the panchromatic and colour channel camera sensors provide
the capabilities for operating even under less than favourable
flight conditions. The DMC can produce small-scale or large-
scale images with ground resolutions of fewer than five
centimetres. The results are images with greatly improved
radiometric resolution and increased accuracy of
photogrammetric measurements (Dórstel 2003).
A further benefit of using the integrated DMC technology
(hardware, firmware, and processing software) as an aerial
photogrammetric solution is the completely digital workflow,
which eliminates the process of scanning and film processing.
This saves a considerable amount of time. In addition,
postprocessing of the digital imagery is very fast; a typical
flight project can be processed in a few hours.
The high radiometric sensitivity of the CCD array, together
with the pixel size of 12um and the forward motion
compensation by electronic time-delayed integration (TDI),
increases the amount of time allowed for running flight
missions.
The DMC system is composed of multiple components and is
divided into two parts: airborne and ground-based. The DMC
396
system components are illustrated in Figure 1. ImageStation
Mission Planning (ISMP) is the part of the DMC system that
provides tools to quickly create and optimize a flight plan to be
navigated with T-Nav, ASMS, or supported third-party photo
flight control systems. ISMP can also use the mission planning
data and the flight data to create or update a Z/l
photogrammetric data management environment, generate
reports, and create photo indexes in a so-called ISPM project.
The Airborne Sensor Management System (ASMS) consists of
hardware (the ASMS Real-Time Controller (RTC)) and the
software used to interact with the ASMS RTC. ASMS is the
part of the DMC system that provides the navigation, camera
triggering, and exposure position recording of the photo flights
planned in ISMP.
As mentioned before, the DMC uses frame-based CCDs. This
approach offers the best geometric accuracy for
photogrammetric applications as determined by the two
dimensional matrix of the CCD pixels structured on the silicon
wafer. Besides this very stable image geometry, the DMC
offers an outstanding ground resolution, even for large-scale
imagery, because of the embedded Forward Motion
Compensation (FMC). The electronics of the CCD matrix
sensors, which are used in the DMC camera heads, can be
operated in TDI mode. This allows a fully electronic FMC of
the digital image that compensates for image blur (Hinz, 1999).
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