Sandau R. Digital Airborne Camera: Introduction and Technology
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7.1 The ADS40 System 295
Fig. 7.1-18 Gyro-stabilized Camera mount PAV30
In 2009 the PAV80 has been designed for the ADS80 with the aim of
eliminating some operational restrictions enforced on the ADS40 user by the
PAV30.
The most important improvement of the PAV80 is its adaptability to the weight
of the payload. Thus the mass compensator is unnecessary. This reduces the weight
on board the aircraft by a further 39 kg.
7.1.7 The Radiometric und Geometric Calibration
Radiometric information plays a growing role in imaging data. Airborne dig-
ital sensors are now capable of providing high quality radiance information.
Therefore laboratory calibration facilities with integrating spheres have been
installed in various regions of the world to ensure the radiometric accuracy of
the ADS40.
From the data processing software GPro 3.0 onwards, the radiometric calibration
factors are used to calculate standardized images for photogrammetry. For remote
sensing applications radiance calibrated images can easily be calculated, which are
the basis for further data products like ground reflectance images
The geometric calibration process, which was used for the SH40, used a com-
bined approach of self-calibration in bundle adjustment and a polynomial fit on
the residuals of each sensor line. The polynomial fit was necessary, because the
296 7 Examples of Large-Scale Digital Airborne Cameras
“Brown” parameter set could not model the relative shift of more than three CCD
lines (Brown, 1976). The situation changed with the SH51/52. The parameter set
has now to cover nothing more than the basic opto-mechanical properties of the
components. These are the principal distance, the radial-symmetric distortion and
the position and the orientation of the individual CCD lines in the focal plane.
A subset of these parameters should also be suitable for self-calibration on-the-job
to compensate for effects like abnormal atmospheric refraction.
Estimation of ADS calibration parameters in ORIMA is always done rel-
ative to an existing input “calibration”. ORIMA uses the ADS sensor model
library to convert tie and control point measurements into “calibrated” focal plane
coordinates. On the output side, ORIMA applies the effects of the estimated
calibration parameters to the input calibration and writes out a new calibration
data set.
Tie points for such a self-calibration are extracted from 88 scenes of a flight of a
two-height double-cross ADS calibration block as shown in Fig. 7.1-19.
This method offers the great advantage that it is not a factory laboratory
calibration and can be repeated by users anywhere in the world based on
cross flights made in the users own environment and according to the national
requirements.
Fig. 7.1-19 Example of cross-flight self-calibration result with the ADS40
7.1 The ADS40 System 297
7.1.8 Data Processing
The digital sensor revolution happening right now will result in an information
explosion. The processing and management of data acquired by digital sensors
requires an enormous computational effort. The Aerial Digital Sensor ADS40 from
Leica Geosystems AG generates large amounts of data of over 100 GB of raw data
per hour if all the CCD lines are active. The ADS40 is a high performance digital
sensor, capable of delivering photogrammetric accuracy with multi-spectral remote
sensing quality imagery. The ADS40 is a three-line-scanner that captures imagery
looking forwards, nadir and backwards from the aircraft. Every portion of the
ground surface is imaged multiple times. With its simultaneous capture of data from
three panchromatic and up to two times four multi-spectral bands, the ADS40/SH52
provides unparalleled qualities of image and position data. (Fig. 7.1-20) Digital
workflow from flight planning through acquisition to product generation is one of
the major advantages of the sensor.
Fig. 7.1-20 Data collection scheme of 12 bands with 100% forward overlap in the SH52
and SH82
This data passes through different levels of processing before products are gen-
erated; the first step in the workflow is downloading the data and adding the
geo-positioning information using data supplied by the Inertial Position and Attitude
System IPAS10/20 and the IPAS Pro software. The geo-referenced images are then
298 7 Examples of Large-Scale Digital Airborne Cameras
rectified to a plane to create stereo-viewable and geometrically corrected Level 1
images. The Level 1 images are also useful for the next process which is automatic
point matching. Based on the accuracy requirements, the images are then trian-
gulated using ORIMA, Leica’s triangulation package. Finally, ortho-photo images
using existing DTM or DTM generated from the triangulated images are created.
Due to the large amount of data being processed this workflow could take an
extended time. GPro and now XPro the 3rd generation are the ground process-
ing software packages for the ADS40 and ADS80 that control the workflow as
described. They provide full functionality to download, generate geo-referenced and
ortho-rectified images from the recorded imagery and positioning data. They consist
of highly optimized and threaded applications that are designed to handle large data
sets (Fig. 7.1-21). In addition they also allow the user to perform various automated
processes and data management tasks.
The 3rd generation data processing software XPro released in 2008.
Software solutions such as Leica XPro, which are specifically designed
to post-process line sensor data, facilitate the generation of highly accu-
rate image strips even in areas where no or little ground control data is
available.
For a long time there was a perception in the market that the processing of push-
broom data would require special and extensive knowledge and would differ hugely
Fig. 7.1-21 Overview of the ADS40 and ADS80 Data Processing Workflow
7.1 The ADS40 System 299
from the traditional frame based processing and analysis. Over the past years more
and more software solutions came to the market, which were especially designed to
process line sensor data. With the correct software, simple sensor design, the use of
IMU’s and innovative algorithms users today can process even the largest data sets
much faster than what is possible with large format digital frame cameras. Leica
XPro, for example, uses the power of the graphics card when visualizing large data
sets. Simplified triangulation workflows in black box design in a distributed process-
ing environment reduce the processing time significantly whilst maintaining data
quality, and support the generation of orthophotos or stereo imagery “at the speed
of flight”.
The combination of highest image quality, multipurpose applications, high-
est productivity and simply delivering more information show clearly that the
pushbroom principle is not only the preferred design in satellite based remote
sensing, but more and more establishes itself as a standard in airborne digital
imaging.
7.1.9 Images Acquired with the ADS40
Fig. 7.1-22 Vaihingen, Germany, Orthophoto 1:500, altitude 0.5 km, GSD 5 cm
300 7 Examples of Large-Scale Digital Airborne Cameras
Fig. 7.1-23 Balgach, Switzerland, Orthophoto for forest inventory 1:1500, altitude 1.5 km, GSD
15 cm
Fig. 7.1-24 Walensee, Switzerland, Orthophoto for alpine area mapping 1:5000, altitude
2.0-/3.6 km, GSD 20/36 cm
7.1 The ADS40 System 301
Fig. 7.1-25 Waldkirch, Switzerland, Orthophoto 1:2000, altitude 2.0 km, GSD 20 cm
Fig. 7.1-26 Waldkirch, Switzerland, Vector map 1:2000, altitude 2.0 km, GSD 20 cm
302 7 Examples of Large-Scale Digital Airborne Cameras
Fig. 7.1-27 Waldkirch, Switzerland, Orthophoto map 1:2000, altitude 2.0 km, GSD 20 cm
Fig. 7.1-28 Waldkirch, Switzerland, 3D perspective, altitude 2.0 km, GSD 20 cm
7.1 The ADS40 System 303
Fig. 7.1-29 Aalen, Germany, Image strip 1:35,000 for sensor calibration, altitude 1.2 km, GSD
12 cm
Fig. 7.1-30 Aalen, Germany, Overview map 1:2500 (zoom of 7.1-29), altitude 1.2 km, GSD 12 cm
304 7 Examples of Large-Scale Digital Airborne Cameras
Fig. 7.1-31 Aalen, Germany, Orthophoto 1:1000 (zoom of 7.1-29), altitude 1.2 km, GSD 12 cm
Fig. 7.1-32 Aalen, Germany, Orthophoto of the stadium 1:1000, altitude 1.2 km, GSD 12 cm