Andreas Keim
computer, a clock generator, and a disk array unit with a capacity of 256 GB for data recording. The movement and
position of the aircraft is measured and stored by a flight control system containing a DGPS system and an Inertial
Navigation System (INS). Additional information about the AeS-1 System is reported by Schwäbisch and Moreira
(1999).
Operating Frequency 9.35 — 9.75 GHz
Wavelength 3.12 — 3.25 cm
Polarization HH
PRF 1.5 kHZ — 16 kHz
Peak Power 1.9 KW
Ground Resolution upto0.5 mx0.5 m
Radiometric Resolution up to 1.8 db
Swath Width 1 — 15 km
Flight Velocity 50 — 200 m/s
Typical Flight Altitude 500 — 9000 m
InSAR Baseline 0.5 or 1.8 m
Dimensions W: 1.2 m, H: 1.0 m, D: 0.6 m
Weight 210 kg including antennas
Power 28 V, 60 A maximum
Table 1: System parameters of AeS-1 flight segment
Figure 1: Gulfstream Commander 1000 with AeS-1
X-band antenna boom construction
3 DATA PROCESSING AND VALIDATION
The processing of the digitally stored “latent” SAR raw data to visible images can be divided into three processing
steps. First the raw data stored on hard disks are transcribed and backuped on Digital Linear Tapes (DLTs). In SAR
processing the raw data are read from the DLT, decoded and correlated by using a Range/Doppler algorithm. The
positional acurracy is improved by including the motion compensation data, generated itselves of the DGPS and INS
data. Single-look images in complex format are the SAR processor output. Multi-look processing eliminates the harmful
influence of the Speckle on image radiometry at the cost of lowered ground resolution. Hence, a trade-off between
speckled appearance and resolution must be found. In figure 2 for example a 37 look image with ground resolution of
2.5 meters was generated from the initial 0.2 meters single look image. In a further step an interferometric processor
coregistrates the images of the two antennas for producing an interferogram and a DEM in slant-range geometry. Alsoa
magnitude of the complex correlation coefficient and the SAR magnitude is carried out. In a last step the geometry of
the ready processed data must be changed from slant-range to a georectified cartographic reference system. This is done
using marked and measured reference points, so called Corner Reflectors (CR) (see white spot in the center of figure 2).
To obtain images of a predefined area, e.g. of a map sheet, the single tracks must be mosaicked and trimmed. To
suppress artifacts in the data, e.g. caused by Radar shadows, data sets flown in opposite directions also can be
combined.
Before deriving information from the SAR data, the positional and height accuracy must be verified. This was made
with a data set from a well-known testsite near Solothurn, Switzerland, located on the border of the Swiss Jura
mountains and the tertiary basin. The site contains different kinds of surface structures e.g. plains, hills, and open areas,
as well as forests, rivers and build-up areas in a small space.
The positional accuracy was checked by superimposing the SAR amplitude image with a large scaling topographic map
(1: 10,000) (Fig. 2). The deviations between the map and the image are less than three meters. For validating the height
acurracy of the INSAR-DEM it was compared with 24 trigonometric fixed points of the Federal Office of Topography
Wabern, Switzerland. The average difference was 13.7 cm with standard deviation of 17.3 cm (Meier 1999). This
accuracies allow the production of topographic maps in scales ranging from 1 : 10,000 to 1 : 50,000 and smaller. The
highest resolution is occasionally necessary for map derivation. For small scaled maps a lower resolution is sufficient,
which leads to a faster processing and a cheaper production.
174 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.
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