The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008 
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DTM 
5m 
(nominal) 
Type I: 0.7m 
Type II: 1.0m 
WGS84/ 
EGM96/ 
Geographic 
ORI 
1.25m or 
2.5 m 
(nominal) 
2.0m 
WGS84/ 
Geographic 
Baseline 
length (m) 
0.93 
0.96 
0.93 
0.94 
Look 
direction 
left or 
right 
left or 
right 
left or 
right 
left or 
right 
Best image 
solution (m) 
1.25 
1.25/0.6 
1.25/0/6 
1.25/0.6 
Table 1: System Parameters of Intermap’s STAR Systems (* 
Terrain dependent) 
2.3 Airborne IFSAR Mapping Products 
IFSAR mapping is essentially a process of producing 3-D map 
products by processing raw radar data collected by airborne 
IFSAR systems. Ground thematic information is derived from 
the synthetic aperture radar (SAR) images. Height information 
is obtained by using the phase difference between two coherent 
SAR images simultaneously obtained by two antennas 
separated by an across-track baseline in a single-pass mode. The 
major steps of the operation and production workflow of a 
typical airborne IFSAR mission are summarized as follows: 
• Mission planning and acquisition, 
• Field QC and Navigation process, 
• SAR image formation, 
• Interferometric process and geo-coding, 
• Editing and post-process. 
Figure 2 illustrates the mapping process of the STAR 
technology, see Li et al, 2004 and Bryan, 2007 for the details of 
the STAR system operation and production process. 
The direct products of Intermap’s IFSAR systems are the 
Orthorectified Radar Image (ORI) and the Digital Surface 
Model (DSM) that represents the surface visible to the radar 
sensor. With the Intermap’s proprietary bare-earth processing 
methodology a bare-earth Digital Terrain Model (DTM) is 
derived for many terrain types in order to deliver the 
topographic surface of the Earth. ORI, DSM and DTM are three 
core products of Intermap’s airborne IFSAR mapping system. 
Table lists the major parameters of three core products. 
STAR 
Product 
Post 
Spacing 
RMSE 
Accuracy 
Datum 
Coordinate 
Systems 
DSM 
5m 
(nominal) 
Type I: 0.5m 
Type II: 1.0m 
Type III: 3.0m 
WGS84/ 
EGM96/ 
Geographic 
Table 2: Specifications of Intermap's Core Products 
(* - Other datum, projections and coordinate systems are also 
supported depending on the area and requirements.) 
2.4 Image Quality and DEM Accuracy 
2.4.1 Image Quality: In general the image quality of SAR 
image is measured by following three parameters of the system 
impulse response: 
• Image resolution (mainlobe -3dB width) 
• Peak side-lobe ratio (PSLR) 
• Integrated side-lobe ratio (ISLR) 
Table 3 lists the image quality parameters of STAR systems 
with different bandwidth. As indicated in Table 3 Intermap’s 
STAR systems can provide the image with spatial range 
resolution of 1.25 and 0.65 m for the pulse bandwidth of 135 
and 270 MHz. 
STAR 
system 
Image 
resolution (m) 
PSLR (dB) 
ISLR (dB) 
135 MHz 
1.26-1.3 
-18.3-22.3 
-35.7-40.2 
270 MHz 
0.65-0.68 
-22.2-24.2 
-36.7-38.8 
Table 3: Image quality of STAR system 
Figure 3 shows the comparison of images with different 
resolution (pulse bandwidth) for the same area. As 
demonstrated in Figure 3 the edge definition of the roads and 
the edge of buildings are noticeably improved by the high 
resolution images of STAR systems with 135 MHz band width. 
2.4.2 DEM Accuracy: Applying the error propagation to 
equations (1) and (2) for geocoding using interferometric 
process results the height error, in terms of standard deviation, 
can be expressed by 
°h = 
Oh = 
sin{(p - a)cos ß ■ a p 
(3) 
p cos tp cos(tp -a) cos ß 
„ . o b 
(4) 
a sirup 
 pcos(tp- a)cosß 
(5) 
4 n B sirup 
p• cos(rp-a)cosß • <7 a 
(6) 
p ■ sin(ç? - a) sin ß ■ <7ß 
(7) 
In equation (3) to (7) the time delay and the bias of the baseline 
length can be precisely estimated by the calibration. Since the 
pitch error is not sensitive to the height error, the 
interferometric phase error and the roll error of the SAR 
antenna platform are the dominating error sources of the D T E 
heights. 
Figure 4 shows the histogram of typical height errors comparea 
to the reference DEM with the statistics of DEM errors: mean = 
0.012 m and standard deviation = ±0774 m. Figure 5 shows the 
height errors compared to external ground control points (GCP)