‚CA, 9-11 Nov. 1999 
  
  
  
  
irborne Interferometric 
| by baseline 'B', receive 
n the same ground pixel, 
ce ‘5’ between the two 
le ‘0,’ is obtainable from 
e aircraft height is known 
'om antenna to pixel is the 
> trigonometry to compute 
of these quantities. The 
ndirectly from the phase 
d wavefronts. Because the 
icasured between 0 and 27 
ite phase ambiguity which 
> aid of a coarse ground 
se unwrapping" technique 
Thus, the extraction of 
unwrapped” phase. 
'ECIFICATIONS AND 
[ANCE 
en operating the STAR-31 
nuary, 1997. The system 
ider contract to DARPA 
Projects) and was referred 
The IFSARE system was 
(1994), and is briefly 
nal point of view in the 
metric SAR, is carried in a 
ler ideal circumstances, of 
single operational day. 
mpensation are achieved 
reference platform closely 
st-processed GPS. One of 
s would be performed at 
d in this mode it would 
10 km ground swath. At 
-noise ratio is larger and 
s (Zebker and Villasenor, 
ative accuracy; however, 
> DEM created from the 
processed, and an ortho- 
ultaneously produced. A 
     
  
correlation image, which reflects the degree of complex 
correlation between the two antennas, is also created and 
is used for quality masking purposes as well as in 
research applications. Most of the operational 
acquisition is currently done at altitudes of 20,000 ft to 
25,000 ft. 
Processing is currently performed on a local network of 
Ultra SPARC II workstations which in the absence of 
unusual circumstances is able to keep up with the 
acquisition. Work currently under-way will result in a 
new processor which will enable field processing and 
quasi-real time throughput performance. 
Numerous tests have been performed of DEM accuracy 
under various terrain and operating conditions both 
internally and by independent external organizations. 
The external tests are summarized on the website 
http://www.intermap.ca. 
4. COMPARATIVE SYSTEM SPECIFICATIONS 
OF SELECTED PARAMETERS 
In Table 1, we show the comparative specifications 
(selected) of the three laser systems from which the data 
sets described in Section 6 were acquired. The purpose 
of this table is to illustrate the major differences among 
the laser systems with respect to the STAR-3i radar in a 
standard operational mode. It should be noted that the 
parameters associated with the laser systems are those 
International Archives of Photogrammetry and Remote Sensing, Vol. 32, Part 3W14, La Jolla, CA, 9-11 Nov. 1999 
believed to be appropriate to the particular data 
acquisitions described in this paper. A wider choice of 
operating parameters is of course utilized under different 
circumstances by the operators, although these may be 
typical. The data for the lasers was obtained either from 
their literature or personal communication. The laser 
accuracies are those claimed by the operators. The radar 
accuracies relate to the results of the external tests 
referenced in Section 3. It should be noted that the radar 
accuracies can be further improved by the simple 
operational expedient of flying lower; however this 
would be at the expense of swath width and would 
impact cost. 
The major differences noted between laser and radar 
relate ultimately to the vertical accuracies and to the 
acquisition rates. The latter translates into price 
performance as noted in Section 5. 
5. COMPARATIVE DEM PRICES 
From the foregoing discussions and comparative 
performance table, it is clear that laser-derived DEMs 
offer vertical accuracy performance advantages with 
respect to the STAR-3i radar system as it is currently 
operated. On the other hand, the acquisition rate 
advantage enjoyed by STAR-3i translates into a price 
advantage which is exemplified in Figure 2. 
  
Typical Operating Parameters 
STAR-3i vs. Laser Systems 
  
  
  
P ; STAR-3i Earthdata EagleScan Topscan 
arameter Units 
Radar Laser Laser Laser 
Operational Altitude (this project) feet 20,000 5,000 6,000 1,000 (est) 
Operational Speed km/hr 750 -200 ~200 (est) ~200 (est) 
PRF pulses/sec 1,200 15,000 4,000 2,000 
Incidence Angles (this project) degrees 30 to 55 -20 to +20 -9 to +9 -20 to +20 
Swath Width (ground plane) meters ~8,000 1,100 600 720 (max) 
DEM Sample Spacing meters 25 5m 4m 3-5m 4-6m 
DEM Vertical Accuracy 
Absolute (RMSE) m or cm 71.5 m(5) ^10 cm ~15 cm ~15 cm 
Relative (1 9) m or cm <1.0m 2 710 cm ? 
DEM Horizontal Accuracy meters <25m 0.5m -^1m «Tm 
Collection Rates 
Maximum (km"/hr) km"/hr 6,000 220 130 145 
Typical (km?/hr) km^/hr 1,000 ? ? ? 
Ortho-Rectified Image Yes No Yes No 
Pixel Size meters 2-5 - 0.30 - 
Sensor Source ERIM Azimuth Custom Optech 
  
  
  
  
  
  
Notes: 
1 Laser operating parameters may differ for other projects. 
  
2 Laser accuracies as published or quoted by operators and presumably under benign terrain and operating conditions. 
3 STAR-3i accuracies as obtained in various published test results and references bald earth, moderate terrain conditions. 
4 STAR-3i results assume GPS base station within 200km. Laser results require base station within 20 km. 
5 STAR-3i absolute accuracies assume absence of GCPs. With GCPs, absolute accuracy similar to relative accuracy (sub-meter). 
6 Typical STAR-3i acquisition rates account for line lengths, turns, overlap, etc. 
  
  
Table 1: Comparison of typical operating parameters and associated performance specifications for STAR-3i and 
three commercial laser systems