The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
where the GCP coordinates are determined by GPS. Both 
DEMs are generated by the airborne data at flight altitude of 
30,000 ft. They demonstrate the achievable accuracy of DEM 
using STAR systems. 
(a) Image of low resolution from original Star-3 i system 
(b). High resolution image from Star3i system (135 MHz 
bandwidth) 
Figure 3: Comparison of different image resolution 
x iq 7 Height Error Histogram (flight altitude 30,000 ft) 
4. , 
Height Error (m) 
Figure 4: Histogram of height error of Star3i system 
3. AIRBORNE GRAVITY MAPPING SYSTEM 
3.1 System Overview 
Utilizing the GPS/INS components of the STAR system, 
Intermap Technologies joint with the University of Calgary has 
developed a new airborne gravity system called Airborne 
Inertial Gravity System (AIGS). The STAR AIGS consists of 
the Honeywell H-770 strapdown system with the output rate of 
1200 Hz and differential GPS. The major functions of the AIGS 
process are described in Figure 6. Using the airborne gravimetry 
system the gravity measurements can be quickly and 
homogenously collected over large areas. This is a significant 
improvement over conventional gravity measurement 
techniques which are time consuming, laborious, and 
logistically difficult. 
C3CP Height Error vs- Depression Angle 
-1 1 
•1,5 
Ò 4 05 0.6 0 7 o'a 09 1 
Oppression Angl« (raclions) 
Figure 5: Height errors at GCP’s 
Figure 6: Diagram of Airborne Inertial Gravity System 
The gravity anomaly determined by the airborne inertial gravity 
system contains long-term errors due to INS measurement 
biases and drifts. To eliminate the long-term errors of airborne 
gravity anomaly estimates, a crossover adjustment technique is 
applied using the least-squares adjustment for the crossover 
points. 
One major function of the airborne gravimetry is to determine 
the geoid surface. Intermap has developed the gravity and geoid 
process software STARGRAV for precise geoid determination 
using the airborne gravity measurements combined with a 
global gravity model and terrain data. For more general 
applications, STARGRAV can process either the gravity 
anomaly or the gravity disturbance at the acquisition height or 
on the ground. The airborne gravity-derived geoid can be used 
as a precise vertical reference for orthometric heights. 
Figure 7 shows the process diagram of geoid determination 
using airborne gravity measurements by STARGRAV. For 
geoid determination, the gravity anomalies along the flight 
trajectory are interpolated at grid points of the flight area and 
then continued downward to the geoid surface by using the