X Y Z no. 
Control points. | 0.699 | 0.310 | 0.109 4 
RMS (m) 
Check points 2.748 | 4.791 9 
RMS (m) 
Image residuals 0.11 0.61 348 
(pixels) 
Avg. standard 2.43 2.18 8.67 47 
error (m) 
  
  
  
  
  
  
Table 9: Test (c )Results, 4 Control Points Used 
With Nadir Only Pushbroom Sensor 
  
  
  
  
  
  
  
  
  
œ (deg.) 0 (deg.) K (deg.) 
Flightline 1 2.1025 5.7231 3.3090 
Flightline 2 1.7699 5.4316 3.1400 
Flightline 3 2.0822 5.7064 2.6167 
  
Table 10: INS/Sensor Offset Angles for 
Test (c) 
This is due to a poorer geometry with the absence of fore and 
aft channels. However, the image residuals are very low 
indicating a good internal consistency. Finally, the 
distorted image contained in Figure 3 is geocorrected and 
shown in Figure 4. 
  
Figure 4: Geocorrected image 
Overall, the test results show that georeferencing by 
airborne sensors is possible for pushbroom scanners and 
CCD frame imagers of this accuracy class. The size of the 
residuals at the check points seems mainly due to the quality 
of the ground control (2-3 m), and the pixel size. 
Georeferencing errors seem to play a minor role at this level 
of accuracy. Additional tests using airborne 
photogrammetry and a precisely controlled field of ground 
targets are planned in the near future. They will provide a 
reliable estimate of current system accuracies. 
CONCLUSIONS 
Results presented in this paper indicate that georeferencing 
of airborne remote sensing data is possible by an onboard 
GPS/INS system using currently available off-the-shelf 
hardware. In this system, GPS provides accurate position 
information, while INS provides precise attitude and 
velocity information. If a high precision INS is used as a 
component of the integrated system, all current accuracy 
requirements, including those for high precision 
engineering and cadastral applications, can be met. If a 
system for the somewhat lower accuracy requirements in the 
resource sector are needed, a medium accuracy INS can be used 
and the total hardware costs can be reduced to one half. A 
georeferencing system based on GPS technology only, 
needs further testing before its suitability for these 
applications could be affirmed. 
Results of a first series of tests with the casi system indicate 
that the georeferencing requirements for this pushbroom 
scanner are met if four ground control points are used for 
system calibration. It appears that the residual errors on 
check points are dominated by errors in the control points 
(non-targetted) and the pixel size. A more stringent test to 
assess the capability of the current system using 
photogrammetric techniques is planned in the near future. 
ACKNOWLEDGEMENTS 
Work on this project was supported by an NSERC Strategic 
Grant to the first four authors. Itres Research Ltd is thanked 
for its interest in this project and its participation in system 
testing. Dr. Ming Wei and Mr. Gengsheng Zhang are 
acknowledged for contributing to the INS specifications. 
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