Dean Merchant 
range at Casa Grande, Arizona, provided sufficient information for conducting a self-calibration adjustment. The 
results of this in situ calibration made it possible to compare exposure station coordinates based on a standard 
laboratory to an in situ calibration. A series of single photo resections were computed by using both calibration results. 
The differences in exposure station coordinates were large, particularly in elevation, signifying again the contributions 
made by the environment to the aerial photogrammetric measurement process. Differences of 6 meters in resected 
elevation for the same photograph was not unusual. 
With the advent of the Global Positioning System (GPS) to provide exposure station position, and affordable inertial 
systems to provide orientation, the logical trend has been to rely on these devices to supplement or replace the need for 
ground control. The ideal application of airborne GPS as control should, in theory, permit a complete and adequate 
solution for a photogrammetric block without need for ground control other than for checking and quality control 
purposes. Current experience in practice seems to indicate that ground control, at least in the corners of the block, is 
still required. Perhaps this could have been predicted from the Mt Graham/Casa Grande experiment. 
The following discussions describe experiments and results of comparisons of resected exposure stations based on in 
situ and laboratory (conventional) camera calibrations. 
3. OPERATIONAL EXPERIMENTS 
The primary objective during this investigation is to measure the differences in photogrammetrically determined 
exposure station coordinates based on both in situ and laboratory camera calibrations to corresponding coordinates 
determined by GPS. For these experiments the Trimble 4000 GPS receivers were used. Appropriate atmospheric 
models were used in all cases for alteration of the images. The magnitude of differences between the photogrammetric 
and the GPS coordinate values provides insight into the adequacy of the two methods of calibration. 
Since GPS is used here as a standard of comparison, it is necessary to assure that GPS itself is not a significant 
contributor to the coordinate differences. Discussions with GPS specialists gave assurance that for these short distances 
to the base station and these small altitude differences, the error contribution by GPS is probably negligible. 
3.1 THE MADISON TEST FIELD 
The Madison Calibration Range [low altitude] is located a few miles north of London, Ohio. It was established and 
is maintained by the Ohio Department of Transportation for the calibration and test of its own and contractor’s airborne 
photogrammetric systems. 
The range consists of 102 targeted points located within a rectangular region 2.25 km east to west and 1.80 km north 
to south. Assuming a conventional 15/23 mapping camera, and allowing for a 10% navigational error, photography 
is normally acquired at 1370 meters above ground level. This assures a wide distribution of imagery for calibration 
purposes. The targets consist of flat white circles 0.80 meters in diameter centered on flat black circles 2.4 meters in 
diameter. 
For purposes of in situ calibration and test of airborne digital cameras, a portion of the targets are distributed radially 
from a four-way road intersection beginning with a separation of only 20 meters. The interval is increased radially by 
the cube root of two to provide adequate distribution density for the narrow field angles typical of today’s digital 
cameras. 
The range was surveyed by GPS methods and adjusted. Three bracketing high accuracy [HARN-NADS3 (1995)] 
stations were held fixed, including MADI, the ground base station used during airborne GPS operations. For purposes 
of this investigation, in order to preclude any possible significant contribution due to knowledge of geoidal undulations, 
the coordinates of all stations were transformed into a local three-dimensional rectangular system with origin at MADI 
plus offsets. Standard deviations after adjustment indicated that the easterly and westerly components of error were 
less than 0.008 meters and elevation less than 0.017 meters. 
  
572 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 
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