International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
During the course of this development, a number of interested 
organizations participated in addition to the USGS. The 
software development was a cooperative program between The 
Ohio State University and the University of Calgary with a 
grant from USGS. The Madison Test and Calibration Range 
was developed and maintained by the Ohio Department of 
Transportation / Aerial Engineering Office. Flight testing of 
the digital cameras was accomplished by Topo Photo, Inc. of 
Columbus, Ohio. 
2.1 In situ Approach to Calibration 
In a benchmark publication by Eisenhart (1962), found in the 
Proceedings of the National Bureau Standards, a rationale for 
the calibration of measurement systems is set forth. His work 
provides clear guidance for designing and applying a calibra- 
tion program for the airborne sensors associated with the aerial 
mapping industry. To summarize Eisenhart’s concept of 
calibration: 
e Establish. first... the 
Specifications” 
e [Exercise the measurement system as specified and 
compare results to a standard of higher accuraey until 
sufficient information is available to achieve a “State 
of Statistical Control" 
"Measurement System 
The system specifications describe all aspects of the system 
including hardware, software, environment of the system and 
operational procedures necessary to achieve the final 
measurement. Procedures may include specified ranges within 
which the system will operate. In the aerial case, for instance, a 
range in altitude can be specified that, by its definition, 
represents an important practical aspect of the concept. 
By accepting the concept of measurement system calibration, it 
is clear that certain aspects of camera calibration, as 
traditionally practiced, need to be reconsidered. For the aerial 
camera, independent of the added sensors, the primary 
difference in measurement accuracy for application is due to 
temperature differences between a laboratory and an in situ 
method of data collection. This difference is most evident for 
an open-port windowed aircraft, most typical of the aerial 
industry. For the closed-port, the addition of the window adds 
an additional optical component to the system not conveniently 
treated during the laboratory approach to calibration. 
Experimental data collected under applicational cireumstances 
tend to support the need for adopting an in situ approach to the 
calibration of the aerial camera. 
For the aerial case, the choice of camera platform, as with 
digital cameras, offers a wide range of possibilities with the 
technically best being the most expensive. The choices. 
discussed below, range from the minimum cost, single-engine, 
open-port aircraft to the multi-engine, windowed-port aircraft. 
2.1.1 Single-Engine Open-Port In the United States one 
popular, relatively inexpensive, aircraft is the Cessna 207. The 
aircraft represents an adequately stable platform for carrying 
the camera, mount and supporting equipment. However, when 
considering use of airborne GPS for survey control, one must 
assume that a significant disturbance is generated in the volume 
20 
of air below the aircraft through which the camera must 
function. The engine exhaust may be diverted, however, the 
cooling air for the conventional reciprocating engine can cause 
a rise in temperature from external ambient to cowl exit of 
66°C. In addition, as with all open port systems, the influences 
of temperature differences between cabin and external air will 
have an influence on the metric characteristics of the camera. 
2.1.2. Multi-Engine Open-Port Probably the most widely used 
aircraft for colleting photography of photogrammetric quality is 
a light twin, open port platform. With this aircraft, no 
significant disturbance to the volume of air beneath the aircraft 
is expected. However, the influence of the temperature 
difference between cabin and outside air can be extreme. The 
difference causes a change in relationship between the optical 
and image collecting components of the aircraft. This change 
usually is seen as a centering error that can be represented as a 
corresponding change in the camera constant. Accordingly, 
recording temperatures within the cabin and at the camera lens 
may become a means for accounting for the open port 
installation errors. 
2.1.3. Multi-Engine Windowed-Port The ideal, but most 
expensive aerial platform includes a windowed port. The 
window consists of high quality glass as specified by military 
standards and others. Clearly, in application, the window 
becomes part of the optical system and must be included as part 
of the photographic system during calibration. When operating 
without cabin pressurization, the influences of temperature 
differences are mitigated. When pressurized, the differences 
between cabin and external pressure generates a stress/strain 
relationship on the window, producing an image deformation, 
that - requires additional mathematical modeling during the 
calibration process (a component of the system specification). 
3. USGS/OSU PROJECT 
The USGS project is viewed as an initial step leading to a 
means of camera system calibration on a national basis. 
Software was developed for the image measurement process 
and for the subsequent computation of interior orientation, the 
primary components of the camera calibration. 
Subsequently, a series of flights were conducted over the 
Madison range to verify the systems approach to camera 
calibration for both the digital and film-based cameras. 
3.1 Software Development 
The programming, accomplished in Visual C++ language, 
resulted in two programs. 
3.1.1 Image Measurement Program The first program, 
termed “Image Measure” (IM) software, was designed for 
measurement of image coordinates and production of files for 
subsequent introduction to the calibration program. The 
observation of target images is facilitated by computation of a 
single photo resection after the first four targets have been 
identified and manually measured. At that point, the program 
indicates the residuals of the fit to control, and selects only 
those targets that appear within the current photograph. This is 
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