weather in the limited area sustained by the ground stations ties the hands
of the operating units until suitable photo weather occurs. Months of
waiting can make this procedure exceedingly costly.
In this paper I will explain a new approach to the problems of aerial
mapping which has been developed into a new streamlined operational concept
and by which horizontal and vertical control data can be obtained by the
aircraft rapidly and efficiently. This concept was first envisioned using
a highly stable aerial platform which is worthy of explanation.
The Boeing KC-135 aircraft was conceived and designed as a high speed,
high altitude stable platform for air refueling missions. To maintain its
high altitude, high speed stability while rapidly discharging its many
tons of fuel was solved by retaining its center of gravity throughout the
refueling operation. The aircraft was also designed to consume its
internal fuel (including tanker fuel), for maximum range or ferry operations.
All of its tanker fuel is below the cargo floor. Above this floor an area
the size of a bowling alley will accommodate multiple cameras, electronic
survey equipment, etc.
The skilled engineering of the auto pilot compliments the stability
characteristics of the aircraft and maintains it rigidly in space as a
firm stable platform ideal for the aerial mapping mission.
Before proceeding with our discussion on the aircraft development, I
would like to relate my views of the task of the photogrammetrist. This
skilled technician receives the geometrically perfect (less than 10 micron
distortion) aerial photographs which were taken by the mapping aircraft.
The camera, if cradled in our present stabilized mount, is pointing almost
vertically when the aerial photographs are taken. But which way that first
photo was tilted and how much cannot be determined without the aid of ground
control. Accurately surveyed ground positions which can be identified or
plotted on the mapping photograph must be correlated with the aerial
exposure to correct it to its true vertical. When one photograph has been
properly oriented to the ground survey control data, then overlapping
stereo photographs can be leveled and the control extended by aero
triangulation. Aero triangulation works fine over a short distance, but
accuracy gradually deteriorates as it is cantilevered from the first
model or bridged between two separate models. Approximately seven successive
stereo photographs are generally considered to be the maximum extension
possible for first order aero triangulation.
In summary, it would seem reasonable to conclude that it would be a
very major benefit to the photogrammetrist when he can rapidly determine
the true vertical axis of the mapping camera in our new aerial mapping
system. The vertical readout of the inertial platform optically recorded
and synchronized with the aerial exposure to less than 30 arc seconds will
greatly enhance the photogrammetric accuracy of extensions by cantilever
and bridging.