46 BALLISTIC PHOTOGRAMMETRY, SCHMID
the photogrammetric record must be considered as the most important phase in the se-
quence of operations leading to the final measuring result.
Like any other field of application, Ballistie Photogrammetry must concern itself
with the problem of providing optimum field instrumentation. The design of such instru-
ments must be accomplished as a compromise between:
a. the demand for maximum metric accuracy;
b. the adaptability of the instruments to various measuring tasks by:
1. providing precision metric lenses with considerable range in focal length and at
the same time having maximum light gathering power.
2. incorporating precision azimuth and elevation cycles in combination with levels
for securing the stability of the parameters of exterior orientation for prolonged
periods of operation.
3. featuring primary and secondary shutter systems, allowing adjustable sequences
of exposures (up to about 40 per sec), synchronized or time controlled to + 100
usec. or better, depending on the relative location of various instruments, which
may be separated from each other by distances of from 100 miles to a few thou-
sand miles. In addition, shutter actions must be possible which produce adjustable
star trail patterns, whereby the corresponding opening and closing intervals must
be controlled to = 0.05 sec with respect to Universal Time.
c. and the need for mobility, including provisions necessary for operating instruments
under extreme climatie conditions.
The development of present-day field instrumentation in Ballistic Photogrammetry
has followed the experience gained in the manufacturing of photo-theodolites, especial-
ly the version which was produced during the last war by the Askania Werke, Berlin,
for meeting the requirements in the field of advanced ballisties, in the development of
fast flying aircraft and in the research and testing of rockets.
Any attempt to introduce the photogrammetric measuring method into research and
development in the missile field after the war, was confronted however, with an entirely
new situation, in that, electronic measuring systems with their continuous records and
extremely high sampling rates, promised a far better procedure for accomplishing trajec-
tory measurements. The inability of the photogrammetric method to provide an all weath-
er capability, the almost unavoidable restriction to night observations, together with the
impossibility to provide real time data are serious shortcommings in this particular field
of applications. The reputation which the photogrammetric method presently enjoys at
the missile ranges is due to its freedom of the type of difficulties encountered in elec-
tronic measuring systems i.e. the elimination of systematic errors caused largely by the
effects of propagation in the r.f.-region of the spectrum, still insufficiently understood.
During the past decade, the Ballistic Research Laboratories at Aberdeen, Maryland
have supported a program for the purpose of establishing a precision photogrammetric
measuring system for application especially in the guided missile field. One phase of this
program has been concerned with the task of making available a high precision field
instrumentation system, which can meet the different requirements in Ballistic Photo-
grammetry. In cooperation with the Wild Company, Heerbrugg, Switzerland, the Fred C.
Henson Company, Pasadena, California and the Electronic Engineering Corporation of
California, Santa Ana, California, a flexible system emerged, capable of high precision
with respect to both metric and timing accuracy. Based on the idea of utilizing precision
components tested in geodetic and photogrammetric practice, the Wild BC-4 is essen-
tially a combination of the T-4 astronomical theodolite and camera cones similar to those
used in precision aerial cameras. The adaptability of the instrument to various meas-
uring tasks is assured by a group of lens cones, providing angles of view of about 120°,
90°, 60°, and 40°. Among these is a special lens, the Astrotar with 304 mm focal length
and an maximum aperture of 1 : 2.6. This lens, like the others, was designed by Dr. Ber-
AA aam STAR A de
