The series relates to the functions of Survey and Mapping and Earth
Sciences. The recording agency was responsible for the systematic
geological and geophysical mapping of Australia for mineral exploration
and other purposes. A891 consists of positive black and white prints of
aerial survey negatives. Prints were used for reference purposes during map
making. Each print bears some or all of the following data: location, run
number, negative number, frame number, scale, altitude, and date and time of
flight. Frame numbers and negative numbers for the prints are not necessarily
the same. Negative numbers relate to the original survey films and some prints
have numbers with alphabetical prefixes based on the contractor employed to
carry out the surveys e.g. CAS numbers stand for the Civil Air
Survey. Some prints also include additional information in the form of
handwritten notes, traced areas, flight/control diagrams and calculations.
Areas surveyed include: all states of Australia;
the Northern Territory, with Central Australia
delineated as a separate section; Papua New Guinea. A separate series
was created for the Australian Capital Territory (A896). Images were taken of
built-up and vacant areas, aerodromes and airports, military camps and
projects, stores projects, communications installations, and geomorphic
features. Aerial survey negatives were processed to supply: a positive, for
preparatory checking and scanning; and, a diapositive
(positive transparency) used for photogrammetric
restitution processing.
From
1961, aerial photographic surveys of Australia were conducted for the agency by private
contractors. The exception was when another government agency was known to be
undertaking aerial survey work and arrangements were made to acquire copies of
the negatives. Aerial survey negatives were processed to supply: a positive,
for preparatory checking and scanning; and, a diapositive
(positive transparency) used for the purpose of photogrammetric
restitution.
Photogrammetry is a remote sensing technology that
enables two dimensional images of three dimensional objects to be used to
reconstruct accurate models of the original three dimensional scenes. Two or
more images are taken from adjacent positions. Measurements are made in the
images and common points identified in each image. Lines of sight (or rays) can
then be plotted using the location the images were taken from and the
identified points on the images. Triangulating the rays reconstructs the
three-dimensional location of the identified points. The photogrammetric
restitution process was a plotting instrument that, when set, reproduced maps
and profiles from the diapositives, creating an
optical stereoscopic model of the photographed terrain. These stereoscopic
models were used to create accurate maps and survey plans and multiple printed
copies could be produced from one original.
Additional
information
Crustal Study has been defined as tracking the evolution of the Earth’s
crust through time and space from “an integrated geological-geophysical perspective”
for the purposes of discerning “the natural resources contained within the
crust and at its surface, and the natural hazards that result from geological
processes acting within it”.
Sources
Series
documentation
Geoscience Australia website, downloaded 5 May
2009, http://www.ga.gov.au/about-us/history.jsp
Wikipedia.org,
‘Photogrammetry’, downloaded 5 May 2009 from http://en.wikipedia.org/wiki/Photogrammetry
Institute
for Crustal Studies, University
of California at Santa Barbara, downloaded 5 May 2009 from http://www.crustal.ucsb.edu/