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59 
ANNEXURE K 
THE USE OF AERIAL PHOTOGRAPHS IN SOIL SURVEYS IN AUSTRALIA 
by 
C.G. STEPHENS, D.Sec,, F.R.A.C.1I. 
Soil Survey and Pedology Section, Division of Soils, 
C.8.T,R.0,, Australia 
Soon after soil surveys were commenced in Australia during the 19205 vertical 
aerial photographs were used as an aid in the delineation of boundaries between different 
soils, Prescott and Taylor (1930) and Marshall and Hooper (1932) who were associated 
with this work demonstrated that vegetation boundaries, crop vigour and soil features could 
be detected to some extent on the photographs and that soil inspection sites could be lo- 
cated and marked with sufficient accuracy on the face of the photographs. This early use 
of vertical photographs was restricted to detailed soil surveys and they were employed 
solely as an aid in the map drawing stage when boundaries depicted on note-book copies of 
cadastral plans by soil surveyors in the field were Subject to correction in the light of 
indieations on the photographs, 
Only a portion of the boundaries drawn between Soil Types and Phases by the soil 
surveyors could be detected on the photographs, Where boundaries were visible this was 
due either to a change in the neutral background tone of the photograph or because of a 
change in natural vegetation or planted crop as indicated by a variation in the pattern 
recorded on the photograph, It was also quickly discovered that soil boundaries associated 
with changes in relief but otherwise not visible on the photograph could readily be placed 
with the aid of stereoscopic examination of the common parts of pairs of overlapping photo- 
graphs, 
The activities outlined above were associated exclusively with detailed soil 
survey work based on a close grid of rectilinear traverses with Soil examinations at regu- 
lar intervals, most often 10 chains spart, Adequate base plans produced from cadastral 
surveys were also available in the areas surveyed, Later attempts were made to use the 
aerial photographs in the field for direct recording of soil distribution by marking more 
or le transparent overlays, For two main reasons namely, difficulty of keeping consis- 
ss 
tent register with the underlying photograph, and a considerable loss of otherwise visible 
and useful detail, this technique never came into general use, 
   
  
From the late 19505 soil survey became inereasingly influenced by omorphology, 
This has enabled quite a different approach to soil mapping, both detailed and reconnais- 
sance, to be made, This has developed to the point where, in an area subject to survey, 
a landscape analysis is made into topographic and petrographic units of different forms 
and ages, On each of these, where repeated, the same soil unit or pattern of soils is 
encountered, Since 1939 soil surveyors have been using and marking aerial photographs 
of suitable scales preferably 10, 20 or LO chains to the inch in the field, It has been 
found possible to mark out simultaneously the different petrographic provinces and/or the 
geomorphic units and to delineate the soil pattern on these by a system of irregularly 
shaped traverses recorded directly on the photographs. The traverses, designed to pass 
from one landscape unit to the next, record the soil type or pattern of soil types on each 
unit and the boundaries between them by soil examinations spaced at irregular intervals. 
The sites for soil inspections are selected in the light of information derived partly 
from the photograph and partly by inspection of the landscape, Initially soil inspections 
need to be very frequent and often small spot surveys in great detail are necessary but 
with the establishment of soil-landscape relationships and their recognition by inspection 
+ 
of aerial photographs becomes progressively less frequent and mapping speeds up greatly. 
  
The application of the above technique is limited to a variable degree by dens 
forest cover but because of generally favourable conditions it has become the basic approach 
to soil mapping, whether detailed or reconnaissance, throughout the operations of C.S.I.R,O., 
Division of Soils. For detailed mapping it is necessary to see the whole landscape and 
  
to map in the appropriate finer classificational units of Soil Series, Type and Phase. 
For reconnaissance work where the aim is to map associations of Soil Series or broader 
units such as Soil Families or Great Soil Groups the boundaries of the soil map will coin- 
cide largely with the boundaries of the petrographic and geomorphic landscape units, Since, 
after initial field work, these can be identified and marked on the photographs, only a 
limited number of selected investigating and checking traverses are necessary and the map- 
ping of the intervening areas is done directly from the photographs without actually sight- 
ing the cauntry. The proportion sighted would vary from 10 to 30 per cent, In no ease, 
not even the broadest reconnaissance, would soil maps be prepared from aerial photographs 
without some traversing and field inspections of soil profiles, 
The increased use of aerial photographs am marking them in the field has been 
assisted by a number of factors. The growing appreciation of time and money saved and