us-X, Double-X 
use of high 
aphy using 
for assessing 
Carneggie 
ar orbiting 
ERTS-1) and to 
elius et al, 1973; 
wider use of 
the successful 
here been 
rammetric 
isappointing 
e surveys. 
ographs and 
969; Draeger 
nson, 1969), 
t al, 1913). 
' about 18,450 m. 
| in general; 
ilter 
| imagery in 
ration, 
id HFAP imagery 
road + S 
‚er a om 
icluded ?deciduous 
ert as grazin 
tural mne 
pphs, due to 
yd identification 
;,e photography 
of HFAP for 
for example, 
3 for 'wheat! 
j were undesirably 
3 and difficulty 
F-alfa, 
tinger (1972) that 
greater than that 
ment was not 
ssary for increased 
= 1465 - 
accuracy of crop identification’. This suggests there is no major information 
threshold between HFAP at about 1:120,000 and outer space photography at 
1:500,000 and the smaller scale Apollo satellite photography(for this 
particular type of study). However, in the several state surveys of maize blight 
in the USA (1971/72), it was observed, for example, that maize could be identified 
on the IR colour photographs particularly by the banding effect of the individual 
rows spaced at about O.Tm. 
Reference to literature also indicates that there was little attempt in this 
period to refine HFAP photo-interpretation for forest studies, although HFAP 
had been proposed for multi-stage sampling in forest inventory (Langley, 1972). 
Studies of forested areas in Nevada indicated that some species identification 
is possible (e.g. pinon pine/ juniper), and that forest stand density classes can 
be delineated. 
In California (Lauer and Benson, 1973), it was concluded, using black-and-white 
panchromatic photographs at 1:15,840 and IR colour photographs at 1:120,000 that 
the latter enabled forest type boundaries to be properly mapped, that forest 
type identification with the two film-filter combinations had a high correlation 
and cost was greatly reduced with the HFAP, It was judged that the cost of aerial 
photography would be reduced up to six times and photo-interpretation by half or 
more as compared with other conventional photography. However, Hudson et al (1976) 
working in Michigan with colour infrared photographs at scales of 1:60,000 and 
1:120,000 concluded that only four tree species groups were distinguishable at 
these scales as compared with six groups using CIR at 1:36,000. 
Further, thematic mapping/thematic surveys in a number of tropical countries 
(e.g. Kenya, Ivory Coast, Papua-New Guinea, NW Australia and Sierra Leone) have 
indicated that very small-scale photography can be used to successfully map land 
units (Howard 1971; Bleeker and Birchall, 1977; Birchall, 1978; Schwaar, 1978 a), 
current land-use (Kater and Gordon, 1978; Gordon, 1978; Schwaar, 1978 a} and to 
stratify the forests into timber types for ground assessment (Howard, 1976). In 
Australia, black-and-white panchromatic photography at a nominal scale of about 
1:84,000 {socal length 88 m) have been widely used for many years for photogrammetric 
survey including the production of planimetric maps at 1:100,000. 
IV. PHOTOGRAMMETRIC CONSIDERATIONS 
Although RB-57 and U-2 photography was taken in the USA for civilian purposes 
over 10 years ago, a commercial aircraft with a pressurized cabin for this type 
of work was not available until the introduction of the Lear-Jet (US) in 1968. 
This had a ceiling of about 13,400 meters, a velocity of about 800 km/h and a 
range of about 3,000 km. More recently, the Twin jet Mystére 20, also known as 
the Fan Jet Falcon (French), has been adapted to commercial HFAP with an absolute 
ceiling of 13,700 m, a velocity of 800 kn/h and a range of about 4,250 km; and 
the new Lear Jet 24 D has a ceiling of about 15,000 me At a photographic scale 
of 1:120, and with a format of 23 cm, theoretically between about 5000 and 
13,000 km” of ground area can be photographed per flying hour.