To obtain a new set of photographs very quickly 
and at a cost low enough to be readily justifiable 
in the context of such a survey, the use of "Small 
Format Aerial Photography" (SFAP) was then 
considered. 
3 SMALL FORMAT AERIAL PHOTOGRAPHY AS AN ALTERNATIVE. 
Small format aerial photography may be defined as 
a (camera) image format with sides smaller than 12 
cm. It includes the 6x6 cm. roll film formats 
(120,220) and the 70 mm. perforated film format, 
both having an image size of 55 x 55 mm. and the 35 
mm. film format with an image size of 24 x 36 mm. 
(Hofstee, 1982). It is a low cost technique that 
uses the same principles as large format aerial 
photography but without complex and expensive in 
strumentation and only requires light planes. 
There has been increasing interest in recent years 
in the use of supplementary airphotos taken with 
small format cameras to provide up-to-date informa 
tion for planning. 
In 1978, the Bandung Institute of Technology used 
this technique for an Integrated Approach for 
Marginal Settlement Improvement. A light single 
engine Indonesian produced Gelatik aircraft, was 
used with a Canon 35 mm camera mounted in the open 
ing otherwise used for spraying equipment. The 
camera was a normal single lens reflex camera with 
50 mm. lens. The flight altitude was 800 meters, 
negatives were enlarged to 20 and 30 cm size and 
photocopied for use in a self-help survey. Although 
exact scale mapping is not possible, the results are 
more than adequate for the requirements of a mar 
ginal settlement improvement project. (POERBO and 
SHUBERT, 1982) 
Spencer (1978) has experimented with small format 
aerial photography for map revision using a 70 mm. 
camera which was mounted outside the open doorway of 
a Cessna 182 aircraft. Navigation was first based on 
unaided visual observations. The success of the 
trials ensured a continuing use of the approach but 
in order to improve the accuracy of flight line 
navigation and the comfort of flying, the light 
aircraft was modified for internal mounting of the 
camera and fixing point for a drift sight. The 
camera was a Vinten 70 mm fitted with a lens of 3 
in. focal length. It has a format of 56 by 57 mm. 
and was electrically operated. The magazine had a 
film capacity approximately 500 frames (100 ft.). 
Usually, the flying altitude was 10,000 ft. Contact 
negatives of scale 1:28,000 to 1:40,000 were 
obtained; 5,100 hectares of plantations were 
photographed. 
Curran (1981) of Department of Geography, 
University of Reading, England, applied the small 
format, light aircraft photography to study the 
relationship between green biomass vegetation 
productivity and bidirectional reflectance. A Cessna 
172 and Dehavilland Chipmunk aircraft were used with 
Cannon 35 mm camera for hand-held aerial 
photography. Also a Hasselblad 70 mm motor drive 
camera system that fits over an observation port in 
the aircraft fuselage was used for vertical 
photography. In this case the aircraft used was a 
Piper Aztec, a six-seater, twin engined, low wing 
aircraft. 
4 SFAP OPERATIONAL SURVEY FOR BANGKOK METROPOLITAN 
REGION 
Considering the amount of data needed to be col 
lected from the air photographs, processing time, 
cost constraints, and the previous successful experi 
ments of SFAP in a number of small area 
applications, it was decided that SFAP was justifi 
able for the BMR study. In bringing SFAP to an 
operational use for the study of a city of several 
million inhabitants (covering some 5000 sq.km), NHA 
requested technical assistance from the ITC 
Department of Urban Survey and Human Settlement 
Analysis and the Royal Thai Air Force Reconnaissance 
Squadron (RTAF). 
TECHNICAL DETAILS OF THE BMR SFAP EXPERIMENT 
SFAP requires a small aircraft in order to reduce 
fuel consumption. The AU 23-A Peace Maker, normally 
used for taking photographs for reconnaissance 
purposes, was selected because the cost of fuel is 
approximately US $ 111 per hour whereas two engined 
types of aircraft consume approximately US $ 675 per 
hour or more. The camera was the Rollei SLX 55 x 55 
mm format camera, equipped with an intervalometer 
developed at ITC, mounted on a plastic mounting 
base, fitting in the F-231 camera mount. The first 
three pieces of equipment were borrowed from ITC. 
Flight line navigation was observed by a navigation 
sight NT 1. 
The aircrew comprised three members: a pilot, a 
controller and a navigator. The RTAF undertook a 
test of SFAP over the city of Nakorn Pathom (60 km 
west of Bangkok) on October 18, 1984. The test was 
carried out to prove the capability of the staff 
involved, the equipment, the navigation and the 
photographic processing. 
The result of the test, which produced airphoto 
negatives at a scale of 1:47,000, was so satisfac 
tory that the decision to apply SFAP for the whole 
built-up area of BMR was confirmed. 
The area to be flown was divided into 4 zones. 
Each flight line was designed for 30 km (film 
length) and took approximately 10 minutes. The 
navigation was to follow a flight path which was 
along the center line of the square kilometer grids 
marked on the 1:50,000 air navigation chart. This 
provided the mean of identifying accurate land marks 
through the NT1 navigation sight. It follows that 
flight direction was then along N-S axis or E-W axis 
depending on wind direction. The 50 mm lens on the 
Rollei SLX camera, a flying height of 8,500 ft, 
which is below the height at which aircrews need 
oxygen, was calculated to give a useable ground 
coverage of 2 km square. Flight line intervals were 
of 2 km for a 60% forward overlap, a 80% side lap on 
both sides. Shutter speed is preset to 1/500 second, 
interval setting was calculated and set at 17.12 
seconds because of the ground speed of 120 knots 
(222 km/hr) and the aperture was set to automatic. 
Kodak plus X film was used with 24 exposures. It 
was processed with very fine grain developer, such 
as microdol-X. Each negative has been clearly marked 
with its alpha-numerical code numbers for the flight 
index, and can be conveniently stored in an A4 size 
folder. 
The aerial photography took some 10 hours flying 
and was undertaken during January and February 1985. 
The first set of the enlarged SFAP at a scale of 
1:15,000 was available for starting the interpreta 
tion tasks in the beginning of March 1985. 
The actual cost of SFAP for the single mission, 
including processing, enlarging and printing to 
finished photo scale 1:10,000 for an area of 5,000 
sq.km, was Bht. 160,000 (US$ 6154) or Bht. 32 (US$ 
1.18) per sq.km. Estimated cost of 1 set of conven 
tional aerial photograph of the same scale is Bht. 
600,000 (US$ 23,70) or Bht. 128 (US$ 5) per sq.km. 
The SFAP coverage of BMR has demonstrated an 
operational procedure which other agencies can now 
employ as a means of obtaining a data for develop 
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