ues
as
eld
dera-
from
lows:
assel-
2403 (Panchromatic)
2h24 (Infrared Black-and-White),
with suitable filters.
Scale of photography : 1 2 20,000:
Each frame (effective area = 55mm x 55mm) represents an
area of 1,l1km x 1.1km (approximately) on the ground.
The period suitable for an aerial survev in the area under
study is (end of)October - (beginning of)April. The main data
were acquired in the months of November and March, and selective
data in the months of October and December of the year subse-
quent to the main flights.
In view of some nonuniformity (with respect to time) of the
sowing and harvesting practices, one cannot expect, at any par-
ticular time of the year, the same growth stage of the crop in
the whole area. However, the growth stages for paddy and sugar-
cane seem to be ôf the fotlowing general pattern
Growth Stages of
Paddy Sugarcane
November March November March
A1 .3 A1.1 A2.2 A243
Al. A2.h A2.
Test sites were chosen in randomly located places for col-
lecting the so-called "ground truth" data synchronous with the
flight operations over the area. This data serves as the train-
ing set for both visual and automatic data processing.
Remark In an interesting comparative study of the various re-
mote sensors by H.W.Faust (Carl Zeiss. Oberkochen), 37th Photo-
grammetric Week (Stuttgart, September 1977), it is convincingly
brought out that Hasselblad cameras are the cheapest means of
acquiring multiband imagery (in the visible and near infrared
portions of the electromagnetic spectrum) with exceptionally
good resolution. For instance, assuming 50 lines / mm resolu-
tion in the aerisl film. each pixel represents O.lhm x O.hm (ap-
proximately) on the ground, at the 1:20,000 seale.
5. Processing of Photographi c Data An automatic processing
system should at least be able to do whatever the visual system
can do. This requires that we should know exactly what the human
visual system can do.
With respect to the project, the color infrared frames
have been visuallv internreted by trained photointervoreters.Se-
lected frames have been checked against ground data. Standard
techniques are employed for calculation of acreage of each cate-
gory. Yield calculations are made on the basis of average vield
per acre.
Visual interpretation is based on color, texture and con-
textual information on the color infrared frame. It was found
difficult to interpret panchromatic and infrared black-and-white
films. It has been reported in the literature that a color infra
red frame contains more information on agricultural and nonagri-