'el- 
ques. 
it 
acquiring the spectral data at key crop development stages, which may 
be impossible, or to develop an alternative method of crop identi- 
fication independent of the acquisition dates. 
The Landsat data can be used to identify the different plant species 
as well as the impact of the farmer's second choice, how much to 
plant. It was possible to determine planted/harvested wheat acreage 
by studying the field structure, field sizes, field definition and 
similarities and differences between fields. 
Several USDA crop analysts analyzed 150 Landsat segment images which 
each covered an area of 8 km x 9.5 km. These segments were located 
in Saskatchewan, Canada; Kotchetav, U.S.S.R. and the U.S. Great 
Plains. Despite the fact that each of these three areas were major 
wheat producing areas, they contained very different and fundamental 
features. There are features within each of the three countries 
which were consistent over a limited area, but distinctly different 
from other sets of common features covering other areas. The 
fundamental differences, which were readily distinguished in the 
Landsat imagery, related exclusively to field pattern characteristics. 
A.1 Field Conditions 
The dominating field characteristics or features observed were 1) the 
existence of fields, 2) the number of fields in the segment, 3) the 
size of the fields, 4) the field heterogenity, 5) field similarity, 
and 6) field history. There was evidence of field patterns in all 
the agricultural areas. The existence of field patterns seemed to 
be related to seasonal crops such as wheat. There was no effort to 
look for any form of field patterns in either range land or in 
working forests. 
The number of fields in the segment are related to the size of the 
segment, in this case 77.5 km, and the size of the individual fields. 
The larger the area and the smaller the fields, the greater the 
number of fields. There was a feature about the field sizes that 
was consistent in each segment. All the fields in a segment were 
about the same size, very seldom was there any mixture of very small 
and very large fields. In most cases the fields were well defined 
and homogeneous, but this depended on the time of the year and the 
meteorological conditions. Field definition was a function of what 
was contained in the adjoining fields. If it was different then 
usually the individual fields could be separated. Field homogeneity 
depended on the growth stage, field size, and the meteorological 
effects on the crop. If the vegetation completely covered (or did 
not cover) the field the spectral image of that field would look 
uniform when the fields were not large e.g. less than 200 acres. If 
the fields were large there could be spectral variability within 
the field due to soil types, irrigation, plant damage, etc. If 
the meteorological conditions had been unfavorable, differences