oampiece error = 
CHANGE DETECTION 
One can use LANDSAT images to detect changes in irrigated lands 
from one year to the next by using transparencies of two LANDSAT wavebands 
from the present year with one waveband from a previous year. Certain 
conditions should be observed; for example, images from the same growing 
periods in each year should be selected and for best geometric registration 
of images the images from the same satellite, LANDSAT I with I, LANDSAT 
III with III, etc. should be used. 
If the interpreter has an optical combiner available; he can combine 
the 1:3,300,000 scale LANDSAT images by using the following combinations 
of years of imagery, wavebands and filters. For the current imagery, 
use a green filter with the red (5) waveband and a blue filter with the 
near IR (7) waveband. For the old imagery, register it on the new 
imagery and project a red filter through the near IR (7) waveband. With 
this combination, the fields which are now being irrigated and which 
were not under irrigation at the time of the older imagery will appear 
purplish to light blue. The fields which were under irrigation at both 
time periods appear red. The projected image can then be copied onto 
color film and subsequently printed for enumeration and measurement of 
the newly irrigated fields. 
An identical result may be obtained if an optical combiner is not 
available by using 1:1,000,000 LANDSAT black and white transparencies. 
The same wavebands are used, i.e., 5 and 7 of the old imagery and 7 of 
the new. In place of filters, a color foil product (3M, GAF) manufactured 
for the color printing industry can be used. An appropriately colored 
foil is exposed under ultraviolet light and developed in ammonia fumes. 
Because the color foils respond in direct proportion to the darkness of 
the LANDSAT transparencies, complementary color foils to the filter 
colors described above must be used. For example, on the new imagery, a 
magenta foil is used with band 5 and a yellow foil with band 7. Similarly, 
on the old imagery a cyan foil is used on band 7. With careful registration 
of the three developed foils, a very similar result may be obtained. 
Beginning in October 1978, the EROS Data Center in Sioux Falls, 
South Dakota will begin producing rectified and geometrically corrected 
LANDSAT products. With such products, it will be simpler to overlay 
imagery from one year to the next.