IRRIGATED LANDS CAN BE ESTIMATED
ACCURATELY BY PHOTO INTERPRETATION
OF LANDSAT: COLOR COMPOSITES
Robert C. Heller
Research Professor
College of Forestry, Wildlife and Range Sciences
University of Idaho
Moscow, Idaho, USA
Kim A. Johnson
Research Analyst
Idaho Department of Water Resources
Boise, Idaho, USA
INTRODUCTION
During the peak of crop growth in irrigated fields, near infrared
reflectance of plant growth (0.7 to 1.1 um) is very high. During this
growing period, on LANDSAT color infrared (CIR) images produced by the
EROS Data Center or NASA's Goddard Space Flight Center, irrigated
croplands show up as geometrically regular shapes in strong reddish
hues. Since most irrigated lands occur in arid to semi-arid areas of
the world, the contrast between irrigated cropland and surrounding dry
lands is great and the two land uses are easily separable on LANDSAT
color infrared transparencies.
A good part of southern Idaho is considered high desert and native
vegetation consists of sagebrush species (Artemisia spp.) and various
rangeland grasses. However, there is an adequate source of water for
irrigation purposes from the Snake River and the Snake River aquifer.
Flood irrigation has been practiced for at least 80 years in some parts
of the state. More recently, sprinkler irrigation methods (especially
central pivot installations) have been used in developing new fields for
agriculture. Because the rate of growth of newly installed irrigation
systems is difficult and expensive to assess by, ground records and
visits, the Idaho Department of Water Resources— was interested in
trying new techniques to help them inventory irrigated lands. These
data in turn would be used to determine water demand from existing known
water sources and permit more realistic planning for future uses of
available supplies.
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~The study described herein was done cooperatively and partially funded
by the Idaho Department of Water Resources, Boise, Idaho.