80% of the incident sunlight should pass through the rectenna and the expected heat rise beneath the rectenna should be approximately one degree centigrade. From this information, multiple use cannot be said to be precluded. However, the use of land area beneath a rectenna will pose cultivation problems, repair and maintenance problems and will require design modifications. This alternative of multiple use should be examined in much greater detail prior to determining its feasi bi 1i ty. Reliability of the Data: At this time, the U.S.D.A. is compiling detailed maps of the prime agricultural lands of the United States. The definition of "prime" agricultural lands is exceedingly complex, having several categories and subcategories. The expectation is that prime lands will vary substantially at the county level, and only by examining detailed maps on a county by county basis can one determine whether the agricultural lands in question are indeed "prime". This data may not be available for the entire United States until the early 1980's. Given this situation, two "proxy" variables were established for prime lands. In Figure 15, areas that are irrigated farmland and areas that are almost totally cropland are mapped. In Figure 16, regional classifications of land area on the basis of its suitability for cultivation are shown. Figure 15 was derived from the U.S.G.S.'s Land Use Map of the United States in the National Atlas of the United States. Although all of the areas mapped in Figure 15 may not meet the S.C.S.’s definition of prime or unique farmlands, the expectation is that most of the land areas included in this map would be so classified. The major shortcoming of this map is that substantial acreages of prime agricultural lands exist beyond those areas mapped in Figure 15. For this reason, Figure 16 was developed. This map was derived from a United States Soil Conservation Service publication titled "2/3 of Our Land: A National Inventory", published in 1971. This figure classi-
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