The basic problem in any field survey is to delineate bodies of similar objects and to make sure that the boundaries between map units are accurate and meaningful. Remotely sensed data cannot replace on-site investigations in soil surveys because the same color patterns, reflectance values, etc., do not always relate to the same kind of soil, even in a local survey area. But remotely sensed data is an extremely valuable tool in extending on-site observations and in locating and extending the boundaries between many map units. Field scientists should have ready access to maps of various scales and origin to aid in locating and extrapolating the boundaries between map units. Any data such as black and white or color infrared photography, Landsat MSS data, or side-looking radar is never fully satisfactory in any area. Yet a combination of these data can supplement each other and give the field surveyor another view of the survey area. There is little need to justify the use of black and white high altitude photography, color infrared photography, or Landsat data in soil survey. All have been found useful under varying conditions. The future use of color infrared images and Landsat data in soil survey will depend primarily upon the ability to provide up-to-date data quickly and at low cost.
The National Cooperative Soil Survey has 511 active progressive surveys underway in 1980. About 90 to 100 new surveys are scheduled to start each year for the next 5 years. The average area for each survey now being mapped is 800,000 acres and for new surveys about 700,000 acres. We have a potential for using color infrared photography or Landsat MSS data, or both, for about 70 million acres each year. An agreement has been reached by several U.S. Government Agencies to obtain high altitude photography on about one third of the United States each year. Black and white 20 x 20 inch sheets and color infrared contact prints will be available a t a cost of about .002 cents per acre, or for about $1300 for black and white and $1650 for color infrared photography for a 700,000 acre county. New photography will be available every 3 years and the use of color infrared photography in soil surveys probably will increase considerably.
The use of Landsat data in soil survey will depend upon ease of obtaining satisfactory maps, the cost of the maps, and overcoming the skepticism about the value of the data by many users. A question that we should examine is how refined do we want to make Landsat data. Soil surveyors are used to interpreting the variation in shading on aerial photography, but are not used to interpreting the symbolization and the square blocks of highly refined Landsat data. We need to examine the question of how we should present Landsat data to soil surveyors, the scales needed, and whether or not we need a cartographically correct map. Unless Landsat data can compete with the high quality color infrared and black and white photography in cost per acre, availability, and reduction in field time, its use will be severely limited.
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