FIGURE 112 (above). Color composite ERTS-1 image of the Everglades National Park area of Florida (1242-15240). [larger image] FIGURE 113 (below). Annotated ERTS-1 image showing water-management conservation areas in the Everglades National Park area of Florida (1242-15240, band 6). [larger image]

The water supply for southeast Florida, which has a population of 2.5 million, depends upon the retention of water in four major impoundment areas in the Everglades water basin (figs. 112, 113) : (1) Lake Okeechobee, (2) Conservation Area No. 1, (3) Conservation Area No. 2, and (4) Conservation Area No. 3. Shark River Slough, an important source of water for the Everglades National Park, at the downstream end of these interconnected water bodies, also depends upon overland flow from adjoining Conservation Area No. 3. An accurate accounting of the amount of water in surface storage is difficult because land-surface profiles are not available. The shallow water depths of 0.3 to 1.0 m, the flat terrain, the abundant vegetation, and the vast area of 3,600 km² of the Everglades preclude the feasibility of determining accurate volumes by conventional methods. In the conservation areas and the Shark River Slough, the water does not pond in the usual manner but slowly flows over the gently sloping land surface.

Several water-budget studies for the conservation areas are underway by the U.S. Army Corps of Engineers and the Central and Southern Florida Flood Control District. Elements that need more accurate definition in the existing water-budget studies are rainfall, evapotranspiration, seepage losses, and surface storage.

The ERTS water-management model uses the DCS to provide quantitative in-situ data on the elevation of the water surface and MSS data to provide information on the areal extent of the water surface (Higer and others, 1973). Knowing the relation between the surface-water area and surface elevation for the range of water levels, the storage can then be calculated (figs. 114, 115). In addition, knowing the change in storage and the surface inflow and outflow (input and output) from the system, it is possible to calculate evapotranspiration and seepage (Higer and others, 1974).

At present the DCS data are transmitted from the Everglades stations to the satellite and relayed via two ground tracking stations to the Goddard Space Flight Center, Greenbelt, Md. The data are then transmitted by teletype to the Miami office of the U.S. Geological Survey. The perforated teletype tape is then processed daily through a minicomputer to convert the data to engineering units and place it into the format requested by the Corps of Engineers. The data are then transmitted to the Corps of Engineers, Jacksonville, Fla., by telecopier. The time required for the transmission of the data from the Everglades via the satellite, the NASA tracking stations, and the US. Geological Survey to the Corps of Engineers is less than 2 h.

The importance of the space-relayed data can be shown by a comparison of the accuracy and frequency of those data received through the Miami teletype with data from the existing remote radio-transmission systems in southern Florida. The great line-of-sight distances involved in the radio-transmission systems often provide "rare" and garbled data messages. The frequent meteorologic disturbances in southern Florida prevent the transmission of the accurate synoptic information on rainfall and water stage that is essential for managing the water for optimum conservation. ERTS-1 provides the U.S. Geological Survey with five transmissions per day of these parameters and warns when any DCP recorder becomes faulty, so that it can be repaired within 24 h. This enhances the opportunity for a constant flow of information and makes it possible for the Corps of Engineers to make daily decisions to optimize its water-control policy to conserve a greater proportion of the seasonally deficient water resource.

FIGURE 114 (above). Determination of surface-water storage in Conservation Area No. 1. Schematic diagram of the use of space-relayed data to calculate surface-water storage. ERTS data from three successive passes on Feb. 14, Mar. 4, and Mar. 22, 1973, of Conservation Area No. 1 are used to demonstrate the feasibility of determining surface-water storage. [larger image] FIGURE 115 (above). Electronically processed part of ERTS-1 image 1242-15240 of Conservation Area No. 1. Each dot represents 4 ha of surface water. [larger image]

References:

• Higer, A.L., Cordes, E.H., and Coker, A.E., 1973, Modeling subtropical water-level dynamics distribution [abs.]: NASA Goddard Space Flight Center, Symposium on Significant Results Obtained from the Earth Resources Technology Satellite-1, 2d, New Carrollton, Md., Mar. 1973, Proc., v. 1, sec. A, p. 793.
• Higer, A.L., Coker, A.E., and Cordes, E.H., 1974, Water-management models in Florida from ERTS-1 data: NASA Goddard Space Flight Center, Symposium on the Earth Resources Technology Satellite-1, 3d, Washington, D.C.., Dec. 1973, Proc., v. 1, sec. B, p. 1071-1088.