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4. Comments and Concerns <br />The multi-temporal satellite image analyses used for this application were effective in identifying both <br />large and small water bodies in the SPDSS study area. Many of the water bodies fluctuate in extent at <br />different times throughout the growing season and a <br />Figure 3. North Sterling Reservoir at Low Level single image will not capture the maximum water level <br />of all water bodies. By analyzing multi-date imagery, <br />the maximum extent of all water bodies was well <br />represented. As an example, Figure 3 shows North <br />Sterling reservoir at a low water level, as compared <br />with the same reservoir in Figure 1, at a high water <br />level. <br />In accordance with the SPDSS Phase 3 Scope of <br />Work, water bodies with size three acres and greater <br />were mapped. The water bodies less than three acres, <br />which make up an additional 10 percent, <br />approximately, were eliminated from the results. <br />These smaller water body delineations are not accurate <br />and their utility is very limited without extensive <br />review and editing. <br />The Normalized Difference Water Index (NDWI) was <br />tested under this application. The NDWI is not awell- <br />documented procedure and it was determined to be <br />less accurate and less effective than the multi-date <br />hybrid classification procedure used. <br />Page 3 of 3 ~fxlversfde Technology, fnc. <br />V.Lrrc- Aesourc.~s Frr4r.~ec.•mq .m~Y Corzsuxrnq <br />Figure 2. Example of Water Bodies from <br />Figure 1. Example of Large Reservoir Extent <br />