Laserfiche WebLink
MEMO 93 <br />imagery. Results were evaluated and adjusted to represent irrigated areas more accurately. Pixels with <br />NDVI values above the predetermined NDVI thresholds for any of the Landsat acquisition dates passed <br />the threshold and were classified as potentially irrigated. The potentially irrigated NDVI rasters were <br />then used as guides for distinguishing between irrigated and non-irrigated vegetation while delineating <br />irrigated parcels. <br />4.1.2 Irrigated Parcel Delineation <br />Irrigated parcels were delineated using a hierarchal approach. The 2001 parcel layer served as the starting <br />point for the 1987 parcel layer. The 1987 parcels were used as a starting point for the 1976 parcels, and <br />1976 parcels for the 1950s mapping (Figure 5). <br />2001 Irrigated <br />Parcels <br />1987 Final <br />Irrigated Parcels <br />1987 Satellite <br />imagery <br />1976 Satellite <br />imagery <br />1976 Final J <br />Irrigated Parcels <br />1950s Aerial <br />Photo Indexes <br />1950s Final Irrigated <br />Parcels <br />Figure 5. Process flow for historical irrigated parcel creation and update. <br />4.1.2.1 1987 and 1976 Parcels <br />The 1987 and 1976 preliminary parcel layer was updated using afive-step procedure similar to that used <br />for the 2001 parcels as described in SPDSS Technical Memorandum 90.2. The five-step process <br />included: printing maps, interpreting maps and drawing boundaries, QC/QA of field boundary drawings, <br />digitizing boundaries, and QC/QA of the digitized field boundaries. As described in SPDSS Technical <br />Memorandum 90.2, large format maps were printed for the portions of the majority of the study area with <br />irrigated parcels. Printed maps aided in interpretation and update of the 2001 parcels to 1987, and 1987 <br />to 1976. The maps were printed at a convenient size with a scale of 1:24,000 for 1987 and 1:30,000 for <br />1976. Two maps were printed for each area and are described as follows: <br />a. The first map displayed the NDVI threshold composite, as described in Section 4.1.1 of this <br />memo. These maps were primarily used as supplemental information for manual photo <br />interpretation of irrigation status. <br />b. The second map displayed 1999 DOQs overlaid with asemi-transparent NDVI composite <br />threshold raster (as described in Section 4.1.1 of this memo), overlaid with the historic <br />preliminary irrigated parcels layer. These maps were used as the base for updating irrigated <br />parcel boundaries. Parcels were added, modified or removed, and parcel attributes were updated <br />for irrigation type and status. <br />Page 10 of 59 ,Rereradde ~eshn~P~gy, ~os~ <br />