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MEMO 93 <br />2.5 Image Enhancements: NDVI <br />As described in SPDSS Technical Memorandum 89.2, multi-temporal NDVI images produced by layer <br />stack of individual NDVI rasters for each Landsat frame were used along with the DOQs in manual photo <br />interpretation of irrigated parcel boundaries, as well as in subsequent processing for crop classification. <br />NDVI was derived from the difference between the near-infrared (NIR) bands and the visible red bands <br />region (e.g. Landsat TM Band 3) using the following equation: <br />NDVI =NIR Band -Red Band Where <br />NIR Band + Red Band <br />NIR band =Near infrared band (TM =band 4, MSS =band 4) <br />Red band =Red band (TM =band 3, MSS =band 2) <br />NDVI rasters for both Landsat TM and MSS were rescaled from floating point to 8-bit unsigned rasters as <br />described in SPDSS Technical Memorandum 89.2, Section 2.3.1. <br />Landsat MSS imagery is collected with a 4-bit sensor, translating into a brightness value range of 0-16. <br />The USGS later rescales all Landsat MSS imagery to 8-bit format before delivery to customers. This 8- <br />bit format is consistent with Landsat TM and ETM imagery, which corresponds to a brightness value <br />range of 0-256. This characteristic was taken into consideration when classifying Landsat MSS imagery, <br />as discussed in Section 4.2 of this memo. <br />3. Reference data <br />3.1 Crop Types/ Land Use Records <br />Extensive searches were conducted under SPDSS Task 93.1 for historic land use records, reference data, <br />and area specific crop type records for the period 1950 thorough the 1980s.Numerous state, federal, and <br />local agencies were searched, including the FSA, U.S. Department of Agriculture (USDA), USGS, <br />National Resources Conservation Service (NRCS), Agricultural Research Service (ARS), Colorado State <br />University (CSU), Northern Colorado Water Conservancy District (NCWCD), but no parcel specific crop <br />type data was found for 1987, 1976, or for the 1950s. For 2001 mapping, field specific crop types were <br />retrieved from the FSA through special arrangements with the FSA and the State of Colorado and through <br />extensive field surveys. However, the FSA destroys crop type records after a period five years, therefore <br />this valuable data was not available for this task. <br />The USGS land use/land cover (LULC) dataset and the USGS Front Range Infrastructure and Resource <br />Project (FRIRP) dataset were analyzed for potential use in SPDSS historic mapping. Both data sets <br />categorize land use to the Anderson Classification Level 3 (e.g. planted/cultivated) for 1990, 1970, 1950, <br />and 1930 (Anderson et al, 1976). This information covered a different time period than SPDSS historic <br />mapping and was determined to be insufficient for crop type mapping. <br />Two other detailed sources of historic land use records were reviewed and utilized for SPDSS historic <br />mapping activities: The 1930s hand-drawn maps available for Division 1, and a 1973 CSU research report <br />titled "Agricultural Land Use in the Poudre Valley" containing sketches of parcels with crop types for the <br />majority of Division 3. These data sets were reviewed and used to compare general trends and patterns of <br />irrigation practices compared to SPDSS irrigated lands mapping results. The mismatch of time period for <br />these historical land use records compared to SPDSS historic mapping activities prohibited detailed <br />comparison for this task. In addition, both data sources would require an excessive amount of preparation <br />time and labor before detailed information could be extracted from them. <br />Page 7 of 59 tij,Rareradde ~eshn~P~gy, ~os~ <br />