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MEMO 93 <br />The Landsat MSS imagery was obtained in SOM projection to facilitate scan line corrections necessary <br />on any Landsat MSS imagery. Scan line corrections are discussed further in Section 2.3 of this memo. <br />Historic aerial photo indexes originally collected by the Farm Service Agency (FSA) were obtained from <br />the Aerial Photography Field Office (APFO) in hardcopy prints, and then scanned at 300dpi to GeoTiff <br />file format. (For more details on aerial photo indexes acquired for this project, refer to SPDSS Technical <br />Memorandum 93.1.) <br />2.1 Geometric Correction <br />The geometric correction followed the processes documented in SPDSS Technical Memorandum 89.2, <br />Section 2.2.2. Some Landsat MSS scenes were processed by a separate contractor for increased accuracy <br />of geocorrected imagery over mountainous terrain within frames 37/32, 36/32, 36/33, and for correcting <br />within-scene geometric anomalies in frame 35/32. Riverside Technology, inc. (RTi) conducted geometric <br />correction for all Landsat TM frames and for Landsat MSS frames (34/32 and 35/33) using procedures <br />described in SPDSS Technical Memorandum 89.2. The native resolution of Landsat MSS is 80 meters; <br />USGS then resamples the imagery to 60 meters before sale and distribution. RTi resampled all Landsat <br />MSS imagery to 30-meter resolution during geometric correction to aid comparison with 30 meter 1987 <br />and 2001 Landsat TM/ETM imagery. Landsat TM and MSS geometric correction root mean squared <br />(RMS) errors were less than one pixel (30 meters). <br />As described in SPDSS Technical Memorandum 93.1, Section 3, the historical aerial photo indexes are <br />actually a "collage" of individual photos stapled together. For geometric correction, aerial photo indexes <br />were corrected with a third order polynomial model to match 2001 Digital Ortho Quadrangles (DOQs) <br />with 5-10 points per aerial photo index. Due to the internal errors of each photo index, RMS errors were <br />greater than the one pixel standard used with satellite imagery, as expected. The geometric correction <br />applied to each of the 69 aerial photo indexes was intended only to place the photo index into <br />approximately the correct geographic location. Geometric correction applied to aerial photo indexes was <br />further refined during parcel update procedures (described in Section 4.1.2.2 of this memo). <br />Figure 2 compares a similar area of geometrically corrected Landsat TM, MSS, and aerial photo index <br />for an area near Fort Collins, Colorado. <br />Page 3 of 59 tij,Rarera~de ~eshn~f~gy, ~os~ <br />