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MEMO -TASK 90.1 <br />Table 1. Source of imagery used for Image Base Map <br /> <br />Source <br />Area (ac) <br />Percent of Total Range of Source <br />Date Ground <br />Resolution Distribution <br />Restrictions <br />USGS 8,876,952 61.6% 1988-2002 1 Meter Public <br />USGS/CWCB <br />Update <br />3,114,191 <br />21.6% <br />1998-1999 <br />1 Meter <br />Public <br />IRS 72,874 0.5% 1997 6 Meter Public <br />Landsat 36,501 0.3% 2001 15 Meter Public <br />eld County 2,310,274 16.0% 1998-2001 1-3 ft Restricted <br />Total 14,410,792 <br />Table 2. Date of ima~erv used for lma~e Base Ma <br />1988 - 1990 272,820 1.9% <br />1991 - 1993 155,450 1.1 <br />1994 - 1995 337,815 2.3% <br />1996 - 1997 72,874 0.5% <br />1998 - 1999 10,934,939 75.9% <br />2000 - 2002 2,636,894 18.3% <br /> 14,410,792 <br />The procedure used to create the image base map for the SPDSS study area is summarized as follows: <br />• Available USGS DOQQs, in GeoTiff format, were acquired for the study area. The dates of <br />these DOQQs range from 1988 to 2002. In addition, the USGS was contracted by CWCB, <br />under cooperative agreement to update 340 DOQQs that were from 1993 and older. <br />• Digital orthophotography for Weld County was obtained under agreement with CWCB and <br />Weld County. This imagery was acquired by Weld County in 1998 and 2001. <br />• IRS 1-C satellite imagery and Landsat panchromatic imagery was used to fill in a small portion <br />of the image base, which was unavailable from the USGS or other sources. <br />• All of the imagery was mosaicked and compressed into MrSID format. The image was then <br />broken into 23 seamless tiles for ease of distribution and storage (Figure 5). <br />Due to the large size of the study area and the high resolution of the Image Base Map data, a compression <br />technology was selected to reduce the data files to manageable sizes. The MrSID compression format, a <br />technology of LizardTech, Inc. of Seattle, Washington, was chosen for the image compression. MrSID <br />provides a 12:1 compression ratio for grayscale imagery while maintaining geometric accuracy. The <br />image base map was made from the Generation 2 MrSID format. MrSID files can be used in <br />ArcExplorer, ArcView 3.x, and ArcGIS 8.x. The compressed imagery can be viewed with these software <br />packages by simply adding the data as with any other GIS data layer. In ArcView 3.x, the MrSID Image <br />Support extension must be checked "on". The extension is included with standard ArcView 3.x software. <br />3. Deliverables <br />Accompanying this deliverable are two DVDs containing the image base and associated data (Table 3). <br />The DVD entitled "SPDSS Image Base Map 10/30/2003 (CWCB Use Only)" contains the most current <br />image base map with proprietary data from Weld County. The DVD entitled "SPDSS Image Base Map <br />10/30/2003 (Distributable)" contains the distributable version of the image base map, with older USGS <br />data substituted for Weld County. Both DVDs contain shapefiles with source image boundaries and <br />Page 3 of 8 fRrversFde Technology, Itrc, <br />Wamr Resoarccs Engineering and Cunsuiting <br />