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<br />- ----- 0-----... ---- - ---"-----~~.:..___'~~____'~_'_~="'"_~~....._..,_ __~.~_...k;_'____'"__~.J.,~. .,.'-':_._.,1~.~_~C'~. ~__';;:J-.._~::...___._~ ,-:~_~_",,'-"----_~"',~""'" ....=.-:.:'.,. <br /> .-, ...~, --"""".."""'-....~"Ua.&..,> <br /> <br />18 - <br /> <br />area of 23,392 m2 at Island Park. Airborne videography acquired on the,same <br />date for the same river segment resulted in a total backwater area of <br />21,611 m2 or a difference of only 7.6 percent. Some backwaters identified <br />on the aerial photography were not identified on the videography by the <br />interpreter. In addition, some flow through areas were mistakenly <br />identified as backwaters on thevideography. Thirty backwaters, or <br />71 percent, were common to both the photography and video images. The.. <br />backwater area of the 30 videography backwaters was 19,206 m2, or about <br />82 percent of the aerial photography total (23,392 m2). <br /> <br />A total of 34 backwater polygons were compared for area calculations between <br />aerial photography/GIS and airborne videography/MIPS acquired on August:-23; <br />1988, at the Jensen site. Backwater area was calculated as 10,989 and <br />10,604 m2for the aerial photography and airborne videography, respectively. <br />This was about a 3.5 percent difference between the two techniques. The <br />average backwater size was 323 and 312 m2 for aerial photography and <br />airborne videography, respectively. Differences in mean backwater size were <br />not significant (P <.001) and a simple sign test indicated that <br />videography/MIPS did not consistently over or under estimate backwater area. <br />Regression of photography and videography backwater areas on a log x log <br />scale was highly significant (r2 => .98). <br /> <br />Airborne videography was acquired on September 7, 1988, for the same segment <br />of Island Park. Videography was acquired with an Ikigami video camera <br />rather than the Panasonic camera used for the August 23 videography. The <br />resulting images were of better quality than the Panasonic video which had <br />excessive blue and insufficient red tones, possibly hindering image <br />interpretation. Backwater area calculated from the September 7 data was <br />25,170 m2. Green River flow on this date at the USGS Jensen gauge was <br />912 ft3/s. Although no concurrent aerial photography was available for this <br />flow or date, an interesting observation was noted. Aerial photography <br />(1:4,000 scale) acquired during the summer of 1987 during six different <br />flows at Island Park was used to calculate Backwater area. A regression <br />equation from these data [backwater area = 31,200 + (-10.2)ft3/s] predicted <br />backwater area for Island Park at a flow of 912 ft3/s to be 23,200 m2, or- <br />only 8 percent less than the backwater area calculated from the September 7, <br />1988 videography. <br /> <br />Table 17-presents cost comparisons between aerial photography/GIS and <br />airborne videography/MIPS techniques. <br />