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<br /> <br />United States Department of the Interior <br /> <br />GEOLOGICAL SURVEY <br />Box 25046 <br />Denver Federal Center <br />Denver. Colorado 80225 <br />Mail Stop 11415 <br /> <br />IN REPLY REFER TO: <br /> <br />Water Resources Division <br />Colorado District <br /> <br />r <br /> <br /> <br />October 21, 1975 <br /> <br />Memorandum <br /> <br />To: <br /> <br />The Record <br /> <br />From: <br /> <br />R. C. Christensen, WRD, Lakewood, Colorado <br /> <br />Subject: MEETINGS -- Quality control review of Palmer Lake and <br />Jefferson County aerial photogrammetry <br /> <br />On October 15, 1975, McCain, Petsch, Jarrett and Christensen traveled <br />to Loveland, Colorado and met with Ron Hogan and others of Hogan and <br />Olhausen, P. C. to discuss problems encountered in quality control <br />check of valley cross sections obtained by aerial photogrammetry at <br />Palmer Lake and two ground control elevations in Jefferson County. <br /> <br />Harold Petsch reviewed the differences found between the USGS cross <br />sections determined by field surveys at road crossings and those from <br />aerial photogrammetry. Cross section shapes generally agreed but <br />differences in elevation varied up to three feet. .These differences <br />in the cross sections were difficult to understand when field surveys <br />on several ground control targets checked within 0.07 foot. Ron Hogan <br />quickly surmised that the problem probably lies in the proper adjustment <br />of the stereo plotter. The plotter had recently been checked by the <br />manufacturer and some adjustments made. Mr. Hogan said they would <br />reset the stereo models and check the cross sections to determine <br />the problem. All cross sections at Palmer Lake will be rerun if found <br />necessary. <br /> <br />Rulon Christensen reported that two ground control elevations in Jefferson <br />County had been found in error by 6.3 and 1.7 feet. All other ground <br />control points in the area were found within ~ 0.2 foot. Subsequent <br />checking ;n the field on the following day, it was found that the <br />two ground control points found in error had been moved a short distance <br />to new locations that corresponded with the given elevations. <br /> <br />Ron !logan indicated that about one-third of the valley cross sections <br />\.UT/afor Jefferson County were done and the remaining cross sections would <br />~~~~~O~~. ~.:omPleted about November 20. <br /> <br />.;c ~?J~'--I <br />~ ~ ( J' 'm <br />~7-i- ~~ ,,1 <br /> <br />'?;-6_191D ..", <br />