WSP11909

• File Number: 8220.101.10.B
• Description: Colorado River-Water Projects-Glen Canyon Dam/Lake Powell-Glen Canyon Adaptive Management-TWG
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 2/26/2003
• Title: Packet for Distribution to TWG-GCMR Bibliography-Aerial Imagery Inventory-Remote Sensing Reports
• Water Supply Pro - Doc Type: Report/Study

An accuracy assessment of UDAR data acquired over Atlantic coastal beaches abo showed
LIDAR dala to he parallel 10. but oflset from. the true ."Jur/lce (Shrestha el al.. 19QQ). Thc obse("\ed
offst"ts ranged from +0.20 m to -0.10 m. The ohse("\'ed oflSefs r-ere used to adjust the U[)AR data down
or up to the true ground surface. This adjustment approach could be l'mploy ed in the Grand Canyon. but
(he approach \\ould require careful selection of the "ground truth". points 10 maKe thc adjustmenls. The
ground truth points would ha\e 10 tle much larger in area than the hori1olllal positional accuracy of
UDAR and the elevations of the ground truth points "ould have to t.: stable. similar to a lopographic
control networK.

Assuming that elevation otTsels could be accurately dc-tennined in an operational sense lor
UDAR data acquired in the Grand Cany(m. \.loe applied the elevation offsets found at each study area (0
Iheir respecti\c L1D..\R data and recomputed the elevation errors at each sludy area. The adjusted
ele\'alion errors for the RAMS L1DAR data are lo\\er than their unadjusted elevation errors in all the
stud~ areas; the adjusted elevation errors range from 0.06 In to 0.17 m n able :2). In contrast. the adjusted
elevation errors for the ALMS L1DAR data are nearly Ihe same as the unadjusted error values at most
sites (ranging from 0.:21 m to a.85m: Table 2). This disparily bct""een the datasets reflects the- fact that the
RAf\.IS UDAR data has a consistent parallel otTset from the surface (and is therefore potentially
correctable). \\hile the A Lf\'1S L1DAR data Iluctuates in an inconsistent manner Ihal maKes it impossiblt.'
10 appl~ a correction factor.

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