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WSP02238
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Last modified
1/26/2010 12:35:30 PM
Creation date
10/11/2006 11:00:00 PM
Metadata
Fields
Template:
Water Supply Protection
File Number
8220.101.10
Description
Colorado River-Water Projects-Glen Canyon Dam/Lake Powel-Glen Canyon Adaptive Management
Basin
Colorado Mainstem
Water Division
5
Date
1/1/2004
Author
Phillip Davis
Title
Review of Results and Recommendations from the GCMRC 200-2003 Remote Sensing Initiative for Monitoring Environmental Resources Within the Colorado River Ecosystem
Water Supply Pro - Doc Type
Report/Study
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<br />00848 <br /> <br />submerged cobble bars or debris Ilows. The photogrammetric approach using stereo-pair images, <br />which was suggested by Ihe remole-sensing PEP (Berlin et al.. 1998). is extremely difficult to <br />apply in watcr due to corrections for refraction and would be limited in its application to clear- <br />water regions. We investigated the use of stereo image data to derive substrate elevations for <br />shallow, calm-water areas that had ground truth bathymetry and found that the lack of texture on <br />sandy substrates precluded image correlation between the stereo images. which is necessary for <br />derivation of topography. Therefore. the backscatter multibeam approach appears to be thc most <br />viable approach for channel bathymetry despite its data processing limitation. <br /> <br />Grain-size distribution on the channel substrate is currently mapped using a combination <br />of side-scan sonar and underwater videography. The sonar beam scans across the channcl <br />substrate producing a single image strip that has different perspective views on each side oflhe <br />sonar image (centered on the boat position). Such imagery is extremely difficult to orthorectify <br />and mosaic due to a lack of the sonar's fish pointing characteristics (pitch, roll, and yaw) and <br />point-perspective distortions. Consequently, side-scan sonar has not proven to be a productive <br />tool for imaging the substrate. In addition, the resulting rectified sonar image data have <br />positional accuracies of only 2-3 m at best. Videography is used in conjunction with the side- <br />scan sonar surveys to record the surface characteristics of the substrate. which was initially <br />recommended by the remote-sensing PEP (Berlin et aI., 1998), but the panel subsequently <br />recommended that videography be replaced with alternative sensors. New software (QTC <br />Multiview) for processing backscatter multibearn data can supposedly map bed composition. but <br />the software has not yet been fully evaluated to determine its mapping accuracy for grain-size <br />distribution on the channel tloor. <br /> <br />Thcre are airborne imaging approaches that may provide good water penetration in <br />order to image the channel substrate under clear water conditions. This approach is rather simple <br />and rapid in its image processing, is cost-effective, and provides wide-area coverage with <br />positional accuracies of at least I meter. Photographic lilm acquired with long exposures or <br />digital image data acquired with a high-gain state provide maximum water penetration, but digital <br />cameras that can record a larger range of radiance provide better image data for channel <br />substrates. 10 August and September of 2000, an experiment was performed using a digital <br />(CCD) panchromatic imaging system that acquired main-stem image data above Lees Ferry using <br />a high-gain detector setting (equivalent to increasing the exposure time on photographic film). <br />The Iwo image acquisitions bracketed a spike Ilow in early September; the resulling image data <br />clearly show morphologic detail on the channel substrate and clearly show changes in channel <br />sand storage due to the spike-tlow release (Figures 23-25; Chavez et aI., 2002a). The image data <br />appear superior to the image data produced by side-scan sonar _~lthough this technique requires <br />relatively clear water for substrate imaging, there are periods when sediment input is quite low <br />(such as 2002 and 2003). The present condition oflow sediment input has allowed the physical <br />resource program to extend this experiment to include the first 100 miles of the eRE using Pat <br />Chavez's CIR sensor, which has one wavelength band optimized for water penetralion. The Ihree <br />wavelenglh bands were acquired at different gain states. The blue-green band was acquired at <br />high-gain for water penetration, the red band at moderate gain for moderate water penetration, <br />and the NIR band at normal gain to provide land data for image registration. This sensor is <br />capable of obtaining images at 8-cm resolution. close to the 3-5-cm rcsolulion provided by side- <br />scan sonar, which is necessary to detect differences in grain size on the substrate. Such high <br />resolutions acquire a Ilight height of about 100 m, and the NPS did not allow this low-altitude <br />Ilight wilhin the Grand Canyon. However, data were acquired at 300 m AGL within the Grand <br />Canyon producing CI R data with 15-cm spatial resolution. Even at this lower resolution, the <br />high-gain image data clearly showed locations of various types of sediment storagc within the <br />channel, where the water depth allowed light penetration to the substrate. In fact, variation in <br /> <br />21 <br />
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