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~..."w Proceedmgs of the Seventh Federal Interagency Sedimentation Conference. March 25 to 29, 2001. Reno, Nevada . ROTATING SIDE-SCAN SONAR TECHNOLOGY Hardware: Rotating side-scan sonar is well suited for field observations of bedform migration. It scans circular areas of the bed and has a range of tens of meters and a resolution of a few cm; it works in turbid water; and it can record sequential observations from a single point over time intervals of many hours. The first bed-deployed rotating sonar was an analog system that weighed several hundred pounds (Rubin et aI., 1983). Modern commercially available systems are digital and weigh just a few pounds. The system that we tested operates at 675 kHz and records up to 2000 acoustic pixels per acoustic ping. The transducer is mounted approximately 1 m above the bed. At a range of 10 m, it records 1000 pixels per ping (I per cm) and takes 1-2 minutes to complete each circular scan. A typical deployment recorded several hundred complete scans over a duration of 10-20 hours. Data Drocessiol!: Sequential images at a site were converted into digital movies and displayed frame by frame on a computer screen. Individual dunes were tracked, and their migration speeds determined from the observed migration distances and times. Dune height was determined from fathometer profiles collected when the rotating side-scan sonar was deployed or by calculations from dune wavelength and assuming a height/wavelength ratio of 1/15. A preferable option would be to use a rotating interferometric or multibeam system to record 3-dimensional topography, rather than the 2-dimensional planfonn images recorded by standard rotating side- scan sonar. . EXAMPLE The rotating side-scan sonar was deployed at approximately 20 locations in the Colorado River in Grand Canyon, Figure I. shows two images and bedform-migration vectors at one of these sites. . III - 140