1. Division of Engineering Science, California Institute of Technology, Pasadena, California 91125.
2. On leave from Laboratory for Hydrospheric Processes, Oceans and Ice Branch, Code 971, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771
3. Division of Engineering Science, California Institute of Technology, Pasadena, California 91125
4. Department of Civil Engineering, University of California at Irvine, Irvine, California 92697
5. Laboratory for Hydrospheric Processes, Observational Science Branch, Code 972, NASA GSFC, Wallops Flight Facility, Wallops Island, Virginia 23337;