properties of the terrain. The few data sets collected to date 

 have not provided sufficient coverage nor adequate ground truth 

 information to allow such a comparison. 



DISCUSSION OF 1987 NURP SPONSORED PROGRAM 



During the September-October 1987 Alvin expedition sponsored 

 by NURP and the NOAA VENTS program, a simultaneous experiment was 

 funded by NURP to collect a complete Sea Beam backscatter data 

 set at Axial Seamount. Axial Seamount is located on the central 

 Juan de Fuca Ridge and has been the focus of extensive 

 geological and geophysical investigations by NOAA's VENTS 

 research program (see Embley et al., Chapter II, this volume). 

 The experiment resulted in over 2.5 gigabytes of backscatter data 

 concentrated at Axial Caldera. In addition to a full coverage 

 survey of the seamount summit, an intensive, transponder- 

 navigated survey of the ASHES hydrothermal vent field within the 

 caldera was conducted. 



These data, collected within transponder coordinates over an 

 area with tens of thousands of bottom photographs also 

 transponder navigated, provide the best controlled data set to 

 date for relating acoustic backscatter information to the 

 controlling physical properties. Since the data were collected 

 only weeks before the Undersea Symposium, no results are 

 available at this time. The method may prove particularly 

 applicable to NURP ' s future submersible operations. 



The presence of hydrothermal sediment and extreme black 

 smoker terrains associated with the ASHES vent field may produce 

 a very distinctive backscatter signature. Since much of the 

 current submersible-based research being conducted in the deep 

 ocean involves the investigation of hydrothermal systems, the 

 technique may provide a remote sensing tool for identifying 

 hydrothermal areas. As the Sea Beam equipment and Alvin reside 

 on the same platform, the two systems may be used in tandem for 

 exploration. 



LITERATURE CITED 



Clay, C. S., and H. Medwin. 1977. Acoustical Oceanography: 



Principles and Applications . New York, N.Y. , John Wiley & 

 Sons. 544 pp. 



deMoustier, C. 1986. Beyond bathymetry: mapping acoustic back- 

 scatter from the deep seafloor with Sea Beam. Jj_ Acoust . 

 Soc. Amer. , Vol. 79, No. 2, pp. 316-331. 



deMoustier, C. 1985. Inference of manganese nodule coverage 



from Sea Beam acoustic backscatter data. Geophysics , Vol. 

 50, No. 6, pp. 989-1001. 



