incidence, and found that it depended not only on the median 

 size of the particles making up the bottom, but also on the 

 sorting of the particles and on the bottom topography. 

 Working at 17 stations near Woods Hole, Massachusetts, 

 he obtained the following in situ reflection coefficients for 

 five gradations of materials at the sediment -water interface: 



mud to 0.20 



mud-sand 0.20 to 0.40 



sand-mud 0.40 to 0.60 



sand 0.40 to 0.85 



stony 0. 50 to 0.85 



It can be seen that sand and stony bottoms have the best 

 reflecting ability. Lieberman stated that an exact treatment 

 of the reflection from an irregular surface may be given 

 only if the geometry of the surface is completely specified. 



DEFINITION OF MICRORELIEF 



Earth forces and water movements have created 

 great trenches, rises, mountain ranges, seamounts, scarps, 

 and other significant relief features in deep-sea environ- 

 ments. The sediments that are continually forming at the 

 sea floor are also not without relief, even though this relief 

 is of very small magnitude compared to that of the larger 

 features. 



The term "underwater microrelief" usually refers to 

 those very small features not ordinarily detected by modern 

 echo-sounders. Laughton used the term "microtopography" 

 and defined it as referring to those features of the sea floor 

 that can be visually observed in the scale range of 50 meters 

 to 1 mm. (He regarded 50 meters as approximately the 

 limit of visibility in the clearest of oceanic water. ) Carsola 12 

 defined microrelief on the arctic sea floor as consisting of 

 the smallest features that can be resolved at depths between 

 and 200 fathoms (366 meters) with the NMC and NMC-2 



10 



