SEA-SURFACE CONDITIONS REMOTELY-SENSED BY UPWARD-LOOKING ADCPS

Surface data obtained from 153-kHz acoustic Doppler current profilers deployed in the Greenland Sea at about 350-m depth during the winter o f 1988/89 were investigated under several aspects. First a method is d escribed to improve the instrument depth measurements using the binned backscattered energy profile near the surface. The accurcy of the dep th estimates is found to be significantly better than 0.5 m. Further, improvements of wind speed estimates were found by using the ambient n oise in the 150-kHz band in favor of the surface backscattered energy as suggested by Schott. Limitations of the ambient sound method at low wind speeds are presented when thermal noise overwhelms the wind-indu ced noise. Finally, a method to detect the presence of sea ice above t he ADCP is presented by cross correlating the surface backscatter stre ngth and the magnitudes of all Doppler velocity components. The result ing time series of ice concentration are in overall good agreement wit h Special Sensor Microwave/Imager estimates but allow for higher tempo ral resolution. Further, in the vicinity of the ice edge, enhanced hig h-frequency ambient noise in the 150-kHz band was observed.