m 



FUTURE DIRECTIONS IN OCEAN SCIENCES W 



vations from ships or instrumented drifters are required to im- 

 prove the mathematical relationships (algorithms) for calibrating 

 satellite observations to in situ values. 



A suite of satellites launched by the United States, the Euro- 

 pean Space Agency, and Japan and with many joint satellite mis- 

 sions should provide many data required by physical oceanogra- 

 phers during the next decade. Advances in physical oceanography 

 are tied closely with satellite views of the ocean and telemetry of 

 data from Earth's surface. Coordination of satellite projects with 

 ocean science objectives and in situ ocean measurements is re- 

 quired. The satellite time series of sea surface temperature, winds, 

 sea ice, ocean color, and ocean height must be continued without 

 interruption to provide a complete record of their variability. 



Tracers Distribution of ocean properties can be used to depict 

 the pattern of ocean currents and the effects of mixing within the 

 ocean because water masses from different source regions vary in 

 their physical and chemical signatures. Traditionally, tempera- 

 ture, salinity, oxygen, and nutrient concentrations have been used 

 to track the movement or spreading of ocean water masses. Other 

 more exotic chemicals present in minute concentrations (tracers) 

 are now commonly used to track water masses. For example, 

 chlorofluorocarbons, carbon- 14 and tritium from atmospheric nuclear 

 bomb testing, and other natural and synthetic substances with 

 known rates and times of input to the atmosphere have been used 

 as tracers. Tracers average the spreading action of ocean circula- 

 tion at a variety of scales and integrate the effects of many pro- 

 cesses. The infiltration of naturally occurring and synthetic chemical 

 tracers into the ocean provides insight about the time scales of 

 ocean circulation and mixing. The development of baseline time 

 series of tracer concentrations is important. 



Acoustic Techniques Because the ocean is transparent to sound 

 but opaque to light, acoustic techniques provide oceanographers 

 with the opportunity to see the interior of the ocean. In a real 

 sense, the hydrophone array serves as the underwater eyes and 

 ears of the oceanographer. The enormous bandwidth of available 

 underwater acoustic instrumentation (10"-^ to 10^ hertz) allows 

 sound to be used as a probe of structures and processes whose 

 scales range from millimeters to ocean basin scales. The ocean is 

 especially transparent to low-frequency sound. Consequently, 

 underwater sound is becoming an important means of studying 

 the three-dimensional structure of the ocean below its surface. 

 Continuous measurements of current velocity from shipboard acoustic 



