POSITIONING OF THE GULF STREAM 

 BY MEANS OF AERIAL INFRARED RADIATION THERMOMETER MEASUREMENTS 



J. C. Wilkerson 



U.S. Naval Oceanographic Office 



Washington, D.C. 20390 



INTRODUCTION 



Fluctuations of the position and shape of the Gulf Stream can be 

 examined by three methods. One method consists of tracking the path 

 of the Stream by ship with a temperature sensor towed at a depth of 

 200 meters (Fuglister and Voorhis, 1965). By steering the ship along 

 the IS^C isotherm, which characterizes the horizontal temperature 

 gradient of the Gulf Stream's inner edge at 200 meters, the position 

 and shape of the Stream can be charted over long distances. The sec- 

 ond method is to fly along the length of the current guided by radio- 

 metric observations of the sea surface structure. Stommel et al. 

 (1953), von Arx and Richardson (1953), and von Arx, Bumpus, and 

 Richardson (1955) developed the technique and conducted repeated 

 aerial surveys of the Gulf Stream boundary. Aerial observations, 

 made with an airborne radiation thermometer, position the inshore 

 boundary of the Gulf Stream at points of sudden change in character- 

 istics of the contrast in surface temperature between the Gulf Stream 

 and adjacent slope water. The Gulf Stream boundary can be followed 

 by positioning of the aircraft at frequent intervals and by steering 

 the aircraft so as to intersect the line of sudden temperature change 

 at the sea surface. The third method of examining the Gulf Stream is 

 observation of the thermal emission of the sea surface by satellite 

 with a high resolution infrared radiometer such as those used aboard 

 the NIMBUS II meteorological spacecraft. In the absence of clouds, 

 the contrast in surface temperature between the Gulf Stream and colder 

 slope water (as much as lO'C in several hundred meters) is clearly 

 visible in infrared imagery (Wilkerson, 1967). The inshore boundary 

 of the Gulf Stream can be tracked for distances of 1000 km seaward 

 from the east coast of the United States by means of repeated satel- 

 lite observations under cloud-free conditions. 



The relationship between the frontal position detected from 

 ships and aircraft has been studied by Strack (1953), who found that 

 the frontal outcrop at the surface is closely associated with the 



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