AIRBORNE INFRARED OCEANIC MAPPING 



by Paul M, Moser, U. S. Naval Air Development Center, 

 Johns ville, Pennsylvania 



INTRODUCTION 



Since October 1957 the U.S. Naval Air Development Center has been conducting 

 studies of the sea surface by means of an infrared radiometer and a variety of infrared 

 mapping devices installed in aircraft. Quantitative information on both intensive and ex- 

 tensive variables of the sea surface are obtained. The radiometer measures infrared 

 radiation emitted and reflected by the sea surface along the flight path of the aircraft; the 

 mapping devices provide thermal pictures which reveal the size, shape and structure of 

 thermal patterns on the sea surface. In this manner, it is possible to identify fluctuation 

 of the recording pen of the radiometer (that might otherwise be disregarded as "noise") with 

 the surface thermal expressions of a large variety of oceanic phenomena. 



INSTRUMENTS 



The radiometer, which was built by Barnes Engineering Company, has an 8-inch 

 diameter, f/l.5, Cassegrainian optical system and employs two germanium-immersed 

 thermistor bolometer detectors yielding angular fields -of -view of 2.0° by 0.4°. The noise- 

 equivalent-temperature-difference (sensitivity) of the radiometer is 1.3 x 10~3 c°. In 

 flight, this sensitivity is degraded to approximately 0.01C°. 



The infrared mapping devices are essentially scanning radiometers whose outputs are 

 recorded on photographic filmas continuous-tone thermal pictures of the sea surface. Repre- 

 sentative equipments used belong to the Reconofax family of infrared mapping devices built 

 by HRB-Singer, Inc. The pictures produced are "strip-maps" whose widths correspond 

 typically to a distance of 5.5 times the altitude of the aircraft and whose lengths correspond 

 to the distance traveled by the aircraft while the device is operating. The sensitivities of 

 the mapping devices can be made comparable to that of the radiometer. 



OBSERVATIONS AND CONCLUSIONS 



The following is a summary of observations and conclusions based upon studies of 

 thermal pictures of over one hundred square miles of ocean surface. 



A. Factors that act at the air/sea interface to influence infrared radiation therm- 

 ometer (IRT) readings. 



1. Evaporation (Rate of evaporation is a function of air temperature, water 

 temperature, solar irradiation, humidity, wind speed, surface films.) 



-37- 



