COMMENTS ON THE VALIDITY OF SEA SURFACE TEMPERATURES AS MEASURED WITH 

 THE BARNES INFRARED THERMOMETER* 



by Robert A. Ragotzkie, Department of Meteorology, University of Wisconsin, 

 Madison. Wisconsin 



The Barnes IT-1 and IT-2 (Infrared Thermometer) are being used extensively for 

 surveying the surface temperature of lakes in Wisconsin and central Canada north to the 

 Arctic coast and for mapping surface temperature of Lakes Michigan and Superior. In the 

 course of these airborne measurements, a number of field checks on the validity of the IT 

 results have been made. Airborne measurements were made from either a U.S. Navy P2V 

 or from a Cessna 195 floatplane at an altitude of 1000 feet or less. Surface checks were 

 made by measuring the water temperature in the upper 5 cm layer with a thermistor therm- 

 ometer which had been calibrated against a certified mercury thermometer. 



These measurements were made either from a small boat directly under the flight 

 path of the aircraft or from the float plane which landed im.mediately after the airborne 

 measurement was complete. On Lake Superior checks have been obtained from University 

 of Wisconsin geophysicists aboard Coast Guard vessels. A calibrated thermistor therm- 

 ometer supplied by us was used, and measurements were made at the time of fly-over by our 

 aircraft. Results were transmitted by radio and compared to the airborne measurement 

 immediately. The points below 20 °C were obtained on Canadian Lakes and those above 20°C 

 on Wisconsin Lakes. Table 1 gives additional paired data which are not included in figure 1. 



In the paired data given in figure 1 the airborne measurements are in all cases either 

 equal to or higher than the in situ measure m.ents with a tendency for the differences to be 

 larger as the roughness of the water surface decreases. However, later measurements (see 

 table) indicate that airborne measurements can be either higher or lower than in situ meas- 

 urements. For example the 1 June 1964 data were all collected between 1545 and 1645 CDT, 

 and all but one of the airborne measurements indicated a lower surface temperature. Water 

 temperatures were measured at the surface (5 cm) and at 25 cm intervals down to 50 or 100 

 cm. On Lake Koshkonong where the airborne temperature was slightly higher, the water sur- 

 face was nearly smooth and the top meter of water was thermally stratified indicating sur- 

 face heating was occurring. In the other three cases for this date the airborne measurement 

 was lovv and the top layer of water showed a slight inverse temperature stratification indi- 

 cating surface cooling probably due to increased evaporation from wind action. On Lake 

 Superior the differences were in both directions, but there is insufficient surface data to 

 attribute the discrepancies to any particular factors. 



It is clear that the water temperature obtained from an airborne IT may be either 

 higher or lower than that obtained in situ . Even disregarding atmospheric absorption or 

 emission errors and small reflection errors, it is clear that the results of infrared 



* This research was sponsored by the Geography Branch of the United States Office of 

 Naval Research under contract No. Nonr 1202(07). 



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