Field Determinations of Surface Emissivity and Temperature for Lake Ontario

Abstract

Field determinations of surface emissivity and temperature were carried out at the western end of Lake Ontario between July and November 1969. Emissivity was obtained from infrared thermometer measurements using an aluminum cone. Surface temperature was measured directly with floating thermistors and estimated from outgoing longwave radiation. Emissivity was constant at 0.972 with no detectable variation with water turbidity and chemical content changes. Float and infrared thermometer temperatures were in good agreement at times when there were no sensor problems. Temperatures calculated from the radiation balance agreed well at night with the other methods but showed irregular fluctuations and systematic overestimation during daytime probably due to errors in determining outgoing longwave radiation. Comparison with float data over the experimental period showed temperature differences ?T with a change of sign in September corresponding to a sign change in the difference between air and water surface temperatures. Both the sign and order of magnitude of ?T may have been due to divergence of the upward longwave radiation flux.