perturbations and residual navigation errors, remain in the printed scene. The
distortions are adjusted for with the aid of land/water boundaries when the
analysed data are transferred to the map.
Temperature values for individual point locations can also be extracted
from the printout and stored in computer-accessible format.
| ATMOSPHERIC ENVIRONMENT SERVICE
| HYDROMETEOROLOGY DIVISION
Surface Water Temperature
Area LAK NTARI
Satellite NV — 7 Orbit 2396 —
Date 30 SEP/E/ Time _ Q9. GMT
Mean Temperature — — 12.5 Cc
| Scale
0 50 100 km
78°
Fig..‘2 Lake Ontario temperature analysis from data of Fig. 1.
ATMOSPHERIC CORRECTION
The water temperatures are retrieved from radiances in the 10.5-11.5 um
spectral region where attenuation by water vapour and other gases is relatively
small and reflection from a water surface is also minimal. Hence, water
temperature can be calculated radiometrically, using Kirchhoff's law and the
Planck functions, providing that attenuation by the gases, water vapour and
aerosols is accounted for.
The atmospheric correction method that is used to correct indicated
temperature is based on concepts sinilar to those of Wark et al. (1962). The
method employs the radiative transfer equation to integrate the contributions
by the different radiating, absorbing and reflecting sources in small wave-
number increments over the filter band-pass range of the sensor and through a
layered atmosphere. A method had been developed previously to correct water
temoeratures measured by an airborne sensor (Shaw and Irbe, 1972), which
yielded good results (standard error 0.5 C) in temperature surveys on the Great
Lakes (Irbe, 1972). This method was incorporated with the LOWTRAN (Low
Resolution Transmission) model of Selby et al. (1976) for use on satellite-
derived temperatures by Morcrette and Irbe (1978). In a recent study the
root-mean-square difference between SRT and buoy surface temperature
measurements on the Great Lakes has been found to be 0.6 C, if the satellite
zenith angle is less than 45 degrees and the atmosphere is relatively dry and
clear (Irbe et al., 1981).
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