Atmospheric IR Transmission Data for a Temperate Maritime Environment.

Measurements are reported on infrared transmission through the atmosphere at a coastal marine site in a temperate environment. Ten broadband spectral regions were used and variations of transmittance with absolute humidity and visibility over paths of 5 and 9 km investigated. All data have been compared with the predictions of the AFGL computer code LOWTRAN 5. The discrepancy reported previously between the measured and calculated data in the 4.4 to 5.4 micrometer region still exists, although new data on the water continuum absorption coefficients for this region have reduced this. Reasonable agreement has been shown to exist in the 8 to 12 micrometer region for absolute humidities up to 12 gmcu m. The results of the comparisons for the 1 to 2.5 micrometer region showed a greater discrepancy. Some of this discrepancy could be arising from point measurements of aerosol extinction using equipment which is underestimating the aerosol attenuation coefficient. Data on scintillation fluctuations recorded during the transmittance measurements are also presented.