Preliminary assessment of infra-red transmission data measured over ocean-type waters in a temperate environment

Measurements have been made of the near sea infra-red transmission of the atmosphere over paths of 5 and 9 km in a temperature environment. Seven broadband spectral regions have been used and variations with absolute humidity, temperature and visibility are investigated. The data are compared with the predictions of the AFGL computer model LOWTRAN3B. A discrepancy has appeared between the measured and calculated data for the 4.4 to 5.4 micrometers region due, possibly, to either no water continuum absorption being included in the model or an under-estimation of the N2 continuum absorption. Indications are that the dependence of water vapour continuum transmission on precipitable water and temperature in the 8.2 to 11.8 micrometers region may not be accurately described by the LOWTRAN3B model.