Sensitivity of input parameters to modelling of atmospheric transmission of long-wave infrared radiation at sea under warm and humid conditions

Abstract

A joint Australian-Norwegian eld trial (Osprey) was held in February 2018 in Darwin, Australia. The objective of this trial was to measure IR transmission properties of the atmosphere in a marine environment under warm and humid conditions. Darwin is in the tropics (longitude 12 south), and February is the middle of the \wet season". Various temperature-controlled sources (blackbodies) were used during the trial. Land based weather stations recorded a number of meteorological data. The sensors used in the trial included long-wave, mid-wave and short-wave IR cameras. In this paper we present the analysis of measurements performed on two blackbodies across Darwin Harbour. The scene was recorded with an IRCAM LW camera and calibrated to blackbodies with known temperature. We have modelled the atmospheric transmittance using MODTRAN, and from this acquired the equivalent blackbody temperature of the scene. In our analysis, we are not only interested in the overall agreement between predictions and data, but also on the sensitivity of the predictions to uncertainties of the input parameters (calibration temperatures, air temperature, humidity, etc.). In order to study this sensitivity, we used variance based sensitivity analysis and Monte Carlo simulations to compute sensitivity indices, according to methods developed by Saltelli and others. Our main nding is that uncertainties in calibration parameters (blackbody and camera temperatures) give the dominant contributions to the error in the computed equivalent temperature.