Precipitable water vapour estimation on the basis of sky temperatures measured by a single-pixel IR detector and screen temperatures under clear skies

Precipitable water vapour (PWV) is an important component of the atmosphere, but remains difficult to measure with adequate spatial and temporal resolution under all weather conditions. Over the last four decades several techniques and methods have been developed to measure PWV more accurately, but each carries limitations preventing its widespread use. This paper presents preliminary results of a simple method for inferring PWV from the air temperature and infrared (IR) sky temperature under clear skies. Sky temperatures are measured using a broadband, single-pixel ER radiometer. A parametric model of the physical relationship between these three quantities was created using PWV data derived from a GPS receiver. By inverting the model, PWV estimates can be obtained from new temperature measurements. The measurements were taken between October 2002 and July 2004 in a coastal region of South Australia. The method was found to predict PWV quite accurately, with a mean bias error (MBE) of only -0.009 mm and a root mean square error (RMSE) of 2.311 mm. The model was also compared to a set of 120 radiosonde-derived PWV values, resulting in a MBE and RMSE of 0.262 and 2.601 mm respectively. These preliminary results show that the clear sky PWV can be estimated accurately from sky temperatures obtained using a simple IR detector. Future work will extend the method to different sky and weather conditions. Copyright (C) 2009 Royal Meteorological Society