An improved vertical correction method for the inter-comparison and inter-validation of integrated water vapour measurements

[摘要] Integrated water vapour (IWV) measurements from similaror different techniques are often inter-compared for calibration andvalidation purposes. Results are usually assessed in terms of bias(difference of the means), standard deviation of the differences, and linearfit slope and offset (intercept) estimates. When the instruments are locatedat different elevations, a correction must be applied to account for thevertical displacement between the sites. Empirical formulations aretraditionally used for this correction. In this paper we show that thewidely used correction model based on a standard, exponential, profile forwater vapour cannot properly correct the bias, slope, and offset parameterssimultaneously. Correcting the bias with this model degrades the slope andoffset estimates and vice versa. This paper proposes an improved correctionmethod that overcomes these limitations. It implements a multiple linearregression method where the slope and offset parameters are provided from aradiosonde climatology. It is able to predict monthly mean IWVs with a biassmaller than 0.1  kg m −2 and a root-mean-square error smaller than 0.5  kg m −2 for height differences up to 500 m. The method is applied to theinter-comparison of GPS IWV data in a tropical mountainous area and to theinter-validation of GPS and satellite microwave radiometer data. This paperalso emphasizes the need for using a slope and offset regression method thataccounts for errors in both variables and for correctly specifying theseerrors.

[学科分类] 内科医学