We compare the precipitable water vapor (PWV) determined using a domestic ground-based microwave radiometer (MWR PWV) with PWV measurements from radiosondes (RS PWV), the Global Navigation Satellite System (GNSS PWV), and reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF) (EC PWV). The MWR PWV is affected by precipitation, and thus it differs greatly from the other three observations. The correlation coefficient between the MWR PWV and RS PWV (EC PWV) is 0.934 (0.933), and the root mean square error (RMSE) is 17.19 mm (16.05 mm), whereas the correlation coefficient between the GNSS PWV and RS PWV (EC PWV) is 0.989 (0.986), and the RMSE is 17.04 mm (15.83 mm). The scatter distributions of the MWR PWV and the other observations show a systematic deviation that is negatively correlated with the surface air temperature. After polynomial fitting and corrections are applied, the correlation coefficients between the MWR PWV and the RS PWV and EC PWV increase to 0.993 and 0.99, and the RMSEs decrease to 14.13 and 15.86 mm, respectively. The temperature and water vapor density profiles are retrieved from the bright temperature and can reflect the quality of the bright temperature. Because the PWV retrieved from the ground-based MWR has a linear relationship with the brightness temperature, the accuracy of the PWV can be analyzed in terms of the quality of the brightness temperature. We found that the differences in the temperature profile below 2000 m are smaller, whereas those in the water vapor density profile below 2000 m show the largest difference. This finding reflects the differences in the brightness temperature, which may be the cause of the inaccurate PWV observations.
Atmospheric refractivity sounding is of great importance to the meteorological and military applications. An experiment
was conducted for sounding the atmospheric refractivity on the top of the Wuling Mountain in August, 2005. Profiles of
the atmospheric refractivity were obtained by both the mountain-based GPS and the tomographic method. Comparison
shows that there is a bias of -3.83N and a standard deviation of 7.03N between the mountain-based GPS and the
radiosonde. A bias less than 1% among different receivers proves that the receivers tested can meet the demand of the
radio occultation technique. A very good consistence among the profiles by the mountain-based GPS, the tomographic
method and the radiosonde suggests the effectiveness of both the mountain-based GPS and the tomographic method,
indicating the great potential in the future meteorological application.
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