Validation of brightness and physical temperature from two scanningmicrowave radiometers in the 60 GHz O2 band using radiosonde measurements

摘要

In this paper, we address the assessment of the tropospheric performance of anew temperature radiometer (TEMPERA) at 60 GHz. With this goal, anintercomparison campaign was carried out at the aerological station ofMeteoSwiss in Payerne (Switzerland). The brightness temperature and thetropospheric temperature were assessed by means of a comparison withsimultaneous and collocated radiosondes that are launched twice a day atthis station. In addition, the TEMPERA performances are compared with theones from a commercial microwave radiometer (HATPRO), which has some differentinstrumental characteristics and uses a different inversion algorithm.Brightness temperatures from both radiometers were compared with the onessimulated using a radiative transfer model and atmospheric profiles fromradiosondes. A total of 532 cases were analyzed under all weather conditionsand evidenced larger brightness temperature deviations between the tworadiometers and the radiosondes for the most transparent channels.Two different retrievals for the TEMPERA radiometer were implemented in orderto evaluate the effect of the different channels on the temperatureretrievals. The comparison with radiosondes evidenced better results verysimilar to the ones from HATPRO, when the eight more opaque channels were used.The study shows the good performance of TEMPERA to retrieve temperatureprofiles in the troposphere. The inversion method of TEMPERA is based on theoptimal estimation method. The main advantage of this algorithm is that there is no necessity forradiosonde information to achieve good results in contrast to conventionalmethods as neural networks or lineal regression. Finally, an assessment of the effect of instrumental characteristics as thefilter response and the antenna pattern on the brightness temperature showedthat they can have an important impact on the most transparent channels.