定量遥感地表净辐射通量所需大气下行长波辐射估算模型改进

Improvement of models for the estimation of downward atmospheric long-wave radiation for retrieving net radiation fluxes based on remote sensing

利用半湿润季风气候类型夏季近地层气象观测资料,对得到广泛应用的十种晴天大气下行辐射估算模型和两种昙天大气下行辐射估算模型进行检验。指出其中Iziomon(2003)晴天大气下行辐射估算模型是半湿润季风气候类型夏季较适用的估算模型。然而,在有云天空,Iziomon(2003)昙天估算模型误差比较大。本文依据实测资料,对Iziomon(2003)昙天大气下行辐射估算模型进行修正,修正后的模型估算值与实测值非常接近。由于应用常规气象站的大气温湿度来估算大气下行辐射仅代表近地层大气对其的贡献,不能反映整层大气的贡献,尤其在近地层与高空大气的水汽状况不一致时,上述模型将有较大的误差。为此本文结合Iziomon(2003)晴天模型中大气比辐射率的表达式,提出了运用红外辐射计以37°高度角对天空的观测值,来推算大气下行辐射的新方法。小汤山的试验数据表明,新模型的反演精度优于上述传统模型。

With the measurement data of the downward atmospheric radiation and the air temperature and humidity of the surface layer in 2004 in the Xiaotangshan region of Beijing, the verification was done by making use of the widely-used downward atmospheric radiation model, including ten models for cloud-free days ：Angstrom（1918）, Brunt（1932）, Swinbankl（1963）, Idso ＆ Jackson（1969）, Swinbank2（1963）, Brutsaertl（1975）, Brutsaert2（1982）, Idso（1981）, Prata（1996）, Iziomon et al. （2003） ,and two models for cloudy days： Jacobs（1978） and Iziomon（2003）. The results show. （1）for cloud-free days, Iziomon（2003）＇s model has a good performance and can be used directly for the area; and （2） for cloudy days, the two models, Jacobs（1978） and Iziomon（2003）, have relative large errors. With measured data, this paper puts forward a modified downward atmospheric radiation assessment model based on Iziomon（2003）＇s model and the measurement information. A better match between the estimation value and the actual measured value is achieved. The application of the data about the air temperature and humidity from the regular weather stations only represents the contribution of the surface layer which could not reflect the effect given by the whole atmosphere to the downward atmospheric radiation, so there will be errors if the water vapor situation is different from the surface layer and the upper layer. The basic idea of the modified model is to calculate the downward atmospheric radiation with an expression of the atmospheric emissivity in Iziomon＇s model by making use of the observation value from the thermal infrared thermometer with an angle of 37°.