- 期刊
台灣區HIRS/2遙測頻道大氣穿透率計算模式之研究
Atmospheric Transmittance Model for HIRS/2 Sounding Channels in Taiwan Area
摘要
在應用HIRS（High Resolution Infrared Radiation Sounder）頻道輻射觀測資料來反演大氣垂直溫濕剖面過程中，HIRS各頻道大氣穿透率的快速計算及準確度，對反演結果的時效性及準確性具極大的關鍵作用，因此為了迅速求得反演區域中各高度層準確的大氣穿透率，以供HIRS/2遙測頻道之使用，便於即時求取一些氣象因子（如海面溫度、垂直溫度剖面、水汽剖面等），於是本研究建立兩種簡單計算大氣穿透率模式，其一為混合比為常數，其二為混合比為變數。經由數學計算，考慮穿透率與吸收氣體的溫度、壓力及吸收氣體含量之間的關係，並加入量化近似值、能量參數值，可推得兩組計算大氣穿透率的模式。而HIRS/2遙測頻道主要的吸收氣體為水汽（混合比為變數）和二氧化碳（混合比為常數），因此兩模式所得的穿透率相乘，即為大氣總穿透率。本研究選取20個各種天候之探空資料做為檢驗模式準確度之樣本所得之結果與LOWTRAN-6程式套的穿透率計算模式結果比較，其最大均方根誤差為第12頻道的0.039，而所有頻道之平均誤差僅為0.013因此其準確度頗令人滿意，而在計算時所花費的CPU時間比LOWTRAN-6程式套計算時間快了約19倍。因此，所得之兩組模式可以達到實用性的目的，以供HIRS/2頻道之使用。
並列摘要
In applying HIRS/2(High Resolution Infrared Radiance Sounder) radiance observations to inverse atmospheric soundings, not only the inverse technique is important, but also the atmospheric transmittance of absorbing gases along the observing path is crucial. Thus, for the purpose of fast computing an accurate atmospheric transmittance for HIRS/2 channels to remote sense atmospheric parameters (such as sea surface temperature, vertical temperature and moisture profiles), this study develops two kinds of simple atmospheric transmittance models. One is for the absorbing gas whose mixing ratio is constant in the atmosphere. And the other is for that whose mixing ratio is variable.Atmospheric transmittance varies mainly with the temperature, pressure and amount of the absorbing gases of the path. This study uses simple arithmetic operations to relate these parameters and the atmospheric transmittance function, and applying scale approximation and energy parameterization to derived those two simple atmospheric transmittance models. The main absorbing gases of HIRS/2 channels are CO2 and H2O whose mixing ratio are constant and variable ins pace, respectively. Therefore, The results estimated from the CO2 and H2O atmospheric transmittance models of HIRS/2 channels are multiplied to be their total atmospheric transmittance.This study selected 20 radiosonde observations of different weather conditions as the model accuracy checking samples. The results obtained from this study were compared with the determinations by the LOWTRAN-6 package. The maximum RMSE is about 0.039 occurred on Channel 12. The average RMSE for all channels is only 0.013. These comparisons reveal its good accuracy of this model. Besides, the CPU time consumed by this model is 19 times faster than that by LOWTRAN-6 package. This implies the atmospheric transmittance model of this study is better than LOWTRAN-6 package for the use in HIRS/2 sounding retrievals.