二氧化碳4.3微米吸收帶的反射陽光及其訂正

The Reflected Sunlight and its Corrections in the 4.3 μm Carbon Dioxide Band

曾忠一(Chung-Yi Tseng) ； 李衍民(Yen-Min Li)

《大氣科學》 23卷3-4期 (1995/12) Pp. 359-381

摘要

二氧化碳4.3微米紅外吸收帶頻道可以用來探測氣溫垂直分布，但這個波段的短波部分白天時會受到反射陽光的影響，使得這個吸收帶頻道無法應用。本文使用離散方向法配合複雜的下邊界條件來建立散射大氣的輻射傳遞模式，以便對二氧化碳4.3微米吸收帶頻道做一探討，希望能了解反射陽光的影響。資料來源為1993年5月18日氣象衛星NOAA-11號上輻射計HIRS/2第13到17頻道的觀測資料。在與衛星資料校驗方面，這五個頻道的模擬結果在天頂角小於45°時和觀測資料都相當一致，但天頂角大於45°時則誤差隨著增大，這種類似系統性的誤差，我們認為可能是模式所考慮的模式大氣和所使用的散射相位函數未能與真實大氣一致所引起的。在反射陽光訂正方面，我們將雙頻道訂定法和理論模擬的結果相互比較，由於雙頻道訂正法只考慮海面的反射部分，並沒有包含大氣的散射效應，所以二者會有差異是可以預期的。因此除了有必要進一步研究當地的大氣光學性質和散射相位函數之外，如果能對誤差來源提供一定量分析的方法，將可有效地改善模式的架構，以增進模式實際應用的能力。

關鍵字

輻射傳遞模式 ； 反射陽光 ； 雙頻道訂正法

並列摘要

The radiative transfer equation in a scattering atmosphere was solved by the discrete ordinate method together with complex lower boundary conditions. This model was then used to study the reflected component of solar radiation in the 4.3μm carbon dioxide band. This band, as compared with the 15μm carbon dioxide band, has the advantage of greater sensitivity to vertical temperature gradients except at lower temperatures and of greater carbon dioxide absorption so that one can sense higher in the atmosphere. However, due to strong solar reflectivity, the channels in this band cannot be used to retrieve temperature profiles during daytime. The so-called two-channel method is often used to correct 4.3μm channel data for the reflected sunlight.The radiances at the top of the atmosphere were first determined by the model and then compared with those observed by the 4.3μm channel of the HIRS/2 aboard the NOAA satellites. It is found that they are in good agreement for zenith angels less than 45°. However, the error would increase as the zenith angles become larger than 45°. It seems that this kind of systematic errors is due to the difference between the model atmosphere and the real atmosphere. We also investigated the validity of the two-channel method. As is expected, there are some differences between the reflected component of solar radiation computed by the model and two-channel method. They are due to the fact that the multiple scattering processes in the atmosphere are not taken into account in the two-channel method.

並列關鍵字

Radiative transfer model ； Reflected sunlight ； Two-channel method