- 學位論文
由地暉測量得到地球反照率之模擬
Simulation on Earth's Albedo from Earthshine Measurements
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摘要
當太陽光照射到地球上時，有一部分被地球反射回太空中 (其餘的被地球吸收)。反射光中有一部份是照射到月球上，使得我們看到的上弦月或下弦月盤面上，暗的部份也帶有一點光線，這個光線稱為地暉 (earthshine)。由於地暉是來自被地球反射到太空中的陽光，它的亮度便會與地球的反照率 (albedo) 有關。而地球的反照率是描述全球輻射能量平衡 (radiation energy budget) 的一個重要的參數，因此我們計畫在全球設立多個觀測站，進行長期的地暉觀測，藉此觀察地球反照率長期的變化。本論文的主題是地暉測量與地球反照率的模擬，包括地球反射光在月球處的強度的計算，以及地球的反照率月平均值的計算。進行模擬的目的在於讓我們了解地暉觀測的相關因素，以及提供我們一個方法來測試及評估由地暉測量估計得到的地球反照率的準確性。模擬的方法中，我們用到輻射分布模型Angular Radiation Distribution Models for the Earth Radiation Budget Experiments (ERBE)，以及用ERBE和International Satellite Cloud Climatology Project (ISCCP) 所提供的地表型態和雲量分布資料作為模型的輸入。模擬計算的時間範圍為1983年7月到2004年12月。我們也利用ERBE的人造衛星短波段 (此指陽光的波段) 的測量結果來計算地球的反照率，此結果可與模擬計算的結果比較。我們利用了模擬的結果，來測試Danjon所提出的由地暉估計地球反照率的方法，並發現用此方法來估計地球反照率的變化是有可能的，特別是估計反照率長期的變化。
並列摘要
The earth reflects a fraction of incident sunlight into the space (the remaining being absorbed by the earth). Some of the reflected sunlight reaches the moon and is further reflected back to the earth. This is called the earthshine and can be observed in the dark portion of the disk of a waxing or waning moon. Since the earthshine comes from sunlight that is first reflected by the earth, the intensity of earthshine is related to the earth's albedo, which is an important parameter concerning the global radiation energy budget. Thus we plan to set up long-term and multi-site earthshine observation in order to monitor the variation of the earth's albedo. The subject of this thesis is on the simulation of earthshine measurements and the earth's albedo, including the calculation of the flux of Earth-reflected sunlight at the moon, and the earth's monthly mean albedo. The purpose of doing simulation is to help us investigate the factors related to earthshine measurement, and to provide us a tool to test methods we will use to estimate the earth's albedo from earthshine measurements. The simulation is based on the angular radiation distribution models for the Earth Radiation Budget Experiments (ERBE), with surface geographical type data and cloud amount data given by the ERBE and the International Satellite Cloud Climatology Project (ISCCP) as the input. The temporal coverage of simulation is from July 1983 to December 2004. We also use satellite shortwave measurements of the ERBE to calculate the earth's monthly mean albedo for comparison with the simulation result. The simulation results are used to test Danjon's method for estimating the earth's monthly mean albedo from earthshine flux, with the outcome showing that it is possible to estimate the earth's albedo variations, especially long-term variations, from earthshine flux using this method.
參考文獻
Minnis, P. et al. (1993) Radiative Climate Forcing by the Mount Pinatubo Eruption, Science, 259, 1411.
Palle, E. et al. (2005) A Multi-data Comparison of Shortwave Climate Forcing Changes, Geophysical Research Letters, 32, L21702.
Smith, G. L. et al. (1986) Inversion Methods for Satellite Studies of the Earth's Radiation Budget: Development of Algorithms for the ERBE Mission, Rev. of Geophysics, 24, 407-421.
Chou, D.-Y. and Sun, M.-T. (2003) Earthshine Measurements with Automated Telescopes, Mem. S.A.It. Suppl., 2, 168-171.
Danjon, A. (1954) Albedo, Color, and Polarization of the Earth, in The Earth as a Planet, edited by Kuiper, The University of Chicago Press.