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Earth as an Extrasolar Planet: Earth Model Validation Using EPOXI Earth Observations

机译：地球作为太阳系外行星：使用EPOXI地球观测的地球模型验证

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The EPOXI Discovery Mission of Opportunity reused the Deep Impact flyby spacecraft to obtain spatially and temporally resolved visible photometric and moderate resolution near-infrared (NIR) spectroscopic observations of Earth. These remote observations provide a rigorous validation of whole-disk Earth model simulations used to better understand remotely detectable extrasolar planet characteristics. We have used these data to upgrade, correct, and validate the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional line-by-line, multiple-scattering spectral Earth model. This comprehensive model now includes specular reflectance from the ocean and explicitly includes atmospheric effects such as Rayleigh scattering, gas absorption, and temperature structure. We have used this model to generate spatially and temporally resolved synthetic spectra and images of Earth for the dates of EPOXI observation. Model parameters were varied to yield an optimum fit to the data. We found that a minimum spatial resolution of ∼100 pixels on the visible disk, and four categories of water clouds, which were defined by using observed cloud positions and optical thicknesses, were needed to yield acceptable fits. The validated model provides a simultaneous fit to Earth's lightcurve, absolute brightness, and spectral data, with a root-mean-square (RMS) error of typically less than 3% for the multiwavelength lightcurves and residuals of ∼10% for the absolute brightness throughout the visible and NIR spectral range. We have extended our validation into the mid-infrared by comparing the model to high spectral resolution observations of Earth from the Atmospheric Infrared Sounder, obtaining a fit with residuals of ∼7% and brightness temperature errors of less than 1 K in the atmospheric window. For the purpose of understanding the observable characteristics of the distant Earth at arbitrary viewing geometry and observing cadence, our validated forward model can be used to simulate Earth's time-dependent brightness and spectral properties for wavelengths from the far ultraviolet to the far infrared. Key Words: Astrobiology—Extrasolar terrestrial planets—Habitability—Planetary science—Radiative transfer. Astrobiology 11, 393–408.
机译：EPOXI机会发现任务重用了深冲飞行器，以获取在空间和时间上分辨的可见光度和对中分辨率近红外（NIR）光谱的地球观测。这些远程观测结果对整个磁盘地球模型模拟进行了严格的验证，这些模拟用于更好地了解可远程检测到的太阳系外行星的特征。我们已经使用这些数据来升级，纠正和验证NASA天文生物学研究所的虚拟行星实验室的三维逐行，多散射光谱地球模型。该综合模型现在包括来自海洋的镜面反射，并明确包括大气影响，例如瑞利散射，气体吸收和温度结构。我们已经使用该模型生成了EPOXI观测日期的时空分解的合成光谱和地球图像。改变模型参数以产生对数据的最佳拟合。我们发现在可见盘上的最小空间分辨率约为100像素，并且需要四类水云，这是通过使用观察到的云位置和光学厚度来定义的，以产生可接受的拟合。经过验证的模型可同时拟合地球的光曲线，绝对亮度和光谱数据，多波长光曲线的均方根（RMS）误差通常小于3％，而整个绝对亮度的残差约为10％可见光和NIR光谱范围。通过将模型与大气红外测深仪对地球的高光谱分辨率观测值进行比较，我们将验证扩展到了中红外，从而获得了约7％的残差和在大气窗口中亮度温度误差小于1K的拟合。为了了解在任意观察几何结构和观察节奏下遥远地球的可观测特性，我们经过验证的正向模型可用于模拟地球的随时间变化的亮度和从远紫外到远红外的波长的光谱特性。关键词：天体生物学，太阳系外行星，可居住性，行星科学，辐射传递。天体生物学11，393–408。

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