Mt. Etna tropospheric ash retrieval and sensitivity analysis using Moderate Resolution Imaging Spectroradiometer measurements
Mt. Etna tropospheric ash retrieval and sensitivity analysis using Moderate Resolution Imaging Spectroradiometer measurements
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DOI：
10.1117/1.3046674
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发表时间：
2008-01-01
影响因子：
1.7
通讯作者：
Gangale, Gabriele
中科院分区：
文献类型：
--
作者：
Corradini, Stefano;Spinetti, Claudia;Gangale, Gabriele
利用中分辨率成像分光辐射计的测量结果，对埃特纳火山对流层火山灰进行了反演。美国航天局中分辨率成像分光仪卫星仪器获取的图像光谱范围为0.4至14微米，最低点的空间分辨率为1公里。2006年11月24日发生的喷发被认为是这项工作的一个测试案例。为了获得灰羽的光学厚度，颗粒的有效半径和总质量，亮度温差程序已被应用到中分辨率成像光谱仪通道31（以11 μ m为中心）和32（以12 μ m为中心）。通道5（中心在1.24 μ m）已被用来改善云的歧视，利用不同的反射率的气象和火山云在近红外光谱范围。通过对中分辨率成像光谱仪数据进行大气水蒸气校正，火山灰像素的检测得到了显著改善。与原始方法相比，该过程将识别为包含火山灰的像素数量增加了一倍。反演得到的0.55 μ m处的平均光学厚度、平均粒子有效半径和羽流中的总灰质量分别为0.4、3.5 μ m和3620吨。已经进行了详细的灵敏度分析，调查在检索中的各种参数的不确定性所造成的错误：表面温度和发射率，羽流几何形状（高度和厚度），灰类型和大气水蒸气。结果表明，对反演误差贡献最大的是地面参数、气溶胶类型和大气水汽含量的不确定性。对流层火山灰平均AOT、平均有效半径和总质量的反演误差分别为30%、30%和40%。
A retrieval of tropospheric volcanic ash from Mt Etna has been carried out, using measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS). The NASA-MODIS satellite instrument acquires images in the 0.4 to 14 mu m spectral range with a spatial resolution of 1 km at nadir. The eruption which occurred on 24 November 2006 is considered as a test case in this work. In order to derive the ash plume optical thickness, the particle effective radius and the total mass, the Brightness Temperature Difference procedure has been applied to MODIS channels 31 (centered at 11 mu m) and 32 (centered at 12 mu m). Channel 5 (centered at 1.24 mu m) has been used to refine the cloud discrimination, exploiting the distinct reflectivity of meteorological and volcanic clouds in the near infrared spectral range. The detection of volcanic ash pixels has been significantly improved by applying an atmospheric water vapor correction to MODIS data. This procedure doubles the number of pixels identified as containing volcanic ash compared to the original method. The retrieved mean ash optical thickness at 0.55 mu m, mean particle effective radius and the total ash mass in the plume are 0.4, 3.5 mu m and 3620 tons, respectively. A detailed sensitivity analysis has been carried out to investigate errors in the retrieval caused by the uncertainty in various parameters: surface temperature and emissivity, plume geometry (altitude and thickness), ash type and atmospheric water vapor. Results show that the largest contributions to retrieval errors are from uncertainty in surface parameters, aerosol type and atmospheric water vapor. The total tropospheric volcanic ash retrieval errors are estimated to be 30%, 30% and 40% for mean AOT, mean effective radius and total mass retrieval, respectively.