Factors affecting the accuracy of thermal imaging cameras in volcanology
Factors affecting the accuracy of thermal imaging cameras in volcanology
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DOI：
10.1029/2005jb003829
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发表时间：
2006-11-07
影响因子：
3.9
通讯作者：
Pinkerton, H.
中科院分区：
文献类型：
--
作者：
Ball, M.;Pinkerton, H.
火山观测站和研究人员正在认识到热成像相机在火山爆发之前和火山爆发期间的潜在用途。明显的应用包括测量活动熔岩圆顶和熔岩流的表面温度，以确定这些潜在危险特征中最活跃部分的位置。如果采取适当的预防措施，新一代的热成像照相机可用于提取关于火山活动的定量和定性信息。例如，它们可以用来测量熔岩喷发时的温度，并揭示地壳在流动就位期间如何冷却。这对于验证熔岩流模型是很重要的。为了确保收集到有意义的温度，必须对热成像数据进行仪器误差、成像表面的发射率、大气衰减、视角和表面粗糙度的校正。控制实验室实验已经进行，以确定发射率的光滑和粗糙的样品和视角的影响，并量化的错误。测量的发射率范围从0.973 +/- 0.002的光滑样品的玄武岩和0.984 +/- 0.004的粗糙样品。对于1100摄氏度的熔岩，发射率校正温度的误差在+/-15摄氏度以内。来自提供单个像素温度数据的单个传感器接收器的变化被发现为0.6%，所使用的相机的仪器误差为0.1%。发现视在温度的变化小于仪器误差的视角高达30度，从正常到熔岩，此后增加了类似的1摄氏度每度。通过将埃特纳火山上的一个小喷口的视距离从1.5米增加到30米，由于在增加的像素区域上辐射的综合平均，最高温度被示出降低了53摄氏度。在250米的观察距离处，最大温度降低了近似200摄氏度，由于相对湿度为50%的大气衰减，进一步降低了75摄氏度。然而，相对湿度测量的误差可能导致大气衰减校正误差高达200摄氏度，观察距离为1公里。我们展示了如何使用热成像相机测量的温度可以进行校正，以提高估计的温度分布在表面上的活性熔岩流。
Volcano observatories and researchers are recognizing the potential usefulness of thermal imaging cameras both before and during volcanic eruptions. Obvious applications include measurements of the surface temperatures of active lava domes and lava flows to determine the location of the most active parts of these potentially hazardous features. If appropriate precautions are taken, the new generation of thermal imaging cameras can be used to extract quantitative as well as qualitative information on volcanic activity. For example, they can be used to measure the temperature of lava on eruption and to reveal how the crust cools during flow emplacement. This is important for the validation of lava flow models. To ensure that meaningful temperatures are collected, thermal imaging data must be corrected for instrumental errors, emissivity of the surface being imaged, atmospheric attenuation, viewing angle and surface roughness. Controlled laboratory experiments have been undertaken to determine the emissivity of smooth and rough samples and the effects of viewing angle and to quantify the errors. Measured emissivities range from 0.973 +/- 0.002 for smooth samples of basalt and 0.984 +/- 0.004 for rough samples. Errors in emissivity-corrected temperatures are within +/-15 degrees C for lava at 1100 degrees C. Variations from individual sensor receptors, which provide individual pixel temperature data, were found to be 0.6% and instrumental errors of the cameras used were 0.1%. Apparent temperatures were found to vary by less than the instrumental error for viewing angles up to 30 degrees from normal to lava, and thereafter increased by similar to 1 degrees C per degree. By increasing the apparent viewing distance of a small vent on Mount Etna from 1.5 to 30 m, the maximum temperature is shown to decrease by 53 degrees C due to integrated averaging of radiance over increased pixel areas. At a viewing distance of 250 m the maximum temperature decreased by similar to 200 degrees C with a further 75 degrees C decrease due to atmospheric attenuation for a relative humidity of 50%. However, errors in relative humidity measurements can lead to atmospheric attenuation correction inaccuracies up to 200 degrees C at viewing distances of 1 km. We show how temperatures measured using thermal imaging cameras can be corrected to give improved estimates of temperature distributions on the surface of active lava flows.