High resolution geodesy for active, deforming volcanoes

一些火山爆发会造成巨大的经济和人道主义损失，但有助于预测火山爆发的测量方法可以减少火山爆发的影响。岩浆到达地表的路径不可能直接观察，我们必须依靠小地震、气体排放和地表变形等次要迹象来推断岩浆运动。我们拟议的工作使用后者。具体而言，我们将使用被称为干涉合成孔径雷达的卫星雷达干涉测量技术来检测地球表面位置的小于1厘米的变化。干涉合成孔径雷达可以测量岩浆库的增压，这种增压通常会使几十公里外的地表变形，并持续数年。然而，越来越清楚的是，火山上还有其他规模较小、发生速度较快的信号，目前使用的干涉合成孔径雷达不太适合这些信号。我们计划使用TerraSAR-X卫星观测这些信号，该卫星的工作波长比其前身短，每11天生成分辨率为2米的图像。我们选择以拉丁美洲一系列活跃喷发的火山为目标，这些火山靠近主要人口中心和基础设施，特别令人关切。雷达测量在这一地区特别重要，因为频繁的云层覆盖会使直接和空中观测变得困难。我们将讨论与火山圆顶的增长，火山侧翼的主要不稳定性和伴随爆发危机的地表变形模式有关的科学问题。有些火山几乎连续不断地喷发，但每隔一两年就会发生特别危险的喷发危机。在这些火山，我们将使用频繁的TerraSAR-X图像来了解是否发生隆起和沉降：1）在大爆发前持续数月的地震和爆炸的高度时期; 2）在爆发期间迅速或3）随着火山在爆发后进入平静期而缓慢。其他火山正在从缓慢移动的粘性岩浆中形成新的熔岩圆顶。当新的材料添加得特别快时，圆顶非常不稳定，坍塌伴随着危险的流动和灰柱。高分辨率雷达图像中的细微特征将为我们提供有关圆顶状态、增长速度和坍塌事件的线索。最后，低分辨率图像显示，哥斯达黎加的阿纳尔火山的侧翼正在迅速下滑，因为新的熔岩流和火山灰福尔斯堆积-突然的故障可能导致大规模山体滑坡，甚至可能引发大规模爆炸性喷发。新的，更高分辨率的图像将告诉我们火山侧翼是作为一个单一的连贯块移动，还是实际上被分解成许多以不同速度移动的较小块。我们将与负责监测这些火山的火山观测站密切合作，最大限度地发挥我们工作的实际效用。

Some volcanic eruptions have enormous economic and humanitarian costs, but measurements that help anticipate them can reduce their impact. The pathway of the magma to the surface is impossible to observe directly and we must rely on secondary signs such as small earthquakes, gas emission and surface deformation to infer magma movement Our proposed work uses the latter. Specifically, we will use the satellite radar interferometry technique known as InSAR to detect changes of less than 1 cm in the position of the earth's surface. InSAR can measure the pressurisation of magma reservoirs, which typically deforms the ground surface over distances of tens of kilometres and lasts for several years. Yet, it is becoming increasingly clear that there are other signals on volcanoes that are smaller in scale and occur more rapidly for which the current use of InSAR is poorly suited. We plan to observe these signals using the satellite TerraSAR-X, which operates at a shorter wavelength than its predecessors, producing images with 2 m resolution every 11 days. We have chosen to target a range of actively erupting volcanoes in Latin America, whose proximity to major population centres and infrastructure are a particular cause for concern. Radar measurements are especially important in this region since frequent cloud cover can make direct and airborne observations difficult. We will address scientific questions related to the growth of volcanic domes, major instabilities on the flank of the volcanoes and the patterns of surface deformation that accompany eruptive crises. Some volcanoes erupt almost continuously, but with especially dangerous eruptive crises occurring every year or two. At these volcanoes, we will use the frequent TerraSAR-X imagery to learn whether uplift and subsidence occur 1) during the heightened period of earthquakes and explosion lasting several months before a major eruption; 2) rapidly during the eruption itself or 3) more slowly as the volcano relaxes into a quiet period following the eruption. Other volcanoes are forming new lava domes from slow-moving, viscous magma. When new material is added particularly quickly, the dome is very unstable and collapses are accompanied by dangerous flows and ash columns. Subtle features in the high resolution radar images will give us clues as to the state of the dome, its growth rate and collapse events. Finally, low resolution images have shown that the flank of Volcan Arenal in Costa Rica is sliding rapidly downhill as new lava flows and ash falls accumulate - a sudden failure could cause a massive landslide and possibly even trigger a major explosive eruption. The new, higher resolution images will tell us if the volcano flank is moving as a single coherent block, or is actually broken up into a number of smaller blocks moving at different rates. We will work closely with the volcano observatories responsible for monitoring these volcanoes to maximize the practical utility of our work.