High Resolution Radar Imaging of Pyroclastic Density Currents

火山碎屑密度流（PDCs）是火山爆发时产生的火山灰和岩石云，以高速向下传播。它们是许多活火山的主要危险，已经造成数千人死亡。我们目前预测它们的行为和计划其影响的能力是有限的，部分原因是我们对它们的流动动力学知识不完整。拟议的研究将彻底改变我们对PDCs的理解，通过使用先进的定制雷达系统（GEODAR）首次获得移动PDCs密集核心的时间位置测量，从而获得速度。GEODAR已被开发并成功用于雪崩，大大提高了我们对其动力学的了解。该项目将建立和部署三个GEODAR系统，其空间范围分辨率为0.375米，并将以100 Hz的频率对密集的核心流进行成像：这是以前在PDC研究中从未实现过的空间和时间分辨率。GEODAR将很容易穿透灰云成像密集，破坏性的底流，并可以观察到所有颗粒大于30毫米。这种新的系统将能够跟踪PDCs沿着其流动路径，并将使我们能够成像内部浪涌，滚波和流动前沿和重建移动PDCs的速度结构。这些数据将能够对PDC流动模型进行严格的测试，并提供对其流动的基本见解，以便开发改进的模型。此外，流动路径和PDC的沉积物将由无人机以30 mm分辨率进行数字映射，以解决流动的横向范围和位置。数字地形图中的特征将直接与雷达数据中观察到的特征相匹配，这将大大增加对PDC就位机制的理解。对于某些流动，我们希望在事件发生前后都有高分辨率的DTM，我们将制作侵蚀和沉积图。这些数据输入到项目的最后一部分，即PDC的计算机模拟。所产生的仿真代码将有助于预测PDC的路径和力，这对于拯救生命和保护基础设施是必要的。该代码将免费提供，并将举办一个关于其使用的研讨会。数字地面模型将用于运行SHALTOP代码，其结果将与GEODAR数据以及侵蚀和沉积图进行比较。SHALTOP是一个模拟代码开发，在过去的十五年里，由法国团队合作伙伴在这个项目。它可以与各种流动定律一起运行，我们将确定哪种流动定律最适合数据，并从那里我们开发改进。由于缺乏来自流动PDC的数据，以前从未进行过如此详细的比较。我们选择了危地马拉的瓜拉尼托火山作为试验地点。它是世界上最活跃的火山之一，自1922年以来一直在喷发，每年都会产生数十个PDC。该团队在该网站上拥有丰富的工作经验，当地的火山观测站是该项目的热情参与者。此外，火山周围的地形非常适合GEODAR的位置，几乎完全可以看到可能的流动路径。这些系统将使用次声和地震信号的组合进行远程触发。这三个GEODAR系统将是独立的太阳能动力装置，并通过卫星电话数据链路进行通信。数据存储将在安装在防火碰撞盒中的SSD上，以便它们能够承受淹没。这项研究将产生有史以来第一个高分辨率的位置，因此速度，流动PDC密集核心的数据，以及有史以来第一个与这些数据进行比较的模型。该项目将开发改进的PDC理论和计算模型，并提高火山周围危险评估的准确性。最终目的是提高对这些破坏性自然灾害的物理知识，有可能挽救数百人的生命。

Pyroclastic density currents (PDCs) are clouds of ash and rock, generated during eruptions, which propagate down volcanoes at high speed. They are the major hazard at many active volcanoes and have killed thousands of people. Our current ability to predict their behaviour and plan for their effects is limited, in part, by our incomplete knowledge of their flow dynamics. The proposed research will revolutionise our understanding of PDCs by obtaining, for the first time ever, measurements of position in time, hence velocity, of the dense core of moving PDCs using an advanced custom-built radar system (GEODAR). GEODAR has been developed and successfully used on snow avalanches, dramatically improving our knowledge of their dynamics. The project will build and deploy three GEODAR systems that have a spatial range resolution of 0.375 m and will image the dense core flow at 100 Hz: a spatial and time resolution never achieved before in studies of PDCs. GEODAR will easily penetrate the ash cloud to image the dense, destructive underflow, and can observe all particles larger than 30 mm. This novel system will be able to track PDCs along their flow paths and will allow us to image internal surges, roll-waves and flow fronts and reconstruct the velocity structure of moving PDCs. This data will enable the rigorous testing of PDC flow models and provide fundamental insights into their flow so that improved models can be developed. In addition, the flow path and deposits of the PDCs will be digitally mapped by a drone at 30 mm resolution in order to resolve the lateral extent and location of the flow. Features in the digital terrain maps will be directly matched with the features observed in the radar data and this will greatly add to the understanding of PDC emplacement mechanisms. For some flows we expect to have high resolution DTMs both before and after the event, and we will produce erosion and deposition maps. This data feeds in to the final part of the project which is the computer simulation of PDCs. The simulation code produces will be useful for predicting the path and forces of PDCs which is necessary for saving lives and protecting infrastructure. The code will be made freely available and a workshop run on its use. The DTM will be used for running the SHALTOP code and the results will be compared with GEODAR data and the erosion and deposition maps. SHALTOP is a simulation code developed, over the past fifteen years, by a French team partner in this project. It can be run with a variety of flow laws and we will determine which flow law best matches the data and from there we develop improvements. Such a detailed comparison has never been done before due to the lack of data from flowing PDCs. We have chosen Santiaguito volcano, Guatemala, as the test site. It is one of the world's most active volcanoes, which has been erupting since 1922 and dozens of PDCs are generated every year. The team has extensive experience working at this site and the local volcano observatory is an enthusiastic participant in the project. In addition, the terrain around the volcano is ideally suited for the location of GEODAR, with nearly complete sight-lines to the likely flow paths. The systems will be remotely triggered using a combination of infrasound and seismic signals. The three GEODAR systems will be stand- alone solar-powered units and communicate via a satellite-phone data link. The data storage will be on SSDs mounted in fireproof crash boxes so that they can withstand inundation.This research will produce the first ever high resolution position, and hence velocity, data for the dense core of flowing PDCs and the first ever model comparison with such data. The project will develop improved theoretical and computational models for PDCs and improve the accuracy of hazard assessments around volcanoes. The ultimate aim is to improve physical knowledge of these destructive natural hazards with the potential to save hundreds of lives.