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由火山灰和岩石组成的云，它们以高速向下传播。它们是许多活火山的主要危害，已经造成数千人死亡。我们目前预测它们的行为和计划它们的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了解不完全。拟议的研究将彻底改变我们对pdc的理解，通过使用先进的定制雷达系统（GEODAR），首次获得移动pdc密集核心的及时位置测量，从而获得速度。GEODAR已被开发并成功用于雪崩，极大地提高了我们对其动力学的认识。该项目将建立和部署三个空间分辨率为0.375 m的GEODAR系统，并将在100 Hz下对致密岩心流进行成像：这是PDCs研究中从未达到的空间和时间分辨率。GEODAR可以很容易地穿透火山灰云，成像密集的破坏性底流，并可以观察到所有大于30毫米的颗粒。这种新颖的系统将能够沿着其流动路径跟踪pdc，并使我们能够对内部浪涌、滚波和流锋进行成像，并重建移动pdc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，并为其流动提供基本的见解，从而可以开发改进的模型。此外，PDCs的流动路径和沉积物将由无人机以30毫米分辨率进行数字测绘，以解决流动的横向范围和位置。数字地形图中的特征将与雷达数据中观察到的特征直接匹配，这将大大增加对PDC放置机制的理解。对于一些流，我们期望在事件前后都有高分辨率的dtm，并且我们将生成侵蚀和沉积图。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的路径和力量，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。DTM将用于运行SHALTOP代码，并将结果与GEODAR数据以及侵蚀和沉积图进行比较。SHALTOP是一个模拟代码，在过去的15年里，由这个项目的一个法国团队合作伙伴开发。它可以在各种流动规律下运行，我们将确定哪种流动规律最符合数据，并从那里进行改进。由于缺乏流动PDCs的数据，以前从未做过如此详细的比较。我们选择了危地马拉的Santiaguito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。该团队在该地点拥有丰富的工作经验，当地火山观测站是该项目的热心参与者。此外，火山周围的地形非常适合GEODAR的位置，几乎可以完全看到可能的流动路径。该系统将使用次声和地震信号的组合远程触发。三个GEODAR系统将是独立的太阳能供电单元，并通过卫星电话数据链进行通信。数据存储将在安装在防火防撞箱中的固态硬盘上，这样它们就可以抵御洪水。这项研究将产生有史以来第一个高分辨率的流动pdc密集岩心位置和速度数据，并首次与这些数据进行模型比较。该项目将开发改进的PDCs理论和计算模型，并提高火山周围危害评估的准确性。最终目标是提高对这些有可能挽救数百人生命的破坏性自然灾害的物理认识。

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.