Doppler radar sounding of volcanic eruption dynamics at Mount Etna
Doppler radar sounding of volcanic eruption dynamics at Mount Etna
复制标题
DOI：
10.1007/s00445-003-0324-8
复制
发表时间：
2004-07
影响因子：
3.5
通讯作者：
G. Dubosclard;F. Donnadieu;P. Allard;R. Cordesses;C. Hervier;M. Coltelli;E. Privitera;J. Kornprobst
中科院分区：
文献类型：
--
作者：
G. Dubosclard;F. Donnadieu;P. Allard;R. Cordesses;C. Hervier;M. Coltelli;E. Privitera;J. Kornprobst
多普勒雷达除了在大气研究中普遍使用外，也是一种很有前途的火山爆发主动遥感工具，但在这一领域的应用很少。本文介绍了1998年10月11日至12日埃特纳火山东侧火山口7小时的斯特隆波利火山喷发期间用中功率超高频多普勒雷达（Voldorad）所作的观测资料。对射流轴两侧两个距离门记录的多普勒频谱进行分析，得到雷达回波的主要特征。根据探测的几何形状，可以区分出上升和下降弹射对各多普勒频谱的贡献。上升目标反向散射总功率的时间演化与火山震动的时间演化非常相似，并能很好地再现火山爆发前、爆发中和爆发后的整体演化过程。此外，在爆发后爆发活动急剧减少期间，对视频（来自摄像机记录），雷达和地震测量的详细分析显示，雷达和视频信号同时开始减少，大约在震颤减弱后2.5分钟。这种延迟被解释为通过岩浆管道上升的时间，这些岩浆管道来自一个浅源，大致估计在东南火山口下约500米处。在高采样率模式下，对火山喷发过程也进行了详细的分析。在上升抛射所对应的多普勒光谱的一半上，可以清楚地识别出单个突出的特征：背散射功率的时间变化表现出准周期性波动，而在每个光谱上测量的最大速度在每次突出开始时都表现出一个尖锐的峰值，然后随着时间的推移缓慢衰减。功率变化的周期性（在3.8和5.5秒之间）与在SE通风口目测到的爆炸发生一致。在副风阶段和重新活动期间测得的最大垂直速度超过160 m s - 1。最后，通过一个模拟雷达回波特性的简化模型，我们发现当Voldorad工作在高采样率模式时，功率和最大速度变化与穿过天线波束的粒子的大小和速度差直接相关。
Besides their common use in atmospheric studies, Doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field. We present the observations made with a mid-power UHF Doppler radar (Voldorad) during a 7-h Strombolian eruption at the SE crater of Mount Etna on 11–12 October 1998. Main characteristics of radar echoes are retrieved from analysis of Doppler spectra recorded in the two range gates on either side of the jet axis. From the geometry of the sounding, the contribution of uprising and falling ejecta to each Doppler spectrum can be discriminated. The temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before, during and after its paroxysm. Moreover, during the sharp decrease of eruptive activity following the paroxysm, detailed analysis of video (from camera recording), radar and seismic measurements reveals that radar and video signals start to decrease simultaneously, approximately 2.5 min after the tremor decline. This delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the SE crater. Detailed analysis of eruptive processes has been also made with Voldorad operating in a high sampling rate mode. Signature of individual outburst is clearly identified on the half part of Doppler spectra corresponding to rising ejecta: temporal variations of the backscattered power exhibit quasi periodic undulations, whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time. Periodicity of power variations (between 3.8 and 5.5 s) is in agreement with the occurrence of explosions visually observed at the SE vent. Maximum vertical velocities of over 160 m s−1were measured during the paraoxysmal stage and the renewed activity. Finally, by using a simplified model simulating the radar echoes characteristics, we show that when Voldorad is operating in high sampling rate mode, the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam.