Development of a GNSS Volcano Ash Plume Detector

Abstract:

Global Navigation Satellite Systems (GNSS), broadcast signals continuously from mid Earth orbit at a frequency near 1.5GHz. Of the four GNSS constellations, GPS and GLONASS are complete with more than 55 satellites in total. While GNSS signals are intended for navigation and timing, they have also proved to be useful for remote sensing applications. Reflections of the GNSS signals have been used to sense soil moisture, snow depth, and wind speed while refraction of the signals through the atmosphere has provided data on the electron density in the ionosphere as well as water vapor and temperature in the troposphere. Now analysis at the University of Colorado has shown that the attenuation of GNSS signals by volcanic ash plumes can be used to measure the presence and structure of the ash plume. This discovery is driving development of a distributed GNSS sensor network to complement existing optical and radar based ash plume monitoring systems. A GNSS based sensing system operating in L-band is unaffected by weather conditions or time of day. Additionally, the use of an existing signal source greatly reduces the per sensor cost and complexity compared to a radar system. However since any one measurement using this method provides only the total attenuation between the GNSS satellite and the receiver, full tomographic imaging of a plume requires a large number of sensors observing over a diversity of geometries.

This presentation will provide an overview of the ongoing development of the GNSS sensor system. Evaluation of low priced commercial GNSS receivers will be discussed, as well as details on the inter sensor network. Based on analysis of existing GPS receivers near volcanic vents, the baseline configuration for an ash plume monitoring network is a 1km spaced ring of receivers 5km from the vent updating every 5 seconds. Preliminary data from field tests will be presented to show the suitability of the sensor system for this configuration near an active volcano.