Fleet’s Geode: A Breakthrough Sensor for Real-Time Ambient Seismic Noise Tomography over DtS-IoT

Abstract

As most of the outcropping and shallow mineral deposits have been found, new technology is imperative to finding the hidden critical mineral deposits required to transition to renewable energy. One such new technique, called ambient seismic noise tomography, has shown promise in recent years as a low-cost, low environmental impact method that can image under cover and at depth. Wireless and compact nodal seismic technology has been instrumental to enable industry applications of ambient noise tomography, but these devices are designed for the active seismic reflection method and do not have the required sensitivity at low frequencies for ambient noise tomography, and real-time data transmission in remote locations requires significant infrastructure to be installed. In this paper, we show the development and testing of the Geode—a real-time seismic node purpose-built by Fleet Space Technologies for ambient seismic noise tomography on exploration scales. We discuss the key differences between current nodal technology and the Geode and show results of a field trial where the performance of the Geode is compared with a commercially popular nodal geophone. The use of a 2 Hz high sensitivity geophone and low noise digitiser results in an instrument noise floor that is more than 30 dB lower below 5 Hz than nodes that are commonly used in the industry. The increased sensitivity results in signal-to-noise ratios in the cross-correlation functions in the field trial that are more than double that of commercially available nodal geophone at low frequencies. When considering the full bandwidth of retrievable correlations in our study, using the Geode would reduce the required recording time from 75 h to 32 h to achieve an average signal-to-noise ratio in the cross-correlation functions of 10. We also discuss the integration of a real-time direct-to-satellite Internet of Things (DtS-IoT) modem in the Geode, which, together with edge processing of seismic data directly on the Geode, enables us to image the subsurface in real-time. During the field trial, the Geodes successfully transmitted more than 90% of the available preprocessed data packets. The Geode is compact enough so that several devices can be carried and installed by one field technician, whilst the array of stations do not require a base station to transmit data to the cloud for further processing. We believe this is the future of passive seismic surveys and will result in faster and more dynamic seismic imaging capabilities analogous to the medical imaging community, increasing the pace at which new mineral deposits are discovered.

Real-Time Ambient Seismic Noise Tomography of the Hillside Iron Oxide–Copper–Gold Deposit

“…Fleet Space Technologies (Fleet) has commercialised an ANT service named ExoSphere, utilising purpose-built real-time compact seismic nodes called Geodes. These Geodes offer increased sensitivity to low-frequency signals, reducing data gathering time compared to conventional nodal geophones [15]. Fleet's Geodes are equipped with a real-time direct-tosatellite Internet of Things (DtS-IoT) modem and edge processing capabilities, enabling rapid data transmission for cloud-based further processing.…”

“…Fleet's Geodes are equipped with a real-time direct-tosatellite Internet of Things (DtS-IoT) modem and edge processing capabilities, enabling rapid data transmission for cloud-based further processing. This breakthrough allows for unprecedented speed in subsurface imaging, thus accelerating the discovery of new mineral deposits [15].…”

An Effective Method for Improving Low-Frequency Response of Geophone

“…Schimmel et al used only one seismic sensor (geophone) collocated with an infrasound sensor, and the signal was sent to a microcontroller that ran the detection algorithm [ 12 ]. Olivier et al adopted a 2 Hz high sensitivity geophone and low noise digital converter as a real-time seismic node [ 13 ]. Marchetti et al [ 10 ] and Belli et al [ 14 ] adopted seismographs (LE-3Dlite MkIII, Lennartz Electronic, Tübingen, Germany) to record ground vibration signals in the measurement range of 1–100 Hz.…”