Published reports on February 11, 2016 state that drilling machines search for Hamas tunnels on the Israeli side of the border with Gaza, Nearly 100 pieces of heavy engineering equipment are currently trying to locate other potential tunnels along the border. This is laborious and generally hit and misses at best. The search for better solutions is urgently required as the threat to USA/Israeli interests is continuous and considered on the increase.
Proposed Acoustic Zoom Surveyance Solution: Fused Active And Passive Beamforming Of Signals Generated And Listened To:
The Active Part
Acoustic Zoom® is a novel seismic technique adapted from sonar applications that enables high resolution imaging of buried structures using advanced multi-aspect beamforming and beam-steering techniques. The method employs purpose designed steerable phased arrays, analogous to the arrays used in radio astronomy, for both the source and receiver arrays.
The higher resolutions attainable in the method are derived from its use and reliance on having a densely clustered high frequency _ seismic capture from a specially modified, high fidelity sound source.
This source is tuned to deliver higher frequency energy sweeps, in a stacked mode, than are conventionally seen or possible. The - precision of the narrow beam combined with beamforming and steering capabilities of the resultant transmitted and received - signals make possible the delivery of unprecedented resolution cells capable of capturing features such as clandestine tunnels, c deep chambers and buried ordnance targets.
As in the radio astronomy analog and in contrast to conventional soundings or surveying, the beam can be steered to look beyond the footprint of the array. This wide-angle steering ability means that the array can be smaller in size and still have the ability to investigate large lateral ranges and depths compared to conventional seismic arrays where the volume of investigation is constrained to lie (well) inside the bounds of the footprint of the array placement area.
Image detection and associated data processing techniques rely on inversion protocols, which discriminate against the diffuse, non-specular, backscattered energy that are critical in imaging tunnel targets. Acoustic Zoom’s images are built on these diffuse returns.
The Passive Listening Part
In addition to the active Acoustic Zoom beamforming detection approach, the AZ receiver antenna is also used to passively capture micro-seismic level signals. Tunnel construction activities can generate instantaneous geomechanical strains or micro-slips in the area of the tunneling, which in turn (such structural movement of the earth) releases energy in the form of micro-seismic signals. These micro-seismic signals can be recorded but are typically difficult to characterize, as it is difficult to know where they originated.
The problem at hand is such passive listening techniques by themselves are basically non-directional and do not account for the influences of the earth ‘s signal propagation influences. Passive listening cannot derive or incorporate realistic velocity propagation models of the region’s earth. Hence this prevents being able to directly locate tunneling micro-seismic signal sources with any defining vectorial merit. To focus onto such weak seismic sources is therefore flawed and beamforming is not effective. Yet the objective in passively recording these weakly propagating signals from tunneling and from installation generated noise such as from underground placed electrical appliances, lighting and generators is to characterize the source locations and to be able to gain a reliable threat snapshot. Getting this from the geomechanical earth strains that generate the micro-seismic returns is very complex and such simple passive approaches alone cannot justify relying on the signal returns’ magnitude to lead to a detection of clandestine underground activities. Such an overly simplified approach is highly limiting and would not produce activity related directivity or present information or a means to characterize what these faint micro-seismic signals listened to and collected are truly about.
Acoustic Zoom’s Fused Active And Passive Approach Is A Solution
Acoustic Zoom’s active part generates a region’s velocity model even in complex heterogeneous earth conditions. This in turn produces imagery from diffused non-specular energy especially propagating from tunnel structures that act as diffractors. Acoustic Zoom can also characterize and baseline any naturally occurring earth fissures and discontinuies.
Since the receivers are co-located then the passive listening can avail of these imageries derive sophisticated earth signal propagation models to aid in the passively listened to data. An analysis of the resulting micro-seismic signals can be made using differences in the polarization and radiation characteristics of the seismic waves.
Characterizing the micro-seismic source can therefore take on a more comprehensive unifying form of source attributes computed by applying kinematic earthquake fracturing models to deduce the stress changes resulting from the seismic strain, and the amount and area of slip caused by tunnel earth moving. Our method involves modeling the seismic slip to match the observed seismic pulses using amplitude and frequency/time duration to estimate source strength, slip area and stress release. In addition, the Acoustic Zoom fused analysis would be applied to quantify the seismic radiation characteristics from different directions and to define the tunnel plane orientation.
Seismic moment tensor inversion, where the source strain tensor is estimated may be a very effective technique to add given that there is a sophisticated heterogeneous velocity model already derived by the active AZ approach. This combined fused approach is proprietary to Acoustic Zoom and patented and could be used to gain an insight into the tunnel earth digging/fracturing beyond simply mapping the far-field earth geometry. It is attractive to use all aspects of the active interrogation routines and micro-seismic data to establish confidence in the sensing and analysis.
In summary, Acoustic Zoom data involves full volumetric rendering of its data collected with very accurate receiver and transmitter locations. The result of the AZ proprietary data analysis both in its active and in its passive modes leads to exceptional imagery. AZ differentiates itself through its high resolution enhancement processing. The AZ answer product delivers new information that truly characterizes the earth’s subtle discontinuities, micro-fissures, faults and spatial geological character revealing in imagery and by its micro-seismic signatures the presence of tunneling activities even at depths in the earth where remote sensing becomes very limiting.
The Advancement And Partnership Being Sought
The advancement being considered in this joint project is to take our current Acoustic Zoom image processing beamforming protocols both for active and passive and attack the issue of tunnel detection and characterization with unprecedented resolution. Through this venture, a pilot would be conducted providing the over all Homeland Securities’ solution, instrumentation design for optimum receivers and transmission sources. Both groups would work together to deliver the tunnel monitoring and detection answer product. We would also study various visualization architectures such as what Acoustic Zoom is currently pioneering to uniquely view 3D seismic data. The goal is to prototype together an approach and experiment with AZ’s volumetric data techniques and analysis in a directed way to view tunnel activities in an unambiguous manner.
Visualization AZ Data ‘Under Foot’ Concept
[IMG] Imaging-Whilst-Drilling A Further Approach To Consider In Our Partnership
Through an associated company to Acoustic Zoom Inc. called Intelligent Sciences Ltd. a system for imaging rock formations while drilling a wellbore was conceived which includes a drill collar and a plurality of acoustic emitting transducers mounted in the drill collar at angularly spaced apart locations and oriented to emit acoustic energy at least one of laterally away from the drill collar and longitudinally away from the drill collar.
This approach could enhance the technique in use in Israel where drilling machines are used to search for Hamas tunnels on the Israeli side of the border with Gaza. The concept would deliver spatial images in the surrounding rock or ground, which would aid in the detection and capturing of tunnel activity. Current well bores/cores would not be able to provide this information without intensive drilling.
The receiver for both look ahead and look sideways relies on a number of rows of 60 elements equally spaced along a 5m section of the drill collar. Focussed beamforming and beam steering is then applied to the received signals to great advantage. The drill rotates, a target will appear and disappear and thus for multiple targets at different ranges and angles high resolution imagery can be produced in which target positions in angle can be indicated and can be seen many times over. Positions in range is done both by the resolution in time due the pulse length and the depth of focus resulting from the nearfield processing. This can be increased by post processing as a synthetic aperture.
As the drill column rotates with transmit/receive at each position these data can then be combined into a synthetic aperture, which would have an aperture about the same as the diameter of the drill collar. This results in sharpened details of potential targets such as associated with tunnels being started or formed at depth. The forward progress of the drill will be slow enough to amalgamate the forward and side look data and to watch the forward target gradually become a sideways target.The resolution cell will sharpen in a dramatic manner into tens of centimeter resolution cells. A high number of coherent stacks are possible lowering the noise floor due to slow progress and known rotational speed of drill collar. A unique form of synthetic aperture will augment the focusing onto subtle discontinuities. Discontinuities in the environment of greater then 0.5 (typically 1m diameter) would be detectable out to a range from the drill collar of 30m and located in range to about 1m.
The approach delivers multiple descending spatial views and data readings giving detailed 3D acoustic lateral slices of target area with drill information. Product is a very high-resolution structural geo-hazard and formation map of large solid objects, fissures, fractures and geo-changes related to tunnel disturbances. Quantifiable data are co-located with the drill information leading to unprecedented detection and classification imagery, specific to earth geological anomalies that could be related to security threats.
Descending layer-by layer acoustic slice sections backfilled with corresponding geotechnical co-located drill data all viewed through Acoustic Zoom’s virtual reality data visualization.