Method and system for analysing a target region beneath a surface using generated noise

Abstract

Methods, systems, and computer-readable media are disclosed for determining one or more ground properties of a target region beneath a surface, comprising: inserting a seismic sensor into the target region beneath the surface; generating a noise signal; outputting noise, by a noise source, at or incident on the surface and based on the generated noise signal to generate seismic waves in the target region; receiving a response signal, the response signal indicative of the generated seismic waves measured by the seismic sensor; determining one or more ground properties of the target region based on the received response signal. Unlocking insights from geodata, the present disclosure further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world.

Description

METHOD AND SYSTEM FOR ANALYSING A TARGET REGION BENEATH A SURFACE USING GENERATED NOISE FIELD 

[0001] The disclosure relates to methods and systems for analysing a target region beneath a surface using generated noise. More particularly, the disclosure relates to a method and system for determining one or more ground properties of a target region beneath a surface based on generated noise output by a noise source at or incident on the surface based on a generated noise signal. Unlocking insights from Geo-Data, the present invention further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world.  BACKGROUND

[0001] There is a general and ongoing need to improve data acquisition of subsurface surveying. The determination of subsurface characteristics is used to identify objects below the surface of the ground, as well as determining the soil characteristics, such as soil type, density, moisture content, shear modulus, and the like, which may be used in foundation planning and / or management. Subsurface information may be used for e.g., site characterisation for infrastructure projects, foundation calculations, and the like. For such applications, it is important to generate a comprehensive understanding of the subsurface with a high degree of accuracy in an efficient manner.

[0002] One of the methods of performing such tests is generally known as a seismic cone penetration test (SCPT). SCPT is a geotechnical method that integrates standard cone penetration testing (CPT) with in-situ measurements of seismic wave velocities, which is are the velocities at which seismic waves move through a material. Seismic wave velocities are a key parameter for the determination of ground characteristics in a volume of interest. SCPT is employed in geotechnical site investigations to evaluate the mechanical properties of soils, including stiffness and shear strength.

[0003] During a SCPT a cone penetrometer with a seismic sensor is pushed into a target region in the ground and seismic waves are generated in the target region using an impulsive source, such as hammer or often an airgun in an offshore environment. The seismic waves generated by the impulsive source are measured by the seismic sensor to determine the seismic wave velocity of seismic waves produced by an impulsive source. Typically, the cone penetrometer comprises two seismic sensors at a fixed spacing. The seismic waves generated by the impulsive source are measured at two depths simultaneously. The seismic wave velocity across a depth range is then determined by calculating the travel time difference between the two receivers.

[0004] A further method of performing such tests is generally known asvertical seismic profiling (VSP).Vertical seismic profiling is a geophysical method often used in oil and gas industry to measure the seismic velocities by deploying an array of seismic sensors in a vertical borehole or a well. An impulsive source, such as hammer or often an airgun in an offshore environment, is used to generate seismic waves in the target region for detection by the array of seismic sensors in a vertical borehole or a well. VSP can take various forms, examples of which include a zero-offset VSP, where the impulsive source is positioned on top of the well or borehole, and a walkaway VSP, where the impulsive source is moved progressively further away from the well or borehole while acquiring the data.VSP data can be processed in two ways: 1) by inverting the travel time of the direct wave path from the impulsive source to the array of seismic sensors, or 2) by imaging the seismic energy reflected from changes in the soil properties.VSP data can also be used to relate surface seismic data to in-situ seismic measurement. This is often done to convert data from time to depth or to calibrate seismic properties obtained from seismic inversion of seismic reflection method (i.e., providing background velocity models).

[0005] SCPTs and VSPs are both types of in-situ seismic wave velocity measurement tests. These tests require the use of impulsive noise sources, such as hammers or airguns.Impulsive sources release acoustic energy within their environment (for example a body of water)in a very short amount of time and can produce high sound pressure levels. They have limited control in terms of frequency content, repeatability, and the released pressure levels. They can also be detrimental to wildlife and the environment, e.g., cause disturbance to the local fauna and contribute to a negative environmental footprint. Airguns, hammers and other impulsive sources can lead to devasting effects like injury, hearing loss, and behavioural changes to species in the surrounding environment.

[0006] As a result, there is a need for improved in-situ seismic wave velocity measurement tests that do not have the above disadvantages.  SUMMARY 

[0007] This summary introduces concepts that are described in more detail in the detailed description. It should not be used to identify essential features of the claimed subject matter, nor to limit the scope of the claimed subject matter.

[0008] According to a first aspect of the present disclosure, there is provided method for determining one or more ground properties of a target region beneath a surface, the method comprising. In some implementations, the method comprises inserting a seismic sensor into the target region beneath the surface. In some implementations, the method further comprises generating a noise signal. In some implementations, the method further comprises outputting noise, by a noise source, at or incident on the surface and based on the generated noise signal to generate seismic waves in the target region. In some implementations, the method further comprises receiving a response signal, the response signal indicative of the generated seismic waves as measured by the seismic sensor. In some implementations, the method further comprises determining one or more ground properties of the target region based on the received response signal.

[0009] Advantageously, one or more ground properties of the target region can be based on measurements of seismic waves generated using a noise source that outputs a generated noise signal, avoiding the disadvantages associated with the use of impulsive sources. The advantages of being able determine ground properties of such a target region without the use of impulsive noise sources such as airguns are numerous. It is simpler, faster, cheaper, less energy intensive, and less impactful on local environment and wildlife than existing intrusive methods for site analysis and methods that make use of impulsive noise sources. This is because no impulsive noise stimulation is required. Additionally, and crucially, the disclosed method is both accurate and reliable, making it a practical and technically attractive technique. The disclosed method is especially well suited to use in offshore environments due to its low impact characteristics.

[0010] Advantageously, the use of a generated signal output by a noise source can enable improved accuracy and precision of the determination of ground properties over the use of impulsive noise sources, such as airguns. Impulsive sources release acoustic energy in a very short amount of time, and they have limited control in terms of frequency content, repeatability, and the released pressure levels. These problems are addressed by the use of a generated signal output by a noise source.

[0011] Furthermore, including a generated noise signal output by a noise source can enable further improvements to the resolving of ground properties of a subsurface target region. As will be discussed further herein, seismic wave propagation is influenced by the physical properties of the subsurface. Noise from impulsive sources may be limited in frequency range and / or content at specific frequencies. As a result, this may negatively affect the quality of retrieved seismic wave information and therefore the determination of ground properties at specific depths. By using a generated noise signal output by a noise source, the frequency content of the generated noise can be controlled meaning ground properties can be determined at a range of depths of interest and with improved efficiency. Additionally, using a generated noise signal output by a noise source can enable improved quality (e.g., accuracy and precision) of the determination of the ground properties by providing control over the intensity, location, frequency profile, duration, and noise profile of the noise that is output by the noise source, as will be discussed further herein. Finally, using a generated noise signal output by a noise source enables greater control over frequency, intensity and sound pressure levels used in geotechnical imaging. This facilitates signal generation at lower amplitude than impulsive sources, such as airguns, lowering the environmental impact of geotechnical imaging processes.

[0012] In some implementations, the noise source may be a vibratory noise source, such as a speaker. Using a vibratory noise source enables greater control over frequency, intensity and sound pressure levels used in geotechnical imaging. This facilitates signal generation at lower amplitude than impulsive sources, such as airguns, lowering the environmental impact of geotechnical imaging processes. Examples of vibratory noise sources that can be used in the systems and methods described herein include transducers and low frequency electrodynamic sound projectors.

[0013] Ambient noise, or seismic ambient noise, may be generated by one or more ambient sources. The ambient sources may be natural (that is, naturally occurring vibrations) or cultural (that is, vibrations from human activity). For example, the ambient sources may include ocean(s) (for example, tidal or wave noise), wind, industry, industrial machinery, vehicles such as cars or trains, and human noise (for example, footsteps).

[0014] The present method includes a noise source that generates noise which may be similar to, the same as, or shares characteristics with the ambient noise generated by the ambient sources. In particular, such a noise source may be included as part of the disclosed methods to generate noise to be received / measured by the receivers (interchangeably referred to as sensors or seismic sensors herein - a seismic sensor may have several seismic sensor element, each configured to detect seismic waves). As will be discussed further herein, by generating noise that is similar to ambient noise, there is less impact on local environment and wildlife compared to more intrusive methods and methods that make use of impulsive noise sources, such as an airgun. At the same time, such noise sources can be used to supplement the existing ambient noise, which enables the determination of the one or more ground properties of a target region beneath a surface of the earth to be improved. A noise source is configured to output noise based on a generated noise signal. The noise output by the noise source is referred to herein as “generated noise”.

[0015] In some implementations, the receivers used in the present methods may be geophones, accelerometers (such as vertical or triaxial accelerometers), particle velocity sensors, fibre-optic based sensors, seismometers, vibration sensors, pressure sensors, vibration sensors, hydrophones and / or transducers or an array of any of these types of receivers. In some implementations, the receivers may collect data over a significant period of time. For example, the generated noise may be measured consecutively over a period of five days. This longer recording time results in the adequate retrieval of seismic wave information from the noise recorded at or near the surface of the target region. The recording time required to obtain adequate retrieval of seismic wave information is dependent on the quality and quantity of the noise measured by the receivers. In scenarios where seismic wave information is insufficient, a longer recording time may be used to compensate for this by summing seismic wave information together to produce a stronger signal. Advantageously, the use of generated noise signal output by a noise source can provide the adequate seismic wave information instead of requiring recording time to be prolonged. In fact, incorporating use of generated noise signal output by a noise source can in most cases reduce the reduce the time necessary to obtain adequate retrieval of surface wave information. As such, improved operational efficiency, i.e., more effective use of time, human resources, and hardware resources are enabled, while minimising disruption / impact on local environment, wildlife, and communities.

[0016] As will be apparent to the skilled person, the noise source used in the present methods may be any device capable of generating vibrations. In some implementations, the noise source can output noise for an extended period of time.

[0017] Each response signal may be indicative of the P-waves and / or S-waves caused by the generated noise.

[0018] In some implementations, the method further comprises, optionally, outputting the one or more ground properties of the target region to user, for example. via a user device).

[0019] In some implementations, the method further comprises receiving a further response signal, the response signal indicative of the generated seismic waves as measured by the seismic sensor at a location different from the location at which the response signal is received (for example, a vertically offset location), the method further comprising: cross-correlating or deconvolving the response signal and the further response signal; and performing an inversion using the cross-correlated or deconvolved response signal and further response signal to generate the two-dimensional ‘2D’ or three-dimensional ‘3D’ model of the target region in terms of the one or more ground properties.

[0020] In some implementations, the response signal and the further response signal are measured simultaneously by vertically offset seismic sensors elements of the seismic sensor.

[0021] In some implementations, the response signal and the further response signal are measured sequentially by moving the seismic sensor between two locations for each measurement.

[0022] In some implementations, the step of cross-correlating the response signal and / or the further response signal comprises cross-correlating the response signal with the output noise and / or cross-correlating the further response signal with the output noise.

[0023] In some implementations, the step of determining one or more ground properties of the target region based on the received response signal comprises determining a vertical seismic profile, VSP, using the received response signal.

[0024] In some implementations, the step of determining one or more ground properties of the target region based on the received response signal comprises performing a seismic cone penetration test, SCPT, using the received response signal.

[0025] In some implementations, the noise signal is generated using a pseudorandom binary sequence. Advantageously, pseudorandom binary sequences are deterministic and may be generated efficiently using simple underlying hardware implementation. Additionally, the use of pseudorandom binary sequences can enable data acquisition time to be shortened, thereby providing effective use of time and hardware resources. Moreover, pseudorandom binary sequences have similar acoustic properties to white noise, which has the advantage of reducing impact / disruption to the environment and wildlife.

[0026] In some implementations, the pseudorandom binary sequence is at least one of a maximum length sequence, Gold sequence, or Kasami sequence. In some implementations, any pseudorandom binary sequence can be used, which shares characteristics with noise like properties, e.g., white noise, or other colours of noise. In some implementations, any combination of the aforementioned pseudorandom binary sequences may be used to generate a noise signal.

[0027] In some implementations, the noise signal is generated using a random number generator.

[0028] In some implementations, the noise signal is output at an intensity which is based on, matches, is equal to, or is audibly equal to the average intensity of ambient noise measured at the seismic sensor. This enables a noise source to output noise at an intensity that minimises disruption / impact on local environment and wildlife.

[0029] In some implementations, the noise signal output by the noise source is limited to a threshold output level. The threshold output level can, in some implementations, be the average intensity of ambient noise across all directions in the ambient noise profile, or, in some implementations, be the aforementioned average intensity of ambient noise received at the seismic sensor. However, as will be discussed further herein, the threshold output level can be any suitable threshold, such as the highest ambient noise recorded, based on an environmental standard / regulation, and so forth. In some implementations, the threshold output level can comprise one or more threshold output sublevels according to one or more frequency values or frequency ranges of the generated noise / noise signal

[0030] In some implementations, the noise signal is generated to contain frequency content with a specific frequency range of 30-200 Hz. This frequency has been found to contribute to the generation of S-waves in the target region. 

[0031] In some implementations, the noise signal is generated to contain frequency content with a specific frequency range of 30-1000 Hz. This frequency has been found to contribute to the generation of P-waves in the target region.

[0032] In some implementations, the noise signal is modulated to a specific frequency range, such as the above ranges. In some implementations, the noise signal is filtered to attenuate frequencies outside a specific frequency range, such as the above ranges. By filtering the noise signal to attenuate frequencies outside a specific frequency range, similar to the aforementioned modulation of a noise signal, the noise signal can be controlled to increase the energy / intensity of the noise at specific frequencies or frequency ranges. In some implementations, the noise signal is filtered to attenuate frequencies outside a specific frequency range. By filtering the noise signal to attenuate frequencies outside a specific frequency range, similar to the aforementioned modulation of a noise signal, the noise signal can be controlled to increase the energy / intensity of the noise at specific frequencies or frequency ranges, such as the above ranges. Advantageously, this ensures the noise signal includes the frequency content required to generate P-Waves and / or S-Waves for geotechnical imaging within the target region.

[0033] In some implementations, the noise source comprises a plurality of noise sources. In some implementations, a second noise source can be provided at a different location to the first. In some implementations, the second noise source comprises a plurality of noise sources. Advantageously, by including a noise source that comprises a plurality of noise sources, the plurality of noise sources can further improve the accuracy and precision of the determination of ground properties, as will be further discussed herein.

[0034] In some implementations, the plurality of noise sources is configured to output the noise signal sequentially. By having the plurality of noise sources output the noise signal sequentially (i.e., one at the time following a predefined or in some implementations random order), this ensures the output noise signals are not correlated with each other as they do not overlap in time. This enables efficient determination of the Green’s functions and can shorten data acquisition time. As such, even if the noise signal output by each of the plurality of noise sources are identical, there is no correlation between the noise sources.

[0035] In some implementations, the noise signal output at each noise source of the plurality of noise sources are different. That is, the noise signal output by each of the plurality of noise sources are not identical to each other. Advantageously, having each of the plurality of noise sources output noise based on a different noise signal can provide output of noise that is similar, mimics, or shares characteristics with the ambient noise.

[0036] In some implementations, the different noise signal output at each noise source of the plurality of noise sources are not correlated with each other.

[0001] In some implementations, the one or more ground properties may comprise one or more elastic properties of the target region, such as the shear-velocity, Vs. Retrieving the shear-velocity of the target region provides a valuable insight to the ground properties of the target region, such as the small-strain shear modulus of the target region. This allows engineers to identify areas of weakness in the target region beneath a surface, say, or lateral variations in the geology.

[0002] As useful context, the shear-velocity Vs is the velocity at which a shear wave moves through the material and is controlled by the shear-modulus of the material. The relationship between shear-velocity and shear-modulus G is defined by Vs = √G / ρ, where ρ is the density of the material. Measurement of Vs therefore provides a valuable insight to the ground properties of a subsurface ground region. Small-strain shear modulus (Gmax) is also important in foundation design, wherein Gmax = ρ.Vs2. Shear modulus is a measure of the elastic shear stiffness of a material and represents the deformation of a solid when it experiences a force parallel to one of its surfaces while its opposite face experiences an opposing force. Such forces and their effects in subsurface ground volumes, are an important parameter for study before and during the design of land based and offshore building and infrastructure projects. To determine the shear modulus of a volume, the shear velocity, Vs, is determined. This in turn gives an indication of the stiffness of the subsurface material, and its ability to support structures extending above and / or through the volume. In the context of ground study, two types of waves are generally distinguished: P-waves and S-waves. In P-waves, particles in the volume oscillate in the direction of movement of the wave, which causes a compression and de-compression of the ground as the waves propagate through the ground. Meanwhile S-waves are shear waves, in which particles oscillate in a direction perpendicular to the direction of propagation of the waves.

[0037] In some implementations, the step of processing may comprise processing the first and / or second response signals to accentuate the representation of the received noise. Put another way, to accentuate the broad band characteristics of the received noise. For example, by removing the instrument response and / or by filtering out large amplitudes. Such large amplitudes may be caused by (undesired) signals from earthquakes. Advantageously, this prevents large amplitude events from overpowering the generated noise (and ambient noise, if present) response that is of interest.

[0038] In some implementations, the step of inserting a seismic sensor into the target region comprises pushing the seismic sensor into the target region.

[0039] In some implementations, the step of inserting a seismic sensor into the target region comprises boring a hole in the target region and inserting the seismic sensor into the borehole.

[0040] In some implementations, the seismic sensor comprises at least two vertically offset seismic sensors elements.

[0041] In some implementations, the seismic sensor comprises at least one of a: pressure sensors, geophones, hydrophones, accelerometers (such as vertical or triaxial accelerometers), particle velocity sensors, fibre-optic based sensors, seismometers, vibration sensors and / or transducers.

[0042] In some implementations, the seismic sensor comprises a seismic cone penetrometer.

[0043] In some implementations, the seismic cone penetrometer comprises at least three seismic sensor elements.

[0044] In some implementations, the noise source is coupled to at least one of: a structure on the surface; and a vehicle on the surface, such as a truck or crawler.

[0045] In some implementations, the noise source directly contacts the surface.

[0046] In some implementations, the surface is a surface of a bed of a body of water.

[0047] In some implementations, the seismic sensor is coupled to a vessel, for example, via a pushrod dispensed from the vessel. In some implementations, the vessel comprises a driving mechanism for driving the pushrod into the target region. In some implementations, comprises means for drilling a borehole.

[0048] In some implementations, the noise source is coupled to one of: a structure on the bed of the body of water; and a vessel on or within the body of water, such as a ship, USV or ROV.

[0049] In some implementations, the noise source is coupled to a tow cable of the vessel on or in the body of water.

[0050] In some implementations, the noise source is coupled to the same vessel as the seismic sensor.

[0051] In some implementations, the step of outputting noise by the noise source based on the noise signal, where the noise source is located within the body of water, comprises generating a pressure wave in the body of water incident on the surface of the bed of the body of water.

[0052] In some implementations, the pressure wave is incident on the surface of the bed of the body of water at an angle within the range of 10 to 40 degrees, optionally, at an angle of 30 degrees. This angle has been found to optimise the generation of P- and / or S-waves at the surface and in the target region.

[0053] In some implementations, the noise source comprises an array of noise sources configured to form a beam of noise incident on the surface of the bed of the body of water. This enhances the generation of P- and / or S-waves at the surface and in the target region.

[0054] In some implementations, the beam of noise is incident on the surface of the bed of the body of water at an angle within the range of 10 to 40 degrees, optionally, at an angle of 30 degrees. This angle has been found to optimise the generation of P- and / or S-waves at the surface and in the target region.

[0055] In some implementations, the response signal and / or further response signal comprise P-waves and / or S-waves generated in the target region by the output noise.

[0056] In some implementations, the noise source moves relative to the surface of the bed of the body of water.

[0057] In some implementations, a motion correction operation is applied to the response the response signal and / or the further response signal to account for the movement of the noise source relative to the surface of the bed of the body of water. Using motion correction to account for relative movement of the noise source improves the accuracy of the method.

[0058] According to a further aspect, there is provided a program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any preceding claim.

[0059] According to a further aspect, there is provided a system comprising: one or more processors; one or more memories having stored thereon computer readable instructions configured to cause the one or more processors to perform operations comprising the steps of the method of the first aspect or any method described herein.

[0060] According to a further aspect, there is provided a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of the first aspect or any method described herein.

[0061] According to another aspect, there is provided a system comprising: a noise source, a seismic sensor, one or more processors; and one or more memories having stored thereon computer readable instructions configured to cause the one or more processors to perform operations to control the system to perform the steps of the first aspect or any method described herein.

[0062] According to another aspect, there is provided a system comprising: a noise source, a seismic sensor, a vessel, wherein the seismic sensor is coupled the vessel. In some implementations, the noise source is coupled to a further vessel on or in the body of water. In some implementations, the noise source is coupled to the same vessel as first receiver and / or second receiver. In some implementations, vessel and / or the further vessel are a ship, an uncrewed surface vessel, USV, or a remotely operated vehicles ROV. In some implementations, the system further comprises one or more processors; and one or more memories having stored thereon computer readable instructions configured to cause the one or more processors to perform operations to control the system to perform the steps of the first aspect or any method described herein.  BRIEF DESCRIPTION OF THE DRAWINGS 

[0063] In order to describe the manner in which the above-recited and other advantages and features of the disclosure can be obtained, a more particular description of the principles briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary implementations of the disclosure and are therefore not to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0064] Figure 1 showsan example system for determining one or more ground properties of a target region beneath a surface;

[0065] Figure 2 shows a method for determining one or more ground properties of a target region; and

[0066] Figure 3a block diagram of one implementation of a computing device which can be used to perform the methods described herein.

[0067] Throughout the description and drawings, like reference numerals refer to like features. DETAILED DESCRIPTION 

[0068] The following is a description of certain embodiments of the invention, given by way of example only and with reference to the drawings.

[0069] Various implementations and examples of the disclosure are discussed in detail below. While specific implementationsand examples are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognise that other components and configurations may be used without parting from the spirit and scope of the disclosure. Thus, the following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description. A reference to an implementation or example in the present disclosure can be a reference to the same implementation or example, or any other implementation or example. Such references thus relate to at least one of the implementationsor examples herein.

[0070] The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Alternative language and synonyms may be used for any one or more of the terms discussed herein, and no special significance should be placed upon whether or not a term is elaborated or discussed herein. In some cases, synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only and is not intended to further limit the scope and meaning of the disclosure or of any example term. Likewise, the disclosure is not limited to various implementations given in this specification. References to ranges of values or values “between” two values should be interpreted as encompassing the end points of those ranges unless otherwise specified.

[0071] A method for determining one or more ground properties of a target region beneath a surfacewill now be described. A more detailed explanation of the method is provided below in relation to Figure 2.In short, the method involves inserting a seismic sensor into a target region beneath a surface,generating a noise signal, outputting noise, by a noise source, at or incident on the surface and based on the generated noise signal to generate seismic waves in the target region,receiving a response signal, the response signal indicative of the generated seismic waves as measured by the seismic sensor, and determining one or more ground properties of the target region based on the received response signal.This provides a valuable insight into the composition of the target region. In turn, this can be used to influence subsequent site surveys and construction decisions in either a onshore or offshore environment, as shall be described below.

[0072] The method is an in-situ seismic wave velocity measurement test, and can, in some implementations, follow conventional processing steps inSCPT and VSP. The key difference being the generating of a noise signal and the outputting of noise, by a noise source, based on the generated noise signal to generate seismic waves in the target region.

[0073] The use ofgenerated noise avoids the need for impulsive noise sources, such as hammers or airguns. Impulsive sources release acoustic energy within their environment (for example a body of water) in a very short amount of time and can produce high sound pressure levels. They have limited control in terms of frequency content, repeatability, and the released pressure levels. They can also be detrimental to wildlife and the environment, e.g., cause disturbance to the local fauna and contribute to a negative environmental footprint. Airguns, hammers and other impulsive sources can lead to devasting effects like injury, hearing loss, and behavioural changes to species in the surrounding environment. The use of generated noise addresses each of these issues, as shall be explain be explained below.

[0074] Ambient noise is generated from various ambient sources. The ambient sources fall under two categories: natural and cultural. Natural sources are those such as oceans or the wind which cause naturally occurring vibrations. Cultural sources are those which stem from human activity, such as industry, industrial machinery, vehicles such as cars or trains, power lines, and human noise.

[0075] Generated noise is generated based on a generated noise signal and is output by a noise source at or near the surface of a target region. In some implementations, the generated noise is similar to, the same as, or shares characteristics with the ambient noise generated by ambient sources. In this manner, the environmental and other detrimental effects of the generated noise may be mitigated as compared with impulsive sources.

[0076] More specifically, each response signal of the method is measured by a seismic sensor. The response signals are indicative of the amplitude of generated noise that was transmitted from the noise source, as explained more below, through the subsurface and measured by the seismic sensor. In particular, seismic waves such as P- and S- waves can be measured. Seismic waves may be generated by cultural or natural processes occurring at or near the surface (i.e., ambient noise), or generated by generated noise output by one or more noise sources.

[0077] The seismic sensor, may include one or more of geophones, accelerometers (such as vertical or triaxial accelerometers), particle velocity sensors, fibre-optic based sensors, seismometers, pressure sensors, vibration sensors, hydrophones and / or transducers or an array of any of these types of sensors.

[0078] The noise source may be any device capable of generating vibrations through a medium (or media). In some implementations, the noise source can output noise for an extended period of time. In some implementations, the noise source is a vibratory noise source or vibrator (used interchangeably herein), which is electromagnetically driven, hydraulically driven, or otherwise driven to generate vibrations. In some implementations, the noise source is a speaker, a woofer, a subwoofer, a buzzer (e.g., piezoelectric), a tweeter, or any other device capable of producing sound, vibrations, or seismic activity. In some implementations, the noise source is a combination of one or more of the aforementioned devices. The noise source can be placed at or near the surface of a target region, though in some implementations, the noise source can be placed at a distance from the target region.

[0079] Vibratory noise sources can emit any type of acoustic signal including chirps, sweeps and pseudorandom sequences (e.g., maximum length sequences). These signals can be tuned to be “as quiet as possible”. This means that the sound pressure levels of the generated signal can be as close as possible to the measured ambient noise levels (sound levels that already exists in the environment) but high enough to ensure a minimum required signal-to-noise ratio required for processing. The release of excess acoustic energy into the environment is avoided.

[0080] Advantageously, the vibratory noise source produces an acoustic signal that is repeatable and controllable in terms of frequency generating a suitable noise signal. Using vibratory noise sources, it is possible to generate P- and S-waves in the target region for the purpose of measuring in-situ seismic velocity by generating noise in the frequency bandwidth required to generate P- and S-waves. This method may also be used to enhance the correlation between in-situ and surface seismic measurements, contributing to a more accurate and comprehensive analysis of subsurface geological characteristics. Having control over the frequency content of the noise source allows the emitting of generated noise that matches a required vertical spatial resolution. This is beneficial when surface seismic data (i.e. data relating to seismic waves detected at a surface) is correlated with in-situ measurements of seismic wave velocities, such as SCPT or VSP data. Ensuring they have the same frequency bandwidth and hence the same vertical resolution enables easier correlation between in-situ and surface seismic measurements.

[0081] Fig. 1 shows an examplesystem for determining one or more ground properties of a target region beneath a surface. The system may be used to carry out the method as described above and in relation to Figure 2 below.Figure 1 shows a first vessel 102 and a second vessel 108 on a body of water 110. A remotely operated vehicle, ROV, 104 has been deployed by the first vessel 102 and is operating within the body of water 110. Coupled to the ROV 104 is a noise source 106 for directing generated noise 114 at a surface 112 of the bed of the body of water 110 above a subsurface volume 118 (such as the target region of the method described in connection with Figure 2 - subsurface volume and target region are used interchangeably) within the bed of the body of water 110. The generatednoise 114 generates seismic waves 120 in the subsurface volume 118. A seabed frame 134 is located on the surface 112. The seabedframe comprises a driving mechanism 116 for driving a pushrod 130, dispensed by the second vessel 108, into the subsurface volume 118. A further noise source 132 for directing noise (not depicted) at a surface 112 to generate seismic waves 120 in the subsurface volume 118 is provided on the seabed frame 134.In some implementations, only one of the noise source 106 and the further noise source 132 is provided.

[0082] At the end of the pushrod 130 is a seismic sensor 128 for measuring the seismic waves 120 generated by either or both of the noise sources 106 and 132.The seismic sensor 128 comprises a first seismic sensor element 122 vertically offset from a second seismic sensor element 124. At its distal end, the seismic sensor 128 comprises a cone penetrometer 126.

[0083] The impact of the generatednoise 114generated by either or both of the noise sources 106 and 132 at the surface 112 of a bed of the body of water 110 generates seismic waves 120 in the subsurface volume 118 that are detected by the seismic sensor 128 within the subsurface volume 118. Example seismic waves 120include P- and S- waves, which can be used for high resolution sediment characterisation. P-waves, excited in the body of water 110, can convert to S- waves at the surface 112 of the bed of the body of water 110 or at any interface where the elastic properties of the soil changes (e.g. sediment layers). These various converted modes can be recorded by seismic sensor 128. A more detailed discussion of this process is described in relation to Figure 2.

[0084] The first vessel 102 of Figure 1 could be any suitable vessel or a ship, including an uncrewed surface vessel (USV) or an ROV, located on or in the body of water 110. The firs vessel 102 may be controlled by an operator located at the first vessel 102 or in a remote operating centre (not depicted). The firstvessel 102 could also be autonomously controlled.

[0085] The ROV 104 of Figure 1 may be controlled from the firstvessel 102, for example by a cable (as depicted in Figure 1) or via wireless communication (not depicted). In another example, the ROV 104 may be controlled by an operator located at the firstvessel 102 or in a remote operating centre (not depicted).

[0086] Either or both of the noise sources 106 and 132may be a device capable of generating vibrations through a medium (or media). In some implementations, the noise sources 106 and 132can output generatednoise 114for an extended period of time. In some implementations, either or both of the noise sources 106 and 132are a vibratory noise source or vibrator (used interchangeably herein), which is electromagnetically driven, hydraulically driven, or otherwise driven to generate vibrations. In some implementations, the either or both of the noise sources106 and 132is a speaker, a woofer, a subwoofer, a buzzer (e.g., piezoelectric), a tweeter, or any other device capable of producing sound, vibrations, or seismic activity. In some implementations, either or both of the noise sources 106 and 132 is a combination of one or more of the aforementioned devices. Either or both of the noise sources 106 and 132can be placed at or near the surface 112 of the subsurface volume 118, though in some implementations, either or both of the noise sources 106 and 132can be located at a distance from the subsurface volume 118.

[0087] The noise source 106 of Figure 1 could be an array of noise sources (as depicted in Figure 1) and the nature of the noise sources is discussed in greater detail below. The location and direction of the noise source 106 may be altered by controlling movement of the ROV 104. In an alternative example, the noise source 106 can be coupled directly to the firstvessel 102 via, for example, a tow cable. The noise source 106 is capable of generating noise 114 in the form of a pressure wave in the body of water 110 incident on the surface 112.

[0088] In some implementations, there may be multiple ROVs 104 provided in the system of Figure 1, each with a respective noise source 106.

[0089] In some implementations, there the noise source 106 may be coupled to a structure (not depicted) on the surface 112 of the bed of the body of water 110, rather than being coupled to the ROV 104 or the firstvessel 102.

[0090] The further noise source 132of Figure 1 is provided on the seabed frame 134. As with thenoise source 106, the further noise source 132could be an array of noise sources. The further noise source 132 is capable of generating noise in the form of a pressure wave in the body of water 110 incident on the surface 112.

[0091] The second vessel 108 of Figure 1 could be any suitable vessel or a ship, including aUSV or an ROV, located on or in the body of water 110. The second vessel 108 may be controlled by an operator located at the second vessel 108 or in a remote operating centre (not depicted). The second vessel 108 could also be autonomously controlled. The second vessel 108 is configured to dispense pushrod 130 as it is inserted into the ground.

[0092] In some implementations,the pushrod 130 is provided on the second vessel 108 in a coiled configuration, and the driving mechanism drives the pushrod 130 into thesubsurface volume 118 as it is uncoiled. In some implementations,the pushrod 130 is a segmented pushrod, in which segments of the pushrod are screwed together or otherwise coupled as it is inserted into the ground.

[0093] The seabed frame 134of Figure 1 is located on the surface 112 of the bed of the body of water 110. In some implementations, the seabed frame 134 is lowered onto the surface 112 by the second vessel 108.

[0094] The seabed frame comprises the driving mechanism 116 for driving the pushrod 130, as it is dispensed by the second vessel 108, into the subsurface volume 118. The driving mechanism 116 could, alternatively, be located on the second vessel 108. Any suitable driving mechanism may be used for this purpose.

[0095] At the end of the pushrod 130 is a seismic sensor 128 for measuring the seismic waves 120 generated by either or both of the noise sources 106 and 133.The seismic sensor 128 comprises a first seismic sensor element 122 vertically offset from a second seismic sensor element 124. The vertical offsetenables seismic waves generated by the impulsive source are measured at two depths simultaneously. The seismic wave velocity across a depth range is then determined by calculating the travel time difference between the first seismic sensor element 122 and thesecond seismic sensor element 124.

[0096] The seismic sensor elements 122 and 124 are configured to detect the seismic waves 120 generated by either or both of the noise sources 106 and 133. Either or both of the seismic sensor elements 122 and 124 may comprise at least one of pressure sensors, geophones, hydrophones, accelerometers (such as vertical or triaxial accelerometers), particle velocity sensors, fibre-optic based sensors, seismometers, vibration sensors and / or transducers.In some implementations, the seismic sensor 128 is configured to carry out the seismic testing of a standard seismic cone penetration test(SCPT).

[0097] In some implementations, the seismic sensor 128 comprises three or more seismic sensor elements.

[0098] At its distal end, the seismic sensor 128 comprises a cone penetrometer 126. The cone penetrometer 126 may be configured to carry out the cone penetration testing of an SCPT. In some implementations, the seismic sensor 128 may be provided without the cone penetrometer 126.

[0099] Although the examplesystem of Figure 1 comprises a pushrod 130 that can be driven into the subsurface volume 118 to perform, for example, an SCPT, the system may instead be configured to deploy an array of seismic sensors in a vertical borehole or a well, for example in a vertical seismic profiling (VSP) type application. In such an example implementation, the second vessel 108 may comprise means for drilling a borehole and / or means for deploying an array of seismic sensors within the borehole. Such an array of seismic sensors comprises similarly vertically offset seismic sensor elements, such as the seismic sensor elements 122 and 124. They may have the same features as the seismic sensor elements 122 and 124 described herein.

[00100] Although the examplesystem of Figure 1 is depicted in an offshore context, it will be understood that example implementations described herein are not limited to an offshore context. The components could equally be provided in an onshore environment. For example, the components provided on the first vessel 102 and the second vessel 108 could be provided on equivalent land based components, such as land or air basedvehicles and / or structures. More specifically, the noise source 106 could be provided on a structure on the surface or on a vehicle on the surface, such as a truck or crawler. Means for dispensing the pushrod and driving it into the ground could be provided ona structure on the surface a vehicle on the surface, such as a truck or crawler.

[00101] This applies equally to the example system configured to deploy an array of seismic sensors in a vertical borehole or a well, for example in a vertical seismic profiling (VSP) type application. The components of this system could be similarly onshore.

[00102] An exemplary method 200 for determining one or more ground properties of a target region, such as subsurface volume 118 of Figure 1, is shown in 2. The method 500 may be a computer-implemented method. Computer apparatus 300 which can be used to perform the method is described later in reference to Figure 3. The method may be carried out using the setup shown in Figure 1 (or any variations thereof described herein) and like reference numerals with respect to Figure 1denote the same features. For the purposes of this method, it is assumed that only one of the noise source 106 and the further noise source 132 is present, although both may be present in certain implementations.

[00103] At step 202 a seismic sensor 128 into the target region 118 beneath the surface 112. This could be by a driving mechanism 116 pushing the seismic sensor 128 into the target region or the seismic sensor could be inserted into an existing well or borehole. The seismic sensor 128 is inserted to a depth at which it is desired for seismic testing to occur, such as SCPT or VSP.

[00104] At step 204, a noise signal is generated. The noise signal may be designed to include the frequency content required to generate P-waves and / or S-waves for measurement by the seismic sensor 128 within the target region 118. Having control over the frequency content of the generated noise 114 allows the output noise to be tailored to generate desired seismic waves in the target region 118. For example, frequencies in the range of 30-200 Hz can contribute to the generation of S-waves andfrequencies in the range of 30-1000 Hz can contribute to the generation of P-waves.

[00105] The noise signal may, in some examples, be the same as, similar to, or share characteristics with the ambient noise. As will be apparent to the person skilled in the art, a noise signal can be generated in any number of ways to resemble ambient noise. In some implementations, the noise signal mimics / matches the ambient noise by recording the ambient noise for replicated output by the noise source 106, 132. For example, the generated noise signal may be based on the ambient noise profile of the target region 118 determined separately based on measurements by the seismic sensor 128 while the noise source 106, 132 is inactive. In some implementations, the noise signal is based on colours of noise, such as white noise. In this way, the generated noise 114 can be integrated with the ambient noise for receiving by the receivers, if such functionality is required.

[00106] Where the noise signal used for output is the same or similar to ambient noise, the impact and disruption caused by of the generated noise 114 is reduced or in some cases is unnoticeable by the local environment, wildlife, and communities. By replacing an impulsive source (such as an airgun) with such a noise source 106, 132, the acoustic energy is spread over a longer duration which reduces the peak pressure in the body of water 110 or surrounding environment for onshore implementations, greatly reducing the environmental impact. The signals generated can be also designed to improve the signal-to-noise ratio of the measured seismic wave arrivals by emitting a longer signal. This is beneficial when the operational noise (from the vehicles, vessels, thrusters and the like) is high which and can negatively impact the quality of the data.

[00107] In some implementations, the noise signal is generated as a chirp, a sweep (linear, non-linear, optimised) or using a pseudorandom binary sequence. In some implementations, the signal is spread over a wide frequency band, for example at least one of, 2-120 Hz, 5-100 Hz,30-200 Hz and 30-1000 Hz. Spread spectrum techniques may be used to do so. In some implementations, the pseudorandom binary sequence is at least one of a maximum length sequence, Gold sequence, or Kasami sequence. As will be apparent to the skilled person, any kind of sequence (pseudorandom binary or otherwise) or other approaches can be used to generate a noise signal which shares characteristics with noise like properties. Advantageously, pseudorandom binary sequences are deterministic and may be generated efficiently using simple underlying hardware implementation. For example, a maximal length sequence can be generated using a combination of linear-feedback shift registers, and a gold sequence (i.e., a gold code) can be generated using two maximal length sequences.

[00108] In some implementations, the noise signal / the noise that is output by the noise source 106, 132 is generated to comply with environmental, health, safety standards, laws, regulations, or guidance. The methods and systems described herein can be applied to, for example, offshore marine applications. Marine seismic or geophysical surveys typically use airguns which can lead to devasting effects like injury, hearing loss, and behavioural changes to species in the surrounding environment. By using a noise signal that is similar to ambient noise, the impact and disruption to marine life is minimised.

[00109] In some implementations, the noise signal is processed to output noise by the noise source 106, 132 at an intensity which matches, is equal to, or is substantially equal to the average intensity of ambient noise received at, e.g., seismic sensor 128. In some implementations, the amplitude of the noise signal is decreased or increased to match the ambient noise intensity. In some implementations, the noise source 106, 132 is (in additional or alternatively to the processing of the noise signal) controlled to output noise based on the noise signal at an intensity / volume which matches the ambient noise intensity by increasing or decreasing the output intensity / volume of the noise source 106, 132 accordingly. By matching the noise output by the noise source 106, 132 to the average intensity of ambient noise, impact, and disruption of the noise to the local environment, wildlife, and communities can be controlled and minimised.

[00110] In some implementations, the noise signal output by the noise source 106, 132 is limited to a threshold output level. The threshold output level can be the average intensity of ambient noise across all directions in the ambient noise profile. However, the threshold output level can also be any suitable threshold, such as the highest ambient noise recorded, based on environmental, health or safety standards, laws, regulations, or guidance, and so forth.

[00111] In some implementations, the threshold output level can comprise one or more threshold output sublevels according to one or more frequency values and / or frequency ranges. In some implementations, the threshold output level is based on the species living in the environment at or near the surface of the target region. For example, the noise signal can be modified or designed to comply with a maximum permitted noise level at specific frequencies and / or one or more frequency ranges, e.g., with respect to a species. In some implementations, there are one or more threshold output levels for each of one or more respective species living in the environment at or near the surface of the target region. In a further implementation, the threshold output level is based on the species with the lowest threshold output level.

[00112] In some implementations, the generated noise signal can be processed in a number or ways to boost, tune, or otherwise manipulate the noise signal to target a specific frequency range, or specific frequencies of interest. In some implementations, the specific frequency range is 2-120 Hz or optionally, 5-100 Hz ensures the noise signal includes the frequency content required to generate Scholte waves, P-Waves and / or S-Waves for geotechnical imaging at the surface 112 and / or within the target region 118. Frequencies in the range of 30-200 Hz can be used as they contribute to the generation of S-waves andfrequencies in the range of 30-1000 Hz can be used as they can contribute to the generation of P-waves.In some implementations, the signal is spread over one or more of the aforementioned frequency bands, for example, using spread spectrum techniques.In some implementations, the noise signal can be processed using, e.g., a cost function to reward increasing the intensity (boosting) certain frequencies or frequency ranges, at the expense of other frequencies or frequency ranges. In some implementations, the noise signal is generated using a random number generator using different seeds, which enables noise signals (and the resulting noise output by the noise signal) to be generated that is not correlated with each other. In some implementations, the noise signal is filtered to attenuate or boost frequencies outside a specific frequency range, such as, by using a digital filter, a high-pass filter, a low-pass filter, etc. In some implementations, filtering can be implemented using, e.g., the aforementioned cost function. In some implementations, an optimisation function is used that increases the intensity at certain frequencies or frequency ranges without affecting the intensity at other frequencies. By processing the generated noise signal in this way, impact and disruption to the local environment, wildlife, and communities can be reduced.

[00113] In some implementations, there may be a second noise source 106, 132 or one or more noise sources included the disclosed methods and systems, for example provided in an array coupled to a single ROV 104 or where a plurality of ROVs 104 are provided, each coupled to a respective noise source 106, 132 to increase the generation of P-Waves and / or S-Waves within the target region 118. The impact and disruption to the local environment, wildlife, and communities can also be minimised by, e.g., using a plurality of noise sources 106, 132 to output noise at a lower intensity compared to if there was a singular noise source, while maintaining or even reducing data acquisition time.

[00114] In some implementations, the noise signal output at each noise source 106, 132 of the plurality of noise sources 106, 132 are generated to be different and / or generated to be uncorrelated with each other. In some implementations, noise signals may be generated to be uncorrelated with each other using a random number generator with different seeds (e.g., for each noise signal). In some implementations, noises signals may be uncorrelated with each other by outputting the noise signal via different types / kinds of devices for the plurality of noise sources 106. In some implementations, noise signals may be generated to be uncorrelated with each other by processing the noise signal via modulation, filtering, and / or shifting the phase of the noise signal. In some implementations, the phase of the noise signal is shifted by outputting the noise signal by each noise source 106, 132 of the plurality of noise sources 106, 132 at different times / timeframes with respect to each other. In some implementations, a set of uncorrelated noise signals are generated using a pseudorandom binary sequence, e.g., using a gold sequence, in which each of the plurality of noise sources 106, 132 outputs a different noise signal from the set of uncorrelated noise signals. As will be apparent to the skilled person, there are a number of ways to generate uncorrelated noise signals, and any of the aforementioned examples may be combined to produce uncorrelated noise signals.

[00115] Next, at step 206, noise is output, by the noise source 106, 132 based on the generated noise signal to generate a pressure wave in the body of water 110 incident on the surface 112 or directly incident on the surface for the noise source 132provided on the seabed frame 134 (onshore applications could create pressure waves in the airincident on the surface 112). This, in turn, generates seismic waves in the target region 118.As discussed, incorporating a noise source 106, 132 to output noise can enable improved quality (e.g., accuracy and precision) of the determination of the ground properties of a target region without the environmental impact of an impulsive source, such as an airgun.

[00116] In some implementations, the noise is output, by the noise source 106, 132, at various locations on the surface of increasing distance from the seismic sensor 128, for example, to perform a walkaway VSP. The noise source 106, 132 may be moved progressively further away from the seismic sensor 128 while measuring the seismic waves 120.

[00117] As the noise signal is intended to be emitted for an extended period of time, the signal may be looped, or otherwise extended to satisfy the intended operational time required for noise output. In some implementations, the looping or extension of the noise signal may be carried out at the noise source 106, 132 via a processor on the noise source 106, 132 or by computing device 300. In some implementations, the noise signal may also be processed to control the intensity, duration, and frequency profile of the noise that is output by the noise source 106, 132 at the processor on the noise source, or by computing device 300. In some implementations, the noise signal is generated locally by the noise source 106, 132. In some implementations, the noise signal is generated by computing device 300 and is communicated to the noise source 106, 132 (via wired or wireless communication), for example from at least one of the ROV 104, the first vessel 102, second vessel 108 or a remote operating centre. In some implementations, the computing device 300 controls aspects of the operation of the noise source 106, 132 such as the intensity, frequency profile, duration (including starting and stopping operation of the noise source 106, 132), and / or the noise profile (i.e., what noise is being output by the noise source 106, 132). In some implementations, the noise source 106, 132may be timed or configured automatically or manually to operate only in specific time frames in a day (e.g., in the daytime). In some implementations, where there are one or more noise sources 106, 132 comprises a plurality of noise sources 106, 132 the noise sources 106, 132 can be controlled to operate sequentially, simultaneously, not at all, or in any combination, across the noise sources 106, 132. Similarly, in a further implementation, wherein there are one or more generated noise signals, the noise sources 106, 132can be similarly operated to output the one or more generated noise signals across the one or more noise sources in any combination.

[00118] In some implementations, where the noise source 106, 132 comprises an array of noise sources 106, 132 the array of noise sources 106, 132 may be configured to form a beam of noise incident on the surface 112 of the bed of the body of water 110 to maximise the generation of P- and / or S-waves within the target region 118. In some implementations, the beam of noise is incident on the surface 112 of the bed of the body of water 110 at an angle within the range of 10 to 40 degrees, optionally, at an angle of 30 degrees. This further optimises the generation of P- and / or S-waves.

[00119] Next, at step 208,a response signal indicative of the generated seismic waves as measured by the seismic sensor 128 is received.

[00120] In some implementations, the seismic sensor 128 comprises a first seismic sensor element 122 vertically offset from a second seismic sensor element 124.The vertical offset enables seismic waves 120 generated by the noise source 106, 132 to be measured at two depths simultaneously. The seismic wave velocity across a depth range is then determined by calculating the travel time difference between the first seismic sensor element 122 and the second seismic sensor element 124. In some implementations, the seismic sensor 128 comprises an array of seismic sensors that can measure seismic waves 120 generated by the noise source 106, 132 across the array simultaneously.

[00121] In some implementations, the seismic sensor 128 comprises a single sensor element. The seismic sensor 128 can be moved while the noise source 106, 132 is continuously outputting generated noise enabling the seismic waves to be continuously generated by the noise source 106, 132. As such,the seismic waves can be measured at two depths sequentially, the continuous output and theknown nature of the generated noise output by the noise source 106, 132 making it possible to compare the results to work out the travel time difference between the two locations of the seismic sensor 128. This would not be possible if an impulsive source were used, given the short duration of seismic waves generated by an impulsive source and the lack of control over the nature of the seismic waves generated by successive triggering of an impulsive source. For example, the successive triggering of an airgun might cause a different profile of seismic waves in the target region making it harder to make a comparison.

[00122] Next, at step 210,one or more ground properties of the target region are determined based on the received response signal(and, optionally output to user for example,via. a user device). This could involve conventional SCPT and / or VSP processing steps.

[00123] In some implementations, step 210 may comprise cross-correlating thegenerated noise 114 with the response signal indicative of the generated seismic waves 120 as measured by the seismic sensor 128. By performing this cross-correlation, the seismic data is effectively compressed, allowing for a clearer representation of subsurface structures and geological features. This process is also known as matched filtering, whereby a filter is designed to maximize the signal-to-noise ratio for a specific expected signal.

[00124] In some implementations, step 210 may further comprise determining the difference in travel time of generated seismic waves measured by the seismic sensor 128and using those to compute the seismic velocities.I The arrival times of seismic waves 120 are picked manually or using a thresholding or autopicking algorithm.The arrival times refer to the time that a direct seismic wave 120 takes to travel from the noise source 106 to the seismic sensor 128. The direct seismic wave 120 arrives at a small time delay between the top and bottom sensor. This difference in arrival times is representative of the travel time and is used to compute the seismic velocity for the direct seismic wave 120.

[00125] In some implementations, step 210 may further inverting the arrivals times, for example, using Snell’s law that accounts for the travel paths of the seismic waves (1D medium assumption) or using travel time tomography, to obtain a 2D or 3D seismic velocity model around the target region 118. The inversion process may use the eikonal equation to numerically compute the travel time of a seismic wavefront as it propagates through a medium with varying velocity. The difference between the recorded arrival times and predicted arrival times may be minimised using optimisation techniques by iteratively updating the initial seismic velocity mode.

[00126] While the steps of Figure2 (and other steps described above) are described in order, it will be apparent to the skilled person that the steps may be re-ordered, performed simultaneously in relation to other steps, or performed more than once.

[00127] Figure 3 shows a block diagram of one implementation of a computing device 300 within which a set of instructions, for causing the computing device to perform any one or more of the methodologies discussed herein, may be executed. In alternative implementations, the computing device may be connected (e.g., networked) to other machines in a Local Area Network (LAN), an intranet, an extranet, or the Internet. The computing device may operate in the capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The computing device may be a personal computer (PC), a tablet computer, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single computing device is illustrated, the term “computing device” shall also be taken to include any collection of machines (e.g., computers) that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein.

[00128] The example computing device 300 includes a processor 302, a main memory 304 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 306 (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory (e.g., a data storage device 318), which communicate with each other via a bus 330.

[00129] Processor 302 represents one or more general-purpose processors such as a microprocessor, central processing unit, or the like. More particularly, the processor 302 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processor 302 may also be one or more special-purpose processors such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processor 302 is configured to execute the processing logic (instructions 322) for performing the operations and steps discussed herein.

[00130] The computing device 300 may further include a network interface device 308. The computing device 300 also may include a video display unit 310 (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device 312 (e.g., a keyboard or touchscreen), a cursor control device 314 (e.g., a mouse or touchscreen), and an audio device 316 (e.g., a speaker).

[00131] It will be apparent that some features of computer device 300 shown in Figure 3 may be absent. For example, one or more computing devices 300 may have no need for display device 310 (or any associated adapters). This may be the case, for example, for particular server-side computer apparatuses 300 which are used only for their processing capabilities and do not need to display information to users. Similarly, user input device 312 may not be required. In its simplest form, computer device 300 comprises processor 302 and memory 304.

[00132] The data storage device 318 may include one or more machine-readable storage media (or more specifically one or more non-transitory computer-readable storage media) 328 on which is stored one or more sets of instructions 322 embodying any one or more of the methodologies or functions described herein. The instructions 322 may also reside, completely or at least partially, within the main memory 304 and / or within the processor 302 during execution thereof by the computer system 300, the main memory 304 and the processor 302 also constituting computer-readable storage media.

[00133] The various methods described above may be implemented by a computer program. The computer program may include computer code arranged to instruct a computer to perform the functions of one or more of the various methods described above. The computer program and / or the code for performing such methods may be provided to an apparatus, such as a computer, on one or more computer readable media or, more generally, a computer program product. The computer readable media may be transitory or non-transitory. The one or more computer readable media could be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, or a propagation medium for data transmission, for example for downloading the code over the Internet. Alternatively, the one or more computer readable media could take the form of one or more physical computer readable media such as semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disc, and an optical disk, such as a CD-ROM, CD-R / W or DVD.

[00134] In an implementation, the modules, components, and other features described herein can be implemented as discrete components or integrated in the functionality of hardware components such as ASICS, FPGAs, DSPs, or similar devices.

[00135] A “hardware component” is a tangible (e.g., non-transitory) physical component (e.g., a set of one or more processors) capable of performing certain operations and may be configured or arranged in a certain physical manner. A hardware component may include dedicated circuitry or logic that is permanently configured to perform certain operations. A hardware component may be or include a special-purpose processor, such as a field programmable gate array (FPGA) or an ASIC. A hardware component may also include programmable logic or circuitry that is temporarily configured by software to perform certain operations.

[00136] Accordingly, the phrase “hardware component” should be understood to encompass a tangible entity that may be physically constructed, permanently configured (e.g., hardwired), or temporarily configured (e.g., programmed) to operate in a certain manner or to perform certain operations described herein.

[00137] In addition, the modules and components can be implemented as firmware or functional circuitry within hardware devices. Further, the modules and components can be implemented in any combination of hardware devices and software components, or only in software (e.g., code stored or otherwise embodied in a machine-readable medium or in a transmission medium).

[00138] Unless specifically stated otherwise, as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “providing, “calculating”, “updating”, “generating”, “outputting”, " receiving”, “processing”, “performing”, “determining”, “selecting”, “comparing, and “identifying”, or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

[00139] It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other implementations will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific example implementations, it will be recognized that the disclosure is not limited to the implementations described but can be practiced with modification and alteration within the spirit and scope of the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense. The scope of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

[00140] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist, only some of which have been mentioned above. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.

Claims

1. A method for determining one or more ground properties of a target region beneath a surface, the method comprising:inserting a seismic sensor into the target region beneath the surface;generating a noise signal;outputting noise, by a noise source, at or incident on the surface and based on the generated noise signal to generate seismic waves in the target region;receiving a response signal, the response signal indicative of the generated seismic waves as measured by the seismic sensor; anddetermining one or more ground properties of the target region based on the received response signal. 2. The method of claim 1, wherein the noise signal is generated using a pseudorandom binary sequence. 3. The method of claim 2, wherein the pseudorandom binary sequence is at least one of a maximum length sequence, Gold sequence, or Kasami sequence. 4. The method of any preceding claim, wherein the noise signal is generated using a random number generator. 5. The method of any preceding claim, wherein the noise signal is output at an intensity which is based on, matches, or is equal to the average intensity of ambient noise measured at the seismic sensor. 6. The method of any preceding claim, wherein the noise signal is generated to contain frequency content with a specific frequency range of 30-200 Hz. 7. The method of any of claims 1 to 5, wherein the noise signal is generated to contain frequency content with a specific frequency range of 30-1000 Hz. 8. The method of any preceding claim, wherein the seismic sensor comprises at least two vertically offset seismic sensors elements. 9. The method of any preceding claim, wherein the noise source is a vibratory noise source, such as a speaker. 10. The method of any preceding claim, wherein the noise source is coupled to at least one of: a structure on the surface; and a vehicle on the surface, such as a truck or crawler. 11. The method of any preceding claim, wherein the surface is a surface of a bed of a body of water. 12. The method of claim 11, wherein the noise source is coupled to one of: a structure on the bed of the body of water; and a vessel on or within the body of water, such as a ship, USV or ROV. 13. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any preceding claim. 14. A system comprising: one or more processors; one or more memories having stored thereon computer readable instructions configured to cause the one or more processors to perform operations comprising the steps of any of claims 1 to 12.  15. Computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1 to 12. 

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