A method and system for fast calculation of full-time-domain ocean transient electromagnetic apparent conductivity

Abstract

The present invention discloses a method and system for quickly calculating full-time-domain ocean transient electromagnetic apparent conductivity. The method comprises: obtaining measured transient electromagnetic field response data; obtaining full-time-domain transient electromagnetic theoretical response by given conductivity initial value and given theoretical calculation time range according to a pre-established functional relationship between seabed medium conductivity and full-time-domain magnetic source transient electromagnetic response; calculating the time t corresponding to when the value of full-time-domain transient electromagnetic theoretical response is equal to the measured transient electromagnetic field response data by spline interpolation; m ; By time t m , combined with the given conductivity initial value, the full-time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula. The method of the present invention is a qualitative interpretation method suitable for arbitrary emission waveforms, full time domain, full space, and multiple components. This method only requires one forward modeling, avoiding the time cost of multiple forward modeling calculations in traditional iterative methods, and is more suitable for marine transient electromagnetic data interpretation.

Description

Technical Field

[0001] The present invention relates to the field of ocean and ocean detection technology, and in particular to a method and system for quickly calculating full-time-domain ocean transient electromagnetic apparent conductivity. Background Art

[0002] Marine transient electromagnetic method is an important branch of marine geophysical methods. It uses artificial field sources as the transmitting source and can provide the electrical structure and spatial distribution of seabed media and targets based on the principle of electromagnetic induction. It is an important method in the fields of offshore regional geological surveys, marine resource exploration, seabed engineering and environmental surveys, underwater archaeology and military applications.

[0003] For the processing and interpretation of transient electromagnetic methods, apparent conductivity (the inverse of apparent resistivity) is the most widely used interpretation parameter in practical work because of its advantages of simple calculation and intuitive effect. The definition of apparent conductivity can be used to make a qualitative interpretation of underground media.

[0004] At present, since marine transient electromagnetic is still in the early stage of application in my country, the existing definition of apparent conductivity of marine transient electromagnetic has the following problems: 1) The calculation of marine transient electromagnetic apparent conductivity still mainly follows the traditional ground apparent conductivity calculation method. Since marine transient electromagnetic is a full-space environment, there are differences with the ground response. Directly applying the ground formula will cause interpretation errors. 2) The current apparent conductivity calculation does not take into account the emission waveform of the excitation field source, and uses step response instead of the real emission waveform response. The resulting interpretation error will affect the detection accuracy. 3) The traditional definition of apparent conductivity uses the data iteration method for calculation, which has low calculation efficiency. The marine transient electromagnetic detection system uses a continuous scanning observation method and has a large amount of observation data, and urgently needs a fast and effective data interpretation method. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and to propose a method and system for fast calculation of ocean transient electromagnetic apparent conductivity in the entire time domain.

[0006] In order to achieve the above object, the present invention proposes a method for fast calculation of full-time domain ocean transient electromagnetic apparent conductivity, the method comprising:

[0007] Obtain measured transient electromagnetic field response data;

[0008] According to the pre-established functional relationship between the conductivity of the seabed medium and the transient electromagnetic response of the full-time-domain magnetic source, the full-time-domain transient electromagnetic theoretical response is obtained by a given initial value of the conductivity and a given theoretical calculation time range;

[0009] The time t corresponding to the time when the value of the full time domain transient electromagnetic theoretical response calculated by spline interpolation is equal to the measured transient electromagnetic field response data m ;

[0010] By time t m , combined with the given initial value of conductivity, the full time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula.

[0011] As an improvement of the above method, the method further includes the step of establishing a functional relationship between the conductivity of the seabed medium and the transient electromagnetic response of the full-time domain magnetic source; specifically, the step of:

[0012] Obtain measured transient electromagnetic field response data;

[0013] Based on the measured transient electromagnetic field response data, the full time domain transient electromagnetic response data under arbitrary emission waveform conditions are obtained by convolution calculation of transient electromagnetic theoretical step response and measured emission current;

[0014] The functional relationship between the seabed medium conductivity and the full-time domain transient electromagnetic response of the magnetic source is constructed based on the full-time domain transient electromagnetic response data.

[0015] As an improvement of the above method, the obtaining of measured transient electromagnetic field response data specifically includes:

[0016] A magnetic source is used as a transmitting source, and underwater continuous collection is carried out by towing an electromagnetic response receiving device on a ship or an unmanned platform to obtain measured transient electromagnetic field response data; the magnetic source is a central loop device, an overlapping loop device, a horizontal magnetic dipole source device or a vertical magnetic dipole source device, the transmitting fundamental frequency of the magnetic source is a selected value, the transmitting waveform is a bipolar half-sine wave, a bipolar triangle wave, a bipolar trapezoidal wave or a pseudo-random wave, and the current input to the magnetic source is a pulse current.

[0017] As an improvement of the above method, the full time domain transient electromagnetic response data F(t) under the arbitrary emission waveform condition is:

[0018]

[0019] Among them, F step (t) is the transient electromagnetic theoretical step response, I(t) is the arbitrary emission current time domain signal, and F(t) contains six electromagnetic field components F = [E x ,E y ,E z ,H x ,H y ,H z ], E x ,E y ,E z , is the three-component response of the electric field, H x ,H y ,H z is the three-component response of the magnetic field.

[0020] As an improvement of the above method, the functional relationship between the conductivity of the seabed medium and the full-time domain transient electromagnetic response of the magnetic source is constructed from the full-time domain transient electromagnetic response data; specifically:

[0021]

[0022] Among them, the apparent conductivity σ is a function of u, f(u) is the normalized response kernel function, a is the radius of the transmitting coil, p is the coordinate of the receiving point, t is the sampling time, and I0 is the transmitting current amplitude.

[0023] As an improvement of the above method, the time t corresponding to the time when the value of the full time domain transient electromagnetic theoretical response calculated by spline interpolation is equal to the measured transient electromagnetic field response data is m ; Specifically:

[0024] The measured transient electromagnetic field response data F s (σ s ,p,t s );

[0025] According to the given initial value of conductivity σ0, preferably σ0 = 1S / m, given the time range of theoretical calculation, preferably t0∈[10 -8 ,10 6 ]s, and obtain the full time domain transient electromagnetic theoretical response F0(σ0,p,t0);

[0026] When F is calculated by spline interpolation s (σ s ,p,t s )=F0(σ0,p,t m ), the corresponding time t m , where t m ∈t0.

[0027] As an improvement of the above method, the time t m , combined with the given initial conductivity value, the full-time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula; specifically:

[0028] By time t m , the initial value of conductivity σ0, according to the conductivity fast calculation formula, the full time domain apparent conductivity parameter σ s for:

[0029]

[0030] A full-time-domain marine transient electromagnetic apparent conductivity fast calculation system, characterized in that the system comprises: a transient electromagnetic field response acquisition module, a full-time-domain transient electromagnetic theoretical response calculation module, a spline interpolation calculation module and a conductivity fast calculation module; wherein,

[0031] The transient electromagnetic field response acquisition module is used to acquire measured transient electromagnetic field response data;

[0032] The full-time-domain transient electromagnetic theoretical response calculation module is used to obtain the full-time-domain transient electromagnetic theoretical response according to the pre-established functional relationship between the conductivity of the seabed medium and the full-time-domain magnetic source transient electromagnetic response, given the initial value of conductivity and the given theoretical calculation time range;

[0033] The spline interpolation calculation module is used to calculate the time t corresponding to the time when the value of the full time domain transient electromagnetic theoretical response is equal to the measured transient electromagnetic field response data through spline interpolation. m ;

[0034] The conductivity fast calculation module is used to calculate the conductivity of the m , combined with the given initial value of conductivity, the full time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula.

[0035] Compared with the prior art, the advantages of the present invention are:

[0036] 1. The full-time domain apparent conductivity definition method provided by the present invention is an efficient, high-precision apparent conductivity calculation method that is suitable for any emission waveform;

[0037] 2. The method of the present invention is a qualitative interpretation method suitable for arbitrary emission waveforms, full time domain, full space, and multiple components. This method only requires one forward modeling, avoiding the time cost of multiple forward modeling calculations in traditional iterative methods, and is more suitable for marine transient electromagnetic data interpretation;

[0038] 3. The method of the present invention is not only applicable to marine transient electromagnetic detection systems, but its concept can be further extended to be applicable to ground and aviation detection systems at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of a method for rapid calculation of full-time-domain ocean transient electromagnetic apparent conductivity according to Embodiment 1 of the present invention;

[0040] FIG2( a ) is a schematic diagram showing that the transmission waveform is a bipolar half-sine wave;

[0041] FIG2( b ) is a schematic diagram showing that the transmission waveform is a bipolar triangle wave;

[0042] FIG2( c ) is a schematic diagram showing that the transmission waveform is a bipolar trapezoidal wave;

[0043] Figure 2(d) is a schematic diagram of the transmission waveform being a pseudo-random wave;

[0044] FIG3(a) is a comparison diagram of ocean transient electromagnetic magnetic induction intensity curves when a triangular wave is emitted under different conductivity conditions of the seabed medium;

[0045] FIG3( b ) is a comparison diagram of the ocean transient electromagnetic magnetic induction intensity curves when the seabed medium is a half-sine wave with different conductivity conditions;

[0046] Figure 4 is a schematic diagram of a model in which the seabed is a uniform layered medium in an example of the present invention;

[0047] FIG5(a) is a graph showing the transient electromagnetic numerical response curve under the calculated half-sine wave emission condition;

[0048] FIG5( b ) is a transient electromagnetic numerical response curve diagram under the calculated triangular wave emission condition;

[0049] Figure 6 It is the apparent conductivity curve obtained by the prior art calculation under the condition that the seabed is a layered medium;

[0050] Figure 7 It is a full-time domain apparent conductivity curve diagram calculated by the present invention under the condition that the seabed is a layered medium. DETAILED DESCRIPTION

[0051] The present invention provides a fast, simple and highly applicable method for calculating apparent conductivity based on the analysis of the law and characteristics of ocean transient electromagnetic response under arbitrary excitation waveform emission conditions, thereby further improving the accuracy of ocean transient electromagnetic data interpretation. The method of the present invention includes:

[0052] 1. Plan the survey area and arrange the survey line according to the detection task requirements, and record the location of the observation points;

[0053] 2. Use a magnetic source as the transmitting source, record the parameters of the transceiver system, supply pulse current, and record the transmitting current parameters;

[0054] 3. Conduct underwater continuous observations through ship-borne towing or unmanned platform-mounted modes to obtain measured transient electromagnetic field response data;

[0055] 4. Based on the emission parameters of the above detection system, the full-time domain transient electromagnetic response data under arbitrary emission waveform conditions are calculated by using the convolution of transient electromagnetic theoretical step response and measured emission current, and the functional relationship between the conductivity of the seabed medium and the full-time domain transient electromagnetic response of the magnetic source is constructed;

[0056] 5. The rapid apparent conductivity definition method is used to calculate the full-time domain apparent conductivity parameters of the measured data, thereby achieving a qualitative interpretation of the observed seabed medium.

[0057] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0058] Example 1

[0059] like Figure 1 As shown, embodiment 1 of the present invention proposes a method for fast calculation of full-time-domain ocean transient electromagnetic apparent conductivity, and the specific steps include:

[0060] Step 1) Plan the survey area and arrange the survey line according to the detection task requirements, and record the location of the observation points;

[0061] Step 2) using a magnetic source as a transmitting source, recording the parameters of the transceiver system, supplying a pulse current, and recording the transmitting current parameters;

[0062] The preferred type of magnetic source detection device is one of the following types of coil devices, specifically including:

[0063] (a) Center loop type;

[0064] (b) Overlapping loop type;

[0065] (c) horizontal magnetic dipole source type;

[0066] (d) Vertical magnetic dipole source type.

[0067] Commonly used transmission waveforms include: bipolar half-sine wave, bipolar triangle wave, bipolar trapezoidal wave, pseudo-random waveform and various waveform combination waves, etc. Specific waveform diagrams are shown in Figures 2(a), 2(b), 2(c) and 2(d).

[0068] Step 3) Conducting underwater continuous observations by ship-borne towing or unmanned platform-mounted mode to obtain measured transient electromagnetic field response data;

[0069] Step 4) According to the emission parameters of the above detection system, the full-time domain transient electromagnetic response data under arbitrary emission waveform conditions is calculated by using the convolution of the transient electromagnetic step response and the emission current, and a functional relationship between the conductivity of the seabed medium and the full-time domain transient electromagnetic response of the magnetic source is constructed;

[0070] The theoretical value F(t) of the full time domain transient electromagnetic response under any type of transmitting waveform excitation condition is calculated by the convolution method:

[0071]

[0072] Among them, F step (t) is the transient electromagnetic step response, I(t) is the arbitrary emission current time domain signal, and F(t) contains six electromagnetic field components F = [E x ,E y,E z ,H x ,H y ,H z ], which are the three-component responses of the electric field and the three-component responses of the magnetic field, respectively.

[0073]

[0074] Where a is the radius of the transmitting coil, p is the coordinate of the receiving point, f(u) is the normalized response kernel function, and the apparent conductivity σ is a function of u.

[0075] Step 5) The rapid apparent conductivity definition method is used to calculate the full-time domain apparent conductivity parameters of the measured data, thereby achieving a qualitative interpretation of the observed seabed medium.

[0076] The following steps are involved:

[0077] 501) Determine the actual detection device parameters, including the type of magnetic source device, transmission loop parameters, receiving area and receiving point coordinates;

[0078] 502) Input the measured transient electromagnetic field response data F s (σ s , p,t s ) and the emission current signal I(t s );

[0079] 503) Given the initial value of conductivity σ0, it is generally given as σ0 = 1S / m;

[0080] 504) Given the time range of theoretical calculation, generally t0∈[10 -8 ,10 6 ]s, calculate the full time domain transient electromagnetic theoretical response F0(σ0, p, t0);

[0081] 505) Calculate the measured full-time apparent conductivity value. Specifically:

[0082] When F is calculated by spline interpolation s (σ s , p,t s )=F0(σ0,p,t m ), the corresponding time t m ;

[0083] Through preliminary research, we found that the ocean transient electromagnetic response data under any transmission waveform conditions have a translational nature. As shown in Figure 3(a), it is a comparison of the ocean transient electromagnetic magnetic induction intensity curves when the seabed medium is a triangular wave transmission under different electrical conductivities. Figure 3(b) is a comparison of the ocean transient electromagnetic magnetic induction intensity curves when the seabed medium is a half-sine wave transmission under different electrical conductivities.

[0084] By describing the relationship in the above figure through mathematical expressions, we can further obtain the calculation formula of the measured full-time domain apparent conductivity and obtain the measured full-time domain apparent conductivity parameter σ s for:

[0085]

[0086] like Figure 4 As shown, taking the three-layer model of the seabed medium as an example, the conductivity of the model and the depth of each layer are shown in the figure. The ocean center loop transient electromagnetic detection device is used, and the transmission waveform is selected as a half-sine wave and a triangle wave with a pulse width of 10ms for verification. Figures 5(a) and (b) are the transient electromagnetic response curves of the ocean layered model when the half-sine wave and the triangle wave are transmitted, respectively, calculated by the convolution algorithm. Figure 6 is the apparent conductivity curve calculated using the traditional step wave electromagnetic response approximation. Figure 7 This is the apparent conductivity curve calculated using the full time domain conductivity definition method.

[0087] pass Figure 6 and Figure 7 The comparison of the results shows that the apparent conductivity values ​​calculated by the traditional step wave approximation algorithm have large calculation errors in the early time channel, and there are differences in the conductivity values ​​of the seabed medium calculated by different emission waveforms.

[0088] After adopting the method of the present invention, since the influence of the emission waveform is taken into account during calculation, the calculation accuracy can be improved and the electrical distribution of the seabed medium can be effectively reflected; in addition, the method of the present invention is simple to calculate and can efficiently complete the qualitative interpretation of marine transient electromagnetic data.

[0089] It should be noted that the implementation methods not shown or described in the drawings or the text of the specification are all forms known to ordinary technicians in the relevant technical field and are not described in detail. In addition, the above definitions of various elements and methods are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and ordinary technicians in the field can simply change or replace them.

[0090] Example 2

[0091] Embodiment 2 of the present invention proposes a full-time-domain marine transient electromagnetic apparent conductivity fast calculation system, which includes: a transient electromagnetic field response acquisition module, a full-time-domain transient electromagnetic theoretical response calculation module, a spline interpolation calculation module and a conductivity fast calculation module; the specific processing process is the same as that of embodiment 1; wherein,

[0092] The transient electromagnetic field response acquisition module is used to acquire measured transient electromagnetic field response data;

[0093] The full-time-domain transient electromagnetic theoretical response calculation module is used to obtain the full-time-domain transient electromagnetic theoretical response according to the pre-established functional relationship between the conductivity of the seabed medium and the full-time-domain magnetic source transient electromagnetic response, given the initial value of conductivity and the given theoretical calculation time range;

[0094] The spline interpolation calculation module is used to calculate the time t corresponding to the time when the value of the full time domain transient electromagnetic theoretical response is equal to the measured transient electromagnetic field response data through spline interpolation. m ;

[0095] The conductivity fast calculation module is used to calculate the conductivity of the m , combined with the given initial value of conductivity, the full time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A method for rapid calculation of ocean transient electromagnetic apparent conductivity in the entire time domain, the method comprising: Obtain measured transient electromagnetic field response data; According to the pre-established functional relationship between the conductivity of the seabed medium and the transient electromagnetic response of the full-time-domain magnetic source, the full-time-domain transient electromagnetic theoretical response is obtained by a given initial value of the conductivity and a given theoretical calculation time range; The time t corresponding to the time when the value of the full time domain transient electromagnetic theoretical response calculated by spline interpolation is equal to the measured transient electromagnetic field response data m ; By time t m , combined with the given initial value of conductivity, the full-time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula; The method also includes the step of establishing a functional relationship between the conductivity of the seabed medium and the transient electromagnetic response of the full-time domain magnetic source; specifically, the step of: Obtain measured transient electromagnetic field response data; Based on the measured transient electromagnetic field response data, the full time domain transient electromagnetic response data under arbitrary emission waveform conditions are obtained by convolution calculation of transient electromagnetic theoretical step response and measured emission current; Based on the full-time-domain transient electromagnetic response data, the functional relationship between the seabed medium conductivity and the full-time-domain transient electromagnetic response of the magnetic source is constructed; The functional relationship between the conductivity of the seabed medium and the transient electromagnetic response of the full-time-domain magnetic source is constructed from the full-time-domain transient electromagnetic response data; specifically: Among them, the apparent conductivity σ is a function of u, f(u) is the normalized response kernel function, a is the radius of the transmitting coil, p is the coordinate of the receiving point, t is the sampling time, and I0 is the transmitting current amplitude.

2. The method for rapid calculation of full-time-domain ocean transient electromagnetic apparent conductivity according to claim 1 is characterized in that: The obtaining of measured transient electromagnetic field response data specifically includes: A magnetic source is used as a transmitting source, and underwater continuous collection is carried out by towing an electromagnetic response receiving device on a ship or an unmanned platform to obtain measured transient electromagnetic field response data; the magnetic source is a central loop device, an overlapping loop device, a horizontal magnetic dipole source device or a vertical magnetic dipole source device, the transmitting fundamental frequency of the magnetic source is a selected value, the transmitting waveform is a bipolar half-sine wave, a bipolar triangle wave, a bipolar trapezoidal wave or a pseudo-random wave, and the current input to the magnetic source is a pulse current.

3. The method for rapid calculation of full-time-domain ocean transient electromagnetic apparent conductivity according to claim 2 is characterized in that: The full time domain transient electromagnetic response data F(t) under the arbitrary transmission waveform condition is: Among them, F step (t) is the transient electromagnetic theoretical step response, I(t) is the arbitrary emission current time domain signal, and F(t) contains six electromagnetic field components F = [E x ,E y ,E z ,H x ,H y ,H z ], E x ,E y ,E z , is the three-component response of the electric field, H x ,H y ,H z is the three-component response of the magnetic field.

4. The method for rapid calculation of full-time-domain ocean transient electromagnetic apparent conductivity according to claim 2 is characterized in that: The time t corresponding to the time when the value of the full time domain transient electromagnetic theoretical response calculated by spline interpolation is equal to the measured transient electromagnetic field response data m ; Specifically: The measured transient electromagnetic field response data F s (σ s ,p,t s ); According to the given initial value of conductivity σ0, σ0 = 1S / m, given the time range of theoretical calculation, t0∈[10 -8 ,10 6 ]s, and obtain the full time domain transient electromagnetic theoretical response F0(σ0,p,t0); When F is calculated by spline interpolation s (σ s ,p,t s )=F0(σ0,p,t m ), the corresponding time t m , where t m ∈t0.

5. The method for rapid calculation of full-time-domain ocean transient electromagnetic apparent conductivity according to claim 4 is characterized in that: The time t m , combined with the given initial conductivity value, the full-time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula; specifically: By time t m , the initial value of conductivity σ0, according to the conductivity fast calculation formula, the full time domain apparent conductivity parameter σ s for:

6. A system based on the method for rapid calculation of full-time-domain ocean transient electromagnetic apparent conductivity according to claim 1, characterized in that: The system includes: a transient electromagnetic field response acquisition module, a full-time domain transient electromagnetic theoretical response calculation module, a spline interpolation calculation module and a conductivity fast calculation module; wherein, The transient electromagnetic field response acquisition module is used to acquire measured transient electromagnetic field response data; The full-time-domain transient electromagnetic theoretical response calculation module is used to obtain the full-time-domain transient electromagnetic theoretical response according to the pre-established functional relationship between the conductivity of the seabed medium and the full-time-domain magnetic source transient electromagnetic response, given the initial value of conductivity and the given theoretical calculation time range; The spline interpolation calculation module is used to calculate the time t corresponding to the time when the value of the full time domain transient electromagnetic theoretical response is equal to the measured transient electromagnetic field response data through spline interpolation. m ; The conductivity fast calculation module is used to calculate the conductivity of the m , combined with the given initial value of conductivity, the full time domain apparent conductivity parameters of the measured response are obtained according to the conductivity fast calculation formula.

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