A method, system and transmitter for constructing multi-sequence combined waves

Abstract

This invention relates to a method, system, and transmitter for constructing multi-sequence combined waves, belonging to the technical field of geophysical exploration. The method includes: determining c frequency sequences based on the depth range to be explored and the required vertical resolution, wherein the frequency sequences are geometric progressions with a common ratio of 2, and c is a positive integer greater than or equal to 2; and denoting the lowest frequency in the first frequency sequence as the fundamental frequency f. base The lowest frequency of the remaining frequency sequences satisfies the following relationship with the fundamental frequency: Based on the frequency sequences, a multi-sequence combination wave with consistent frequency density across the entire frequency band is obtained. This invention determines the number of frequency sequences based on the depth range to be explored and the required vertical resolution, and improves the vertical resolution of deep exploration by controlling the relationship between the lowest frequency of the remaining frequency sequences and the fundamental frequency in the first frequency sequence.

Description

Technical Field

[0001] This invention relates to the technical field of geophysical exploration, and in particular to a method, system and transmitter for constructing multi-sequence combined waves. Background Technology

[0002] Traditional high-order pseudo-random wave construction schemes, while capable of arbitrarily combining sequences, have a fixed frequency for each sequence. In exploration environments with industrial electricity, such as urban areas, industrial zones, or near high-voltage power lines, interference from power frequencies and their harmonics can distort the exploration data, making it difficult to obtain high-quality data and thus affecting exploration accuracy. Furthermore, the multi-sequence combination waves constructed by traditional schemes, as the frequency decreases, have longer wavelengths, resulting in low-resolution deep exploration data obtained using low-frequency waves, which is insufficient to meet exploration requirements. Summary of the Invention

[0003] To address the aforementioned technical deficiencies, this invention provides a method, system, and transmitter for constructing multi-sequence combined waves, thereby improving the resolution of deep exploration data acquisition and enhancing anti-interference capabilities.

[0004] To solve the above technical problems, the present invention adopts the following technical solution:

[0005] In a first aspect, embodiments of the present invention provide a method for constructing multi-sequence combined waves, which includes the following steps:

[0006] Based on the depth range to be detected and the required longitudinal resolution, c frequency sequences are determined, wherein the frequency sequences are geometric frequency sequences with a common ratio of 2, and c is a positive integer greater than or equal to 2.

[0007] Furthermore, the lowest frequency in the first frequency sequence is denoted as the fundamental frequency f. base The lowest frequency of the remaining frequency sequences satisfies the following relationship with the fundamental frequency:

[0008]

[0009] Among them, f t f is the lowest frequency of the remaining frequency sequences. base is the fundamental frequency in the first frequency sequence, m is the frequency sequence number, n is a positive integer, and c is the total number of frequency sequences;

[0010] Based on the c frequency sequences, a multi-sequence combination wave with consistent frequency density across the entire frequency band is obtained.

[0011] In some embodiments, obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band based on the c frequency sequences includes:

[0012] Based on the frequency sequence, a corresponding time series matrix is ​​generated for each frequency sequence using a square wave generating function;

[0013] All time series matrices are superimposed and summed. The sum is then subjected to amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0.

[0014] In some embodiments, the superposition and summation of all time series matrices, followed by amplitude correction of the summation result: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thereby obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, wherein A≠0 includes:

[0015] Phase adjustment is performed on at least one of the time series matrices to find the phase that minimizes the mean square relative error of the amplitude corresponding to each main frequency in the multi-sequence combined wave with consistent frequency density across the entire frequency band after superposition, and this phase is taken as the optimal phase of the corresponding time series matrix.

[0016] Based on the optimal phase, all time series matrices are superimposed and summed. The sum is then subjected to amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0.

[0017] In some embodiments, the method further includes replacing the frequency values ​​in each frequency sequence that fall within a preset range with the corresponding values ​​in the preset frequency sequence calculated based on the aforementioned frequencies.

[0018] In some embodiments, the sampling rate corresponding to each of the time series matrices is at least twice its highest main frequency and is divisible by four times the base frequency.

[0019] In a second aspect, embodiments of the present invention provide a multi-sequence combined wave construction system, comprising:

[0020] The frequency sequence confirmation module is used to determine c frequency sequences based on the depth range to be detected and the required longitudinal resolution, wherein the frequency sequences are geometric frequency sequences with a common ratio of 2, and c is a positive integer greater than or equal to 2.

[0021] Furthermore, the lowest frequency in the first frequency sequence is denoted as the fundamental frequency f. base The lowest frequency of the remaining frequency sequences satisfies the following relationship with the fundamental frequency:

[0022]

[0023] Among them, f t f is the lowest frequency of the remaining frequency sequences. baseis the fundamental frequency in the first frequency sequence, m is the frequency sequence number, n is a positive integer, and c is the total number of frequency sequences;

[0024] The multi-sequence combined wave construction module obtains a multi-sequence combined wave with consistent frequency density across the entire frequency band based on the c frequency sequences.

[0025] In some embodiments, the multi-sequence combined wave construction module includes:

[0026] A time series matrix generation component generates a corresponding time series matrix for each frequency sequence based on the frequency sequence using a square wave generation function;

[0027] The multi-sequence combined wave construction component is used to superimpose and sum all time series matrices, and perform amplitude correction on the summation result: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thereby obtaining a multi-sequence combined wave with consistent frequency density across the entire frequency band, where A≠0.

[0028] In some embodiments, it also includes:

[0029] The frequency replacement module is used to replace the frequency values ​​in each frequency sequence that belong to a preset range with the corresponding values ​​in the preset frequency sequence calculated based on the aforementioned frequencies.

[0030] In some embodiments, the sampling rate corresponding to each of the time series matrices is at least twice its highest main frequency and is divisible by four times the base frequency.

[0031] Thirdly, embodiments of the present invention provide a multi-sequence combined wave transmitter, which constructs a multi-sequence combined wave using the multi-sequence combined wave construction method of the first aspect.

[0032] The present invention provides a method, system, and transmitter for constructing multi-sequence combined waves. Compared with the prior art, the technical advantages achieved by the present invention include:

[0033] 1. Based on exploration needs, increase the number of main frequencies within a limited frequency band to improve the density between main frequencies, which helps to improve the resolution during electromagnetic exploration.

[0034] 2. Determine the highest and lowest frequencies based on the depth range to be explored, determine the number of frequency sequences *c* based on the required vertical resolution, and control the relationship between the lowest frequencies of the remaining frequency sequences and the fundamental frequency in the first frequency sequence. This not only improves the required vertical resolution of the exploration but also increases the frequency density in the low-frequency band, resulting in a multi-sequence combination wave with consistent frequency density across the entire frequency band. This leads to higher resolution of the acquired deep exploration data, thus meeting exploration requirements. The relationship between the lowest frequencies of the remaining frequency sequences and the fundamental frequency in the first frequency sequence is as follows:

[0035]

[0036] Among them, f t f is the lowest frequency of the remaining frequency sequences. base denoted as the fundamental frequency in the first frequency sequence, m is the frequency sequence number, n is a positive integer, and c is the total number of frequency sequences. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the waveform and spectrum of a third-order 39 pseudo-random wave with a main frequency of 0.25Hz to 3072Hz in an embodiment of the present invention.

[0038] Figure 2 This is a flowchart of a multi-sequence combined wave construction method according to an embodiment of the present invention;

[0039] Figure 3 Here is a flowchart of the method for step S14;

[0040] Figure 4 This is a schematic diagram of the waveform and spectrum of the multi-sequence combined wave according to an embodiment of the present invention;

[0041] Figure 5 This is a flowchart of another multi-sequence combined wave construction method according to an embodiment of the present invention;

[0042] Figure 6 This is a schematic diagram of a multi-sequence combined wave construction system according to an embodiment of the present invention;

[0043] Figure 7 This is a schematic diagram of the structure of the multi-sequence combined wave construction module 34 according to an embodiment of the present invention;

[0044] Figure 8 This is a schematic diagram of another multi-sequence combined wave construction system according to an embodiment of the present invention. Detailed Implementation

[0045] To enable those skilled in the art to better understand the solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, other solutions obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0046] To facilitate understanding of the embodiments of the present invention by those skilled in the art, the technical terms involved in the present invention are explained below.

[0047] Example 1

[0048] The determination of a typical pseudo-random frequency sequence involves constructing two or more basic unit signals based on exploration requirements. The lowest frequency of the dominant frequency in the first basic unit signal is denoted as the fundamental frequency, and the lowest frequencies of the remaining basic units are 1×2 times the fundamental frequency. p The product of these two numbers is 1, where l is an odd number not equal to 1 and p is a natural number.

[0049] For time-frequency transformation, the minimum data analysis length L min =Fs×t min Minimum data analysis time t min =1 / f base Where Fs is the sampling rate, f base The fundamental frequency is used, and the frequency resolution is Δf = Fs / L. min =f base Therefore, in order to extract each frequency, l must be an odd number that is not 1, and p is a natural number.

[0050] For commonly used pseudo-random sequences, l takes values ​​of 1, 3, 5, and 7, then the pseudo-random frequency sequence F1 = 1 × f base ×2 p F2 = 3 × f base ×2 p F3 = 5 × f base ×2 p F4 = 7 × f base ×2 p Where p is a natural number. The above pseudo-random frequency sequences are merged and arranged in ascending order of frequency, with the first few terms having frequencies of f. base ×2 0 f base ×2 1 3×f base ×2 0 f base ×2 2 5×f base ×2 0 3×f base ×2 1 7×f base ×2 0 f base ×2 3 Therefore, it can be seen that regardless of the combination method, the second lowest frequency is twice the lowest frequency, and with 1×f base ×2 p The main sequence has frequencies with a frequency interval of 2 times the main sequence frequency, which are 0, 1, 3, 3... respectively. In other words, the frequency density of the low frequency band is relatively low.

[0051] like Figure 1As shown, L3 represents a third-order pseudo-random wave, which is a high-order pseudo-random wave formed by combining three sequences. F39 indicates that the pseudo-random wave contains 39 dominant frequencies. 0.25Hz~3072Hz indicates that the dominant frequency range of the pseudo-random wave is 0.25Hz~3072Hz. Figure 1 (a) represents the change of pseudo-random wave over time. The horizontal axis represents time and the vertical axis represents the unit amplitude, which takes the value of 1 or -1. Figure 1 (b) shows the spectrum curve of the pseudo-random wave. The frequency circled in the box is the frequency designed during construction. From the 0.25 to 0.75 Hz frequency range marked by curly braces in the figure, it can be seen that the density of the low frequency range of 0.25 to 0.75 Hz is relatively low, which is significantly lower than other frequency ranges.

[0052] The low-frequency band determines the accuracy of deep exploration data. To obtain high-resolution deep exploration data, the common method is to increase the frequency points in the low-frequency band, but this will have the following problems:

[0053] 1. As mentioned above, for frequency 39, add densification frequencies between 0.25 and 0.5 Hz, such as 0.3125, 0.375, and 0.4375, but these frequencies are not 1×2 of the fundamental frequency of 0.25 Hz. p This multiple makes subsequent construction steps impossible;

[0054] II. According to the minimum data analysis length L min When performing time-frequency transformation on the data to obtain the frequency domain results, the encrypted frequency data could not be extracted due to its frequency resolution of 0.25 for the fundamental frequency. In this case, the analysis time had to be increased to 4 times L. min At this point, the frequency resolution is one-quarter of the base frequency, which is 0.0625. Only then can the encrypted frequency be completely extracted. However, there will be a mismatch between the base frequency and the actual analysis time, which will cause errors in data processing.

[0055] As the above analysis shows, existing methods cannot improve the resolution of deep exploration data. To solve this problem, this embodiment provides the following... Figure 2 The method for constructing a multi-sequence combined wave, shown, includes steps S12 to S14.

[0056] S12. Based on the depth range to be detected and the required longitudinal resolution, determine c frequency sequences, wherein the frequency sequences are geometric frequency sequences with a common ratio of 2, and c is a positive integer greater than or equal to 2.

[0057] Currently, the maximum detection depth of the wide-area electromagnetic method is about 7km. Since the inversion algorithm of the electromagnetic method depth sounding part adopts a peeling method from the surface to the inside, shallow information is also very important. Therefore, during detection, the highest frequency is generally defined as the highest frequency that the instrument can transmit and receive, which is generally 9600Hz. Of course, the determination of the highest and lowest frequencies of electromagnetic waves is ultimately determined by the actual detection requirements.

[0058] Preferably, the depth range to be detected is first determined, and then the two extreme values ​​of this depth range are substituted into the electromagnetic exploration depth formula H to obtain the highest and lowest frequencies of the electromagnetic waves. The electromagnetic exploration depth formula H is:

[0059]

[0060] Where H is the detection depth, ρ is the background resistivity of the exploration area, and f is the frequency of the exploration electromagnetic wave.

[0061] The background resistivity ρ can be determined by collecting previous geophysical, geological, or well logging data of the exploration area. Using the above formula, the highest and lowest frequencies of the required electromagnetic waves are calculated based on the depth range to be explored. To ensure the exploration depth, the lowest frequency during actual operation should be several frequency points lower than the theoretically calculated lowest frequency. Preferably, half of the theoretical value of the lowest frequency is selected.

[0062] In actual exploration, the longitudinal resolution can be determined based on the size of the target body. Preferably, the longitudinal resolution is determined based on the diameter-to-depth ratio of the target body, where the diameter-to-depth ratio is the ratio of the longitudinal thickness of the target body to its burial depth. Preferably, since the longitudinal resolution limit of electromagnetic exploration is about 10%, any calculated longitudinal resolution less than 10% is treated as 10%.

[0063] Based on the highest frequency, lowest frequency, and vertical resolution, c frequency sequences are determined, wherein the frequency sequences are geometric frequency sequences with a common ratio of 2, and c is a positive integer greater than or equal to 2.

[0064] Furthermore, the lowest frequency in the first frequency sequence is denoted as the fundamental frequency f. base The lowest frequency of the remaining frequency sequences satisfies the following relationship with the fundamental frequency:

[0065]

[0066] Among them, f t f is the lowest frequency of the remaining frequency sequences. base is the fundamental frequency in the first frequency sequence, m is the frequency sequence number, i.e., the m-th frequency sequence, n is a positive integer, and c is the total number of frequency sequences.

[0067] Therefore, each frequency sequence can be expressed by the following formula:

[0068]

[0069] Where m is the frequency sequence number and is a positive integer, F m It is the m-th frequency sequence, where a is the frequency sequence coefficient greater than or equal to 1, n is a positive integer, and f base Let be the fundamental frequency in the first frequency sequence, c be the total number of frequency sequences, and p be a natural number.

[0070] The fundamental frequency of the multi-sequence combination wave generated by the above frequency sequence combination is:

[0071]

[0072] Where fx is the fundamental frequency of the multi-sequence combination wave, n is a positive integer, and c is the total number of frequency sequences.

[0073] For example, when the required vertical resolution for exploration is relatively low, two frequency sequences are determined and used to combine them to generate a multi-sequence combined wave, where c = 2, n = 1, and f t =3 / 2×f base Furthermore, it can be seen that the first frequency sequence can be expressed as F1 = a × f base ×2 p The second frequency sequence can be represented as F2 = 3 / 2 × a × f base ×2 p Where p is a natural number, the fundamental frequency of the multi-sequence combination wave generated by combining the above two frequency sequences is: fx = 1 / 2 × f base ;

[0074] When the required vertical resolution for exploration is relatively high, such as around 10% or even lower, four frequency sequences are determined for combining to generate a multi-sequence combined wave. In this case, c = 4, n = 2, and f t = (m+3) / 4×f base That is, the lowest frequency of the second frequency sequence is 5 / 4 × f base The lowest frequency of the third frequency sequence is 6 / 4 × f base The lowest frequency of the fourth frequency sequence is 7 / 4 × f. base Furthermore, it can be seen that the first frequency sequence can be expressed as F1 = a × f base ×2 p The second frequency sequence can be represented as F2 = 5 / 4 × a × f base ×2 p The third frequency sequence can be represented as F3 = 6 / 4 × a × f base ×2 p The fourth frequency sequence can be represented as F4 = 7 / 4 × a × f base ×2p Where p is a natural number, the fundamental frequency of the multi-sequence combination wave generated by combining the above four frequency sequences is: fx = 1 / 4 × f base ;

[0075] When the required vertical resolution for exploration falls between the two mentioned above, three frequency sequences need to be determined for combining to generate a multi-sequence composite wave. Since both c=3 and 4 satisfy n=2, 2 n-1 +1≤c≤2 n Given the given conditions, we first determine four frequency sequences, then randomly select three of them to combine and generate a multi-sequence combination wave, i.e., c = 4, n = 2, f t = (m+3) / 4×f base That is, the lowest frequency of the second frequency sequence is 5 / 4 × f base The lowest frequency of the third frequency sequence is 6 / 4 × f base The lowest frequency of the fourth frequency sequence is 7 / 4 × f. base Furthermore, it can be seen that the first frequency sequence can be expressed as F1 = a × f base ×2 p The second frequency sequence can be represented as F2 = 5 / 4 × a × f base ×2 p The third frequency sequence can be represented as F3 = 6 / 4 × a × f base ×2 p The fourth frequency sequence can be represented as F4 = 7 / 4 × a × f base ×2 p Where p is a natural number, then, from the above 4 frequency sequences, any 3 frequency sequences are randomly selected to combine and generate a multi-sequence combination wave, whose fundamental frequency is also: fx = 1 / 4 × f base ;

[0076] Based on the required vertical resolution of the exploration, c frequency sequences need to be determined for combining to generate a multi-sequence combined wave, and c satisfies n=3, 2 n-1 +1≤c≤2 n When considering the conditions, first determine 2. n There are 8 frequency sequences, where n = 3. First, 8 frequency sequences are determined. If c is less than 8, then c frequency sequences are randomly selected from the 8 to generate a multi-sequence combination wave, whose fundamental frequency is: fx = 1 / 8 × f base .

[0077] As can be seen from the above, the staff can determine c frequency sequences based on the vertical resolution required for exploration, where c is a positive integer greater than or equal to 2. The determination of other frequency sequence combinations is not much different from the above description, and will not be repeated here.

[0078] S14. Based on the c frequency sequences, a multi-sequence combination wave with consistent frequency density across the entire frequency band is obtained.

[0079] like Figure 3 As shown, the specific implementation of step S14 includes the following sub-steps:

[0080] S142. Based on the frequency sequence, use the square wave generating function to generate a corresponding time series matrix for each frequency sequence.

[0081] Substitute each frequency sequence obtained above into the square wave generation function to generate the corresponding square wave matrix, which is also called the time series matrix.

[0082]

[0083] Where Y is the time series matrix, sq is the square wave generating function, F is the frequency sequence, and t is the time series matrix. i Let i be the sampling time. For phase.

[0084] According to the Nyquist sampling theorem, the sampling rate corresponding to each time series matrix must be at least twice the highest main frequency. Considering the response characteristics of analog circuit filters, the sampling rate preferably needs to reach 2.4 times or more of the highest main frequency, and the sampling rate should be divisible by 4 times the fundamental frequency.

[0085] S144. Superimpose and sum all time series matrices, and perform amplitude correction on the sum: correct amplitudes greater than 0 to A, and correct amplitudes less than 0 to -A, thereby obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0.

[0086] The above time series matrices are superimposed and summed. The sum is then subjected to amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent density across the entire frequency band, where A≠0.

[0087] Preferably, phase adjustment is performed on at least one of the time series matrices to find the phase that minimizes the mean square relative error of the amplitude corresponding to each main frequency in the multi-sequence combination wave with consistent frequency density across the entire frequency band after superposition, and this phase is taken as the optimal phase of the corresponding time series matrix.

[0088] Specifically, a Fast Fourier Transform is performed on the multi-sequence combined wave to obtain its spectrum, and the amplitude of each dominant frequency is extracted. Then, the mean square relative error of the amplitude is calculated. Preferably, the phase is adjusted by one degree each time.

[0089] Then, based on the optimal phase, all time series matrices are superimposed and summed, and the sum is adjusted by amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0, making the amplitudes of each frequency more even, thereby improving the overall anti-interference capability of the multi-sequence combination wave.

[0090] Preferably, the results of the sum are subjected to amplitude correction: amplitudes greater than 1 are corrected to 1, and amplitudes less than -1 are corrected to -1, thereby obtaining a multi-sequence combination wave with consistent density across the entire frequency band.

[0091] Finally, the amplitude -1 or -A is corrected to 0, and A is corrected to 1, so that the multi-sequence combination wave consists only of 0 and 1.

[0092] For example, when the frequency sequence coefficient a = 1, and four frequency sequences are determined based on the required vertical resolution for exploration, and used to generate a multi-sequence combined wave, i.e., c = 4, n = 2, f t = (m+3) / 4×f base That is, the lowest frequency of the second frequency sequence is 5 / 4 × f base The lowest frequency of the third frequency sequence is 6 / 4 × f base The lowest frequency of the fourth frequency sequence is 7 / 4 × f. base Furthermore, it can be seen that the first frequency sequence can be represented as F1 = 1 × f base ×2 p The second frequency sequence can be represented as F2 = 5 / 4 × f base ×2 p The third frequency sequence can be represented as F3 = 6 / 4 × f base ×2 p The fourth frequency sequence can be represented as F4 = 7 / 4 × f base ×2 p , where p is a natural number.

[0093] After combination, the frequencies in the low-frequency range, from low to high, are 1×f. base ×2 0 ,5 / 4×f base ×2 0 ,6 / 4×f base ×2 0 ,7 / 4×f base ×2 0 ,1×f base ×2 1 ,5 / 4×f base ×2 1 ,6 / 4×f base ×2 1 ,7 / 4×f base ×21 ..., for 1×f base ×2 p For the main sequence, the number of frequencies between the frequency differences of 2 times the main sequence is 3, and the frequency density remains consistent from low frequency to high frequency, such as Figure 4 ,in Figure 4 (a) is a waveform diagram of a multi-sequence combination wave. Figure 4 (b) is a schematic diagram of the spectrum of a multi-sequence combined wave.

[0094] As can be seen from the above analysis, the frequency density of the multi-sequence combination wave generated by combining c frequency sequences in this embodiment is c. From... Figure 1 and Figure 4 The comparison shows that the frequency density of the multi-sequence combination wave generated in this embodiment is significantly greater than that of the traditional pseudo-random wave in the frequency range below 1 Hz.

[0095] This embodiment determines the highest and lowest frequencies based on the depth range to be explored, determines the number of frequency sequences c based on the required vertical resolution, and controls the relationship between the lowest frequency of the remaining frequency sequences and the fundamental frequency in the first frequency sequence. This not only improves the required vertical resolution of exploration but also increases the frequency density in the low-frequency band, resulting in a multi-sequence combination wave with consistent frequency density across the entire frequency band. This leads to higher resolution of the acquired deep exploration data, thereby meeting exploration requirements.

[0096] Example 2

[0097] like Figure 5 As shown, based on the above embodiments, the multi-sequence combination wave construction method in this embodiment further includes the following steps:

[0098] S13. Replace the frequency values ​​in each frequency sequence that belong to the preset range with the corresponding values ​​in the preset frequency sequence calculated based on the aforementioned frequencies.

[0099] Based on exploration experience and the spectral characteristics of power frequency and its harmonics, a preset range is defined as 50n±w Hz. That is, the frequency values ​​in each frequency sequence that belong to the 50n±w Hz range are replaced with the corresponding values ​​in the preset frequency sequence calculated based on the aforementioned frequencies, where n is a positive integer and w is a number less than 10. Preferably, w=4, which allows for more frequencies to be selected, thereby generating a multi-sequence combined wave that is both dense and highly resistant to interference.

[0100] Preferably, the preset frequency sequence is selected from frequency sequences that satisfy the following formula, i.e., at least one of them is selected.

[0101]

[0102] Where m is the frequency sequence number and is a positive integer, Fm It is the m-th frequency sequence, where a is the frequency sequence coefficient greater than or equal to 1, n is a positive integer, and f base Let be the fundamental frequency in the first frequency sequence, c be the total number of frequency sequences, and p be a natural number.

[0103] Furthermore, our research revealed that some frequency sequences do not fall within the 50 Hz ± ω Hz range. Therefore, these frequency sequences are preferentially selected as preset frequency sequences. For example, among commonly used frequency sequences, 4096 and 2048 Hz in frequency sequence F1 fall within the 50 Hz ± ω Hz range; 96 and 48 Hz in frequency sequence F3 fall within the 50 Hz ± ω Hz range; and 896 and 448 Hz in frequency sequence F4 fall within the 50 Hz ± ω Hz range. However, all frequencies in frequency sequence F2 completely avoid the 50 Hz ± ω Hz range. Therefore, frequency sequence F2 is preferably selected as the preset frequency sequence.

[0104] To perform frequency replacement, first identify the frequency values ​​within a preset range in each frequency sequence, denoted as f. g .

[0105] Perform the following calculations sequentially on each frequency F:

[0106] If rem(F / 50) > 25, then f = 50 - rem(F / 50); otherwise, f = rem(F / 50).

[0107] If f ≤ w, then f g =F, and then calculate P in the frequency sequence formula using the following formula.

[0108]

[0109] Then substitute the obtained P into the preset frequency sequence F i The formula is used to calculate f. g Similar f i Then f g Replace with f i .

[0110]

[0111] In the above formula, F is a frequency value selected from each frequency sequence at each time, rem is the modulo operation, f is a temporary variable, w is the w within the preset range mentioned above, and f gThis refers to the frequency values ​​falling within the 50n±w Hz influence range. p is the p in the frequency sequence formula, i.e., a natural number. ceil is the floor function. c is the c in the frequency sequence formula, i.e., the total number of frequency sequences. n is n in the frequency sequence, a positive integer. a is the frequency sequence coefficient greater than or equal to 1. f base Where i is the fundamental frequency, and f is the frequency sequence number. i It is a temporary variable, a variable in the preset frequency sequence related to f. g Similar frequencies.

[0112] Each frequency in each frequency sequence is first determined, through the above calculations, whether it falls within a preset range. If it does, it is replaced with the corresponding value in the preset frequency sequence calculated based on that frequency. In other words, this method replaces all frequency values ​​within the preset range that are susceptible to interference and would lead to poor exploration data quality with frequency values ​​that are more resistant to interference and enhance exploration data quality. This results in a multi-sequence composite wave that possesses both high low-frequency density and strong anti-interference capabilities, thus avoiding the influence of frequencies within the preset range and improving the overall quality of exploration data to meet higher exploration requirements.

[0113] For example, when exploring in areas with thick cover, the effective exploration signal is weak. Combining the frequency division coefficient and the empirical formula of waveform, since the frequency resolution of 4 frequency sequences is higher, but the signal strength is weaker, resulting in weaker anti-interference, we generally choose 3 frequency sequences for exploration so that the obtained multi-sequence combined wave has both strong anti-interference and high frequency resolution. Therefore, frequency sequence F2 is selected as the preset frequency sequence, and frequency sequences F1, F3 and F4 are selected for combination to generate multi-sequence combined wave.

[0114] Example 3

[0115] Figure 6 This diagram illustrates the structure of a multi-sequence combined wave construction system according to an embodiment of the present invention. Figure 6 It can be seen that the multi-sequence combined wave construction system includes: frequency sequence confirmation module 32 and multi-sequence combined wave construction module 34;

[0116] The frequency sequence confirmation modulus 32 is used to determine c frequency sequences based on the depth range to be detected and the required longitudinal resolution, wherein the frequency sequences are a geometric frequency sequence with a common ratio of 2, and c is a positive integer greater than or equal to 2.

[0117] Currently, the maximum detection depth of the wide-area electromagnetic method is about 7km. Since the inversion algorithm of the electromagnetic method depth sounding part adopts a peeling method from the surface to the inside, shallow information is also very important. Therefore, during detection, the highest frequency is generally defined as the highest frequency that the instrument can transmit and receive, which is generally 9600Hz. Of course, the determination of the highest and lowest frequencies of electromagnetic waves is ultimately determined by the actual detection requirements.

[0118] Preferably, the depth range to be detected is first determined, and then the two extreme values ​​of this depth range are substituted into the electromagnetic exploration depth formula H to obtain the highest and lowest frequencies of the electromagnetic waves. The electromagnetic exploration depth formula H is:

[0119]

[0120] Where H is the detection depth, ρ is the background resistivity of the exploration area, and f is the frequency of the exploration electromagnetic wave.

[0121] The background resistivity ρ can be determined by collecting previous geophysical, geological, or well logging data of the exploration area. Using the above formula, the highest and lowest frequencies of the required electromagnetic waves are calculated based on the depth range to be explored. To ensure the exploration depth, the lowest frequency during actual operation should be several frequency points lower than the theoretically calculated lowest frequency. Preferably, half of the theoretical value of the lowest frequency is selected.

[0122] In actual exploration, the longitudinal resolution can be determined based on the size of the target body. Preferably, the longitudinal resolution is determined based on the diameter-to-depth ratio of the target body, where the diameter-to-depth ratio is the ratio of the longitudinal thickness of the target body to its burial depth. Preferably, since the longitudinal resolution limit of electromagnetic exploration is about 10%, any calculated longitudinal resolution less than 10% is treated as 10%.

[0123] Based on the highest frequency, lowest frequency, and vertical resolution, c frequency sequences are determined, wherein the frequency sequences are geometric frequency sequences with a common ratio of 2, and c is a positive integer greater than or equal to 2.

[0124] Furthermore, the lowest frequency in the first frequency sequence is denoted as the fundamental frequency f. base The lowest frequency of the remaining frequency sequences satisfies the following relationship with the fundamental frequency:

[0125]

[0126] Among them, f t f is the lowest frequency of the remaining frequency sequences. base is the fundamental frequency in the first frequency sequence, m is the frequency sequence number, i.e., the m-th frequency sequence, n is a positive integer, and c is the total number of frequency sequences.

[0127] Therefore, each frequency sequence can be expressed by the following formula:

[0128]

[0129] Where m is the frequency sequence number and is a positive integer, F m It is the m-th frequency sequence, where a is the frequency sequence coefficient greater than or equal to 1, n is a positive integer, and f base Let be the fundamental frequency in the first frequency sequence, c be the total number of frequency sequences, and p be a natural number.

[0130] The fundamental frequency of the multi-sequence combination wave generated by the above frequency sequence combination is:

[0131]

[0132] Where fx is the fundamental frequency of the multi-sequence combination wave, n is a positive integer, and c is the total number of frequency sequences.

[0133] For example, when the required vertical resolution for exploration is relatively low, two frequency sequences are determined and used to combine them to generate a multi-sequence combined wave, where c = 2, n = 1, and f t =3 / 2×f base Furthermore, it can be seen that the first frequency sequence can be expressed as F1 = a × f base ×2 p The second frequency sequence can be represented as F2 = 3 / 2 × a × f base ×2 p Where p is a natural number, the fundamental frequency of the multi-sequence combination wave generated by combining the above two frequency sequences is: fx = 1 / 2 × f base ;

[0134] When the required vertical resolution for exploration is relatively high, such as around 10% or even lower, four frequency sequences are determined for combining to generate a multi-sequence combined wave. In this case, c = 4, n = 2, and f t = (m+3) / 4×f base That is, the lowest frequency of the second frequency sequence is 5 / 4 × f base The lowest frequency of the third frequency sequence is 6 / 4 × f base The lowest frequency of the fourth frequency sequence is 7 / 4 × f. base Furthermore, it can be seen that the first frequency sequence can be expressed as F1 = a × f base ×2 p The second frequency sequence can be represented as F2 = 5 / 4 × a × f base ×2 p The third frequency sequence can be represented as F3 = 6 / 4 × a × f base ×2 p The fourth frequency sequence can be represented as F4 = 7 / 4 × a × f base ×2p Where p is a natural number, the fundamental frequency of the multi-sequence combination wave generated by combining the above four frequency sequences is: fx = 1 / 4 × f base ;

[0135] When the required vertical resolution for exploration falls between the two mentioned above, three frequency sequences need to be determined for combining to generate a multi-sequence composite wave. Since both c=3 and 4 satisfy n=2, 2 n-1 +1≤c≤2 n Given the given conditions, we first determine four frequency sequences, then randomly select three of them to combine and generate a multi-sequence combination wave, i.e., c = 4, n = 2, f t = (m+3) / 4×f base That is, the lowest frequency of the second frequency sequence is 5 / 4 × f base The lowest frequency of the third frequency sequence is 6 / 4 × f base The lowest frequency of the fourth frequency sequence is 7 / 4 × f. base Furthermore, it can be seen that the first frequency sequence can be expressed as F1 = a × f base ×2 p The second frequency sequence can be represented as F2 = 5 / 4 × a × f base ×2 p The third frequency sequence can be represented as F3 = 6 / 4 × a × f base ×2 p The fourth frequency sequence can be represented as F4 = 7 / 4 × a × f base ×2 p Where p is a natural number, then, from the above 4 frequency sequences, any 3 frequency sequences are randomly selected to combine and generate a multi-sequence combination wave, whose fundamental frequency is also: fx = 1 / 4 × f base ;

[0136] Based on the required vertical resolution of the exploration, c frequency sequences need to be determined for combining to generate a multi-sequence combined wave, and c satisfies n=3, 2 n-1 +1≤c≤2 n When considering the conditions, first determine 2. n There are 8 frequency sequences, where n = 3. First, 8 frequency sequences are determined. If c is less than 8, then c frequency sequences are randomly selected from the 8 to generate a multi-sequence combination wave, whose fundamental frequency is: fx = 1 / 8 × f base .

[0137] As can be seen from the above, the staff can determine c frequency sequences based on the vertical resolution required for exploration, where c is a positive integer greater than or equal to 2. The determination of other frequency sequence combinations is not much different from the above description, and will not be repeated here.

[0138] The multi-sequence combined wave construction module 34, based on the c frequency sequences, obtains a multi-sequence combined wave with consistent frequency density across the entire frequency band.

[0139] like Figure 7 As shown, the multi-sequence combined wave construction module 34 includes: a time series matrix generation component 342 and a multi-sequence combined wave construction component 344.

[0140] The time series matrix generation component 342 generates a corresponding time series matrix for each frequency sequence based on the frequency sequence using a square wave generation function.

[0141] Substitute each frequency sequence obtained above into the square wave generation function to generate the corresponding square wave matrix, which is also called the time series matrix.

[0142]

[0143] Where Y is the time series matrix, sq is the square wave generating function, F is the frequency sequence, and t is the time series matrix. i Let i be the sampling time. For phase.

[0144] According to the Nyquist sampling theorem, the sampling rate corresponding to each time series matrix must be at least twice the highest main frequency. Considering the response characteristics of analog circuit filters, the sampling rate preferably needs to reach 2.4 times or more of the highest main frequency, and the sampling rate should be divisible by 4 times the fundamental frequency.

[0145] The multi-sequence combined wave construction component 344 is used to superimpose and sum all time series matrices, and perform amplitude correction on the summation result: the amplitude greater than 0 is corrected to A, and the amplitude less than 0 is corrected to -A, so as to obtain a multi-sequence combined wave with consistent frequency density across the entire frequency band, where A≠0.

[0146] The above time series matrices are superimposed and summed. The sum is then subjected to amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent density across the entire frequency band, where A≠0.

[0147] Preferably, phase adjustment is performed on at least one of the time series matrices to find the phase that minimizes the mean square relative error of the amplitude corresponding to each main frequency in the multi-sequence combination wave with consistent frequency density across the entire frequency band after superposition, and this phase is taken as the optimal phase of the corresponding time series matrix.

[0148] Specifically, a Fast Fourier Transform is performed on the multi-sequence combined wave to obtain its spectrum, and the amplitude of each dominant frequency is extracted. Then, the mean square relative error of the amplitude is calculated. Preferably, the phase is adjusted by one degree each time.

[0149] Then, based on the optimal phase, all time series matrices are superimposed and summed, and the sum is adjusted by amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0, making the amplitudes of each frequency more even, thereby improving the overall anti-interference capability of the multi-sequence combination wave.

[0150] Preferably, the results of the sum are subjected to amplitude correction: amplitudes greater than 1 are corrected to 1, and amplitudes less than -1 are corrected to -1, thereby obtaining a multi-sequence combination wave with consistent density across the entire frequency band.

[0151] Finally, the amplitude -1 or -A is corrected to 0, and A is corrected to 1, so that the multi-sequence combination wave consists only of 0 and 1.

[0152] For example, when the frequency sequence coefficient a = 1, and four frequency sequences are determined based on the required vertical resolution for exploration, and used to generate a multi-sequence combined wave, i.e., c = 4, n = 2, f t = (m+3) / 4×f base That is, the lowest frequency of the second frequency sequence is 5 / 4 × f base The lowest frequency of the third frequency sequence is 6 / 4 × f base The lowest frequency of the fourth frequency sequence is 7 / 4 × f. base Furthermore, it can be seen that the first frequency sequence can be represented as F1 = 1 × f base ×2 p The second frequency sequence can be represented as F2 = 5 / 4 × f base ×2 p The third frequency sequence can be represented as F3 = 6 / 4 × f base ×2 p The fourth frequency sequence can be represented as F4 = 7 / 4 × f base ×2 p , where p is a natural number.

[0153] After combination, the frequencies in the low-frequency range, from low to high, are 1×f. base ×2 0 ,5 / 4×f base ×2 0 ,6 / 4×f base ×2 0 ,7 / 4×f base ×2 0 ,1×f base ×2 1 ,5 / 4×f base ×2 1 ,6 / 4×f base ×2 1 ,7 / 4×fbase ×2 1 ..., for 1×f base ×2 p For the main sequence, the number of frequencies between the frequency differences of 2 times the main sequence is 3, and the frequency density remains consistent from low frequency to high frequency, such as Figure 4 ,in Figure 4 (a) is a waveform diagram of a multi-sequence combination wave. Figure 4 (b) is a schematic diagram of the spectrum of a multi-sequence combined wave.

[0154] As can be seen from the above analysis, the frequency density of the multi-sequence combination wave generated by combining c frequency sequences in this embodiment is c. From... Figure 1 and Figure 4 The comparison shows that the frequency density of the multi-sequence combination wave generated in this embodiment is significantly greater than that of the traditional pseudo-random wave in the frequency range below 1 Hz.

[0155] This embodiment determines the highest and lowest frequencies based on the depth range to be explored, determines the number of frequency sequences c based on the required vertical resolution, and controls the relationship between the lowest frequency of the remaining frequency sequences and the fundamental frequency in the first frequency sequence. This not only improves the required vertical resolution of exploration but also increases the frequency density in the low-frequency band, resulting in a multi-sequence combination wave with consistent frequency density across the entire frequency band. This leads to higher resolution of the acquired deep exploration data, thereby meeting exploration requirements.

[0156] Example 4

[0157] like Figure 8 As shown, based on the above embodiments, the multi-sequence combined wave construction system of this embodiment further includes:

[0158] The frequency replacement module 33 is used to replace the frequency values ​​in each frequency sequence that belong to a preset range with the corresponding values ​​in the preset frequency sequence calculated based on the aforementioned frequencies.

[0159] Based on exploration experience and the spectral characteristics of power frequency and its harmonics, a preset range is defined as 50n±w Hz. That is, the frequency values ​​in each frequency sequence that belong to the 50n±w Hz range are replaced with the corresponding values ​​in the preset frequency sequence calculated based on the aforementioned frequencies, where n is a positive integer and w is a number less than 10. Preferably, w=4, which allows for more frequencies to be selected, thereby generating a multi-sequence combined wave that is both dense and highly resistant to interference.

[0160] Preferably, the preset frequency sequence is selected from frequency sequences that satisfy the following formula, i.e., at least one of them is selected.

[0161]

[0162] Where m is the frequency sequence number and is a positive integer, F m It is the m-th frequency sequence, where a is the frequency sequence coefficient greater than or equal to 1, n is a positive integer, and f base Let be the fundamental frequency in the first frequency sequence, c be the total number of frequency sequences, and p be a natural number.

[0163] Furthermore, our research revealed that some frequency sequences do not fall within the 50 Hz ± ω Hz range. Therefore, these frequency sequences are preferentially selected as preset frequency sequences. For example, among commonly used frequency sequences, 4096 and 2048 Hz in frequency sequence F1 fall within the 50 Hz ± ω Hz range; 96 and 48 Hz in frequency sequence F3 fall within the 50 Hz ± ω Hz range; and 896 and 448 Hz in frequency sequence F4 fall within the 50 Hz ± ω Hz range. However, all frequencies in frequency sequence F2 completely avoid the 50 Hz ± ω Hz range. Therefore, frequency sequence F2 is preferably selected as the preset frequency sequence.

[0164] To perform frequency replacement, first identify the frequency values ​​within a preset range in each frequency sequence, denoted as f. g .

[0165] Perform the following calculations sequentially on each frequency F:

[0166] If rem(F / 50) > 25, then f = 50 - rem(F / 50); otherwise, f = rem(F / 50).

[0167] If f ≤ w, then f g =F, and then calculate P in the frequency sequence formula using the following formula.

[0168]

[0169] Then substitute the obtained P into the preset frequency sequence F i The formula is used to calculate f. g Similar f i Then f g Replace with f i .

[0170]

[0171] In the above formula, F is a frequency value selected from each frequency sequence at each time, rem is the modulo operation, f is a temporary variable, w is the w within the preset range mentioned above, and f gThis refers to the frequency values ​​falling within the 50n±w Hz influence range. p is the p in the frequency sequence formula, i.e., a natural number. ceil is the floor function. c is the c in the frequency sequence formula, i.e., the total number of frequency sequences. n is n in the frequency sequence, a positive integer. a is the frequency sequence coefficient greater than or equal to 1. f base Where i is the fundamental frequency, and f is the frequency sequence number. i It is a temporary variable, a variable in the preset frequency sequence related to f. g Similar frequencies.

[0172] Each frequency in each frequency sequence is first determined, through the above calculations, whether it falls within a preset range. If it does, it is replaced with the corresponding value in the preset frequency sequence calculated based on that frequency. In other words, this method replaces all frequency values ​​within the preset range that are susceptible to interference and would lead to poor exploration data quality with frequency values ​​that are more resistant to interference and enhance exploration data quality. This results in a multi-sequence composite wave that possesses both high low-frequency density and strong anti-interference capabilities, thus avoiding the influence of frequencies within the preset range and improving the overall quality of exploration data to meet higher exploration requirements.

[0173] For example, when exploring in areas with thick cover, the effective exploration signal is weak. Combining the frequency division coefficient and the empirical formula of waveform, since the frequency resolution of 4 frequency sequences is higher, but the signal strength is weaker, resulting in weaker anti-interference, we generally choose 3 frequency sequences for exploration so that the obtained multi-sequence combined wave has both strong anti-interference and high frequency resolution. Therefore, frequency sequence F2 is selected as the preset frequency sequence, and frequency sequences F1, F3 and F4 are selected for combination to generate multi-sequence combined wave.

[0174] Example 5

[0175] This embodiment provides a multi-sequence combined wave transmitter, which uses a multi-sequence combined wave construction method to obtain a multi-sequence combined wave with consistent frequency density across the entire frequency band, meeting exploration requirements.

[0176] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for constructing multi-sequence combined waves, characterized in that, Includes the following steps: Based on the depth range to be detected and the required longitudinal resolution, c frequency sequences are determined, wherein the frequency sequences are geometric frequency sequences with a common ratio of 2, and c is a positive integer greater than or equal to 2. Furthermore, the lowest frequency in the first frequency sequence is denoted as the fundamental frequency f. base The lowest frequency of the remaining frequency sequences satisfies the following relationship with the fundamental frequency: in, f is the lowest frequency of the remaining frequency sequences. base is the fundamental frequency in the first frequency sequence, m is the frequency sequence number, n is a positive integer, and c is the total number of frequency sequences; Based on the c frequency sequences, a multi-sequence combination wave with consistent frequency density across the entire frequency band is obtained; including: Based on the frequency sequence, a corresponding time series matrix is ​​generated for each frequency sequence using a square wave generating function; All time series matrices are superimposed and summed. The sum is then subjected to amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0.

2. The method for constructing multi-sequence combined waves according to claim 1, characterized in that, The process involves superimposing and summing all time series matrices, and then performing amplitude correction on the sum: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thereby obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0 includes: Phase adjustment is performed on at least one of the time series matrices to find the phase that minimizes the mean square relative error of the amplitude corresponding to each main frequency in the multi-sequence combined wave with consistent frequency density across the entire frequency band after superposition, and this phase is taken as the optimal phase of the corresponding time series matrix. Based on the optimal phase, all time series matrices are superimposed and summed. The sum is then subjected to amplitude correction: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thus obtaining a multi-sequence combination wave with consistent frequency density across the entire frequency band, where A≠0.

3. The method for constructing multi-sequence combined waves according to claim 1 or 2, characterized in that, The sampling rate corresponding to each of the time series matrices is at least twice its highest main frequency and is divisible by 4 times the base frequency.

4. A multi-sequence combined wave construction system, characterized in that, include: The frequency sequence confirmation module is used to determine c frequency sequences based on the depth range to be detected and the required longitudinal resolution, wherein the frequency sequences are geometric frequency sequences with a common ratio of 2, and c is a positive integer greater than or equal to 2. Furthermore, the lowest frequency in the first frequency sequence is denoted as the fundamental frequency f. base The lowest frequency of the remaining frequency sequences satisfies the following relationship with the fundamental frequency: in, f is the lowest frequency of the remaining frequency sequences. base is the fundamental frequency in the first frequency sequence, m is the frequency sequence number, n is a positive integer, and c is the total number of frequency sequences; A multi-sequence combined wave construction module, based on the c frequency sequences, obtains a multi-sequence combined wave with consistent frequency density across the entire frequency band; including: A time series matrix generation component generates a corresponding time series matrix for each frequency sequence based on the frequency sequence using a square wave generation function; The multi-sequence combined wave construction component is used to superimpose and sum all time series matrices, and perform amplitude correction on the summation result: amplitudes greater than 0 are corrected to A, and amplitudes less than 0 are corrected to -A, thereby obtaining a multi-sequence combined wave with consistent frequency density across the entire frequency band, where A≠0.

5. The multi-sequence combined wave construction system according to claim 4, characterized in that, The sampling rate corresponding to each of the time series matrices is at least twice its highest main frequency and is divisible by 4 times the base frequency.

6. A multi-sequence combined wave transmitter, characterized in that, A multi-sequence combined wave constructed using any of the multi-sequence combined wave construction methods described in claims 1-3.

Images