CN105301664A - Artificial source tensor electromagnetic exploration method with far references - Google Patents
Artificial source tensor electromagnetic exploration method with far references Download PDFInfo
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Abstract
The invention provides an artificial source tensor electromagnetic exploration method with far references. The method comprises the following steps of: (1) arranging one or more far reference points while arranging measuring points, and synchronously recording a time variable of current sending of an artificial field source, and electromagnetic fields of the measuring points and the far reference points; (2) constructing a measuring point matrix X and a reference data matrix Xr; (3) utilizing the reference data matrix Xr to solve a natural electromagnetic field source polarized parameter [alpha], calculating a polarized parameter [beta] according to the time variable of current sending of the artificial field source, and then utilizing [alpha] and [beta] and X to solve a corresponding spatial modulus U of the measuring points to a natural field source and a corresponding spatial modulus V to the artificial field source; and (4) utilizing U and V to solve natural field tensor impedance and artificial field tensor impedance of each measuring point. Based on a conventional artificial field electromagnetic method, one or more far reference points are additionally arranged for data collection; and based on unified data equations, the natural field tensor impedance and the artificial field tensor impedance of each measuring point are simultaneously obtained by one time of processing, and earth electrical parameters required by interpretation are obtained.
Description
Technical field
The present invention relates to a kind of electromagnetic exploration method reconnoitring geophysics field, particularly a kind of artificial source's tensor electromagnetic exploration method with reference far away.
Background technology
In prospecting geophysics electromagnetic method field, natural field source electromagnetic method (Magnetotelluric, MT; Audio-frequencyMagnetotelluric, AMT) investigation depth is large, and harvester is light, but signal to noise ratio (S/N ratio) is low, and anti-noise ability is weak; Traditional reference magnetotelluric method far away introduces a reference point far away while district's Natural electromagnetic field is surveyed in observation, utilize library track signal and survey district's signal correction, the incoherent characteristic of noise, in compacting Liao Ce district, the impact of noise, improves impedance data quality to a certain extent; But the problems such as the data skew in the frequency range (MT " dead frequency band " as near AMT " dead frequency band ", the 1Hz within the scope of 5k ~ 1kHz) that Natural electromagnetic field pickup electrode is weak are still difficult to obtain gratifying effect.For this problem, controlled-source audiomagnetotellurics method (ControlledSourceAudio-frequencyMagnetotelluric, CSAMT) adopt artificial electromagnetic field source as excitation, in certain observation area, observe artificial electromagnetic field, improve data SNR; But effective impedance data needs to obtain in " far field ", and in " near region " and " zone of transition " of artificial field source, impedance data can produce and distort and the explanation results led to errors.Although scholars have successively developed a series of process means, as proposed the definition and numerical procedure etc. of various Data correction strategy, APPARENT RESISTIVITY, ground telecommunications breath in extracting section " zone of transition ", but for " near region " observation data, still cannot be used.In addition, unified observation electromagnetic field isolates as natural field and artificial field two class independently signal by existing technical scheme, and develops corresponding method system; As in natural field source electromagnetic method, artificial source's signal is regarded as correlation noise, and in controlled-source audiomagnetotellurics method, Natural electromagnetic field signal is regarded as correlation noise, causes the loss of data message all to a certain extent.
Summary of the invention
Technical matters solved by the invention is, for the deficiencies in the prior art, a kind of artificial source's tensor electromagnetic exploration method with reference far away is provided, data acquisition of the present invention increases on traditional electromagnetic method basis, artificial field lays one or more reference measuring point far away, observation electromagnetic field is considered as the unified data volume in natural field and artificial field, based on unified data equation, single treatment obtains natural field tensor impedance and the artificial field tensor impedance of measuring point simultaneously, gather the advantage of NATURE SOURCE ELECTROMAGNETIC SOUNDING and artificial field source electromagnetic method, higher-quality tensor impedance data can be obtained at high band, the plane wave tensor impedance data do not distorted can be obtained in low-frequency range.
Technical scheme of the present invention is:
With artificial source's tensor electromagnetic exploration method of reference far away, comprise the following steps:
Step 1, Observation Design:
Determine observed object and the target exploration degree of depth, design survey line and measuring point; According to the target exploration degree of depth and survey district's the earth background conductance rate determination observing frequency scope, and according to the observation interval of observing frequency scope determination measuring point and signal sampling rate; For each observing frequency, calculate the time domain sampling number needed for single frequency spectrum according to time-frequency convert, window width when determining, utilize observation interval divided by time window width obtain observation corresponding to each observing frequency time window number;
Step 2, laying transmitting terminal device and receiving end device:
Lay transmitting terminal device: in survey district, lay N number of artificial field source, N be more than or equal to 1 integer; Transmitting terminal device and traditional artificial field source electromagnetic method similar, using ground connection HORIZONTAL ELECTRIC DIPOLE or earth-free vertical magnetic dipole as artificial field source, can lay by tensor mode or other forms; With Traditional Man source electromagnetic method unlike, source, the present inventor workshop need send the current value of different size when multiple in window, and record does not send the size of electric current in the same time.
Lay receiving end device: earth's surface arranges one or more measuring point in survey district; Each measuring point place lays the 2 orthogonal horizontal magnetic fields in road and surveys orthogonal horizontal component of electric field survey road (Measurement channel) in road and 2 roads; Outside survey district, arrange at least 1 synchronous reference point far away, the installation position of reference point far away is far away identical with reference to the reference point far away in magnetotelluric method with routine; Lay the 2 orthogonal horizontal magnetic fields in road at reference point place far away and survey road, increase the orthogonal horizontal component of electric field in laying 2 road during conditions permit and survey road; Located level electric field is not surveyed road and can be obtained result yet, but lays 2 orthogonal horizontal component of electric fields survey roads, road, and is conducive to after recording corresponding data obtaining more accurate result;
Step 3, data acquisition:
Data acquisition is divided into the data acquisition of receiving unit and the data acquisition of transmitting portion, is specially electric field and the magnetic-field component data at each measuring point of synchronous acquisition and reference point place far away, after carrying out time-frequency convert, obtains the domain observations data that each observing frequency is corresponding; Data corresponding to each observing frequency are separate, and processing mode is identical; To wherein arbitrary observing frequency, if window number is I during its observation, corresponding observation data comprises the data of transmission current data three parts of measuring point observation data, reference point observation data far away and artificial field source;
Part I, measuring point observation data: comprise and survey measuring point all survey roads recorded data in district, comprise the 2 orthogonal horizontal magnetic fields in road and survey road and 2 roads orthogonal horizontal component of electric field survey road, total survey number of channels is 4 roads; Measuring point signal space-time data matrix X is built according to measuring point observation data:
Wherein, X is 4 × I rank matrixes; H
xi, H
yi(i=1,2 ..., I) magnetic field, horizontal x direction of window, magnetic field, horizontal y direction when being respectively i-th; E
xi, E
yi(i=1,2 ..., I) horizontal x direction electric field, the horizontal y direction electric field of window when being respectively i-th;
Part II, reference point observation data far away: comprise J' all survey roads of reference point far away recorded data, builds Natural electromagnetic field signal space-time data matrix X according to reference point observation data far away
r:
Wherein,
for kth (k=1,2 ..., K') Ge Ce road i-th (i=1,2 ..., I) individual time window observation data;
Part III, the transmission current data of artificial field source: record the transmission current value of each artificial field source at each time in window, and assignment is to artificial field source electrode parameter beta:
Wherein, N × I rank matrix β is artificial field source electrode parameter, and only the time window of field source artificial with each changes relevant; N is the number in source, artificial field, β
nibe n-th (n=1,2 ..., N) source, individual artificial field i-th (i=1,2 ..., I) individual time window transmission current value;
Step 4, data processing, calculate natural field tensor impedance and the artificial field tensor impedance of measuring point:
Data processing substep carries out, and the first step, utilizes Natural electromagnetic field signal space-time data matrix X
robtain natural field source polarization parameter α;
If the number of natural field source is M, by K' × I rank matrix X
rbe written as the product form of space matrix and time matrix,
X
r＝U
rα+ε
r,(3)
Wherein,
M × I rank matrix α is natural field source polarization parameter, only with natural field source number and when observing window relevant, α
mi(m=1,2 ..., M; I=1,2 ..., I) be its element, represent the polarization parameter of window during m natural field source i-th; U
rfor X
rit is corresponding to the space modulus of natural field source polarization parameter α, only relevant with natural field source number and Ge Ce road, space,
for its element, represent that jGe Ce road corresponds to the space modulus of m natural field source; ε
rfor X
rin uncorrelated noise;
By to X
rcarry out matrix decomposition, obtain the estimated value of natural field source polarization parameter α;
Second step, utilize the estimated value of natural field source polarization parameter α, the artificial field source electrode parameter beta of observational record and the measuring point signal space-time data matrix X that have obtained, solve the space modulus V of space modulus U and X corresponding to artificial field source that X corresponds to natural field source;
Measuring point observation data responds two parts superposition by the response of natural field and artificial field and forms, and measuring point signal space-time data matrix X is written as the product form of space matrix and time matrix:
Wherein W=[UV], γ=[α β]
*, ε is the uncorrelated noise in X; So try to achieve:
[UV]＝W,(6)
Wherein,
represent associate matrix, superscript
-1representing matrix inverse;
4 × M rank matrix U is only relevant with natural field source number and Ge Ce road, space, U
km(k=1,2,3,4; M=1,2 ..., M) be its element; 4 × N rank matrix V is only relevant with artificial field source number and Ge Ce road, space, V
kn(k=1,2,3,4; N=1,2 ..., N) be its element;
Finally, space modulus U and V tried to achieve is utilized to calculate the natural field tensor impedance Z of measuring point
mTwith artificial field tensor impedance Z
cS:
Wherein, U
h, V
hthe part that horizontal magnetic field surveys road (input end) is corresponded to, with U respectively in representation space modulus U, V
e, V
erepresent respectively and correspond to the part that electric field surveys road:
Need to illustrate, Z herein
mT, Z
cSfor the result of calculation with certain single observation frequency data gained aforementioned, the corresponding electrical information of a certain depth in underground; For different observing frequencies, can independently obtain corresponding Z
mT, Z
cS; And then by receiving the electromagnetic signal of different frequency, the conductive medium distribution of underground different depth can be obtained.
In the Part II of described step 3, Natural electromagnetic field signal space-time data matrix X
rconstruction method be:
When reference point place far away only lays and records 2 orthogonal horizontal magnetic fields survey road, road,
Wherein, K'=2J',
for jth (j=1,2 ..., J') individual reference point far away i-th (i=1,2 ..., I) individual time window horizontal magnetic field measurement vector,
for its horizontal x durection component,
for its horizontal y durection component;
Road is surveyed when reference point place far away increases the orthogonal horizontal component of electric field in laying 2 road, and when recording corresponding data,
Wherein, K'=4J';
for jth (j=1,2 ..., J') individual reference point far away i-th (i=1,2 ..., I) individual time window horizontal component of electric field measurement vector,
for its horizontal x durection component,
for its horizontal y durection component.
In the first step of described step 4, matrix disassembling method can adopt svd, principal component analysis (PCA) and robustness principal component analysis (PCA) etc.For ease of illustrating, the simplest svd is example in the form herein; Concrete steps are:
[
U,
S,
V]＝svd(X
r),(13)
U
r＝(
U)
K'×M,α＝(
SV *)
M×I,(14)
Wherein, the svd of svd representing matrix,
u,
s,
vbe respectively the parameter matrix of svd gained, superscript
*representing matrix transposition; (
u)
k' × Mrepresent
u1 ~ M row composition K' × M rank matrix, (
sV *)
m × Irepresent
sV *m × I rank matrix of the capable composition of 1 ~ M.
The concrete derivation of artificial source's tensor electromagnetic exploration method principle of band of the present invention reference far away is:
In the method, suppose total L field source in recording geometry, comprise M Natural electromagnetic field source and N number of artificial field source, L=M+N; In traditional magnetotelluric method, usually the natural field of hypothesis is uniform plane wave electromagnetic field, now can simplify to think M=2, in the present invention, thinks M=2 equally; The time dependent polarization factor in Natural electromagnetic field source is α, and the time dependent polarization factor of artificial field source is β.
The model of electromagnetic survey is linear time invariant system, and the objects such as the field source related to, the earth and observation station all meet the essential characteristic of linear time invariant system.
Concrete, first, the systematic parameter not time to time change of time-invariant system, excitation is consistent with the time variations of response in other words.Therefore, to a certain natural field source α
m(m=1,2 ..., M), observed responses meets
Wherein, i=1,2 ..., I is window sequence number during observation, m=1,2 ..., M is natural field source label, k=1,2 ..., K is electric field, survey road, magnetic field numbering, α
mibe the natural field source polarization parameter of window during m natural field source i-th, characterize the varying information of field source, not with the spatial position change of measuring point; U
kmfor kGe Ce road corresponds to the space modulus of m natural field source, be distance r and the observation angle of the earth electrical parameter ρ, measuring point and m field source
isoparametric function, does not change in time;
for window during i-th, kGe Ce road corresponds to the natural field response of m natural field source.
Same, to a certain artificial field source β
n(n=1,2 ..., N), observed responses meets
Wherein, n=1,2 ..., N is the label in source, artificial field, β
nibe the polarization parameter of window during the n-th artificial field source i-th, not with the spatial position change of measuring point; V
knfor kGe Ce road corresponds to the space modulus of the n-th artificial field source, do not change in time;
for window during i-th, kGe Ce road corresponds to the noise response of the n-th artificial field source.
Secondly, linear system meets superposition principle, and the combined action of different field source can be considered the superposition of each single field source effect at observation station place.Therefore, actual observation response meets
Wherein, ε
kifor uncorrelated noise, X
kifor kth (k=1,2 ..., K) Ge Ce road i-th (i=1,2 ..., I) individual time window actual observation response.
(17) formula can be written as matrix form,
X＝Uα+Vβ+ε,(18)
Wherein, X is measuring point signal space-time data matrix, and be made up of the observation magnetic field of measuring point and electric field, expansion is as shown in (1) formula; α is natural field source polarization parameter, and β is artificial field source electrode parameter; U is the space modulus corresponding to natural field source, and V is the space modulus corresponding to artificial field source, and ε is uncorrelated noise matrix.The expansion of each parameter is:
In artificial source's frequency domain electromagnetic method of exploration, need to solve each observation station place time-independent space modulus U and V, and from U and V, extract underground electrical parameter ρ.(18), in formula, measuring point signal space-time data matrix X is measuring point receiving end observation data, and artificial field source electrode parameter beta is the numerical value of transmission electric current window at each time of transmitting terminal, is known quantity.And natural field source polarization parameter α and space modulus U and V is unknown quantity, following step is taked to solve it.
The first step, utilizes the time variations item not obtaining natural field source containing artificial reference point far away, i.e. natural field source polarization parameter α; Because reference point far away is enough far away apart from artificial field source, the effect of artificial field source β can be ignored, Natural electromagnetic field signal space-time data matrix X
rcan be written as
X
r＝U
rα+ε
r,(21)
Wherein, U
rfor X
rcorresponding to the space modulus of natural field source polarization parameter α, ε
rfor corresponding uncorrelated noise item.Adopt the mathematical method of matrix decomposition to solve (21) formula, the method for matrix decomposition can use svd, principal component analysis (PCA), robustness principal component analysis (PCA) etc., and this sentences svd is example:
[
U,
S,
V]＝svd(X
r),(22)
U
r＝(
U)
K'×M,α＝(
SV *)
M×I,(23)
Wherein, the svd of svd representing matrix,
u,
s,
vbe respectively the parameter matrix of svd gained, superscript
*representing matrix transposition; (
u)
k' × Mrepresent
u1 ~ M row composition K' × M rank matrix, (
sV *)
m × Irepresent
sV *m × I rank matrix of the capable composition of 1 ~ M.
Second step, the estimated value of sharp natural field source polarization parameter α and the artificial field source electrode parameter beta of record estimate U and V.(18) formula can be written as,
Wherein, X is measuring point signal space-time data matrix; γ=[α β]
*solve item for the first step and second step, its expansion is,
The expansion of item W to be solved is
(24) in formula, the estimated value of W is,
[UV]＝W,(28)
represent associate matrix, superscript
-1representing matrix inverse.
Finally, space modulus U and V tried to achieve is utilized to calculate the plane wave impedance of natural field and artificial field nonplanar wave impedance.With U
h, V
hindicate the part corresponding to horizontal magnetic track (input end) in space modulus U, V, with U
e, V
eindicate the part corresponding to electric road; Concrete, for the measuring point signal space-time data matrix shown in (1) formula,
Define natural field impedance tensor Z
mTmake it satisfied
U
E＝Z
MTU
H,(31)
Or
Satisfy condition because svd decomposes
i is unit matrix, therefore above formula can be reduced to
Similar, definable artificial field impedance tensor
Z
mT, Z
cSbe the to be solved electromagnetic survey interpretation parameters comprising the electrical information in underground, apparent resistivity, phase parameter more intuitively can be further converted to:
Wherein, ω is angular frequency, and μ is magnetic permeability; Z is tensor Z
mTor Z
cNelement, ρ,
for tensor apparent resistivity ρ, phase place
element.
The invention provides a kind of artificial source's tensor electromagnetic exploration method with reference far away, comprise the following steps: while (1) lays measuring point in survey district, laying one or more far away from measuring point apart from surveying low noise district enough far away of district; Artificial field source sends the current value of different size when multiple in window, synchronous recording sends the variations per hour of electric current, surveys the electromagnetic field of measuring point and reference measuring point far away in district; (2) build measuring point data matrix X according to measuring point observation data, build reference data matrix X according to reference point observation data far away
r; (3) reference data matrix X is utilized
rsolve Natural electromagnetic field source electrode parameter alpha, send electric current variations per hour according to the artificial field source of record and calculate its polarization parameter β, recycling α, β and measuring point signal spatio-temporal array data matrix X solves measuring point and corresponds to the space modulus U of natural field source and correspond to the space modulus V of artificial field source; (4) U and V is utilized to solve natural field tensor impedance and the artificial field tensor impedance of each measuring point.Data acquisition of the present invention increases on traditional electromagnetic method basis, artificial field lays one or more reference measuring point far away, based on unified data equation, single treatment obtains natural field tensor impedance and the artificial field tensor impedance of measuring point simultaneously, and then obtains the geoelectric parameter needed for explaining.
Beneficial effect:
The invention provides a kind of artificial source's tensor electromagnetic exploration method with reference far away, one or more reference measuring point far away is laid by increasing on traditional electromagnetic method basis, artificial field, natural field tensor impedance and the artificial field tensor impedance of measuring point can be obtained simultaneously from observation data, improve data separate efficiency; Far away from compared with natural field source electromagnetic method with traditional, this method can by utilizing the high s/n ratio of artificial field signal, and the more rational artificial field impedance tensor obtained in the frequency range (AMT " dead frequency band " as within the scope of 5k ~ 1kHz) that Natural electromagnetic field pickup electrode is weak is estimated; Compared with traditional artificial field source electromagnetic method, this method by extracting high-quality natural field source polarization parameter from reference data far away, and the separation of the different field source responses of measuring point data is carried out with it, occur in the impedance of artificial electromagnetic field source " zone of transition " and " near region " of distortion, more rational natural field plane wave impedance tensor can be obtained and estimate.
Use the present invention, by receiving the electromagnetic signal of different frequency, the conductive medium distribution of underground different depth can be obtained, by observing the Electrical distribution of underground, the electrical characteristics distribution of ground, underground, tectonic structure and distribution of mineral deposits can be found out or solve other engineering, the hydrology and the problems of geo-environment.
Accompanying drawing explanation
Fig. 1 is that recording geometry simplifies noise model.Wherein, Srx, Sry are Natural electromagnetic field source, and Sc is source, artificial field, and Scx, Scy are respectively x, y component of Sc in plane right-angle coordinate; A is observation station, comprises the effect of Srx, Sry, Scx and Scy in observed responses; RR is reference point far away, and distance Scx, Scy are enough far away, and the impact of artificial field source can be ignored, and is mainly the effect of Srx, Sry in observed responses.
Fig. 2 is for this method is to the IMPEDANCE APPARENT RESISTIVITY of Fig. 1 institute representation model observation data, the signal of phase estimation result; Fig. 2 (a) illustrates to the IMPEDANCE APPARENT RESISTIVITY estimated result of Fig. 1 institute representation model observation data for this method; Fig. 2 (b) illustrates to the impedance phase estimated result of Fig. 1 institute representation model observation data for this method; Model is subsurface resistivity is ρ
0homogeneous half space; Horizontal ordinate is observing frequency, and ordinate is for calculating data; ρ
a/ ρ
0represent the apparent resistivity and true resistance rate ρ that calculate according to formula (35)
0ratio,
what expression calculated according to formula (35) looks phase place; ρ
mT,
represent the natural field impedance apparent resistivity, the phase estimation result that adopt the inventive method to obtain respectively, ρ
cS,
represent the artificial field IMPEDANCE APPARENT RESISTIVITY, the phase estimation result that adopt the inventive method to obtain respectively; The xy component products getting impedance tensor in this signal is shown.
Fig. 3 is this method to the IMPEDANCE APPARENT RESISTIVITY of 2 layers of D pattern type, the signal of phase estimation result; Fig. 3 (a) illustrates to the IMPEDANCE APPARENT RESISTIVITY estimated result of 2 layers of D pattern type for this method; Fig. 3 (b) illustrates to the impedance phase estimated result of 2 layers of D pattern type for this method; Model second layer electricalresistivityρ
2with first floor ρ
1ratio be ρ
2/ ρ
1=1/10, the thickness of first floor medium is 100m; ρ
a/ ρ
1represent the apparent resistivity and model first floor electricalresistivityρ that calculate according to formula (35)
1ratio, the meaning such as coordinate axis, legend is identical with Fig. 2; The xy component products getting impedance tensor in this signal is shown.
Fig. 4 is this method to the IMPEDANCE APPARENT RESISTIVITY of 2 layers of G pattern type, the signal of phase estimation result; Fig. 4 (a) illustrates to the IMPEDANCE APPARENT RESISTIVITY estimated result of 2 layers of G pattern type for this method; Fig. 4 (b) illustrates to the impedance phase estimated result of 2 layers of G pattern type for this method; Model second layer electricalresistivityρ
2with first floor ρ
1ratio be ρ
2/ ρ
1=10, the thickness of first floor medium is 100m; The meaning such as coordinate axis, legend is identical with Fig. 3; The xy component products getting impedance tensor in this signal is shown.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is further illustrated.
The method of exploration that the present invention relates to comprises the following steps:
Step 1, Observation Design: determine observed object and depth range, need according to actual depth of exploration and survey district's the earth background conductance rate determination observing frequency scope, and according to the observation interval of required observing frequency determination measuring point and signal sampling rate; According to the design such as the detection of a target and coverage of survey area survey line, measuring point;
Step 2, device are laid: as shown in Figure 1, in survey district, lay artificial field source Sc, measuring point A, and the low noise district simultaneously surveying district enough far away in distance lays reference point RR far away; The laying of artificial field source Sc and the laying of traditional controllable source electromagnetic method transmitting terminal similar, using ground connection HORIZONTAL ELECTRIC DIPOLE or earth-free vertical magnetic dipole as field source, source, an artificial field can be laid, also can lay multiple artificial field source by tensor mode or other forms; Carry out Tensor measuring at observation station A place, lay orthogonal 2 road horizontal magnetic fields and survey road, 2 horizontal component of electric fields survey roads, road; Reference point RR place far away lays orthogonal 2 road horizontal magnetic fields and surveys road, can increase by 2 road horizontal component of electric fields and survey road during conditions permit.
Step 3, data acquisition: at transmitting terminal, utilize artificial field source when multiple, send the current value of different size in window, and record sends the variations per hour of electric current; At receiving end, utilize GPS, the Big Dipper or additive method, the electric field at synchronous acquisition measuring point A and reference point RR place far away and magnetic-field component data;
Step 4, data processing: the electromagnetic field data utilizing observation, according to natural field tensor impedance and the artificial field tensor impedance for the treatment of step provided by the present invention and equations different frequency;
Step 5, post-processed: the natural field tensor impedance obtained according to data processing and artificial field tensor impedance carry out comprehensive data analysis, inverting one-tenth figure and data interpretation.
Fig. 2 is for this method is to the IMPEDANCE APPARENT RESISTIVITY of Fig. 1 institute representation model observation data, the signal of phase estimation result; Model is subsurface resistivity is ρ
0homogeneous half space; Horizontal ordinate is observing frequency, and ordinate is for calculating data; ρ
a/ ρ
0represent the apparent resistivity and true resistance rate ρ that calculate according to formula (35)
0ratio,
what expression calculated according to formula (35) looks phase place; ρ
mT,
represent the natural field impedance apparent resistivity, the phase estimation result that adopt the inventive method to obtain respectively, ρ
cS,
represent the artificial field IMPEDANCE APPARENT RESISTIVITY, the phase estimation result that adopt the inventive method to obtain respectively; The xy component products getting impedance tensor in this signal is shown.Be not difficult to find, utilize artificial source's tensor electromagnetic exploration method of band provided in this article reference far away, obtain corresponding to the apparent resistivity of natural field tensor impedance, phase place and apparent resistivity, the phase place of tensor impedance corresponding to artificial field; Natural field tensor impedance has the meaning of frequency sounding, along with the reduction of frequency, and natural field tensor IMPEDANCE APPARENT RESISTIVITY ρ
awith underground true resistance rate ρ
0unanimously (ρ
a/ ρ
0=1), phase stabilization is 45 °, shows tried to achieve natural field tensor impedance by the impact of artificial field source, can obtain do not distorted the electrical information in underground; In addition, artificial field tensor impedance, in " far field " of artificial field source, is also height, the Mid Frequency (as 10000 ~ 80Hz frequency range in figure) of data, can obtains the frequency sounding data do not distorted equally; And due to the high s/n ratio of artificial field source, in reality, " far field " depth measurement data of artificial field tensor impedance have higher quality than natural field tensor impedance data.
Fig. 3 gives this method to the IMPEDANCE APPARENT RESISTIVITY of 2 layers of D pattern type, the signal of phase estimation result; Model second layer electricalresistivityρ
2with first floor ρ
1ratio be ρ
2/ ρ
1=1/10, the thickness of first floor medium is 100m; ρ
a/ ρ
1represent the apparent resistivity and model first floor electricalresistivityρ that calculate according to formula (35)
1ratio, the meaning such as coordinate axis, legend is identical with Fig. 2; The xy component products getting impedance tensor in this signal is shown.Fig. 4 gives this method to the IMPEDANCE APPARENT RESISTIVITY of 2 layers of G pattern type, the signal of phase estimation result; Model second layer electricalresistivityρ
2with first floor ρ
1ratio be ρ
2/ ρ
1=10, the thickness of first floor medium is 100m; The meaning such as coordinate axis, legend is identical with Fig. 3; The xy component products getting impedance tensor in this signal is shown.
Can find out, under two-layer condition, can obtain and conclusion like aforementioned homogeneous half space condition lower class.Natural field tensor impedance all has the meaning of frequency sounding in whole frequency range, at front end, and natural field tensor IMPEDANCE APPARENT RESISTIVITY ρ
areflection first floor resistivity (ρ
a=ρ
1); Along with the reduction of frequency, natural field tensor IMPEDANCE APPARENT RESISTIVITY ρ
agradually to the transition of bottom-layer resistance rate; At low frequency end, natural field tensor IMPEDANCE APPARENT RESISTIVITY ρ
areflection bottom-layer resistance rate (ρ
a=ρ
2); And phase parameter is all tending towards 45 ° in high and low frequency range, reflect the feature of the first floor to bottom transition at Mid Frequency.Artificial field tensor impedance, in " far field " of artificial field source, is also the high band (if the 10000 ~ 100Hz frequency range in Fig. 3 is with the 10000 ~ 500Hz frequency range in Fig. 4) of data, can obtains the frequency sounding data do not distorted equally; And due to the high s/n ratio of artificial field source, in reality, " far field " depth measurement data of artificial field tensor impedance have higher quality than natural field tensor impedance data; It is worth mentioning that, in reality, 5k ~ 1kHz frequency range is so-called AMT " dead frequency band " frequency range, and in this frequency range, natural field signal is extremely low, and natural field impedance can produce distortion, and artificial field impedance can obtain distortionless impedance data.
Analysis shows, adopt artificial source's tensor electromagnetic exploration method of band provided by the present invention reference far away, natural field impedance and artificial field impedance can be obtained simultaneously, gather the advantage of NATURE SOURCE ELECTROMAGNETIC SOUNDING and artificial field source electromagnetic method, higher-quality tensor impedance data can be obtained at high band, the plane wave tensor impedance data do not distorted can be obtained in low-frequency range; By receiving the electromagnetic signal of different frequency, the conductive medium distribution of underground different depth can be obtained, reach the object of electromagnetic survey.
Claims (4)
1. be with artificial source's tensor electromagnetic exploration method of reference far away, it is characterized in that, comprise the following steps:
Step 1, Observation Design:
Determine observed object and the target exploration degree of depth, design survey line and measuring point; According to the target exploration degree of depth and survey district's the earth background conductance rate determination observing frequency scope, and according to the observation interval of observing frequency scope determination measuring point and signal sampling rate; For each observing frequency, calculate the time domain sampling number needed for single frequency spectrum according to time-frequency convert, window width when determining, utilize observation interval divided by time window width obtain observation corresponding to each observing frequency time window number;
Step 2, laying transmitting terminal device and receiving end device:
Lay transmitting terminal device: in survey district, lay N number of artificial field source, N be more than or equal to 1 integer; Using ground connection HORIZONTAL ELECTRIC DIPOLE or earth-free vertical magnetic dipole as artificial field source; Artificial field source sends the current value of different size when multiple in window;
Lay receiving end device: earth's surface arranges one or more measuring point in survey district; Each measuring point place lays the 2 orthogonal horizontal magnetic fields in road and surveys road and 2 roads orthogonal horizontal component of electric field survey road;
At least 1 synchronous reference point far away is set outside survey district; Lay the 2 orthogonal horizontal magnetic fields in road at reference point place far away and survey road, increase the orthogonal horizontal component of electric field in laying 2 road during conditions permit and survey road;
Step 3, data acquisition:
The electric field at each measuring point of synchronous acquisition and reference point place far away and magnetic-field component data, after carrying out time-frequency convert, obtain the domain observations data that each observing frequency is corresponding; To wherein arbitrary observing frequency, if window number is I during its observation, corresponding observation data comprises transmission current data three parts of measuring point observation data, reference point observation data far away and artificial field source;
Part I, measuring point observation data: comprise and survey measuring point all survey roads recorded data in district; Measuring point signal space-time data matrix X is built according to measuring point observation data:
Wherein, H
xi, H
yi(i=1,2 ..., I) magnetic field, horizontal x direction of window, magnetic field, horizontal y direction when being respectively i-th; E
xi, E
yi(i=1,2 ..., I) horizontal x direction electric field, the horizontal y direction electric field of window when being respectively i-th;
Part II, reference point observation data far away: comprise J' reference point all K' Ge Ce road far away recorded data, builds Natural electromagnetic field signal space-time data matrix X according to reference point observation data far away
r:
Wherein,
for kth (k=1,2 ..., K') Ge Ce road i-th (i=1,2 ..., I) individual time window observation data;
Part III, the transmission current data of artificial field source: record the transmission current value of each artificial field source at each time in window, and assignment is to artificial field source electrode parameter beta:
Wherein, N is the number in source, artificial field, β
nibe n-th (n=1,2 ..., N) source, individual artificial field i-th (i=1,2 ..., I) individual time window transmission current value;
Step 4, data processing, calculate natural field tensor impedance and the artificial field tensor impedance of measuring point:
The first step, utilizes Natural electromagnetic field signal space-time data matrix X
robtain natural field source polarization parameter α;
If the number of natural field source is M, by K' × I rank matrix X
rbe written as the product form of space matrix and time matrix,
X
r＝U
rα+ε
r,(3)
Wherein,
M × I rank matrix α is natural field source polarization parameter, only with natural field source number and when observing window relevant, α
mi(m=1,2 ..., M; I=1,2 ..., I) be its element, represent the polarization parameter of window during m natural field source i-th; U
rfor X
rit is corresponding to the space modulus of natural field source polarization parameter α, only relevant with natural field source number and Ge Ce road, space,
for its element, represent that jGe Ce road corresponds to the space modulus of m natural field source; ε
rfor X
rin uncorrelated noise;
By to X
rcarry out matrix decomposition, obtain the estimated value of natural field source polarization parameter α;
Second step, utilize the estimated value of natural field source polarization parameter α, the artificial field source electrode parameter beta of observational record and the measuring point signal space-time data matrix X that have obtained, solve the space modulus V of space modulus U and X corresponding to artificial field source that X corresponds to natural field source;
Measuring point observation data responds two parts superposition by the response of natural field and artificial field and forms, and measuring point signal space-time data matrix X is written as the product form of space matrix and time matrix:
Wherein W=[UV], γ=[α β]
*, ε is the uncorrelated noise in X; So try to achieve:
[UV]＝W,(6)
Wherein, superscript
represent associate matrix, superscript
-1representing matrix inverse;
4 × M rank matrix U is only relevant with natural field source number and Ge Ce road, space, U
km(k=1,2,3,4; M=1,2 ..., M) be its element; 4 × N rank matrix V is only relevant with artificial field source number and Ge Ce road, space, V
kn(k=1,2,3,4; N=1,2 ..., N) be its element;
Finally, space modulus U and V tried to achieve is utilized to calculate the natural field tensor impedance Z of measuring point
mTwith artificial field tensor impedance Z
cS:
Wherein, U
h, V
hthe part that horizontal magnetic field surveys road is corresponded to, with U respectively in representation space modulus U, V
e, V
erepresent respectively and correspond to the part that electric field surveys road:
2. artificial source's tensor electromagnetic exploration method of band according to claim 1 reference far away, is characterized in that, in the Part II step of described step 3, and Natural electromagnetic field signal space-time data matrix X
rconstruction method be:
When reference point place far away only lays and records 2 orthogonal horizontal magnetic fields survey road, road,
Wherein, K'=2J',
for jth (j=1,2 ..., J') individual reference point far away i-th (i=1,2 ..., I) individual time window horizontal magnetic field measurement vector,
for its horizontal x durection component,
for its horizontal y durection component;
Road is surveyed when reference point place far away increases the orthogonal horizontal component of electric field in laying 2 road, and when recording corresponding data,
Wherein, K'=4J';
for jth (j=1,2 ..., J') individual reference point far away i-th (i=1,2 ..., I) individual time window horizontal component of electric field measurement vector,
for its horizontal x durection component,
for its horizontal y durection component.
3. artificial source's tensor electromagnetic exploration method of band according to claim 1 reference far away, is characterized in that, in the first step of described step 4, matrix disassembling method comprises svd, principal component analysis (PCA) and robustness principal component analysis (PCA).
4. artificial source's tensor electromagnetic exploration method of band according to claim 1 reference far away, is characterized in that, in the first step of described step 4, the matrix disassembling method of employing is svd; Concrete steps are:
[
U,
S,
V]＝svd(X
r),(13)
Ur＝(
U)
K'×M,α＝(
SV *)
M×I,(14)
Wherein, the svd of svd representing matrix,
u,
s,
vbe respectively the parameter matrix of svd gained, superscript
*representing matrix transposition; (
u)
k' × Mrepresent
u1 ~ M row composition K' × M rank matrix, (
sV *)
m × Irepresent
sV *m × I rank matrix of the capable composition of 1 ~ M.
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