CN1052197A - Method in the seismic acquisition configuration that bandwidth increases - Google Patents
Method in the seismic acquisition configuration that bandwidth increases Download PDFInfo
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Abstract
In order to improve the spectral characteristic seismic signal effective system bandwidth of low frequency high amplitude high frequency short arc, a kind of improved geophysical data acquisition system, adopted low frequency end to have to limit the lowcut filter of decay, made from depths low frequency signal in the ground to be included among the output signal.Gain ranging amplifier improves channel gain automatically, amplifies the short arc front end of frequency spectrum.High frequency strengthens wave filter the high fdrequency component of seismic signal is amplified relatively, and therefore channel effective bandwidth obtains increasing.For making system's input noise minimum, strengthening the input stage that wave filter is placed on system.The present invention relates to the frequency spectrum formation method in this system and use the method for this system.
Description
The present invention relates generally to the method in the geophysical data acquisition system, relate in particular to the method in a kind of acquisition system with the geophysics field that makes the Circuits System that system effective bandwidth increases, more particularly the present invention relates to a kind of geophysics acquisition system with Circuits System, this Circuits System can utilize the control of the operator in the course of work of exploration seismic to constitute, to increase the effective bandwidth of earth assembly, earth assembly is talked about the effect of wave filter to seismic signal and geophysics acquisition system, and the present invention has provided the frequency spectrum formation method in such system and the method for this system of use.
Obtaining to such an extent that the register system that for good and all is recorded on the tape especially of geophysical data is widely known by the people in the work on the spot.Purpose for open the application, term " geophysical data " is included in the data obtained in the geologic prospecting environment under the condition of detector that detector can be seismic instrument, seismoreceiver or other type and can is the data of obtaining in the seafari environment under the situation of nautical receiving set etc. at detector.At United States Patent (USP) the 3rd, 819, a kind of typical data field notes system is disclosed in 864.
Have the geophysics acquisition system (also being referred to as seismograph and collection in worksite system) of various designs, the simplest is fixed system, and this moment, the gain amplifier Yu of amplifier was Dinged And and fixing.This class prior art system has the height of prime amplifier level, analog gain stage, lowcut filter, notch filter and each passage by anti alias filter.Multi-channel converter is transformed into modulus (A/D) converter to data channel in order, this one of converter output and the proportional binary signal of input voltage.
An important parameter of this geophysical exploration system is its dynamic range.Dynamic range be defined as can be processed and the maximum input signal (being the signal that its amplitude just is lower than the amplitude that can cause that certain element of system is saturated) of record with can suitably be handled by system and the dB of these two signals of the minimum signal of record (be commonly referred to be signal to noise ratio (S/N ratio) be 1 signal) poor.Dynamic range generally is expressed as ratio maximum and minimum signal, expresses with decibel or dB in typical case.
The progression of the broken sub-signal of A/D converter has determined the precision of system.If be divided into 12, precision was higher when then system's ratio was divided into 8.A/D converter is used for accepting a certain maximum voltage.Importantly, before the described a certain maximum voltage of maximum voltage as close as possible (but being not more than) that is added on the A/D converter, seismic signal (geophysical data) is amplified.Utilize numeral position as much as possible to increase its meaning.The meaning of numeral is relevant with the bits number that is higher than the system noise level recording.In other words, in order to make full use of the geophysics acquisition system, consider from the viewpoint of " meaning ", the A/D amplifier gain reach high as far as possible and do not make electronic circuit saturated before, must amplify signal.To greatest extent when too big, electronic circuit just becomes saturated maximum voltage on being added on A/D converter for converter.
When reaching any concrete gain, digital display circuit can only be operated in the input voltage range of qualification, is unlikely to cause saturated and neither make signal be lower than noise level.Minimum detectable voltage is greater than the threshold voltage or the system noise level of least meaning position.It is such level that maximum can detect voltage, and when being in this level, A/D converter becomes saturated, and And exports the digital number of its maximum possible.The signal that is higher than maximum level is clipped when its emulation mode or after converting digital form to.
System for the special usefulness of petroleum prospecting is used for automatically regulating its gain according to input signal, also is used for writing down the gain that reaches.Many floating-point systems are arranged, and wherein number is that scientific approach with index-mantissa writes down.The output of A/D converter is mantissa, and the gain that reaches is an index.The binary system gain system is the first generation system in these systems; Example is the DFS III that Texas Instruments produces, and this system-gain scope is (single bit shift) in the increment of 6dB.The number of numeral is recorded as 15 word, and gain is with 4 index recording.Utilize the binary gain system, before gain increases, need the calling that several (from 15-60) will be shifted.Individual call need be used for reducing gain.
Gain amplifier register system of future generation is transient floating point (IFP) system.Only need call out with any amount and increase gain with one.The DES IV of Texas InstrumentS and DFS V are the examples of this quasi-instrument.The increment of the gain of these instruments is displacements of 12dB(2 position), but the ratio of other grade can be arranged, as 2: 1(6dB) and 8: 1(18dB) or the like.
When digital signal processing utilized digital filter etc. to be accomplished, its effective dynamic range of signal of considering to be recorded from the viewpoint of most important significance was less than the actual dynamic range that is added in the signal on the A/D converter.For 16 A/D converters (15 mantissa, 1 symbol), the digital processing code element of the effective dynamic range of A/D converter and system is between 40 to 50dB.
When producing a seismic signal, explosive source enters terrestrial time, this signal is actually the composite signal or the summation of many different oscillator signals or ripple, propagate that ， And is reflected or the seismoreceiver of bounce back geophysics acquisition system in the oscillator signal that these are different or the wave direction earth.The frequency spectrum of the signal that produces depends on the shape and the material around thereof of the equivalent of blast and type, blast.In typical earthquake is surveyed, the energy peak in the frequency spectrum of producing in the scope of 10-30Hz, representative value is 15Hz.At the frequency place that is higher than peak value, the every octave of energy reduces 6dB approximately.The shape of the power spectrum that is produced of blowing plant (" air cannon ") and quality crash device is similar to the shape of explosive source.
Can utilize nonlinear sweep to control the spectrum of vibration source (as trade mark is Conoco, the seismic vibrator of Inc. (Vibroseis)).The high-frequency energy of the seismic signal in gained source can increase.
For the power spectrum of being imported the seismic event of the earth by one of above-mentioned source, the earth plays a part attentuating filter.The frequency content of multiple frequency seismic event contains velocity of propagation, and this velocity of propagation is roughly the same concerning any frequency, the 0.5dB but each frequency of composite wave approximately decays on its each wavelength.Attenuation decibel number for every kind of composition of ripple doubles with each letter frequently, the index increment that the decay letter that records with the dB number frequently equals to decay.Therefore, as the function of frequency, seismic event (power spectrum with generation) is exponential damping along with the increase of frequency.
The ripple of propagating by the earth also is exponential damping as the function of time.As a result, the decay spectra of the earth (seeing traffic filter as) is index variation with frequency in time.In any particular moment, the power spectrum of return ripple relies on " earth wave filter " and sensor and works, and this power spectrum is reaching maximal value in 10 to 40Hz frequency range, be exponential damping with frequency then.Consider that the elasticity velocity of wave propagation is well-known, the any particular moment of frequency spectrum after the source is initiated of considering to be produced relies on " earth wave filter " and detector and works, just as " taking snapshot " from a certain degree of depth of the earth energy ingredient to return ripple.The moment that takes snapshot is slow more, and is just dark more to " observation " that form.
From the digital processing system of modern geophysics acquisition system and " effective dynamic range " of A/D converter, " system's effective bandwidth " of the assembly of seismic acquisition configuration and " earth wave filter " can be similar to.In any moment after seismic energy is applied on the earth, the maximum signal amplitudes of spectrum determines that this is because consider setting gain margin Amplifier Gain, to produce one near peaked signal level to A/D converter.Then, effective dynamic range (representing with dB) just deducts from the level of the maximum signal level represented with dB, to produce a signal level that represent with dB, that be lower than maximum signal level, set up the level of attenuation of the earth-acquisition system, be lower than this level of attenuation, just can not have maximum measuring-signal " meaning " as described above.Then, that lower level (or meaning level) makes that just the bandwidth of the effective earth-acquisition system is determined, the bandwidth of this system is recorded with being defined as having most important significance receives the seismic signal band.Effective bandwidth is input in the earth back with take snapshot or the time changes at every turn at seismic signal Chan Sheng And thus defined.
Importantly, the effective bandwidth of the earth-acquisition system is wide as much as possible, can tell the less stratum of relative thickness like this.The limit of resolution can be limited like this, promptly when this limit, two kinds of physical features can be picked out from a kind of effect of physical features.The acquisition system that has increased the effective bandwidth of the earth-acquisition system is simply compared with the acquisition system with less effective bandwidth, has stronger stratum resolving ability.
In prior art, adopted lowcut filter to increase the effective system bandwidth.It is 80Hz making the cutoff frequency of using before the digitizing of geophysics acquisition system that Knapp and Stepples have described a kind of on " geophysics, Vo.51, No.2(1986 February) " the 288th page, the lowcut filter of each octave 24dB.The cutoff frequency of Knapp and Steeples suggestion wave filter should be so not high, trailing edge is so not steep, to such an extent as to all signals of elimination, but important this cutoff frequency in addition will be high enough to make high-amplitude, low frequency signal and the low-frequency noise decay that may bury the low amplitude signal.
General purpose of the present invention provides the method that geophysical data that a kind of increase is used to write down return seismic signal from the earth is adopted system effective bandwidth.
A kind of lowcut filter is provided in the geophysical data acquisition system of the present invention, and it can increase system's effective bandwidth, but can write down return low frequency signal from earth depths simultaneously again.
A kind of lowcut filter of decaying and limiting is provided in the geophysical data acquisition system of the present invention, and the maximum attenuation level was to increase system's effective bandwidth when it had cutoff frequency that an operator selectable selects and low frequency.
A kind of wave filter is provided in the geophysical data acquisition system of the present invention, and it has and is lower than cutoff frequency and constant substantially gain, is higher than cutoff frequency and gain that increases with the jump zone medium frequency and the fixed gain that is higher than the jump zone upper limit.
A kind of frequency spectrum setting wave filter is provided in the geophysical data acquisition system of the present invention, the input that it places system extremely so that system's input noise minimum increases system's effective bandwidth simultaneously.
A kind of frequency spectrum setting wave filter is provided in the geophysical data acquisition system of the present invention, and it has the low cutoff frequency that operator selectable selects, the gain of following this low cutoff frequency after is risen, with the effective bandwidth of the increase earth/acquisition system.
A further object of the present invention provides a kind of method of geophysics work on the spot, utilizes this method, and the work on the spot expert can determine earth spectral characteristic, regulates lowcut filter parameter and frequency spectrum setting filter parameter that decay limits; So that strengthen the spectral characteristic of survey of the earth system, improve the resolution of the signal that obtains thus at the signal at the return certainly concrete energy and position of the earth place.
Utilize a kind of geophysics acquisition system can reach the aforementioned purpose of the present invention and other advantage and characteristics with the input stage that has frequency spectrum setting wave filter.This system also comprises the lowcut filter that a decay limits, and frequency spectrum setting wave filter has selectable low cutoff frequency and gain selectable and that follow after low cutoff frequency is risen.The cutoff frequency of decay during low frequency and low disconnected wave filter also is that operator selectable is selected.
In using geophysics acquisition system of the present invention, geophysics is gathered the expert or the operator at first will be under the situation of no systematic influence, with lowcut filter and frequency spectrum setting wave filter, carry out the test data sheet of system, locate constantly from the return wave spectrum peak value of the earth at one or several that produces seismic signal determining.The decay of cut-off filter that cutoff frequency, decay limit and frequency spectrum setting wave filter or the gain person of being operated are chosen as the function of the frequency of test spectrum peak.
By with reference to the accompanying drawings, it is more clear that purpose of the present invention, advantage and characteristics will become, and identical label is represented identical part in the accompanying drawing, and most preferred embodiment of the present invention has been shown in the accompanying drawing.
Fig. 1 is the block scheme of the typical geophysical data acquisition system of prior art;
Fig. 2 is the block scheme of geophysical data acquisition system of the present invention, and this system has adopted an input stage with frequency spectrum setting wave filter, and frequency spectrum setting wave filter is followed the lowcut filter that decay limits;
Fig. 3 A is the embodiment that has adopted the input stage of single termination frequency spectrum setting wave filter, it is characterized in that low cutoff frequency and the gain rising that is higher than this low cutoff frequency;
Fig. 3 B is the embodiment that has adopted the input stage of single termination frequency spectrum setting wave filter, it is characterized in that the operator low cutoff frequency that can select and the gain rising that is higher than this frequency;
Fig. 4 A has adopted the embodiment of the differential input stage of frequency spectrum setting wave filter, it is characterized in that the low cutoff frequency that the operator can select and be higher than gain this frequency and that the operator can select rising;
Fig. 4 B is the synoptic diagram of Fig. 2 geophysics acquisition system differential input stage most preferred embodiment, comprises a frequency spectrum setting wave filter, is characterised in that the operator low cutoff frequency that can select and the gain rising that is higher than this frequency;
Fig. 5 has low cutoff frequency and the frequency spectrum setting filter gain of gain rising and the relation curve between the logarithm frequency that operator selectable is selected;
Fig. 6 is the example that produces the attenuation spectrum of afterwards some moment place's earth and detector with the earthquake signal, and this example shows the increase of frequency spectrum setting filter system effective bandwidth;
Fig. 7 A is a kind of embodiment that hangs down disconnected wave filter that decays and limit, and it is characterized in that cutoff frequency and the fixed level of decaying at the low frequency place that is lower than this cutoff frequency;
Fig. 7 B is the relation curve between decay and the logarithm frequency, and it shows the frequency response of Fig. 7 A circuit;
Fig. 7 C is the synoptic diagram of the wave filter most preferred embodiment that comprises shown in Fig. 7 A that the decay of the geophysics acquisition system of two-stage filter limits, and this embodiment is characterised in that low cutoff frequency that operator selectable is fixed and in the level of attenuation at low frequency place;
Fig. 8 produces the back at place of some moment with the earthquake signal, and the example of the attenuation spectrum of the earth and detector, this example show the increase of system's effective bandwidth of the lowcut filter that limits in these place's decay of a certain moment constantly.
Fig. 1 is the block scheme of the geophysical data acquisition system of typical, prior art.Usually provide input with a cable that includes many signal conductors to dual-hinge line to a such system.Under the situation that submarine earthquake is surveyed, every pair of twisted-pair feeder is connected to seismoreceiver or geophone package at a certain remote location.Under the situation that submarine earthquake is surveyed, twisted-pair feeder is to being contained in the ribbon, and this ribbon relates to the back of dragging at a detecting ship, and these lines are to being connected to underwater seismic detector or underwater seismic detector group at remote location.In arbitrary situation, many data channels can be inhaled collecting system by data and give record.Every pair of twisted-pair feeder provides a differential signal, and this differential signal and ground are irrelevant.
With reference to Fig. 1, such signal is coupled to the input stage or the prime amplifier 25 of a channel of this data gathering system by lead-in wire 1,2.This signal enters differential amplifier 3, then by providing a difference output to differential amplifier 7 on the differential amplifier 3 online 5,6.Design amplifier 7 provides high common mode inhibition, and this differential signal is converted to single-ended signal on the line 8.Amplifier 3 and amplifier 7 are formed input stage or prime amplifier 25.Amplifier 3 should have lower equivalent input noise and high gain as much as possible.High-gain can make the signal of receiving be amplified to sufficiently high level, so that the noise that provides of device is compared insignificant with the noise that amplifier 3 provides subsequently.Amplifier 7 has usually and is tending towards 1 gain.
Other device that is coupled to this data gathering system in order to the signal with cable is known, the 3rd, 778, and 759 and 3,972, open in No. 020 U.S. patent documents.
The output terminal of this prime amplifier is connected to lowcut filter 9 by lead-in wire 8, and the function of lowcut filter 9 is decay low frequency signals.The output of this lowcut filter 9 is coupled to high-stop filter 11 by line 10, high-stop filter attenuates high frequency signals, and the slope that has 72 decibels of every octaves usually.Since simulating signal will be in this system later a bit on sampling with quantize, so high-stop filter 11 is used for guaranteeing that the frequency that is higher than 1/2 sampling frequency all is attenuated, and turns back to prevent influential frequency.
The output terminal of high-stop filter 11 is connected to notch filter 13 by lead-in wire 12, and the rejection band of notch filter 13 is the center with power supply (line) frequency, with near any signal of decay from picking up the power lead.High-stop filter and notch filter are known in the present technique field, do not need to give unnecessary details at this.Notch filter in some systems is prior to high-stop filter, and perhaps high-stop filter also is known prior to lowcut filter.
The output terminal of this notch filter 13 is connected to the input end of low drift direct current amplifier 15 by lead-in wire 14.Amplifier 15 has usually and is tending towards 1 gain and low output impedance.It is DC coupling that the requirement of low drift results from the surplus of this data acquisition system (DAS).The output terminal of amplifier 15 is connected to multi-way switch 17 by lead-in wire 16, multi-way switch 17 is a semiconductor switch normally, this switch is closed in the extremely short period, so that the data sample of illustrated channel is provided by 18 input ends to gain margin amplifier 19 that go between.
For that part of to this data gathering system of described point, i.e. channel between input signal and the line 18, each channel of the input data that write down for this system all is two bending.Various multiplier switch such as multi-way switch 17 is closed in succession in short time interval, so the simulation sample value from the consecutive order of different pieces of information channel is provided on lead-in wire 18.
These different sample values are fed to A/D converter 20 by line 21 after being amplified by amplifier 19.Digital output signal is fed to register 22 by lead-in wire 23.This register 22 comprises a blattnerphone in most preferred embodiment.As above Gai Shu geophysical data register system provides the digitizing sample value of the multichannel simulated data that receives from this cable on tape.
The A/D converter of the E.B.B. of current use has 80～90 decibels dynamic range, but can be above 120 decibels.When can receiving sample value on lead-in wire 18, gain margin amplifier 19 automatically regulates its gain according to sample value at each counting.This gain obtains adjusting, and necessarily falls within the permissible range of this A/D converter to guarantee the amplifying signal that presents on lead-in wire 21.The actual gain of amplifier 19 location offers register 22 by line 25, so that and the record together of the corresponding digital sample value on the line 23.An a kind of example of suitable gain margin amplifier is the 3rd, 684, and is open on No. 968 U.S. patent documents.The specific embodiment of various parts shown in Figure 1 all is presented in digital field (field) system that the Texas Instruments Inc (Texas Instruments Incorporated of Dallas) of Texas Dallas provides, and trade mark is DFS V.
Fig. 2 is the block scheme of geophysics acquisition system of the present invention, and it is similar to the block scheme of Fig. 1, but it contains the input stage 30 that comprises frequency spectrum setting cut-off filter, also contains the lowcut filter level 35 that decay limits.The system of Fig. 2 contains a high capable pick-up suppressor circuit 40, this circuit with analog information through D/A 42 feed back to gain margin amplifier 19 ', the needs that high row pick-up rejector 40 has been got rid of the notch filter of prior art, it is at unsettled U.S. Patent application 835, given description in 140, this application has transferred assignee of the present invention.Its working condition is not in this description, but it is listed for your guidance.An additional lowcut filter 13 ' to filter extremely low frequency is provided in this channel.
Fig. 3 A is the schematic diagram of input stage 30 that has the frequency spectrum setting cut-off filter 50 single-ended embodiment of differential amplifier 43 and its point.Fig. 5 is the gain and the graph of relation of logarithm frequency, and this figure briefly draws the gain and the frequency characteristic of the circuit of the frequency spectrum setting cut-off circuit 50 of Fig. 3 A and Fig. 3 A, 3B, 4A and 4B.Gain was G1 when input stage 30 was preferably in direct current frequency, and direct current frequency is lower limiting frequency f
1, at f
1After, gain increases along with the rising of frequency, up at cutoff frequency f
2The time gain G that arrive to promote
2The time till.On gain (or decay) and logarithm frequency relation curve map, at this, the gain that cutoff frequency is stipulated more than 3 decibels or following straight line approaches (or decay) response.
An important feature of the present invention has disposed frequency spectrum setting cut-off circuit 50 exactly in input stage 30.Usually, the gain of input stage is high more, the equivalent input noise of this system is just low more, configuring spectrum setting cut-off circuit 50 provides the raising of gain in input stage, and this circuit is placed on that to be placed on the equivalent system noise that causes after the input stage than it in this system before arbitrary higher noise circuit low.
The seismic signal that returns from the earth is from sensor, and for example seismoreceiver is delivered to lead-in wire 1,2(Fig. 3 A), promptly deliver to differential amplifier 43, the gain of this amplifier 43 is 4 or greater than 4.Output on the lead-in wire 44 is added to the positive input terminal of the operational amplifier 51 of frequency spectrum setting cut-off filter circuit 50.Circuit 50 comprises capacitance-resistance (RC) feedback network, and this feedback network is added to the output signal on the lead-in wire 55 negative input end of operational amplifier 51 through lead-in wire 56.The DC current gain G of frequency spectrum setting cut-off circuit 50
1Depend on R
1With R
1, R
2, R
5The ratio of sum.High-frequency gain G
2It is resistance R
1, R
2, R
3And R
5Function.Cutoff frequency f
1And f
2Between gain raise with approximate 6 decibels/octave (20 decibels/decimal system) speed.Lower limiting frequency f
1It is capacitor C
1And resistance R
1, R
2, R
3And R
5Function.Selected lower limiting frequency f
1, DC current gain G
1And gain inequality (or gain promotes) (G
2-G
1) (its unit for decibel) just can determine R
1, R
2, R
3, R
5And C
1Adaptation numerical value.
The input stage of Fig. 3 B is identical with the form of the input stage of Fig. 3 A, and just in the circuit of Fig. 3 B, that be similar to Fig. 3 A circuit resistance value and capacitance can utilize switch S
1, S
2, S
3, S
4, S
5Change its numerical value.Capacitor C1 passes through Closing Switch S in circuit
4Or S
5Or closed S of while
4, S
5Can obtain 3 numerical value.R
31 of 4 numerical value can be by opening or Closing Switch S
2, S
3, make and R
3' R in parallel
3" or R
3" insert or do not insert and obtain.Switch S
1Can close on a plurality of different points (201～204), changing the output signal value on the output lead 55, this signal value is through 56 negative input ends that feed back to operational amplifier 51 that go between.The resistance of Fig. 3 B and the representative value of electric capacity are shown in Table 1.
Table 1
R
187Ω
R
2′ 261Ω
R
2″ 1044Ω
R
2″′ 4176Ω
R
525056Ω
R
3′ 1516Ω
R
3″ 1129Ω
R
3″′ 566Ω
C
1′ 1μF
C
1″ 1.625μF
Can find out switch S significantly from resistance value shown in the table 1 and capacitance
1Control the DC current gain C of this circuit
1
If switch S
1Be connected on position 201,202,203 or 204, then be equivalent to the R among Fig. 3 A
1And R
2Fig. 3 B in R
1Effective value (R
1Eff) and R
2Effective value (R
2Eff) and the current gain of circuit 50 all list in the table 2.
Table 2
Position of the switch DC current gain R
1Eff R
2Eff
201 5.5 5568 0
202 22 1392 4176
203 88 384 5220
204 352 87 5481
Switch S
2And S
3Control this circuit and be higher than DC current gain G
1Lifting gain (G
2-G
1), unit is a decibel.
Because R
3Mark contrasting and capacitor C
1' or C
1" numerical value of the resistance that is connected in series is listed in the table 3 from the amount of gain that DC current gain promotes.
Table 3
Switch S
2And S
3Promote approximately and promote R approximately
3
The position of the switch (decibel) (gain)
S
2And S
3All open 12 4.01 1516
S
2Closed 18 8.0 647
S
2And S
3All closed 24 16.01 302
S
3Closed (not using)
Switch S
4And S
5Control the lower limiting frequency f of this circuit
1, mark C
1As with resistance R
3', R
3" and R
3The electric capacity of the electric capacity that is in series of combination, for S
4And S
5The various position of the switch with lower limiting frequency f
1List in the table 4 its upper cut off frequency f
2Also list in this table.
Table 2,3,4 shows bright run duration on the scene, under operator's control, by gauge tap S suitably
1～S
5Just can set DC current gain G
1, lower limiting frequency f
1With circuit 50(among Fig. 3 B and circuit 30) lifting that increased gain (G
2-G
1), its unit is a decibel.
The frequency spectrum setting that Fig. 4 A shows in an embodiment circuit directly accepting the differential input signal on the lead-in wire 1,2 ends input stage 30.Amplifier 60,61 can be two transistors, and lead-in wire 1,2 is connected with its base stage.The output of the collector C of amplifier 60,61 by being added to operational amplifier 70 with going between 64,65 difference, and the output of operational amplifier 70 (being the output of the frequency spectrum setting of Fig. 4 A embodiment by input stage 30) is added to the positive input terminal (or emitter) of amplifier 60 and 61 through the feedback network identical with feedback network function shown in Fig. 3 B.Switch S
1And S
1' interlock is to guarantee by R
1Add R
2' with R
2" add R
2" the selected DC current gain of suitable ratio identical.Cutoff frequency f
1Select with the method that Fig. 3 B is identical, i.e. selector switch S
4And S
5The position make C
1"/2, or C
1'/2, or C
1'/2 add C
1" the method for/2 places in circuit.By with switch S
2And S
3The location makes 2R
3" and 2R
3' parallel connection, or make 2R
3" and 2R
3' parallel connection, or make 2R
3" and 2R
3" all with 2R
3' parallel connection, frequency spectrum promote (unit is a decibel), i.e. high-frequency gain G
2Deduct low-frequency gain G
1, can select.Resistance value in the table 1 is corresponding with those resistance and electric capacity shown in Fig. 4 A with capacitance.
Resistance R in 1 megaohm
8And R
9Between the common-mode signal that presents of P point place through operational amplifier 71, pass through resistance R again
10And R
11Be added to the emitter of transistor amplifier 60 and 61.The resistance R of Fig. 4 A
10And R
11Preferably 2087 ohm.Transistor 60 and 61 is half of the pair transistor look MAT-01 that can buy on the market, and operational amplifier 70 is the circuit LT1008 that can buy on the market.
Fig. 4 B illustrates the most preferred embodiment of the frequency spectrum setting of Fig. 4 A by input stage.Transistor 60 and 61 is each one side of something of the bag MAT-01 that bought on the market, 15 volts of power supplys resistance R by 100 kilohms
12And R
13Be added to transistor (collector).Operational amplifier 70 is the circuit LT1008 that bought on the market.Common mode operational amplifier 71 is half of the circuit LF442 that bought on the market, and 10 volts of reference power sources are added to its positive input terminal.
Switch S
1And S
1' with the switch S of Fig. 4 A
1And S
1' corresponding, be Control of Voltage field effect transistor (FET).Be added to the voltage of lead-in wire on 80～83 respectively and make corresponding FET conducting, thus, the emitter of transistor 61 and 60 is connected to resistance R
1, R
2', R
2", R
2" and R
5Between.
Switch S
2And S
3Switch S corresponding to Fig. 4 A
2And S
3, be Control of Voltage FET, the voltage that is added to respectively or simultaneously on the lead-in wire 90 and 91 makes switch S
2And S
3Closed.Switch S
4And S
5Switch S corresponding to Fig. 4 A
4And S
5, also all be Control of Voltage FET, the voltage that is added to respectively or simultaneously on the lead-in wire 92 and 93 makes the EFT switch S
4And S
5Closed.
Be added in the voltage of lead-in wire on 80～83 in order to adjust the gain G of input stage 30
1(gain G
1And G
2And lower limiting frequency f
1In Fig. 5, schematically defined).Be added in that the voltage of lead-in wire on 80 pays with " low gain G
1"; Be added in that the voltage of lead-in wire on 81 pays with " middle low gain G
1"; Be added in that the voltage of lead-in wire on 82 pays with " middle high-gain G
1"; And be added in that the voltage of lead-in wire on 83 pays with " high-gain G
1".
Be added in the voltage of lead-in wire on 92 with lower limiting frequency f
1Adjust to high value (seeing above-mentioned table 4), the voltage that is added on the lead-in wire 93 provides lower limiting frequency f
1, the voltage that is added on the lead-in wire 92 and 93 provides lower cutoff frequency.Making alive can not provide from gain G on lead-in wire 90 or 91
1To G
2Low gain promote, the voltage that is added on the lead-in wire 91 can provide from gain G
1To G
2Medium gain promote, the voltage that is added on the lead-in wire 90 and 91 can provide high gain to promote.Preferably power at the voltage that applies on the lead-in wire 80～83 and 90～93 by the digital calculator under operator's control.
Fig. 6 illustrates earthquake the interval attenuation spectrum of earth typical case afterwards takes place, and it is the function of time.The curve representation earth shown in the dotted line is to attenuation of seismic wave, and this is the function of time and frequency.Time can be considered a ginseng to the greatest extent, can think each time die-away curve the instantaneous die-away curve of earth frequency decay like this.The maximum point of every curve has all been annotated A
1, A
2... in the system of Fig. 2, its gain of gain margin amplifier 19 ' can automatically regulate, thereby the combined seismic signal of amplitude peak and be not more than the peak signal of A/D converter 70 ' confirmed.For every time curve of Fig. 6, A/D converter 70 ' and the dynamic range of the digital processing step followed of this A/D converter be taken as 48 decibels, thereby determined efficient system bandwidth (certainly, 48 decibels is an example, in order to explain the beneficial aspect of the present invention).For example from maximum point A
2The frequency spectrum of T=1 second of measuring extends to the P that is about 127 He Zhi
1Point produces line 301.For 1 second seismic event that receive, that return after earthquake takes place, the bandwidth of the earth is about 127 He Zhi (seismic acquisition configuration of Fig. 2 is considered to flat bandwidth shape on interested frequency).
Represent the result that the frequency spectrum of application drawing 3B or 4B circuit promotes at every earth and the block curve above the sensor spectrum curve (dotted line).For example, lower limiting frequency is set in about 20 He Zhi, and it is 24 decibels that the frequency spectrum that obtains promotes.Can see that for the T=1 frequency spectrum of second, frequency spectrum promotes the additional bandwidth that produces about 33 He Zhi.Can also obtain the increase bandwidth of each frequency spectrum of the moment after the earthquake, yet effectively the increase of earth acquisition system bandwidth diminishes in proportion.Increase to about 54 He Zhi from about 51 He Zhi in effective earth acquisition system bandwidth of T=3 during second, promptly increase by 3 He Zhi.
Be in operation, the seismic survey expert makes a test earlier and impacts, the seismic signal that record returns from the earth, determine the frequency of T=1.0 or 2.0 seconds time-frequency spectrum peak dot nidus for example of a certain moment after earthquake takes place then, such frequency spectrum peak dot can be determined with fast Fourier transform technology.The lower limiting frequency f of Fig. 3 B or 4B circuit
1Should be set in the spectral peak dot frequency that is determined identical or greater than its frequency place, the selected then amount of gain that promotes for the interested concrete degree of depth, improves the efficient system bandwidth best.
Referring now to Fig. 7 A, best circuit 100 is described, in two cover input stages (Fig. 7) of the present lowcut filter 35 of this circuit body.Fig. 7 A circuit is the second rank lowcut filter of a modification, and this wave filter has decay and the logarithm frequency response relation curve shown in Fig. 7 B.The response of this circuit is similar to common lowcut filter, and below cutoff frequency fc, along with the decline of frequency, decay increases, yet below cutoff frequency fc, in frequency f
AReach after the maximum attenuation A maximum when maximum, when direct current frequency (being zero frequency), arrive decay point of accumulation A() in dB.
Though lowcut filter that decay of the present invention limits and the frequency response that it has been shown in Fig. 7 B have been shown in Fig. 7 A and 7C, and the lowcut filter that other decay limits also can adopt.Other this wave filter must have such frequency response, promptly it is characterized in that having substantially invariable decay when low frequency, is higher than frequency f corresponding to Fig. 7 B in frequency
ADuring maximum frequency, decay reduces.
With reference to the circuit 100 of Fig. 7 A, regulate variable resistor R
BTo determine the required frequency range minimum attenuation point of accumulation A that stops, regulating variable resistor R2A and R4A to set low cutoff frequency fc.Cutoff frequency and decay that following table 5 illustrates by the various switches adjusting realizations of Fig. 7 A limit (decibel).The switch S of variable resistor R2A
20～S
60Switch S with variable resistor R4A
20'～S
60' interlock.Table 5 following resistance value of hypothesis and capacitance, " 1 " expression switch closure in the table 5; " 0 " expression switch opens.
R
5＝1KΩ C639＝0.15μf
R
10＝249088Ω C638＝0.15μf
R
20＝296716Ω RB1＝29698Ω
R
30＝129625Ω RB2＝13887Ω
R
40＝62585Ω
R
50＝30016Ω
R
60＝13905Ω
2R5＝2000Ω
2R10＝498176Ω
Or the like.
Just as shown in table 5, can change the lowcut filter that this decay limits, with a plurality of cutoff frequency fc that produce three different decay limit A and change from about 3HZ to 104HZ.Shown in the curve of Fig. 7 B, the frequency f A of maximum attenuation
MaxWith the relation of cutoff frequency fc be factor K.Factor K is maximum attenuation frequency f A
MaxRatio with the normal cut-off frequency fc of circuit.Table 6 has been set up decay limit A and factor K, octave than (fA under fc
MaxThe frequency multiplication number of passes that part occurs) and the maximum attenuation A that represents with decibel
MaxRelation.
Table 6
A(db) the K octave compares A
Max(db)
-15.2 2.22 1.15 -20
-18 3.22 1.56 -24
-24 3.67 1.88 -33
A kind of optimum implementation of the lowcut filter 35 of the decay restriction of Fig. 7 C presentation graphs 2.With connecting shown in Fig. 7 A by above-mentioned table 5 and 6 two identical circuit determining 100.Switch S
20-S
60, S
20'-S
60', S
80And S
90Be those voltage-controlled field effect transistors as Fig. 4 B.Be added to 5 lead L
1-L
5Variable resistor R with each circuit 100
2AAnd R
4AOn voltage cut-out S
20-S
60And S
20'-S
60'.Two lead L of each circuit 100
7And L
8Gauge tap S
80And S
90By-pass switch S
100By lead L
6Control, operational amplifier 106 the most handy LT1012 operational amplifiers available on the market.
Fig. 8 is the same with Fig. 6, and expression is as the decay spectra of the typically section of the function of the time that produces from earthquake, and the dashed curve representative is as the ground decay for seismic event of the function of time and frequency.As shown in Figure 6, the time is regarded as a parameter, so can the die-away curve when per see " transient state " of the frequency decay on ground as.Minimal attenuation (the maximum point A on the curve representation ground of T=2.0
4) occur in 16HZ.The effective dynamic range of the 48db of A/D converter/mathematics manipulation system has caused at P
3The effective system bandwidth of about 74HZ of point.
By the lowcut filter circuit 35 that the decay of inserting Fig. 7 C limits, the lowcut filter of decay synthetically, sensor decay and decay restriction (for the purpose of representing supposes not have frequency spectrum intensifier circuit 30) has just produced die-away curve 500.Its maximum signal point occurs in the some A of about 8HZ
7Resultant curve 500 drops to an A
7Under the frequency of 48db be the some P of about 98HZ
4Increase for the effective system bandwidth of T=2 second is about 24HZ.Relatively early moment the effective system bandwidth increase bigger; Transient state 3(to the later moment is T=3.0 second) because the increase of the decay effective system bandwidth on the low frequency slightly reduces.
At work, the seismic prospecting expert is by being added to digital control voltage lead 21-28 gauge tap S effectively
20-S
60, S
20'-S
60', S
80, S
90And S
100, by adjusting circuit 35(Fig. 7 C) the decay and the cutoff frequency of circuit 100, control the shape of curve 500.
Because the source that the energy produces spectrum and above-described the decay, vibroseis has the excess quantity of a low frequency.FFT(fast fourier transform by the checkout area) the curve map expert determines the frequency of spectrum peak, sets the parameter of the lowcut filter of decay restriction then, (is the A of Fig. 7 B so that provide maximum decay at the peak value of approximately testing frequency spectrum
Max).Relation of plane is set the frequency f c that decay limits lowcut filter under the basis then:
The frequency of fc=K test spectrum peak
Here K determines with reference to above-mentioned table 6.Select fading margin (A that represents with decibel) according to the degree of depth on the stratum that will draw with the resolution that increases.The depth capacity of low frequency loss having reduced the to obtain bass reflex on fading margin, maximum decay produces maximum bandwidth increases best thin layer resolution, but dark bass reflex has been decayed.
Vibroseis (such as vibrations equipment) changes its main energy into the surface wave of propagating along the face of land with low speed, and with reflection interference from interested buried regions, usually suppressing cross by source battle array (a plurality of oscillators on a line) and attempt fails the combination of the reception battle array of ripple and controls these cross and fail ripple, owing to the difference of the height in the battle array and because the reflection that is arrived on an angle has the tendency of smearing these reflections for these long gust, thisly smear the effect of playing a high frequency filter, if battle array is reduced, then the interference surface ripple will take the major part of dynamic recording range.
Can be used to reduce this surperficial wave amplitude to decay restriction lowcut filter of the present invention.Adopt apparent arrival rate and the noise analysis of time of arrival of determining this interference can analyze this surface wave problem well.Detailed inspection during these ripples has provided the rough myopia of spectrum peak.More accurate spectrum peak determines that method is that fft analysis is made in the time of arrival and the skew of interference wave interested.In case determined spectrum peak, then the selection of wave filter is the same with the description to vibroseis.
Certainly, as mentioned above, the decay restriction lowcut filter 100 that the frequency spectrum of circuit 30 forms wave filter and circuit 35 can be provided with their parameter, promoting ground acquisition system bandwidth, thereby has increased the high-resolution effective system bandwidth for the buried regions district on ground.
Multiple modification and change for described method all are obvious for the technician in above-mentioned field, and they all can not break away from spirit of the present invention.Therefore, these variations all are included among claims.The claim of only having the right is a limitation of the invention.The describing mode of used proposition embodiment is interpreted as a kind of explanation rather than limits.
Table 5
Gain switch
S20-S60 and S20 '-S60 '
S60 S50 S40 S30 S20
S60 ' S50 ' S40 ' S30 ' S20 ' fc nominal value
0 0 0 0 0 3.0
0 0 0 0 1 5.5
0 0 0 1 0 8.7
0 0 0 1 1 11.2
0 0 1 0 0 14.7
0 0 1 0 1 17.1
0 0 1 1 0 20.2
0 0 1 1 1 22.6
0 1 0 0 0 27.0
0 1 0 0 1 29.3
0 1 0 1 0 32.3
0 1 0 1 1 34.6
0 1 1 0 0 38.0
0 1 1 0 1 40.2
0 1 1 1 0 43.2
0 1 1 1 1 45.4
1 0 0 0 0 52.9
1 0 0 0 1 55.1
1 0 0 1 0 57.9
1 0 0 1 1 60.1
1 0 1 0 0 63.2
1 0 1 0 1 65.3
1 0 1 1 0 68.0
1 0 1 1 1 70.1
1 1 0 0 0 73.9
1 1 0 0 1 75.9
1 1 0 1 0 78.6
1 1 0 1 1 80.6
1 1 1 0 0 83.5
1 1 1 0 1 85.5
1 1 1 1 0 88.0
1 1 1 1 1 90.0
S80 S90 A
00 unlimited f
cNominal value
1 0 24 dB 1.06 f
c
0 1 -18 dB 1.12 f
c
1 1 -15.2 dB 1.15 f
c
Claims (5)
1, a kind of intermediate frequency spectrum manufacturing process at geophysical data acquisition system, its geophysical data acquisition system has at least one passage, is used for record and the proportional signal of earthquake motion, and the method comprising the steps of:
Amplify described signal at low frequency with first gain;
Amplify described signal at high frequency with second gain;
Amplify described signal for the frequency between low cutoff frequency and the higher cutoff frequency with the gain of an increase;
Thereby increased the effective bandwidth of described system.
2, a kind of frequency spectrum formation method in geophysical data acquisition system, this system has at least one channel, is used for record and the proportional signal of earthquake motion, and the method comprising the steps of:
At low frequency with the substantially invariable damping capacity described signal of decaying;
For the detailed decay of the frequency on the low fixed frequency for an increase;
Thereby increased the effective bandwidth of described system.
3,, comprise that also a frequency on cutoff frequency fc stops the step of described increase decay according to the method for claim 2.
4, a kind of method of using improved geophysical data acquisition system, this system has at least one data channel, be used for record and the proportional electric signal of earthquake motion, described system has a spectrum shaping circuit in described channel, it is characterized in that, can select first gain the low frequency operator, the operator can select low cutoff frequency f
1, and can select the gain that increases, the method comprising the steps of:
Record from test record with the proportional electric signal of earthquake motion;
Determine the approximate frequency of the peak amplitude of sort signal from the decay-frequency spectrum of described signal;
The low cutoff frequency f of input stage
1Be provided with to such an extent that the frequency with described peak amplitude is identical basically;
The amount of gain that increases is set a value, to improve the effective system bandwidth characteristic.
5, a kind of method of using improved geophysical data acquisition system, described system has at least one data channel, be used for record and the proportional electric signal of earthquake motion, there is a lowcut filter in described system in described passage, its decay-frequency response should be characterised in that, the operator can select cutoff frequency fc, can select limited damping capacity near the low frequency operator who levels off to the zone of the maximum attenuation amount under zero-frequency and the described cutoff frequency, described maximum attenuation amount is more than or equal to described limited decay, and the method comprising the steps of:
Being set at the gain that zero system increases, record from test record with the proportional electric signal of earthquake motion;
Determine the frequency of the peak amplitude of described signal from the decay-frequency spectrum of described signal;
The frequency setting of the maximum attenuation of described lowcut filter in the frequency that is approximately the spectrum peak of determining by described test record;
Determine the limited damping capacity of described decay restriction cut-off filter, to improve the effective system bandwidth characteristic.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US107,500 | 1987-10-09 | ||
| US07/107,500 US4875166A (en) | 1987-10-09 | 1987-10-09 | Bandwidth enhancing seismic acquisition system and method |
| CN88109120.0A CN1017094B (en) | 1987-10-09 | 1988-10-08 | Bandwidth enhancing seismic acquistion system |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN88109120 Division | 1988-10-08 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1052197A true CN1052197A (en) | 1991-06-12 |
| CN1016822B CN1016822B (en) | 1992-05-27 |
Family
ID=25742533
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 90109974 Expired CN1016822B (en) | 1987-10-09 | 1988-10-08 | Bandwidth enhancing seismic acquisition system and method |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN1016822B (en) |
-
1988
- 1988-10-08 CN CN 90109974 patent/CN1016822B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CN1016822B (en) | 1992-05-27 |
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