cgg模块RAMUR参数.doc

GeneralThe module removes multiples (characterized as events with a slower velocity) orlinear events from a trace gather. The Y-flag must be set at the end of every elementarygather. Input traces must be ordered according to the spatial co-ordinate usedfor the Radon transform. Traces are output in the order of the input elementarygathers.Anti-multiple filtering (first option MA)The module computes a model of primary and multiple events. This computation isbased on data decomposition into user-defined parabolas and performed using ahigh-resolution, de-aliased least-squares method in the frequency-space (f-x)domain for each frequency of the pass-band defined by FMIN and FMAX. Eventscorresponding to parabolas with a greater curvature are considered to be multiples.Events corresponding to parabolas smaller than this threshold are considered to beprimary events. The zone limits between primaries and multiples is user defined(DTCUT). The difference between data and the sum of primary and multiple eventsis considered as linear noise. By default, the module subtracts the model of multiplesor the model of multiples plus the linear noise from the input gather (see theLAMBDA parameter).Anti-noise filtering (first option NA)The module builds signal and (linear) noise events. This building is based on a userdefinedlinear model.On input, a gather is modelled as a superimposition of a number of linear events plusthe random noise.The computation is performed using a high-resolution, de-aliased least-squaresmethod in the frequency- space (f-x) domain for each frequency of the pass-banddefined by FMIN and FMAX.CGG2 RAMUR Users Manual GeoclusterBy default, the module subtracts the model with organized noise or the model withorganized noise plus the random noise from each gather (see LAMBDA parameter).Equalization options (second option PA)Input traces are equalized before filtering. This equalization is similar to thatapplied by the DYNQU module (blank option) with a sliding operator. The PAoption (Preserved Amplitude) reverses equalization after Radon filtering.Geocluster Users Manual RAMUR 3CGGFUNCTION CALLDescriptionColumn contents1 *3-7 RAMUR9-10 First option:MA: Multiple attenuation using modelling of parabolas.NA: Linear noise attenuation.12-13 Second option:Blank: No equalisation/un-equalisation of input traces.PA: Traces are equalised before processing and un-equalised afterprocessing.15-16 Input buffer: contains the trace to be processed.23-24 Output buffer: contains the processed trace.31-80 ParametersParameters common to all optionsMandatory parametersXRMi i = Far trace offset (in meters or feet). This offset is used as a referencewhen computing the Radon model. Integer.YMXj j =Maximum coverage of a unit gather (CDP, shotpoint,). Integer.FMINf f = Minimum frequency (in Hz) of the spectrum used in the computationof the models. Integer.0 f F Nyquist.FMAXg g = Maximum frequency (in Hz) of the spectrum used in the computationof the models. Integer.Maximum (0,FMIN) g F Nyquist.YBk k = Number of the secondary loop to which output traces are transmitted.Integer.1 k 99The selection of the FMIN and FMAX frequencies is essential in the processingcost. The computation of models is only performed on the user-defined frequencyband.CGG4 RAMUR Users Manual GeoclusterParameters describing the area to scanDTMINv v = Lower limit (in milliseconds) for scanning parabolas or straightlines relative to the horizontal. Integer.In option MA, it is the minimum residual NMO at offset XRM. Inoption NA, it is the minimum shift at offset XRM with respect tozero.In general, v is negative or null, and always smaller than DTMAX.When v is positive, flat events cannot be modelled.DTMAXw w = Upper limit (in milliseconds) for scanning parabolas or straightlines relative to the horizontal. Integer.In option MA, it is the maximum residual NMO at offset XRM. Inoption NA, it is the maximum shift at offset XRM with respect tozero.DTMIN w.DDTz z = Increment (in milliseconds) between parabolas or straight linesat offset XRM. Integer.0 z (DTMAX-DTMIN)DTCUTeor DTCUTe, DTCUTfe (,f) = Separating threshold(s) in milliseconds used to define thezone of multiples and linear noises. Integer.If DTCUT is coded once only, the lines or parabolas includedbetween DTCUT and DTMAX are not used to build the signalmodel.If DTCUT is coded twice, the lines or parabolas included betweenthe two DTCUTs are not used to build the signal model.Parts which are not used for the signal model are used to model multiplesor linear noises.The values given to e and f must lie within the DTMIN,DTMAXinterval. If two thresholds are defined e must be smaller than f.orDTKEEPe,or DTKEEPe, DTKEEPfe(,f) = Separating thresholds in milliseconds used to define the zoneof primaries or the signal zone to be preserved. Integer.If DTKEEP is coded only once, only the lines or parabolas includedbetween DTKEEP and DTMAX are used to build the signal model.If DTKEEP is coded twice, only the lines and parabolas includedbetween the two DTKEEPs are used to build the signal model.Parts which are not used for the signal model are used to model theGeocluster Users Manual RAMUR 5CGGmultiples or linear noises.The values given to e and f must lie within the DTMIN,DTMAXinterval. If two thresholds are defined, e must be smaller than f.Parameters for windowing managementNCXm, TAPXnThe Radon filtering is performed on spatial sliding windows made ofm traces with an overlap of n traces. Integer.0 m, 0 n.The size of the sliding spatial window is essential in the quality ofthe results.NCTo, TAPTpThe Radon filtering is performed on o milliseconds time sliding windowswith an overlap of p milliseconds. Integer.0 o, 0 p.Optional parametersProcessing window parametersTIi or KTIr i = Initial time in milliseconds of the processing window after NMO.Integer. By default, i = 0r = Multiplier coefficient of the water bottom values read from theLFD (which must then be defined). Real.LFDd d = Number of the water bottom library. Integer.TAPIi i = Length of the tapering zone in milliseconds between the processedtrace and the original data at the beginning of the processingwindow. Real. By default i = 100 msec.TFf f = Final time in milliseconds, after NMO, of the processing window.Integer. By default f = trace length in milliseconds.0 TI TFTAPFg g = Length of the tapering zone in milliseconds between the processedtrace and the original data at the end of the processing window.Real. By default g = 100 msec.Parameters for windowing managementXCXh h = Length, in meters, of the spatial sliding windows. If XCX iscoded, the spatial sliding windows have a variable number of traces,and NCX is the minimum number of traces in a window.In the MA option, h is indeed the length of the first sliding window(starting at offset zero). The other windows have a constant squaredoffset length (of h2).0 hCGG6 RAMUR Users Manual GeoclusterModel and processing parametersPp p = Factor controlling the focusing of the Radon decomposition. Forlarge P values, the Radon spectra will be better focused, sometimesat the expense of the accuracy of the data modelling. The value 0.0results in identical results to MULTP (no weight).By default, p = p 2.0Fb b = Factor controlling the sparseness of the Radon decomposition.For large b values, the Radon spectra will be sparser, sometimes atthe expense of the accuracy of the data modelling.Real. By default, b = 0.1.0 bSc c =Whitening factor applied to the weight. The value 0.0 can lead tounstable behavior. The value 1.0 results in identical results toMULTP (no weight). Real.0.0 b 1.0By default, b = 0.001FWAd d = Between FMIN and FWA, a same weight is applied, which isaveraged from a preliminary pass on this frequency band.FMIN d FWBBy default, d = FMIN+(FMAX-FMIN)/10FWBe e = Last frequency where the weight is updated. Between FWB andFMAX the weight is kept constant.FWA e FMAXBy default, e = FMAXLTAPt t = Length, in milliseconds, of the taper centered on the separatingthreshold curves. This parameter is referenced to XRM. By default,t = 40 ms. Integer.0 tLTAPMDx x = Length, in milliseconds, of the taper applied to parabolas (OptionMA) or straight lines (option NA) from (DTMIN-x) to DTMIN andfrom DTMAX to (DTMAX+x). Integer.By default, x = 100 ms.0 NCX2 = overdetermined case: should be prefered for NP NPOPTIMAa a = Tau-p modelling.1 = classical exact2 = fast approximate3 = fast approximate (faster than 2 for very large NCX)Integer. By default, a is set according to LSI, NCX and NPOPTIMBb b = Tau-p stack.1 = classical exact2 = fast approximateInteger. By default, b is set according to NCX and NPOPTIMCc c = System solver choice.1 = direct exact solver2 = fast iterative approximate solverInteger. By default, c is set according to LSI, NCX and NPACCAd d = Accuracy (number of digits) of the approximate algorithm selectedby OPTIMA2Integer. By default, d=3ACCCe e = Accuracy (number of digits) of the approximate algorithm selectedby OPTIMC2Integer. By default, e=3Parameters specific to the PA optionOptional parametersAVCj j = Length, in milliseconds, of the equalisation operator.Integer. By default, j = 200 ms (equalisation level set to 5000).0 j.CGG8 RAMUR Users Manual GeoclusterTRACE HEADERStatus of the output trace headerX = updated word 0 = zeroed word blank = directly transcribed1 2 3 4 5 6 7 8 9 0WORDS 1 to 10WORDS 11 to 20WORDS 21 to 30WORDS 31 to 40WORDS 41 to 50WORDS 51 to 60WORDS 61 to 64Geocluster Users Manual RAMUR 9CGGRECOMMENDATIONSRemarks Input traces in RAMUR (MA/NA) must have been NMO-corrected by FANMO. As the running time is proportional to the FMIN to FMAX range, special attentionshould be given to these parameters. They should be selected by looking atthe frequency spectrum of the data within the processing window. The DDT parameter controls the number of functions that are built and the computationtime. An increment of 20 to 32 ms is often sufficient. Tests should bemade to determine the most suitable value for DDT and the DTMIN to DTMAXrange. The F and S parameters control the focalization of the seismic events into theRadon spectra. Large values of F and small values of S lead to sparse spectra atthe expense of the data modelling accuracy. The use of sliding temporal and spatial windows enables you to simplify thenumber of seismic events to handle. With a smaller number of events, the highresolution, de-aliased Radon transform is better focused and avoids the artefactscommonly related to aperture and spatial sampling limitations. RAMUR always outputs the same number of traces with the same offset as input.Invalid traces on input will be invalid traces on output. Too small spatial windows may lead to poor separation between signal and noise.Typical values are: NCX: 20,TAPX: 5,NCT: 400, TAPT: 100. Smaller spatial windows may be used with the NA option To correctly model the primaries, the DTMIN parameter should always be negative. If some algorithmic optimizations are enabled, S0 (the default) can some timeslead to instabilities. To avoid this problem, set the S slightly positive value(0.01). However, it has been observed that strongly aliased multiples are betterattenuated with S0. NCT is automatically raised to the nearest power of 2 (in number of samples) ofthe FFT length. Decreasing the accuracy of the approximate algorithms (ACCA & ACCC)speeds them up. Invalid traces are considered as valid traces containing null values. They shouldtherefore be removed before using RAMUR.CGG10 RAMUR Users Manual GeoclusterLimits The size of the spatial windows (NCX) must be less than 512 traces The number of parabolas must be less than 1024 The length of temporal windows NCT must be less than 16384*SIGeocluster Users Manual RAMUR 11CGGEXAMPLESExample 1Tableau 1:Anti-multiple processing(MA option )Anti-noise processing(NA option )Principle: Create a multiple model to besubtracted to the data to be processed.Principle: Create a model of linear noisesto be subtracted to the data to be processedMultiples are assumed to be parabolas. Multiples are assumed to be lines.Step 1: RAMUR works on NMOcorrectedCDP gathers. It is advisable tofirst playback some gathers which areNMO corrected in order to distinguish theresidual curvatures of the multiples.Step 1: RAMUR works on shotpoint orCDP gathers. It is advisable to firstplayback some gathers which are NMOcorrected.Step 2: The previous step enables you to define essential RAMUR parameters (DTMIN,DTMAX, DDT). The values of DTMIN and DTMAX are given at the far-trace offsetXRM defined by the user. The DDT parameter is given according to the number oftraces. DTMIN and DTMAX must be selected in such a way that they include the totalityof the events present. In particular, they must contain the steepest events.Traces to be processed are ordered inWOR