Changes between Version 1 and Version 2 of ShmDocFilterSimulation


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Timestamp:
01/23/2009 10:44:10 AM (14 years ago)
Author:
MarcusWalther
Comment:

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  • ShmDocFilterSimulation

    v1 v2  
    11= Working with simulation filters = 
    22 
    3 Simulation filters transform records of an instrument, preferably a broadband instrument, into a simulated record of another instrument. Before generating such simulation filters it should be cleared whether the transfer function of the recording instrument allows the simulation of the desired one. The recording system must provide enough signal energy in all frequency ranges of the simulated instrument. E.g. from records of STS-2 seismometers simulations of short- and longperiod instruments like WWSSN-SP and SRO-LP may be computed, but inversely, e.g. from WWSSN-SP to STS-1 is definitely not possible. In principle, the construction of simulation filters is rather simple if we use the poles-and-zeros definition of filters. These numbers can be directly written into an SH-FFT-filter file (see [ShmDocFilterFiles filter formats]). A simulation filter is created by taking the transfer function of the recording instrument (e.g. an STS-2), inverting it (take reciprocal value of the normalization, exchange poles and zeros), multiply it with the transfer function of the simulated instrument (e.g. WWSSN-SP) and shorten all possible values of the rational expression. The resulting filter (example: STS2-to-WWSSN-SP) may be used for application in SHM. Please make sure that all elements (normalization constants, poles-and-zeros definition of the filter) refer to the same recording input (usually either velocity or displacement). In practice, this is quite often a reason for confusion. For a quick view of the amplitude response of your FFT filters use [ShmDocFilterDisplay graphic display] of FFT filters. If you want to create recursive simulation filters, use the utility programs of SH/SHM (in ''$SH_UTIL'', programs ''butrec'', ''simrec'') for some standard cases or follow instructions for computing recursive filters given e.g. in ???. A [ShmDocFilterCreateSim tool] for creating a set of FFT filters for your recording equipment is provided in ''$SH_UTIL''. 
     3Simulation filters transform records of an instrument, preferably a broadband instrument, into a simulated record of another instrument. Before generating such simulation filters it should be cleared whether the transfer function of the recording instrument allows the simulation of the desired one. The recording system must provide enough signal energy in all frequency ranges of the simulated instrument.  
     4 
     5E.g. from records of STS-2 seismometers simulations of short- and longperiod instruments like WWSSN-SP and SRO-LP may be computed, but inversely, e.g. from WWSSN-SP to STS-1 is definitely not possible. In principle, the construction of simulation filters is rather simple if we use the poles-and-zeros definition of filters. These numbers can be directly written into an SH-FFT-filter file (see [ShmDocFilterFiles filter formats]). A simulation filter is created by taking the transfer function of the recording instrument (e.g. an [http://www.seismic-handler.org/portal/browser/SH_SHM/trunk/filter/TF_VEL_GRSN.FLF STS-2]), inverting it (take reciprocal value of the normalization, exchange poles and zeros), multiply it with the transfer function of the simulated instrument (e.g. [http://www.seismic-handler.org/portal/browser/SH_SHM/trunk/filter/TF_VEL_WWSSN_SP.FLF WWSSN-SP]) and shorten all possible values of the rational expression.  
     6 
     7The resulting filter (example: [http://www.seismic-handler.org/portal/browser/SH_SHM/trunk/filter/GRSN_S%2BG_WWSSN_SP.FLF STS2-to-WWSSN-SP]) may be used for application in SHM. Please make sure that all elements (normalization constants, poles-and-zeros definition of the filter) refer to the same recording input (usually either velocity or displacement). In practice, this is quite often a reason for confusion.  
     8 
     9For a quick view of the amplitude response of your FFT filters use [ShmDocFilterDisplay graphic display] of FFT filters. If you want to create recursive simulation filters, use the utility programs of SH/SHM (in ''$SH_UTIL'', programs ''butrec'', ''simrec'') for some standard cases or follow instructions for computing recursive filters given e.g. in ???. A [ShmDocFilterCreateSim tool] for creating a set of FFT filters for your recording equipment is provided in ''$SH_UTIL''. 
    410 
    511When using SHM, the filter files need to match a naming convention so that the files can be found on request. The filter files must be located either in ''$PWD'' or in ''$SH_FILTER''. Looking for the filter files SHM assumes file names of a defined format: