Changes between Version 4 and Version 5 of pick_ew


Ignore:
Timestamp:
05/06/12 19:00:25 (8 years ago)
Author:
branden
Comment:

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  • pick_ew

    v4 v5  
    210210 
    2112113. Station: the first of 3 fields (Station-Comp-Net) that will uniquely identify each trace of seismic data.  Station is a string, up to 5 characters, that identifies the physical site of the seismic instrument. This label must be unique within a given network. 
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     212 
    2132134. Comp: a 3-character string to identify the component of motion recorded by this seismic trace. 
    214     
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    2152155. Net: a 2-character string that identifies the network that operates the seismic instrument. 
    216216 
     
    220220 
    2212217. Itr1: (i5 in earlier code) Sets Itr1 which is used to calculate the zero-crossing termination count.  The pick_ew calculates itrm, the number of consecutive small-zero crossings (zero-crossings where the short-term average is less than the critical termination level) to be allowed before declaring the event over. itrm = Itr1 + m / Itr1 where m is the zero-crossing counter. itrm will start out quite small at the beginning of an event and will increase during an event to a maximum of 50. 
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    2232238. MinSmallZC:  (i6 in earlier code) Defines the minimum number of zero-crossings for a valid pick.  An event is declared over and potentially valid after MinSmallZC zero-crossings. Pick_ew then evaluates the event to determine if it was a seismic event or noise. 
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    2252259. MinBigZC: (i7 in earlier code) Defines the minimum number of "big zero-crossings" for a valid pick. No pick is reported unless at least MinBigZC big zero-crossings occurred while the event was active.  [A "big zero-crossing" amplitude must exceed rbig, where rbig is (the largest amplitude of first 3 half-cycles after event activation)/3.  A "big zero crossing" must also represent a crossing of opposite polarity to the previous crossing]. 
    226226 
    22722710. !MinPeakSize: (i8 in earlier code) Defines the minimum amplitude (digital counts) for a valid pick. No pick is reported unless one of the first three peaks of an event has an amplitude larger than !MinPeakSize digital counts. 
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    22922911. !MaxMint: (hard-wired at 500 in earlier code) Maximum interval (in samples) between zero crossings. If no zero crossings occur within !MaxMint data samples, the pick event is terminated. 
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    23123112. i9: (i9 in earlier code) Defines the minimum coda length (seconds) for a valid pick.  No pick is reported unless its coda is at least i9 seconds long. 
    232232 
     
    236236 
    23723714. !CharFuncFilt: (c2 in earlier code) Sets the filter parameter !CharFuncFilt that is applied in the calculation of the characteristic function of the waveform data. 
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    23923915. !StaFilt: (c3 in earlier code) Sets the filter parameter (time constant) !StaFilt that is used in the calculation of the short-term average (STA) of the characteristic function of the trace. 
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    24124116. !LtaFilt: (c4 in earlier code) Sets the filter parameter (time constant) !LtaFilt that is used in the calculation of the long-term average (LTA) of the characteristic function of the trace. 
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    24324317. !EventThresh: (c5 in earlier code) Sets the STA/LTA event threshold.  An event (a pick) is declared when STA is larger than !EventThresh*LTA.  Once an event is declared, pick_ew enters an event evaluation mode to determine if the event is a P-wave arrival or noise. 
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    24524518. !RmavFilt: Filter parameter (time constant) used to calculate the running mean of the absolute value of the waveform data. Usually set to 0.9961. 
    246246 
     
    25125120. !CodaTerm: (c7 in earlier code) Sets the "normal" coda termination threshold (counts). Two methods are used to determine if the coda length calculation is over.  For quiet stations, the coda is "normally" terminated when the AAV of a 2-second waveform window drops below !CodaTerm digital counts.  For noisy stations, an alternate termination method is used (see !AltCoda & !PreEvent, below).  Pick_ew stops all coda calculations 144 seconds after event activation, even if the coda AAV hasn't reached the termination value.  In the Northern California Seismic Network's convention, !CodaTerm is the number of digital counts produced by a discriminator output signal (input to the Earthworm A/D) of 60 mV. The 2-bit Earthworm A/D has an input range of +/- 2.5 volts and an output range of 0 to 4095 counts (-2048 to 2047 counts).  For such a system, a 60 mV input will produce a sample of 49.1 counts. 
    252252 
    253 21. !AltCoda: (c8 in earlier code) Defines the "noisy station level" at which pick_ew should use the alternate coda termination method.  If the                 AAV of a channel is greater than !CodaTerm*!AltCoda digital counts when an event is declared, pick_ew uses the alternate coda termination method. 
    254     
     25321. !AltCoda: (c8 in earlier code) Defines the "noisy station level" at which pick_ew should use the alternate coda termination method. If the          AAV of a channel is greater than !CodaTerm*!AltCoda digital counts when an event is declared, pick_ew uses the alternate coda termination method. 
     254 
    25525522. !PreEvent: (c9 in earlier code) Defines the alternate coda termination threshold for noisy stations. If the AAV of a channel is greater than                !CodaTerm*!AltCoda digital counts when an event is declared, the coda is considered over when the AAV of a 2-second waveform window drops to            less than !PreEvent*(pre-event signal amplitude).  Pick_ew stops all coda calculations 144 seconds after event activation, even if the coda AAV hasn't reached the termination value. 
    256256 
     
    259259'''Optional Parameters:''' 
    260260 
    261 24. !ClipCount: (added in v5.1 for use by eqcoda, ignored by pick_ew) Specifies the maximum absolute amplitude (in counts zero-to-peak) that can be expected for this channel. Eqcoda calculates clipping thresholds for P-amplitudes and coda-window average absolute amplitudes as a fraction of !ClipCount.    
     26124. !ClipCount: (added in v5.1 for use by eqcoda, ignored by pick_ew) Specifies the maximum absolute amplitude (in counts zero-to-peak) that can be expected for this channel. Eqcoda calculates clipping thresholds for P-amplitudes and coda-window average absolute amplitudes as a fraction of !ClipCount. 
    262262 
    263263=== ADDITIONAL REFERENCES ON THE PICKER ALGORITHM ===