2022-04-22 15:34:12 -04:00
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subroutine echo_snr(sa,sb,fspread,blue,red,snrdb,db_err,fpeak,snr_detect)
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parameter (NZ=4096)
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real sa(NZ)
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real sb(NZ)
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real blue(NZ)
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real red(NZ)
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integer ipkv(1)
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equivalence (ipk,ipkv)
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df=12000.0/32768.0
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wh=0.5*fspread+10.0
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i1=nint((1500.0 - 2.0*wh)/df) - 2048
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i2=nint((1500.0 - wh)/df) - 2048
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i3=nint((1500.0 + wh)/df) - 2048
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i4=nint((1500.0 + 2.0*wh)/df) - 2048
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! call pctile(sb(i1),i2-i1,50,r0)
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! call pctile(sb(i3+1),i4-i3,50,r1)
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! ave=0.5*(r0+r1)
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! blue=sa/ave
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! red=sb/ave
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baseline=(sum(sb(i1:i2-1)) + sum(sb(i3+1:i4)))/(i2+i4-i1-i3)
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blue=sa/baseline
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red=sb/baseline
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psig=sum(red(i2:i3)-1.0)
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pnoise_2500 = 2500.0/df
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snrdb=db(psig/pnoise_2500)
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smax=0.
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mh=max(1,nint(0.2*fspread/df))
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do i=i2,i3
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ssum=sum(red(i-mh:i+mh))
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if(ssum.gt.smax) then
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smax=ssum
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ipk=i
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endif
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enddo
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fpeak=ipk*df - 750.0
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call averms(red(i1:i2-1),i2-i1,-1,ave1,rms1)
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call averms(red(i3+1:i4),i4-i3,-1,ave2,rms2)
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perr=0.707*(rms1+rms2)*sqrt(float(i2-i1+i4-i3))
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snr_detect=psig/perr
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db_err=99.0
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if(psig.gt.perr) db_err=snrdb - db((psig-perr)/pnoise_2500)
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if(db_err.lt.0.5) db_err=0.5
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return
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end subroutine echo_snr
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