2007-01-11 21:25:52 +00:00
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subroutine flatten(s2,nbins,jz,psa,ref,birdie,variance)
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C Examines the 2-d spectrum s2(nbins,jz) and makes a reference spectrum
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C from the jz/2 spectra below the 50th percentile in total power. Uses
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C reference spectrum (with birdies removed) to flatten the passband.
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real s2(nbins,jz) !2d spectrum
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real psa(nbins) !Grand average spectrum
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real ref(nbins) !Ref spect: smoothed ave of lower half
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real birdie(nbins) !Spec (with birdies) for plot, in dB
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real variance(nbins)
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real ref2(750) !Work array
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real power(300)
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C Find power in each time block, then get median
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do j=1,jz
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s=0.
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do i=1,nbins
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s=s+s2(i,j)
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enddo
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power(j)=s
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enddo
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call pctile(power,ref2,jz,50,xmedian)
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if(jz.lt.5) go to 900
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C Get variance in each freq channel, using only those spectra with
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C power below the median.
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do i=1,nbins
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s=0.
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nsum=0
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do j=1,jz
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if(power(j).le.xmedian) then
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s=s+s2(i,j)
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nsum=nsum+1
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endif
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enddo
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s=s/nsum
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sq=0.
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do j=1,jz
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if(power(j).le.xmedian) sq=sq + (s2(i,j)/s-1.0)**2
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enddo
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variance(i)=sq/nsum
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enddo
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C Get grand average, and average of spectra with power below median.
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call zero(psa,nbins)
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call zero(ref,nbins)
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nsum=0
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do j=1,jz
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call add(psa,s2(1,j),psa,nbins)
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if(power(j).le.xmedian) then
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call add(ref,s2(1,j),ref,nbins)
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nsum=nsum+1
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endif
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enddo
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do i=1,nbins !Normalize the averages
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psa(i)=psa(i)/jz
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ref(i)=ref(i)/nsum
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birdie(i)=ref(i) !Copy ref into birdie
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enddo
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C Compute smoothed reference spectrum with narrow lines (birdies) removed
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do i=4,nbins-3
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rmax=-1.e10
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do k=i-3,i+3 !Get highest point within +/- 3 bins
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if(ref(k).gt.rmax) then
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rmax=ref(k)
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kpk=k
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endif
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enddo
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sum=0.
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nsum=0
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do k=i-3,i+3
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if(abs(k-kpk).gt.1) then
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sum=sum+ref(k)
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nsum=nsum+1
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endif
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enddo
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ref2(i)=sum/nsum
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enddo
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call move(ref2(4),ref(4),nbins-6) !Copy smoothed ref back into ref
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call pctile(ref(4),ref2,nbins-6,50,xmedian) !Get median in-band level
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C Fix ends of reference spectrum
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do i=1,3
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ref(i)=ref(4)
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ref(nbins+1-i)=ref(nbins-3)
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enddo
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facmax=30.0/xmedian
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do i=1,nbins !Flatten the 2d spectrum
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fac=xmedian/ref(i)
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fac=min(fac,facmax)
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do j=1,jz
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s2(i,j)=fac*s2(i,j)
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enddo
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psa(i)=dB(psa(i)) + 25.
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ref(i)=dB(ref(i)) + 25.
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birdie(i)=db(birdie(i)) + 25.
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enddo
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900 continue
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return
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end
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