c
c	compute gain, tsys, sefd curves for l-wide receiver
c		ramesh@naic, 09/may/2002
c		(for g54/search project)

c	for tsys,
c		* subtract 3K background
c		* add galactic synchrotron 
c			6.14 K towards G54 (l=54.04, b=0.37)
c			!! use the revised estimate of 8.2 K !!
c		* synchrotron from nebula T_snr=G(t)*S_snr
c			S_snr=0.5 Jy, spectral index=~0.0

	program gain_N_tsys

	integer i,nza,nmax,count
	parameter (nmax=300)
	real za0,dza,za(nmax),gain(nmax),tsys(nmax)
	real term1,term2,term3,sefd(nmax),za1(nmax)
	real avsefd,c0,c1,c2,c3,tcold,tsky,tsnr(nmax)
	real tsys1(nmax)

c	read in gain curve paras from a file	13/05/02

	open(1, file='lwide.gain')
	read(1,*)c0,c1,c2,c3
	write(6,*)
	write(6,*)'The model Gain curve: ',c0,c1,c2,c3
	write(6,*)
	close(1)

	tcold=3.0
c	tsky=6.14	revised estimate=8.2 K
	tsky=8.2 
	ssnr=0.50

	za0=-19.65
	dza= 0.1965
	nza= 200
	avsefd=0.0
	count=0

	do i=1,nza+1
	  za(i)=za0+(i-1)*dza
	  za1(i)=za(i)
	  za(i)=abs(za(i))

	  term1= c0+c1*za(i)
	  if(za(i).gt.14.0)then
	    term2= c2*((za(i)-14.0)**2.0)
	    term3= c3*((za(i)-14)**3.0)
	  else
	    term2=0.0
	    term3=0.0
	  end if
	  gain(i)=term1+term2+term3

	  term1= 36.32+0.153*za(i)
	  if(za(i).gt.14.0)then
	    term2= 0.17094*((za(i)-14.0)**2.0)
	    term3=-0.00741*((za(i)-14.0)**3.0)
	  else
	    term2=0.0
	    term3=0.0
	  end if
	  tsys(i)=term1+term2+term3

c	  subtract cold sky, add tsky + tsnr

	  tsnr(i)=ssnr*gain(i)
	  tsys1(i)=tsys(i)-tcold+tsky+tsnr(i)

 	  sefd(i)=tsys1(i)/gain(i)

c 	  do averaging only for |za|<1.06 deg 	13/05/02

	  if(za(i).gt.1.06)then
	    avsefd=avsefd+sefd(i)
	    count=count+1
	  end if

	  write(*,*)za1(i),gain(i),tsys(i),tsys1(i),sefd(i)

	end do
	avsefd=avsefd/float(count)

	write(*,*)
	write(*,*)'The effective average SEFD: ',avsefd
	write(*,*)
	write(*,*)'Total no of za points: ',nza+1
	write(*,*)'No outside za < 1.06 : ',count
	write(*,*)

	stop
	end

c ignore this!
C current best estimate:
C Gain(za, az)=10.85523-0.10291*za+0.01343*(za-14)^2-0.00717*(za-14)^3 
C Tsys(za)= 36.32 + 0.153*za + 0.17094*(za-14)^2 - 0.00741*(za-14)^3 K
C L-wide:
C gain(za) = 11.00523 - 0.10291*za + 0.01343*(za-14)^2 - 0.00717*(za-14)^3
C Tsys(za) = 36.32 + 0.153*za + 0.17094*(za-14)^2 - 0.00741*(za-14)^3 K