





SPECPR Users' Manual                                                   Page 8-f5.1


_F_5: _C_o_n_t_i_n_u_u_m _R_e_m_o_v_a_l                                   _A_l_i_a_s: _c_o_n_t[_r_e_m]

     The f5 continuum removal is an old algorithm that has  been  superseded
in  most  cases  by  newer routines such as f12 (cubic spline) and f44 (seg-
mented upper hull).  However, it does have an advantage in that it removes a
continuum of a specific shape given by the user in the form of a spectrum.

     To enter the routine, type f5.

     The directions are fairly simple.  The routine fits a  given  continuum
to  a  spectrum.  The routine will prompt for the continuum and spectrum, as
well as the continuum points used for the fit.  Basically,  you  select  two
channels and a straight line is generated through these two channels in both
the given continuum and the spectrum.  The continuum is modified by linearly
changing  its slope so that the same two channels on the continuum match the
values in the spectrum.  Once the fit is complete, the spectrum  is  divided
by the modified continuum.

     First, you will be instructed to enter the two channels for  which  you
want  to  match  the  continuum.   Usually  that  will be on each side of an
absorption band.

     Enter two values to which continuum is to be matched followed by h,  a,
or  n  representing  units  of  channel,  wavelength,  and  energy  (inverse
wavelength, and the wavelength file id and record number.  For example:

              _1_2 _3_3 _h _V_3_6
_o_r
              _1._2 _1._6_5 _a _V_3_6

would be equivalent if  channel  12  =  wavelength  1.2  and  channel  33  =
wavelength 1.65.  The wavelength set is then V36.

     The two points can be entered in whatever units are convenient for you,
in  free format (spaces between numbers, no commas).  The wavelength file is
read, and the two values entered are correlated with the appropriate channel
in  the wavelength set.  You can exit the routine here if you wish with an e
or x command.

     Next, enter the spectrum file id and record number, e to include errors
followed  by  the  continuum file id and record number.  Type e or x to exit
the routine.

     The message on the CRT will say "WORKING" when you hit the  return  key
after entering the information.  The title of the files used will be printed
on the CRT as they are accessed by the program.  The  error  file  with  the
spectrum is accessed if it was requested.

     The continuum spectrum is scaled to the spectral data at the two  given
points  by  calculating a scaled slope and an intercept (or vertical offset)
and converting each data point of the  continuum  to  the  scaled  continuum





through  the  relationship  Y = mx + b where Y is the scaled continuum, m is
the slope, x is the original continuum value at a given channel,  and  b  is
the  intercept.   The spectrum is then divided by the scaled continuum.  The
errors are scaled by a factor of (scaled spectrum / original spectrum).

     Finally, the title and history are made and control is transferred back
to the main program to write the file.


     Original author: Lucy Mcfadden















































