





SPECPR Users' Manual                                            Page 8-f45.1


_F_4_5:  _A_u_t_o_m_a_t_i_c _B_a_n_d _A_n_a_l_y_s_i_s                           _A_l_i_a_s = _a_b_a

     This routine uses the segmented upper hull (see f44) to isolate absorp-
tion  features  in  a  spectrum  and then for each feature the following are
derived:

          Band Center
          Full Width at Half Maximum (FWHM)
          Band Depth
          Error in band depth (assuming that error bars were included with the
                   input spectrum)
          Full Width at Quarter Maximum (FWQM)
          Band Asymmetry
          Continuum reflectance level
          Segmented Upper Hull iteration number

The output is a data set using 9 channels to describe each  feature  (the  8
items above and one additional that is currently unused).  Thus if the input
spectrum contained 26 features, then the output  data  set  would  have  234
channels.

     This routine was used to generate the  features  in  the  USGS  Digital
Spectral Library.

     For a description of the continuum algorithm, see Clark,  R.N.,  T.V.V.
King,  and  N.S. Gorelick, Automatic Continuum Analysis of Reflectance Spec-
tra: _P_r_o_c_e_e_d_i_n_g_s _o_f _t_h_e _T_h_i_r_d _A_i_r_b_o_r_n_e _I_m_a_g_i_n_g  _S_p_e_c_t_r_o_m_e_t_e_r  _D_a_t_a  _A_n_a_l_y_s_i_s
_W_o_r_k_s_h_o_p, JPL Publication 87-30, 138-142, 1987.

     Once the continuum is removed, the band center is found by finding  the
lowest channel in a feature and fitting a parabola to the lowest channel and
the channel in each side of the lowest one.  The FWHM, and FWQM are found by
linear interpolation.  The error bar is found based on the error bars on the
data.  The asymmetry is found by ratioing the distance from the band  center
to  each  FWHM  point.   See also section 9.8, Interactive Band Analysis (it
uses the same algorithms).


















