;
;==========================================================================
;
; FILE: uf_forward_sgate.pro
;
; USAGE:  result = UF_forward_sgate(ufbuf, field)
;         ARGUMENTS  ufbuf  Buffer of UF words for a dwell of radar data
;                    field  Logical number of the data field
;
; ABSTRACT: Return the UF gate number in the Nth data field where the 
;           FORWARD surface gate is located
;
; AUTHOR:  I. Jeff Caylor
;          Science Systems and Applications, Inc.
;          5900 Princess Garden Parkway, Suite 300
;          Lanham, MD  20706
;
;     at:  NASA Goddard Space Flight Center
;          Code 912
;          Greenbelt, MD 20771
;          Voice: (301) 286-3767
;          Fax:   (301) 286-1762
;          Email: jeff.caylor@gsfc.nasa.gov
;
; CREATED: 11 April 1995
;
; MODIFIED: 12 April 1999: change UFgatelength to UFgatespace - LT 
;
;==========================================================================
;

;
; Return the location of the forward surface gate in the Nth data field
; Error = -1
;
FUNCTION UF_forward_sgate, ufbuf, field
;
; Compute the original EDOP gate for the first UF gate
;
;  ufgzero = 1000.0 * UFrangezero(ufbuf, field) / UFgatelength(ufbuf, field)
  ufgzero = 1000.0 * UFrangezero(ufbuf, field) / UFgatespace(ufbuf, field)
;
; Get forward surface EDOP gate
;
  fgzero = UFedop_forwardsgate(ufbuf)
;
; Determine the UF gate for the surface
;
  IF (fgzero GE 0) AND (fgzero GE ufgzero) THEN $
    RETURN, fgzero - UFedop_gatezero(ufbuf) - FIX(ufgzero) $
  ELSE  $
    RETURN, -1
END