CTITLE SANPAVG -- ROTATION AND SUMMING OF GATHER COHERENT STACKS
C***********************************************************************
C                 COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991            *
C***********************************************************************
CA
CA    AUTHOR         J.V.S. HARVEY
CA    LANGUAGE       VS FORTRAN (77) FOR VECTORIZATION
CA    SYSTEM         IBM ONLY
CA    REWRITTEN      29 NOV 1988
C     REVISED        02-17-89 JJC FOR SPARC PRODUCTION.
CA
CA
CA    THIS SUBROUTINE UPDATES THE CUMMULATIVE COHERENCY STACK
CA
CA    ****************************************************************
CA    ***     NOTE:  THIS ROUTINE REPLACES SACNAX (ALL ENTRIES)    ***
CA    ****************************************************************
CA
CA
CA          CALL SANPAVG( NUMFRQ, NUMVEL, CSTACK, SPECTR )
CA
CA
CA    IN/OUT  ARGUMENT  TYPE  DESCRIPTION
CA
CA    IN      NUMFRQ      I4  NUMBER OF FREQUENCY SAMPLES
CA    IN      NUMVEL      I4  NUMBER OF VELOCITY  SAMPLES
CA
CA    IN      CSTACK      R4  INPUT TRACE STACKS
CA               ( 3-D ARRAY DIMENSIONED:  NUMFRQ BY NUMVEL BY 2 )
CA
CA    UPDATE  SPECTR      R4  F-V SPECTRA
CA               ( 2-D ARRAY DIMENSIONED:  NUMFRQ BY NUMVEL )
CAEND
C***********************************************************************
C
C     SUBROUTINES CALLED:  (NONE)
C
C***********************************************************************
C
      SUBROUTINE SANPAVG( NUMFRQ, NUMVEL, CSTACK, SPECTR )
      IMPLICIT INTEGER (A-Z)
C
      REAL  CSTACK(NUMFRQ,NUMVEL,2)
      REAL  SPECTR(NUMFRQ,NUMVEL)
C--------------------------------------------------------------------
C
C                        REAL VARIABLES -- LOCAL
C
      REAL  ASQ
C
      REAL  SQRT
C
C***********************************************************************
C***                                                                ****
C***                     (COMPLEX) ROTATE AND SUM                   ****
C***                                                                ****
C***********************************************************************
C
      DO 10 IVF = 1, NUMVEL
         DO 10 KF = 1, NUMFRQ
            ASQ = CSTACK(KF,IVF,1)**2 + CSTACK(KF,IVF,2)**2
C
            SPECTR(KF,IVF) = SPECTR(KF,IVF) + SQRT( ASQ )
   10       CONTINUE
      RETURN
      END