CTITLESADIST -- FUNCTION TO CALCULATE SHOT RECEIVER DISTANCE            00010001
C***********************************************************************
C                 COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991            *
C***********************************************************************
C                                                                       00020000
CA    AUTHOR       ARCO                                                 00030000
CA    DESIGNER     ARCO                                                 00040000
CA    LANGUAGE     FORTRAN H                                            00050000
CA    WRITTEN      09-01-84                                             00060000
C     REVISED      MO-DA-YR  BY PROGRAMMER                              00070000
C     REVISED      04-02-87  JMP - PUT IN PRODUCTION SPARC.             00071001
C                                                                       00090000
CA    CALLING SEQUENCE:                                                 00100000
CA    X =  SADIST ( ZTHETA, ZALPHA, ZDEPTH)                             00110001
CA                                                                      00120000
CA    IN/OUT ARGUMENT TYPE DESCRIPTION                                  00130000
CA                                                                      00140000
CA    IN     ZTHETA   R8   LOCAL VARIABLE FOR THETA                     00150000
CA    IN     ZALPHA   R8   LOCAL VARIABLE FOR ALPHA OF CURRENT LAYER    00160000
CA    IN     ZDEPTH   R4   LOCAL VARIABLE FOR THICKNESS OF CURRENT      00170000
CA                         LAYER                                        00180000
CA                                                                      00190000
CA    PURPOSE OF PROGRAM:                                               00200000
CA    FUNCTION FOR SHOT-RECEIVER DISTANCE. BASICALLY, THIS FUNCTION     00210000
CA    IS 2*(THICKNESS OF I-TH LAYER)*(TANGENT OF THE RAY ANGLE IN THE   00220000
CA    I-TH LAYER). THIS FUNCTION, HOWEVER, PUTS THE I-TH ANGLE IN       00230000
CA    TERMS OF THETA-1, THE INCIDENT ANGLE FROM THE SHOT. IN THE MAIN   00240000
CA    PROGRAM THIS FUNCTION IS SUMMED OVER I TO GIVE THE VALUE XR.      00250000
CA                                                                      00260000
CA    ROUTINES CALLED:  NONE                                            00270000
CA                                                                      00280000
C---------------------------------------------------------------------  00290000
      REAL FUNCTION SADIST (ZTHETA, ZALPHA, ZDEPTH)                     00300001
C                                                                       00310000
C____________________________________________________________           00320000
C                                                                       00330000
C     LOCAL VARIABLES                                                   00340000
C                                                                       00350000
C____________________________________________________________           00360000
C                                                                       00370000
      REAL     *4  ZDEPTH                                               00380000
      REAL     *8  ZTHETA                                               00390000
     2          ,  ZALPHA                                               00400000
C                                                                       00410000
C     MAKE SURE WE DON'T TRY TO TAKE THE SQUARE ROOT OF A NEGATIVE.     00420000
C                                                                       00430000
      IF (ZALPHA*DSIN(ZTHETA).GE.1.0)                                   00440000
     1                  ZTHETA = 2 * DARSIN(1 / ZALPHA) - ZTHETA        00450000
C                                                                       00460000
      SADIST = 2 * DSIN(ZTHETA) * ZALPHA * ZDEPTH /                     00470001
     1                  (DSQRT(1 - (ZALPHA * DSIN(ZTHETA)) **2))        00480000
      RETURN                                                            00490000
      END                                                               00500000