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C $Id: gaspct.f 3304 2011-01-17 15:25:59Z brideout $
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C
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SUBROUTINE GASPCT(SLATGD,SLON,SR,SLATGC,TM,AZ,EL,RANGE,GDLAT,GLON,
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* GDALT,B,CASPCT,ASPCT)
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C
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C jmh - 3/88
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C
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C *** warning *** this routing used to be called aspect. the name
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C was changed on 3/2/88 to avoid conflict with a
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C new routine of the same name in the geophysics
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C library
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C
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C Calculates the aspect angle between a radar beam and the
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C geomagnetic field at a specified point. the point may be
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C specified either by slatgd, slon, sr, slatgc, tm, az, el, range
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C (range .ge. 0.) or by gdlat, glon, gdalt (range .lt. 0.)
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C
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C Input:
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C SLATGD - station geodetic latitude
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C SLON - station longitude
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C SR - radial distance of station from center of earth
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C SLATGC - station geocentric latitude
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C TM - time in years (e.g. 1975.2)
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C AZ - radar azimuth
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C EL - radar elevation
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C RANGE - range to observation point
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C Input, output:
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C GDLAT - geodetic latitude of observation point
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C GLON - longitude of observation point
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C GDALT - altitude above spheroid of observation point
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C Output:
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C B - geomagnetic field magnitude
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C CASPCT - cosine of aspect angle
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C ASPCT - aspect angle (degrees)
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C
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C
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C
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C .....subroutine parameter specifications.....
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C
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C .....local specifications.....
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C
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C .. Scalar Arguments ..
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DOUBLE PRECISION ASPCT,AZ,B,CASPCT,EL,GDALT,GDLAT,GLON,RANGE,
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* SLATGC,SLATGD,SLON,SR,TM
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C ..
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C .. Local Scalars ..
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DOUBLE PRECISION BFX,BFY,BFZ,BP,BR,BT,CP,CT,DTR,GCLAT,P,PFX,PFY,
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* PFZ,PX,PY,PZ,RFX,RFY,RFZ,RKM,SP,ST,T,XB,YB,ZB
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C ..
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C .. Local Arrays ..
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DOUBLE PRECISION BF(3),PF(3),RF(3)
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C ..
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C .. External Functions ..
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DOUBLE PRECISION SPROD,VMAG
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EXTERNAL SPROD,VMAG
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C ..
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C .. External Subroutines ..
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EXTERNAL CONVRT,GDV,LOOK,MILMAG,POINT,RPCART,VCTCNV
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C ..
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C .. Intrinsic Functions ..
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INTRINSIC ACOS,DCOS,DSIN
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C ..
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C .. Equivalences ..
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EQUIVALENCE (RFX,RF(1)),(RFY,RF(2)),(RFZ,RF(3))
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EQUIVALENCE (PFX,PF(1)),(PFY,PF(2)),(PFZ,PF(3))
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EQUIVALENCE (BFX,BF(1)),(BFY,BF(2)),(BFZ,BF(3))
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C ..
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C .. Data statements ..
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DATA DTR/.0174532925199D0/
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C ..
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C
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C .....calculate observation point coordinates.....
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IF (RANGE.GE.0.D0) THEN
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CALL POINT(SR,SLATGC,SLON,AZ,EL,RANGE,RKM,GCLAT,GLON)
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CALL CONVRT(2,GDLAT,GDALT,GCLAT,RKM)
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ELSE
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CALL CONVRT(1,GDLAT,GDALT,GCLAT,RKM)
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CALL LOOK(SR,SLATGC,SLON,RKM,GCLAT,GLON,AZ,EL,RANGE)
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END IF
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C
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C .....calculate magnetic field at observation point
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T = DTR*(90.D0-GCLAT)
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CT = DCOS(T)
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ST = DSIN(T)
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P = DTR*GLON
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CP = DCOS(P)
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SP = DSIN(P)
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CALL MILMAG(TM,RKM,ST,CT,SP,CP,BR,BT,BP,B)
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CALL GDV(GDLAT,GCLAT,BR,BT,BP,XB,YB,ZB)
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C
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C .....convert radar propagation vector and observation point
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C position to earth centered cartesian coordinates.....
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CALL RPCART(SR,SLATGC,SLON,AZ,EL,RANGE,RFX,RFY,RFZ,PFX,PFY,PFZ)
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C
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C .....convert southward, eastward, upward components of magnetic
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C field at observation point to earth centered cartesian
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C coordinates.....
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CALL VCTCNV(BFX,BFY,BFZ,PX,PY,PZ,BR,BT,BP,RKM,90.D0-GCLAT,GLON,2)
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C
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C .....calculate aspect angle.....
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CASPCT = SPROD(RF,BF)/(VMAG(RF)*VMAG(BF))
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ASPCT = ACOS(CASPCT)/DTR
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RETURN
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END
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