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Fw: Astronomical Refraction: Computational Method for All Zenith Angles
From: Marcel Tschudin
Date: 2005 Aug 22, 18:33 +0300
From: Marcel Tschudin
Date: 2005 Aug 22, 18:33 +0300
Strange things happened to the e-mail just sent. The code at the end of it got cut off and added into an attachment, which cannot be opened. I tried it now again by forwarding the copy in the sent-file to my own address and this worked. I send now a copy of this test and hope it works fine this time. >> Refering my last mail, where I mention that I can not reproduce the >> values shown in the Auer Standish paper using the polytropic atmosphere >> model: >> >> 1) I overlooked the part on the following page: "These values are used to >> compute the coefficients for only that associated region of the >> atmosphere. In order to ensure continuity, the temperature and the >> density must be extrapolated to the boundary, defined by the altitude >> hB." >> >> 2) When introducing what is described there, the results are even worse. >> >> It seems that there is something wrong in my stratospheric part. May I >> ask you, Frank, to have a look at it? May be you can see what is going >> wrong there. >> >> Thanks, Marcel >> >>>>>>>>>>>>>>>>>>>>>>> >> Function getmu (r : Real): Real; // r = REarth + h >> var >> ... >> begin // getmu >> // Poytropic atmospheres: >> Tw:=273.15+RefTemp; // Tw=Temperature at reference point in ?K >> RHOw := 273.15/1013.25 * RefPress/Tw; // RefPress = Pw >> Rw := (REarth+RefHeight)/REarth; // RefHeight = hw >> Rrel := r/REarth; // r relative to REarth >> rr := 1.0/Rrel - 1.0/Rw; >> // nPoly = Polytropic index = 5 >> BETAw := g * REarth / ( Rgas * Tw * (1.0 + nPoly) ); >> Rhb:=(REarth+hB)/REarth; >> >> if R<=Rhb then >> begin // Begin: T r >> o p o s p h e r e >> >> RHOpoly := RHOw * Power( (1.0 + BETAw * rr), nPoly); // Power(x,y) >> calculates x**y >> >> end // End : T r >> o p o s p h e r e >> else >> begin // Begin: S t >> r a t o s p h e r e >> >> Tb:=Tw * ( 1.0 + BETAw*(1.0/Rhb - 1.0/Rw) ); >> RHOw := 273.15/1013.25 * RefPress/Tb; >> GAMMAw := g * REarth / ( Rgas * Tb ); >> rr := 1.0/Rrel - 1.0/Rhb; >> RHOpoly := RHOw * EXP( GAMMAw * rr ); >> >> end; // End : S t >> r a t o s p h e r e >> >> // Nminus1 ... Refractive index of air minus 1: (n-1)=0.00029241 >> getmu := 1.0 + Nminus1 * RHOpoly; >> >> end; // getmu >> >> > > >