Appt-to-Obs Parameters SLA_AOPPA
CALL sla_AOPPA (DATE, DUT, ELONGM, PHIM, HM, XP, YP,
TDK, PMB, RH, WL, TLR, AOPRMS)
DATE | D | UTC date/time (Modified Julian Date, JD2400000.5) |
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DUT | D | UT: UT1UTC (UTC seconds) |
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ELONGM | D | observer’s mean longitude (radians, east +ve) |
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PHIM | D | observer’s mean geodetic latitude (radians) |
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HM | D | observer’s height above sea level (metres) |
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XP,YP | D | polar motion coordinates (radians) |
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TDK | D | local ambient temperature (K; std=273.15D0) |
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PMB | D | local atmospheric pressure (mb; std=1013.25D0) |
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RH | D | local relative humidity (in the range 0D0 – 1D0) |
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WL | D | effective wavelength (, e.g. 0.55D0) |
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TLR | D | tropospheric lapse rate (K per metre, e.g. 0.0065D0) |
AOPRMS | D(14) | star-independent apparent-to-observed parameters: |
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(1) |
| geodetic latitude (radians) |
(2,3) |
| sine and cosine of geodetic latitude |
(4) |
| magnitude of diurnal aberration vector |
(5) |
| height (HM) |
(6) |
| ambient temperature (TDK) |
(7) |
| pressure (PMB) |
(8) |
| relative humidity (RH) |
(9) |
| wavelength (WL) |
(10) |
| lapse rate (TLR) |
(11,12) |
| refraction constants A and B (radians) |
(13) |
| longitude + eqn of equinoxes + “sidereal UT” (radians) |
(14) |
| local apparent sidereal time (radians) |
HM=-29.3D0*TSL*LOG(P/1013.25D0)
where TSL is the approximate sea-level air temperature in K (see Astrophysical Quantities, C.W.Allen, 3rd edition, §52). Similarly, if the pressure P is not known, it can be estimated from the height of the observing station, HM as follows:
P=1013.25D0*EXP(-HM/(29.3D0*TSL))
Note, however, that the refraction is nearly proportional to the pressure and that an accurate P value is important for precise work.