Site information why elevation

PLudwig492@aol.com
Thu, 10 Jun 1999 02:15:50 EDT

kChia recently asked ...
> 
>     I am curious why do we need to specify elevation in addition  to
> longitude and latitude. Does this affect the precise apparent
> positioning fixing of satellite? What is the error involved comparing say
> Sea-level vs someone high up in Colorado..
> 
It seems to me that specifying the elevation becomes more important the 
closer a satellite is  because of the effect of parallax. Using the astronomy 
package of Mathematica the following results are obtained, e.g, for 15 NOAA  
and 
12 NOAA for 6/10/99-22.00.00 at 9 deg 11 min E, 51 deg 13 min N and 
elevations 0 and 2.5 km:

Elevation/km         Ascension          Declination            
   0.0                     12h 15m 40.7s       30 16   06      15 NOAA
   2.5                     12h 15m 41.4s       30 15   31 
 
   0.0                     10h  59m 15.7s      -39 40 41.6     12 NOAA
   2.5                     10h  59m  15.7s     -39 40 37.2

The  effect of elevation  of the point of observation on the coordinates of 
an orbiting object which is much further away than those used here vanishes.

Peter Ludwig