Re: GPS-determination velocity with carrier phase

Hi Filipe,

How much is the time span between two consecutive
phase measurements and how do you get "observed"
range rate from them?

The GPS satellites are accelerating at <1G. That 
gives you a few m/s difference in range rate every
sec.
If you take an "average" range rate using two phase
measurements, i.e. [v(t+dt)+v(t)]/2, the "observed"
range rate is not instantaneous but in the middle of
the time span, dt, by assuming a constant acceleration
during that time. This might give you those small
offsets in your velocity estimates.

Hope this helps,

Tak

--- Filipe Santos <[email protected]> wrote:

> Hello,
> 
> Sorry for my email, but I'm looking for help on GPS
> for determination 
> velocity...
> I'm working on GPS data, and I'm using the carrier
> phase for 
> determination of velocity, but in static test the
> results have a bias  
> (like offset -1m/s , 1.4m /s and 0.4 m/s) , what
> could be the problem? 
> can anyone help-me?
> 
> I use
> 
> obs = Hv
> 
> and H is the direction cossenos
> obs= derived( phase) - dtcorr*v_light + Hv_{velocity
> of satellite, given 
> by derivation of equations of ICD  }
> 
> were dtcorr is the derive clock drift = Eph(2,k)*dt
> + Eph(20,k)
> 
> and solve this by means of least squares..
> should I subtract something else? the relativist
> term should be used?
> 
> the ionosphere and troposphere could be neglected  ?
> 
> I have attached one graf witch the red is velocity
> derived by position 
> and blue is the estimation by using carrier
> phase....
> 
> many thanks,
> Filipe Santos
> > _______________________________________________
> opensource_gps mailing list
> [email protected]
>
http://lists.psas.pdx.edu/cgi-bin/mailman/listinfo/opensource_gps
> 


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