charliebishop
19th January 2008, 08:17 PM
Hello all,
I have a question someone in here may be able to help me with.
I have a time series of GPS positions, longitude and latitude, from a drifter at the top of the ocean, and I am trying to estimate the velocity of surface drift.
What I am doing is taking the difference between my first and last longitude coordinate and convert them to meters. This gives me my "delta x", and dividing by the time over which this occurred "delta t" at the surface, I obtain an estimate of surface velocity U (positive east)
I do the same for latitude,find the difference in latitudes, convert to meters then divide by "delta t", to obtain my velocity V (positive north).
But I need some kind of estimate of the error in these velocities, U and V. I know the appropriate error formulas for propagating error but I am unsure what number to use for my estimate in the error of my longitude and latitude data respectively.
The manual says the GPS is good to within 30m but this is for the radius around a point (lon,lat). What I require is an estimate of the error in the longitude, and a separate estimate of the error in the latitude. Or should I use 30m each for both? or perhaps half that for each ?
Is there any way to figure this out?
or perhaps there may be a different way to estimate my U and V from the gps coordinates and then use the specified error of 30m ?
Any help you can provide me on this would be greatly appreciated!
cheers,
- C
I have a question someone in here may be able to help me with.
I have a time series of GPS positions, longitude and latitude, from a drifter at the top of the ocean, and I am trying to estimate the velocity of surface drift.
What I am doing is taking the difference between my first and last longitude coordinate and convert them to meters. This gives me my "delta x", and dividing by the time over which this occurred "delta t" at the surface, I obtain an estimate of surface velocity U (positive east)
I do the same for latitude,find the difference in latitudes, convert to meters then divide by "delta t", to obtain my velocity V (positive north).
But I need some kind of estimate of the error in these velocities, U and V. I know the appropriate error formulas for propagating error but I am unsure what number to use for my estimate in the error of my longitude and latitude data respectively.
The manual says the GPS is good to within 30m but this is for the radius around a point (lon,lat). What I require is an estimate of the error in the longitude, and a separate estimate of the error in the latitude. Or should I use 30m each for both? or perhaps half that for each ?
Is there any way to figure this out?
or perhaps there may be a different way to estimate my U and V from the gps coordinates and then use the specified error of 30m ?
Any help you can provide me on this would be greatly appreciated!
cheers,
- C