|
Science Forum Index » Geology - Satellite Navigation Forum » why is the vertical error likely to be greater than the hori
Page 1 of 1
|
| Author |
Message |
| Adam Chapman |
 Posted: Sat Jan 20, 2007 1:07 pm |
|
|
|
Guest
|
Hi,
I've just been looking through some of my lecture notes on GPS systems
for air traffic navigation, and at one point it says that the vertical
erroe can be up to 4 times the magnitude of horizontal error.
Could anybody tel me why this is?
The only sources of error I can think of would be anomilies in the
ionosphere or water vapour in the troposhpere "bending" the EM waves
from satellites.
I wouldn't think that the location of antennas on the aircraft, because
it just seems like an unacceptable design limitation to me.
Any help would be greatly appreciated.
Thanks,
Adam |
|
|
| Back to top |
|
| Adam Chapman |
| Posted: Sat Jan 20, 2007 1:25 pm |
|
|
|
Guest
|
Adam Chapman wrote:
Quote: Hi,
I've just been looking through some of my lecture notes on GPS systems
for air traffic navigation, and at one point it says that the vertical
erroe can be up to 4 times the magnitude of horizontal error.
Could anybody tel me why this is?
The only sources of error I can think of would be anomilies in the
ionosphere or water vapour in the troposhpere "bending" the EM waves
from satellites.
I wouldn't think that the location of antennas on the aircraft, because
it just seems like an unacceptable design limitation to me.
Any help would be greatly appreciated.
Thanks,
Adam |
|
|
| Back to top |
|
| Adam Chapman |
| Posted: Sat Jan 20, 2007 1:30 pm |
|
|
|
Guest
|
I guess if i imagined a satellite above the aircraft and a straight
line betwee the two, and imagined a standard error along that vector i
could translate the vector in to horizontal and verticle components.
if the ratio between verticle and horizontal error is 4:1, the angle fo
the satellite above the aircraft's forward flight vector would be about
76 degrees.
Am I on the right track? |
|
|
| Back to top |
|
| Anthony R. Gold |
| Posted: Sat Jan 20, 2007 2:50 pm |
|
|
|
Guest
|
On 20 Jan 2007 09:07:17 -0800, "Adam Chapman"
<adam.chapman@student.manchester.ac.uk> wrote:
Quote: I've just been looking through some of my lecture notes on GPS systems
for air traffic navigation, and at one point it says that the vertical
erroe can be up to 4 times the magnitude of horizontal error.
Could anybody tel me why this is?
I guess the lack of angular diversity between the locked satellites. In
the horizontal plane you can track satellites in up to 360 degrees of sky
but in a vertical plane you are restricted to just up to 180 degrees
because a certain planet is obscuring satellites in the other 180 degrees.
Tony |
|
|
| Back to top |
|
| Allan Sheppard |
| Posted: Sat Jan 20, 2007 3:30 pm |
|
|
|
Guest
|
Hi Adam,
In the case of the horizontal plane the trigometrical calculation is
in two dimensions whereas with vertical (height) you are calculating
in 3 dimensions.
If the satellites could transmit their signals through earth there
would not be a problem.
Quote: I guess if i imagined a satellite above the aircraft and a straight
line betwee the two, and imagined a standard error along that vector i
could translate the vector in to horizontal and verticle components.
if the ratio between verticle and horizontal error is 4:1, the angle fo
the satellite above the aircraft's forward flight vector would be about
76 degrees.
Am I on the right track? |
|
|
| Back to top |
|
| Roy A. Fletcher |
| Posted: Sat Jan 20, 2007 5:47 pm |
|
|
|
Guest
|
Adam Chapman (adam.chapman@student.manchester.ac.uk) wrote:
with editing...
: Hi,
: I've just been looking through some of my lecture notes on GPS systems
: for air traffic navigation, and at one point it says that the vertical
: erroe can be up to 4 times the magnitude of horizontal error.
: Could anybody tel me why this is?
The solution equations are weighted least-squares.
The horizontal coordinates are considered much more important
than the vertical height, so the iterative process tolerates
a larger error in the vertical than the horizontal.
The mathematical figure is stronger in the horizontal than
the vertical, but it is not four times as strong.
The software designers could reduce it from four times to
two times or 1.5 times if they so desired. It used to be
ten times (VDOP was ten times as large as HDOP) (DOP is
dimimuation of precision or what we have to tolerate
to get a solution in reasonable time).
For surveying work, elevation can usually be obtained more
accurately by other mean so VDOP is usually greater than HDOP
by more than four.
You could have less than four if you so desired, but would you
be increasing vertical or reducing horizontal. Methinks
reducing horizontal. But its gonna' cost ya'! Somebody's
gotta rewrite the software, test it and then reburn the
chip. Not cheap! Civilian units got cheap when newcomers
could use the research of the pioneers.
Regards. RAF |
|
|
| Back to top |
|
| zulutime |
| Posted: Sat Jan 20, 2007 6:43 pm |
|
|
|
Guest
|
Anthony R. Gold wrote:
Quote: On 20 Jan 2007 09:07:17 -0800, "Adam Chapman"
adam.chapman@student.manchester.ac.uk> wrote:
I've just been looking through some of my lecture notes on GPS systems
for air traffic navigation, and at one point it says that the vertical
erroe can be up to 4 times the magnitude of horizontal error.
Could anybody tel me why this is?
I guess the lack of angular diversity between the locked satellites. In
the horizontal plane you can track satellites in up to 360 degrees of sky
but in a vertical plane you are restricted to just up to 180 degrees
because a certain planet is obscuring satellites in the other 180 degrees.
Tony
Also, geoid-ellipsoid separation. |
|
|
| Back to top |
|
| Sam Wormley |
| Posted: Sat Jan 20, 2007 9:28 pm |
|
|
|
Guest
|
Adam Chapman wrote:
Quote: Hi,
I've just been looking through some of my lecture notes on GPS systems
for air traffic navigation, and at one point it says that the vertical
erroe can be up to 4 times the magnitude of horizontal error.
Could anybody tel me why this is?
The only sources of error I can think of would be anomilies in the
ionosphere or water vapour in the troposhpere "bending" the EM waves
from satellites.
I wouldn't think that the location of antennas on the aircraft, because
it just seems like an unacceptable design limitation to me.
Any help would be greatly appreciated.
Thanks,
Adam
Geometry
The Earth blocks the signals from all the satellites below your
horizon, so you have a geometric pattern of satellites that that
gives better horizontal accuracy than verticle accuracy. |
|
|
| Back to top |
|
| Sam Wormley |
| Posted: Sat Jan 20, 2007 9:29 pm |
|
|
|
Guest
|
Adam Chapman wrote:
Quote: Hi,
I've just been looking through some of my lecture notes on GPS systems
for air traffic navigation, and at one point it says that the vertical
erroe can be up to 4 times the magnitude of horizontal error.
Could anybody tel me why this is?
The only sources of error I can think of would be anomilies in the
ionosphere or water vapour in the troposhpere "bending" the EM waves
from satellites.
I wouldn't think that the location of antennas on the aircraft, because
it just seems like an unacceptable design limitation to me.
Any help would be greatly appreciated.
Thanks,
Adam
Geometry
The Earth blocks the signals from all the satellites below your
horizon, so you have a geometric pattern of satellites that that
gives better horizontal accuracy than vertical accuracy. |
|
|
| Back to top |
|
| Adam Chapman |
| Posted: Sun Jan 21, 2007 9:20 am |
|
|
|
Guest
|
Thanks to everyone for taking their spare time to help me out.
I am very thankful.
Adam |
|
|
| Back to top |
|
| Thomas Lindberg |
| Posted: Sun Jan 21, 2007 4:12 pm |
|
|
|
Guest
|
"Adam Chapman" <adam.chapman@student.manchester.ac.uk> wrote in message
news:1169385624.316454.116130@s34g2000cwa.googlegroups.com...
Quote: Thanks to everyone for taking their spare time to help me out.
I am very thankful.
Adam
But does it matter, even in aviation?
The altitude meter is still the reference and it is still the oldfashioned
barometric type.
Even for the big airliner guys.
Says Thomas in the tiny Cherokee |
|
|
| Back to top |
|
| John R. Copeland |
| Posted: Sun Jan 21, 2007 5:16 pm |
|
|
|
Guest
|
"Thomas Lindberg" <thomas.h.lindberg@telia.com> wrote in message news:cPPsh.29943$E02.12255@newsb.telia.net...
Quote:
But does it matter, even in aviation?
The altitude meter is still the reference and it is still the oldfashioned
barometric type.
Even for the big airliner guys.
Says Thomas in the tiny Cherokee
If he were operating in the USA under FAA jurisdiction,
even Thomas in his tiny Cherokee could install equipment which
would provide LNAV/VNAV or even LPV approach guidance,
giving glide paths computed directly from GPS/WAAS signals.
But the Minimum Descent Altitudes or Decision Altitudes still
would depend upon barometric altimetry, as Thomas mentioned.
Judging from his message header, Thomas may be operating
his Cherokee in Europe, so he may face some delay before he
can enjoy LNAV/VNAV or LPV approaches.
But I can attest those approaches are enjoyable, when available. |
|
|
| Back to top |
|
| Gerard M Foley |
| Posted: Sun Jan 21, 2007 7:43 pm |
|
|
|
Guest
|
|
| Back to top |
|
| |
