EGNOS update

It's just a load of twaddle and spin to disguise the fact that they recently put back the go live date to 'early' 2006 (as mentioned in the article).

Note that yet again there is no firm date, and given the history of changing dates (it was going to be 2003,then early 2004 then late 2004, then early 2005, then June 2005, then late 2005 etc etc etc - so few who has been following this have any confidence that 2006 go live date is going to be any more realistic than any previous dates they predicted wrongly
 
Re: EGNOS

I have always understood WAAS only to be of use around the USA. I believe that its accuracy deteriorates the further away you go and that it,in fact, could well make your position more inaccurate than the normal GPS signals the further from the States you are.

You could be reducing the accuracy of your position in the Med/Aegean by having it switched on.

Unless anyone knows better, of course.
 
Re: EGNOS

Charles? Do you ever read any of the other posts you comment on, with regard to Egnos and Waas? Other forunutes on this thread seem to have taken on the basics

In summary, don't use Waas outside USA. The correction factors they use from the ground stations there are worthless outside that area. Egnos corrections to GPS are useful in European area, but only once it goes live, and it is not yet, so don't turn on WAAS in Europe yet.

Other alternative GPS solutions will be available in years to come, but not here yet.
 
Thanks

pointing out I'm incorrect.

If you care to look at the WAAS Near Real Time Non Precision Navigation Service Display on http://www.nstb.tc.faa.gov/npa.html you'll find that you and other members of the forum have been grieviously misled and in the majority of UK waters WAAS coverage will give a perfectly adequate indication of GPS signal integrity.

I am however using WAAS at about 40N 19E, where the signal is near the limit of HDOP adequacy. The improved coverage I'm getting is probably from the experimental EGNOS satellites.

If you are referring to the pasted words of wisdom (direct from the FAA site) you may be justified in the comments you're making:-

"WAAS is not yet fully operational and is currently in a testing status, undergoing further development. It is not certified for use as a safety of life navigation system in the maritime navigation environment. WAAS may be used, with caution, in the maritime environment to improve overall situational awareness, but it should not be relied upon for safety-critical maritime navigation. The Maritime DGPS Service, on the other hand, is fully operational and meets all the standards for the harbor entrance and approach phases of navigation WAAS is not optimized for surface (maritime and terrestrial) use, rather, it was designed primarily for aviation use. It is intended to eventually support aeronautical enroute through precision approach air navigation. The current WAAS test signals are transmitted by two geo-stationary satellites on a line-of-sight, L-band radio frequency. This means that if anything obstructs the view of the portion of the sky where the satellite is, the WAAS signal will be blocked. Since geo-stationary satellites are positioned over the equator, the farther north users are, the lower the geo-stationary satellites are in the sky - increasing the likelihood of an obstruction. In contrast, the medium frequency (285-325 kHz) radiobeacon-based Maritime DGPS Service is optimized for surface (maritime and terrestrial) applications because it's ground wave signals "hug the earth" and wrap around objects. This means that the Coast Guard DGPS system is well suited for the marine environment (down in the "ground clutter") where a geo-stationary satellite can be blocked by terrain, harbor equipment and other man-made and natural objects"

My latest GPS receiver can run in 3 modes:-

1.WAAS-only. This requires and HDOP of better than 2.5 and means that such a setting would mean that the unit would display no position information in the area I am currently using it and would have limited availability in UK waters
2. WAAS-optimisation - this is very useful and gives me a constant indication of the level of integrity of the GPS signal and uses muliple WAAS satellites when in line-of-sight to augment the normal GPS signal.
GPS-only gives me 66'-30' dilution and when WAAS augmentation is available this drops to about 15' (I'm sure you can convert these into metres, but being a US set it gives its reading in feet)
3. GPS-only when it's no different to my other fixed 12-channel GPS set (perhaps slightly less so).

In the post to which you have taken exception the availability of WAAS enhancement during the month of June was in the order of 60%, though this was probably not continuous.

I print below the explanations, again from the faa site, of the terms used.

INTEGRITY refers to usability of the satellite signal, and means that the signal has not been corrupted. Integrity is the ability of a system to provide timely warnings to users when the system should not be used for navigation as a result of errors or failures in the system. WAAS improves upon the integrity of the basic GPS signal and detects much smaller errors more quickly.

AVAILABILITY refers to the percentage of time in a given period that the signal is
expected to be received and usable.

CONTINUITY differs from availability, in that it refers to the continuous reception of the signal. A signal could have high availability but numerous short outages.

Perhaps you'd like to review the evidence available and reconsider your position.
 
Re: Thanks

Charles, the ground stations that provide the corrections are based in the USA, so any corrections outside that territory are invalid, even if you can receive a correction signal. If you are improved coverage/reception, it's almost entirely down to you receiving the Egnos test signals. As explained many times on these forums, the Egnos signals are unreliable whilst in the test phase, and can result in hugely increased errors - this will improve with time, and when it goes live, will be very accurate.

PS have a look here for more info
http://www.kowoma.de/en/gps/waas_egnos.htm
 
Re: Thanks

Suggest your assumption is incorrect - have a look at the constantly changing HDOP values on the site referred to which excludes the EGNOS satellites.

If the positioning of the ground stations were so critical WAAS would be useless off the US mainland.
 
Re: Thanks

Not wishing to get into an urination contest, Brendan's summary of EGNOS current status is quite correct.

WAAS and EGNOS are local implementaions of what is generically called SBAS (Satellite Based Augmentation System). Because Garmin is US based, they lazily use WAAS rather tha SBAS to describe the SBAS facility.

You are receiving EGNOS. WAAS cannot be received in Europe or the Med. They are all local solutions. Enjoy but do not rely on the EGNOS signals - they can actually degrade GPS performance.
 
Re: Thanks

[ QUOTE ]
If the positioning of the ground stations were so critical WAAS would be useless off the US mainland.

[/ QUOTE ]

The WAAS satellite is totally useless outside North America. SBAS sats are geo-stationary satellites providing dedicated coverage to a small footprint area such as WAAS (North America), EGNOS (Europe) or MSAS (Asia).

Hate to say this, but be good if you did a bit of homework before pontificating hereabouts
 
As there appears to be a degree of misconception

could I refer all thread-readers to the following sites:-

http://www.nstb.tc.faa.gov/Terms.html

http://www.nstb.tc.faa.gov/npa.html

http://www.nstb.tc.faa.gov/vpl.html

http://ravel.esrin.esa.it/docs/egnos/estb/IMAGEtech/imagetech_realtime.htm

From which they will be able to discover:_

1. The current terms being used in discussing WAAS/EGNOS
2. The fact that US WAAS correction is available in European waters including the Meditarranean but not sufficiently continuous for aviation use (this is a marine BB is it not)
3. The coverage within the US for aviation use (you'll note it does not extend far from shore)
4. the coverage of the current 2 EGNOS corrected satellites.

Then perhaps we can continue a less subjective dialogue. /forums/images/graemlins/wink.gif
 
Re: EGNOS

If you care to refer to the coverage charts for the 2 EGNOS satellites you'll see that neither PRN 124 or PRN 126 are servicing the Mediterranean.

I would deduce from this that it is WAAS coverage that I'm receiving.

If you could produce any objective evidence to correct my illusion I'd be glad to concede your point.
 
Re: As there appears to be a degree of misconception

I think that you will find that Tome is correct.

I am no expert on WAAS but know a little about aviation. Firstly, there are no Wide Area Reference Stations outside North America (are going to be some in S.America but don't think any as yet). So WAAS does not maintain accuracy for outside of the area that those stations can provide corrections for.

The link you show giving NPA Contours and referring to HDOP>4 is the map for Non Precision Approaches only. It does not mean that WAAS precision is attained. I think that you will find that WAAS precision in the horizontal plane is only obtained in the map showing the Vertical Protection Level Contour ie essentially the continental USA excluding Alaska.

Getting back to the NPA contours, service in those areas does not include the ionspheric delay corrections (because there are no reference ground stations). What effect that has on accuracy I do not know (Tome may be able to help here) but I suspect that it is the main ingredient of accuracy and you are not getting it. But the accuracy required for NPA is 220 meters, so knowing that you are inside the NPA HDOP>4 contour is nothing to have any confidence over at all.

What is the accuracy. Well I know that the requirement for CAT 1 approaches (to runway for aircraft) requires a precision of 7.6 meters (actually 16 m in horizontal I believe) and WAAS without the ionospheric corrections does not give that precision but is somewhere between around 16m and 220m. So, one can infer that without the ionospheric corrections precision cannot be more than very little better than GPS uncorrected without selective availability, at best.

As far as I know the non ionspheric corrections are short term for clock corrections and longer term for ephemeris corrections. You may be getting those within HDOP>4 contours. But would seem that they add little by themselves and certainly do not give WAAS accuracy. Perhaps someone knows the accuracy both with and without the ionspheric corrections?

While no one should be navigating a boat depending on WAAS accuracy in any event, it is misleading to claim that such accuracy ever exists in UK or elsewhere in Europe (from WAAS that is, it may with EGNOS).

John
 
Re: EGNOS

Charles

You are confusing NSTB with WAAS. NSTB was discontinued when WAAS became operational and much of the data you point to is before SA was switched off. The WAAS signals only provide a useful improvement in positioning accuracy 200M from the network of ground reference stations, as the following
WAAS useful coverage shows.

Differential corrections from a baseline of over 3000 miles would be totally worthless and would considerably degrade your GPS receiver stand-alone performance if applied. Fortunately, your GPS receiver knows this and will not attempt to use WAAS corrections even if received at this range.

ESTB (which is the test phase of EGNOS) is running and we are currently monitoring it in North Africa. This is what you are receiving. During its current test phase we have frequently observed a degradation of positions so I would be cautious of enabling it before it is declared operational.
 
Re: EGNOS

From the Federal Aviation Authority Site FAQs on WAAS:-

<<A.. WAAS provides better accuracy that GPS alone. Non-aviation WAAS receivers in the aviation WAAS coverage area (http://www.nstb.tc.faa.gov/vpl.html) will get far better accuracies due to the WAAS corrections they are receiving. However, non-aviation users outside of the WAAS aviation coverage area can also benefit from WAAS corrections. Please refer to the Horizontal Protection Limit website (http://www.nstb.tc.faa.gov/npa.html) which shows the areas WAAS can be used for non-aviation and what types of accuracies you may expect.>>

The coverage map to which you refer is the first mentioned and specifically (as I understand it) refers to horizontal accuracy required for aviation use with an approved receiver. Surely this level of accuracy is not expected of marine use furthermore I suspect we'd not know what to do with such accuracy (1-2m) if we had it.

The one to which I refer is the second site above, which infers that one can expect an improvement over uncorrected GPS.

<<A. The WAAS supplies two different sets of corrections: 1) corrected GPS parameters (position, clock, etc) and 2) Ionospheric parameters. The first set of corrections is user position independent - they apply to all users located within the WAAS service area. The second set of corrections is area specific. WAAS supplies correction parameters for a number of points (organized in a grid pattern) across the WAAS service area. The user receiver computes ionospheric corrections for the received GPS signals based on algorithms which use the appropriate grid points for where the user is located. Further, the appropriate grid points may differ for each GPS satellite received and process by the user receiver as the GPS satellites are located at various positions in the sky relative to the user. The combination of the two sets of corrections allows for significantly increased user position accuracy and confidence anywhere in the WAAS service area.>>

Providing you accept the FAA contention that anyone within a better than HDOP4 is obtaining some benefit, the above gives you the unquantified benefits obtained.


My limited experience has been:-

No WAAS - 10-20m
More than 5 WAAS satellites above horizon c 4m.

In view of your comments of position degradation, when I get back to the boat I'll try to exclude use of PRN 124 and 126 and see if there are any results.

As this is one of two fixed GPS sets I'm using as aids to navigation its not ultra-important.
I suppose it all boils down to what one might consider to be the "service area".

In view of the comments from Ciampino (I spent last winter at Fiumicino) I suspect we'll be waiting a log time for EGNOS to give us a VPL coverage to equal North America.
 
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