WAAS

WAAS - Wide Area Augmentation System

Update - May 2008

Still no useful WAAS in Australia so the info below is still valid.

Update - December 2005

From Arthur King,

I spent the last 2 days searching for info on WAAS in Aus!

In summary: we don't have it (yet)
Someone mentioned a base station (in testing) in Canberra.
This station (and one other long range station in Hawaii) is part of
the Japanese MSAS system, which is in testing phase. The signal will
come on and off at various times, according to this timetable,
http://www.kasc.go.jp/MSAS/index_e.html .

The signal is confusing some GPSr's into thinking its MSAS(WAAS)
correction data, but (if you read the FAQ in the pdf) it clearly
states it's not! It's a "test signal" in a data format for highend
aviation GPSr equipment!!

Until Magellan (and others) release firmware compatible with MSAS, the
GPSr will be fooled into thinking it has WAAS correction data.

I was initially fooled after reading lots of info that seemed to
indicate that we are receiving MSAS.
But this has put that to rest (till '07!!)

WAAS should be "OFF"
And by my understanding, the East Coast should have a reasonable MSAS
correction data signal from those MTSAT's.

Update - 23-Oct-2002

How to turn off WAAS on Magellan GPS units

Update - 22-Oct-2002

Morning Brian,
I read your article regarding WAAS with interest. I am in Townsville S19.45 E146.15 and have been performing WAAS observations for some time. Satellite 47 is approx 45deg above horizon and azimuth of approximately 45 deg. Depending upon current satellite geometry, accuracy is improved or diminished. EPE of 1.5 metres have been achieved and also blow outs to 60 metres have been observed. The closest base station is Hawaii and this is the reason for the blow outs. In Brisbane I have not achieved a 2d or 3D differential fix. This is available in Townsville most of the time. The accuracy may improved or blow out.

The role of differential corrections is only part of the reason for WAAS. Its main role is integrity monitoring in that it continuously monitors individual GPS satellites and if there is any abnormality it will not include them in the differential correction. The Jappanese Multifuntion Satellite will hopefully be re launched soon and this will have a footprint covering all Australia. The original was lost on launch about 2 years ago.

As well as supplying weather maps it will also act as a WAAS satellite. The GPS base stations are already in existence and have been there for 15 years as the National Fudicial Network and it is owned by the Commonwealth via Auslig. They would probably require upgrading to output RTCM??? but the network along with the telecommunications network and control centre is there and it is not utilised anything near capacity.

The WAAS system is for category 2 instrument approaches and it is going to be very interesting when international airlines arrive in Australia and discover that this facility no available. Differential corrections with selective availability switched off have about 15 minutes redundancy. The only thing that changes is atmospheric and ionespheric errors and they are stable for up to 15 minutes.

WAAS is a a very good system and the lack of vision by the present government to not involve Australia in it, will in time prove to be of great national detriment.

Regards Kevin Parkes
Geo Positioning Services
47 Ingham Road Townsville

Update 18-Jun-2002

Here are some observations from GPSOZ's location. They are 4 samples taken over 12 hours each. Two receivers, Garmin GPSmap76 and a Magellan Meridian GPS, with and without WAAS enabled. Basically when using a WAAS capable GPS in Australia, turn OFF WAAS.

Garmin GPSMap 76 - WAAS Enabled
Garmin GPSMap 76 - WAAS Disabled
Magellan Meridian GPS - WAAS Enabled
Magellan Meridian GPS - WAAS Disabled

In all cases, the averaging feature of both GPS units reported our location as indicated by the blue + in the centre of the screen.

A couple of people have asked me what WAAS is all about. Briefly, its a set of ground stations that send correction signals to a set of WAAS satellites. These in turn broadcast back to your GPS. If your GPS is capable of receiving these correction signals, your accuracy will improve(?) to around 3m

It was originally designed when accuracy was typically +/- 100m ie when SA was switched on. However the information that I have received to date, indicates that there are no ground stations in Australia and NO plans to build any. Hence WAAS correction information is NOT available in Australia and very unlikely to be.

Interestingly Air Service Australia has just conducted a series of tests and found that the average accuracy in Canberra was 2.2m. Given that WAAS accuracy is typically 3m then why do it? Good question.

There is also a couple of technical reasons why WAAS in its current form will never be implemented in Australia:

It takes around 27 ground stations to cover an area the size of
Australia. (similar to the US).

Currently it takes 5 secs to process and broadcast the data from the
27 US ground stations. Aviation guidelines state information must be available to pilots within 6 seconds. Not much time left!

Correction information can only be sent from ground stations in the
US. Given the previous 6 sec guideline that only leaves 1 sec to
process and transmit to the US data from any other source
eg Australia. Can't be done!

Cost - can 18 million Australians afford to increase the accuracy to
3m? Is there a market, who will fund it? Who will pay for the
upgrades at the US end?

So the bottom line, discount WAAS in your GPS selection process if your sole use is outside the USA. It's a feature that can't be used in Australia.

More info:

gps.faa.gov/Programs/WAAS/waas.htm
and
wwws.raytheontands.com/waas/

www.gpsinformation.net/waasgps.htm

More when it comes to hand.