CGSIC – The Rest (Better Late than Never)

September 24, 2009 By: Richard B. Langley

Here are a few more random notes on some of the other presentations at the CGSIC meeting on Monday and Tuesday.

Civil GNSS Monitoring. Tom Nagle and John Lavrakas gave a presentation on Civil GNSS Signal/Service Monitoring – a presentation that had been given by Karen Van Dyke at the recent ICG meeting in St. Petersburg. Currently, there is no “official” monitoring of the civil GPS signals (C/A-code, L2C, and L5), although the FAA does issue quarterly reports on the performance on the C/A-code-based Standard Positioning Service and some independent international networks, such as that of the International GNSS Service, assess the performance of GPS and GLONASS signals as reflected in position solutions and other products.

At the St. Petersburg meeting, the following ICG principle was proposed:
“Every GNSS provider should establish documented civil performance commitments to inform users about minimum levels of service.” There was not unanimous support for adopting this principle as worded among those at the meeting.

A document (largely written by Nagle and Lavrakas) on proposed monitoring principles has been distributed to GPS Wing contractors and has been made available on the www.pnt.gov website under “April PDF document.”

Included in the document are:

35 system performance monitoring requirements
136 requirements on signal monitoring
4 requirements on non-broadcast data

There is no mention about how the monitoring will be implemented although it is possible that it will be supported by the GPS Wing which intends to upgrade its monitoring stations to track the GPS civil signals as well as those of the other global navigation satellite systems.

Comments on the document, particularly something that may have been overlooked, are welcome.

“Panic” from Recent High DOPs Warning. During Monday morning’s Q&A session, the issue of the recent high DOP predicted GPS “outage” was discussed. Coast Guard personnel defended their decision to issue the warning based on their need to consider safety-of-life applications. However, the warning apparently created “panic” in some circles with some survey crews cancelling work planned for the day of the outage. Such decisions are based on a poor understanding of what such warnings (and related NANUs) really mean. As it turned out, and as reported in the October issue of GPS World, the DOP outages didn’t actually occur as 2SOPS quickly carried out the required satellite maintenance in a time slot not significantly impacted by setting the satellite unhealthy.

WAAS News. The FAA is in the process of acquiring a third GEO satellite. They will lease a transponder on Inmarsat’s 4F3 satellite positioned at 98° W. It is anticipated to be operational by FY 2011.

Russia is developing an ICAO-compliant SBAS.

In Anticipation of Solar Max. In an informative and entertaining presentation, Joe Kunches from NOAA in Boulder, Colorado, gave a status report and prediction on solar activity. The Sun has been extremely quiet for the past couple of years or so with no sunspots visible for months at a time. He raised the possibility that we might be entering a period like the Maunder minimum of the 1600s when very few sunspots were recorded and this might have been related to the “mini-ice-age” at that time. That stable climate period apparently gave rise to extremely healthy tree growth, which produced fine hardwood. It was this hardwood that Stradivarius used to build his famous violins.
A link between violins and sunspots? Strange.

Kunches discussed the effect of recent global warming and its expected effect on Arctic navigation. As more ships start navigating Arctic waters using GNSS, they will have to pay attention to polar ionosphere activity and its effects on GNSS including scintillations. They will have to have “Arctic domain awareness.”

Kunches also reported that a minimum in the sunspot cycle occurred in December 2008 and that sunspot cycle 24 has commenced. It is predicted to be an “average” cycle with a sunspot peak of 90 in May 2013. But there have been very few sunspots of the new cycle yet and the ionosphere remains very benign, although a couple of new sunspots are coming around the edge of the Sun this week. So, will we now have a build up of sunspots or go back to more blank days? And will GNSS users be surprised when the sun eventually comes back to life? Time will tell.

International Session. On Tuesday morning, I attended the international session, chaired by John Wilde. No reports on GLONASS or Beidou/Compass. (Russia and China were also no shows at the ION’s panel discussion on GNSS program updates on Wednesday morning.)

Over Reliance on GPS. Sally Basker gave a report on British efforts to safeguard shipping and the need to 1) better educate mariners on the benefits and pitfalls of GPS and 2) to have a backup to GPS, which in the cause of the British lighthouse authorities, will be provided by e-Loran. Take home message for the U.S. Congress? Get the finger out and finalize the appropriate funding for e-Loran in North America.

Japan. There was a report from Japan during which it was mentioned that the Japanese SBAS (MSAS) has a 95 percentile horizontal accuracy of better than 2.2 metres. The report also included an update on QZSS. The first satellite is currently under test and will be shipped to the launch site in April 2010 for a launch sometime in the July to September timeframe. Indoor positioning in Japan is in high demand and has spurred on, in part, the development of a super-high-sensitivity GPS chip with a reported –165 dBm sensitivity.

Timing Session. On Tuesday afternoon, I attended the timing session. The report of most interest to me was one by Ron Beard on the status of the proposal to abolish leap seconds that is moving through a process at the ITU with glacial speed. Beard is the chairman of Working Group 7A, which has been deliberating the proposal for several years now. The working group has now completed its technical studies and has passed on responsibility for further action on the proposal to its parent, Study Group 7. This happened at the recent meeting in Geneva. The full Study Group 7 received the report from the working group but because it was received late in the week, there was no time on the agenda to begin discussions, which will have to wait for a subsequent meeting.

Beard presented a summary of the views that the working group had received, broken down into three categories:

Those favouring the abolition of leap seconds
Those that were neutral or recommending more study
Those opposing the recommendation or identifying potential difficulties.

He noted, in particular, that the “astronomical community, at large, has moved [away from UTC] to dynamic relativistic time scales based on TT(1980).”

So, now the proposal has to be debated in Study Group 7. If there is consensus in the study group, then it would submit a draft recommendation for consideration at the Radiocommunication Assembly in January 2012. The earliest this can happen is in 2010. Then, at the Assembly, the proposal could be accepted if 70% of member states approve. If the proposal passes this set, then leap seconds would stop around 2020. The hitch in all this is that apparently the proposal cannot move out of the study group unless there is consensus and at the present time, the United Kingdom and China are against the proposal.

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