August 31 Webinar Q&A Follow-up

September 1, 2010  - By

Earlier today (August 31), I conducted a webinar entitled “Solar Activity, SBAS and 24+3 GPS Constellation Updates.” Considering we only announced the webinar three weeks ago, we had a fantastic registration numbers, with more than 570 registered. Thank you for attending if you did. If you weren’t able to you’ll be able to download the presentation by registering here. After registering, you’ll be notified when it’s available for download (usually a couple of days after the webinar).

I had a lot of questions before and during the webinar. As customary, I’d like to address some of those as well as present the poll results here. First, the poll questions and results with accompanying pie charts to illustrate the results.


Poll #1: How concerned are you about solar activity affecting your GNSS operations?

Total votes: 157

Gakstatter comment: These numbers don’t surprise me. Personally, I probably fall in the “Somewhat” category, but my GPS/GNSS field work is pretty flexible so I can easily adjust without much inconvenience. However, if I had several crews using GPS/GNSS on a daily or near-daily basis or I had equipment relying on GPS/GNSS, I think I’d be in the “Very” category because the $$ impact would be much higher.


Poll #2: If it was available, would you be interested in receiving alerts/warnings of solar activity that may affect GNSS operations?

Total votes: 176

Gakstatter comment: I’m not surprised at these results either. When I initially considered this poll, I was thinking about asking which type of platform you would prefer to receive alerts/warnings with the choices being Droid app, iPhone app, Blackberry app, text message, e-mail, etc. If you have a preference on that, fire off a quick e-mail to me. Secondly, a few of you pointed out that NASA has an app for this, but keep in mind that the system I’m considering is focused specifically on high-performance/precision GPS/GNSS users, which would eliminate a lot of the baggage of the alert/warning systems available today.
Poll #3: Do any of your GPS receivers use SBAS (WAAS/EGNOS/MSAS) as a primary source of corrections?

Total votes: 115


Gakstatter comment: Not much to say here except that a substantial number of commercial GPS users are relying on SBAS. This has definitely been the trend over the past five years.


Poll #4: Do you expect that the GPS 24+3 configuration will improve your GPS productivity?

Total votes: 172

Gakstatter comment: Like most of you, I have great expectations for the 24+3 configuration. While launching more satellites with L5 would be nice, that’s a long-term effort, whereas the 24+3 configuration is something we will benefit from in a few months and are seeing some marginal benefit now. In January 2011, once all the satellites have arrived at their destination slots, I’ll plot new visibility charts and see where we stand.


Following are some of the questions that were posed by the audience during the webinar:
Question #1: The blueline ends in late 2009. Any information on up-to-date activity?

Gakstatter comment: This question was in reference to the Solar Cycle 24 prediction chart I displayed. The chart was probably small and difficult to read when displayed on your computer. Here’s a larger version of it. This was a chart released by the NOAA Space Weather Prediction Center in May 2009. Although sunspots don’t directly affect GPS operations, there is some relationship between sunspots and geomagnetic storms. Below it is an updated chart with actual values through the end of July 2010.



Question #2: What tools/online sites can be used to see if there is a TEC anomaly at a specified time, including “today”?

Gakstatter comment: There is a cool real-time chart of the U.S. on NOAA’s Space Weather Prediction Center website. There are other interesting charts on SWPC’s website like the 10-day trend chart. The JPL had a website that displayed a real-time TEC, but I just checked it and it hasn’t been updated since June. Another website to check is the National Satellite Test Bed that displays a real-time plot of the WAAS ionospheric grid points. Click here to view a global real-time (updated every 60 minutes) TEC chart of the world published by the Australian Space Weather Agency.


Question #3: What is better for a receiver, Differential GPS or dual frequency? Any references on this?

Gakstatter comment: With respect to performance during periods of heightened solar activity, definitely dual-frequency receivers. Although I don’t have a specific cite for you right now, there has been plenty written on this subject. Single frequency DGPS receivers are the most vulnerable during periods of heightened solar activity.


Question #4: Is the disruption in the sub-meter scale, single-digit meters, or tens of meters?

Gakstatter comment: It depends on the severity of the geomagnetic storm. During the worst times of the Oct. 2003 event, it was up to 25 meters. That order of magnitude would be rare. Remember, those events occurred in about four days over the 11-year cycle. I have some figures that relate TEC to position error, but I’ll withhold those until I’ve got a better understanding of how practical they are.


Question #5: Is there some type of notification system for GNSS users of major solar events? E-mail alerts? Twitter tweets?

Gakstatter comment: Following are instructions for signing up for the NOAA alerts/warnings. This is a good start. Stay tuned for my alert/warning system later this fall. Follow me on Twitter at

Following are detailed instructions for signing up for alerts:

-Goto the Space Weather Prediction Center website.

-Click on Email products (under the Support Services menu on the left)

-Create an account if you don’t have one already (it’s free).

-Click on Subscribe

You don’t want to subscribe to everything. Here are the ones specific for GPS operations:

-Advisories/Space Weather Bulletin

-Geomagnetic Storm Products/(sign up for both Alerts and Warnings for K6, K7, K8, K9 events.

-For high latitude (55 degrees and higher) users, als
o sign up for Alerts and Warnings for K4 and K5 events.


Question #6: There is already an iPhone/iPod application that gives alerts of solar activity.

Gakstatter comment: Yes, I’m aware of the NASA app and there maybe others, but in my opinion they are too broad for high-performance/high-precision GPS/GNSS users. Personally, I don’t need to know about new sunspots and where they are located on the sun (although it’s cool to see in that app). I need to know when geomagnetic events are occurring that may interrupt or affect my GPS/GNSS fieldwork.


Question #7: Ouch, we’re at 59 degrees north, and 134 west. Seems like these problems are “picking” on Juneau.

Gakstatter comment: The good news for you is that Alaska has the most dense concentration of WAAS Reference Stations in the entire WAAS coverage area. Well, maybe not Juneau, but certainly “mainland” Alaska :-). Seriously, parts of Alaska produce the best WAAS accuracy due to the high density of WAAS reference stations.


Question #8: Will parts of BC, Canada, be affected by the SBAS outage?

Gakstatter comment: Not really, except that you’ll have one less WAAS GEO satellite in view for a month or so until PRN 133 is operational in November. I don’t think you’ll notice any change in performance. The exception would be if your receiver uses SBAS ranging. In that case, you’d be tracking one less satellite between the time that PRN 135 becomes unusable and the time PRN 133 becomes operational.

Following is an elevation plot of the current WAAS GEO satellites (PRN 135 and PRN 138):


Following is an elevation plot of only PRN 138. This is a possible scenario after PRN 135 is unusable in October 2010 and before PRN 133 is placed into service in November 2010.

Following is an elevation plot of PRN 138 and the new PRN 133 GEO which is expected to be placed into service sometime in November 2010.


Question #9: With the 24+3 configuration, is it that some sats were flying almost in tandem and they are spreading them out more?

Gakstatter comment: Yes, that is essentially what is happening. Some believe, including me, that a 24+6 configuration would be even better! But, one step at a time. I feel good that the U.S. Air Force is listening and responding.


I addressed many of the questions from the webinar. Some will take a little research on my side to answer properly. I should be able to address those in the mid-September newsletter. Thanks again to those who registered for the webinar. Feel free to send me an e-mail any time with comments, suggestions or questions.


See you next time.

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This article is tagged with , and posted in Opinions, Survey

About the Author:

Eric Gakstatter has been involved in the GPS/GNSS industry for more than 20 years. For 10 years, he held several product management positions in the GPS/GNSS industry, managing the development of several medium- and high-precision GNSS products along with associated data-collection and post-processing software. Since 2000, he's been a power user of GPS/GNSS technology as well as consulted with capital management companies; federal, state and local government agencies; and private companies on the application and/or development of GPS technology. Since 2006, he's been a contributor to GPS World magazine, serving as editor of the monthly Survey Scene newsletter until 2015, and as editor of Geospatial Solutions monthly newsletter for GPS World's sister site Geospatial Solutions, which focuses on GIS and geospatial technologies.

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