You may not have noticed it, but last Friday we experienced the first serious geomagnetic storm in this solar cycle (Solar Cycle 24), which began in 2009. Not all types of solar activity (sun spots, solar flares, solar burst, and solar radiation) affect GPS receiver operations. Geomagnetic storms are the ones that can cause problems for GPS receivers if those storms are powerful enough.
Last Thursday, I received e-mail from Joe Kunches at NOAA (National Oceanic and Atmospheric Administration).
“The Sun has been erupting and looks like a storm — say G3 level — could be on for Friday, August 5.”
Joe was right, it hit about a day later, on Friday, August 5, as he predicted.
The good news is that Joe says we generally have at least a 24-hour warning before a geomagnetic storm starts disturbing the ionosphere.
That’s what it comes down to, the ionosphere.
GPS signals being delayed as they pass through the ionosphere end up being the largest source of error in GPS positioning. The signals must pass through the ionosphere, which is full of free electrons. The density of these electrons in the ionosphere affects the speed at which GPS signals travel. If the density of the electrons in the ionosphere was consistent, then it would be straight-forward to create a model and largely mitigate its effects. However, that’s not always the case. The ionosphere has been relatively benign since the last solar cycle, and that’s one of the reasons that GPS accuracy has been so good, especially GPS L1 SBAS systems like WAAS/EGNOS/MSAS, which rely on modeling the ionosphere.
The problem is geomagnetic storms. They wreak havoc on the free electrons in the ionosphere, making it difficult to accurately determine how much the GPS signals have been delayed.
The NOAA Space Weather Prediction Center (SWPC) is one of the foremost agencies that monitors the Total Electron Count (TEC) in the ionosphere. With Joe’s help, I was able to obtain dynamic plots of the TEC from last Friday so I could illustrate to you what happened. I was also able to obtain plots from Gavin Schrock at the Washington State Reference Network (WSRN) showing how it impacted the WSRN. I compiled the plots, added some text, and produced the following Youtube video.
As I wrote in the Youtube video, to get the most updated solar activity information that’s related to high-precision GPS users, you should follow me on Twitter at GPSGIS_Eric.
If you’re looking for a good backgrounder on how the ionosphere affects GPS, you might want to read this April 1991 GPS World column. Although it’s dated in some respects, the fundamental concepts are solid.
Last Push on LightSquared
There’s been some confusion on the FCC comment period regarding the LightSquared/GPS interference issue. The comment period was not extended. The public comment period was July 1 to July 30, 2011. The reply comment period is from August 1 to August 15, 2011. However, it appears the FCC is still logging new comments even after the July 30 cut-off date. Either way, do not hesitate to submit your comments before August 15; just mark it (dropdown menu) as a reply to comments.
This is your last chance to speak out and let your government know how important GPS is to your orgnization.
To date, there have been more than 2,900 individual comments electronically filed as well as more than 15,000 submitted in writing to the FCC (15,000 alone from the Boat Owners Association of the United States). The vast majority of the comments support GPS.
Some good news. On Tuesday, August 9, the FCC held an invitation-only press conference. Click here to read PC World’s summary.
To read the 2,900+ comments submitted to date, click here; type in proceeding # 11-109 and search.
Thanks, and see you next time.
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