Yes, Solar Storms Can Ruin Your GPS Day

During this peak year of the current solar cycle, there will be some very-GPS-unfriendly days. Being prepared can minimize the impact on your productivity.

Be prepared: In short, learn how to find and interpret solar activity prediction resources and warnings…. and perhaps it is a good time to upgrade your gear.

Background

We are experiencing the peak of Solar Cycle 25 (the 25^th since solar cycles were first recorded. The rocky times are expected to extend through 2025 and into early 2026. While this solar cycle peak may not be any worse than previous ones, there have already been some significant periods of intense geomagnetic activity. You see the posts and news about Aurora Borealis activity viewable in places that normally do not see it (a sure sign of rough solar periods).

Rather than rehash much of the background, read this article: Preparing for the Effects of Solar Cycle 25 on GNSS Applications. In the months since that article was published, we’ve conferred with RTN operators and GNSS developers who have monitoring arrays. An analysis of data feedback from several solar storms has helped us develop some recommendations for how to prepare for and minimize the effects of, solar events.

 

Analyzing a Solar Event

The May 10, 2024,  Extreme Gannon Geomagnetic Storm, was the most significant since the Halloween storms of 2003. In terms of high-precision GNSS, here are a few things we learned from the analysis.

1. Not all GNSS rovers were affected in the same way. Some saw only slower fixes, others experienced no fixes and/or terrible residuals.
2. Multi-constellation, implemented on both the base (or RTN) and rover, rode out the storm far better than single constellation gear. The former, especially newer gear with the solar activity measures manufacturers have recently added, typically continued to operate just fine. Users may have experienced slightly slower fixes, but residuals were mostly acceptable.
3. Older rovers struggled, or were not useable, though most of this may be due to being limited to single, or dual constellations.
4. There is no other way to say this: bargain rovers failed. As did some drones (thaat use the same boards as are used in bargain rovers).
5. Post-processing does not help; if the base data for a period is affected by the solar storm, then no amount of post-processing can help.

There were, of course, certain exceptions. During such solar storms, the effects of scintillation can be exacerbated. So, even top-performing rovers that were otherwise riding out the storm just fine, may have experienced brief periods of intense effects. And there were users who experienced cellular connectivity and radio issues.

Heed the Warnings

You probably see the frequent, seemingly daily, news bits about “the biggest solar storm ever”. Or you may have subscribed to an email list for solar warnings. The problem is that the sometimes confusing terminology and various index conventions these sources present do not provide a GNSS rover user with a scale that they can relate to exactly what to expect in the field.

While there is an index developed specifically for GNSS, the I-95 ionospheric index. While it is not a predictive resource, it can still be very useful for users to better correlate with the scales presented by the predictive resources. More on I-95 later.

The other challenge of space weather resources and their predictions is that these are expressed mostly in terms of global levels, and may or may not reflect what is happening, or could happen in your specific vicinity. For instance, how does a global G2 storm warning equate to a KP index level for North America?

Fortunately, for different regions of the world, prediction resources are more locally focused. In North America, the National Oceanic and Atmospheric Administration (NOAA) provides a 3-day predictive tool that is expressed in the KP scale. Check this index daily. Don’t’ send your crew out to survey o the other side of the state on what is predicted to be a 7+ Kp day.

For instance, a G1 storm might u[p tp Kp 5, and G2 might bring KP 6+—which is when you might start seeing effects. There are some other prediction resources from vendors like Leica and others.  NOAA has a 27-day prediction tool that can give you a rough idea, but it is best to check again with the 3-day tool.

A Kp of over 7 is a significant event, and you could (depending on your gear) see slow fixes, poor residuals, no fixes, terrible residuals, or even no GNSS at all.

Here is where the I95 index could be very handy. I-95 is calculated by many local, state, or regional Real-time networks (RTN) using data from their fixed stations. I-95 is often expressed in units of expected, uncorrected error (centimeters) and/or color-coded levels.

During rough solar days, users can begin to develop rules of thumb for their gear, by looking at observed Kp levels and locally observed I95 levels. Then you can correlate these with what your gear experienced at different levels. This can make forecast scales more useful in planning your fieldwork.

Updating and Upgrading

This linked article includes some detail about what GNSS rover manufacturers have done, since the last solar peak, to help mitigate the effects of solar storms. In some cases, the features were only practical on newer, multi-constellation rovers (with a lot of processing power). In some cases, a firmware update (for newer gear) activates it. But for older gear, there is no option for this.

I do not want to open a can of worms, but the following must be considered. If you are OK with a few days here and there of no-go-solar-hell-days, a bargain rover will serve your needs (on solar-happy days). For some users that are in high-production environments or projects, the pricier gear, with better performance in mixed environments (as well as rough solar days) can be well worth it.

Drone work can especially be challenging and frustrating during bad solar days. Many (even some of the most popular) drones have small, light, and relatively inexpensive GNSS boards. There are very popular, low-cost GNSS (and GNSS+IMU) boards developed for the nascent autonomy market that are quite appealing to drone manufacturers. Some firms have even taken the same boards and made rovers out of them (some via DIY kits).  This is all great under optimal conditions, but perhaps it is not wise to try to use these during bad solar days. As an RTN operator, most of the calls I got were from drone and low-cost rover users, plus some legacy rover users.

Intense and Inconvenient but Infrequent

So far, in 2024, I’ve recorded a dozen bad solar days. And fortunately, half of these fell on weekends (pure luck). The prospects of a no-go day about once a month might not impact the operations of some users much, but it can be a serious proposition for others.

But don’t fall into the “vibe-ospheric” trap. Yes, we are in the peak of a solar cycle and it casts a d vibe over field operations—but you should not blame everything on it. You might be having comms issues, settings issues, bad multipath, or another issue you should troubleshoot. Instead, some users blame it all on the sun.

Planning ahead for field operations is not new. After all, you can’t do star shots or sun shots on cloudy days. NASA can launch a rocket to the moon, but not on a rainy day. Plan ahead!