Mapping the Ionosphere with Phones | Hacker News Reader

Mapping the Ionosphere with Phones

nature.com

96 pointsgnabgib16 comments

The existing ground-station ionosphere data mentioned has been used to detect missile launches: https://www.armscontrolwonk.com/archive/1216884/detecting-mi...

I imagine you could do the same thing with much better coverage using this distributed ionosphere monitoring method.

We're doing much more work now with RTK devices in our application and this was recently an issue for us.

A customer had been complaining that the RTK devices we were supporting were not working correctly and I got sent out there to have a look. After some back on forth and getting tests done on site, they revealed they often didn't get good fixes with any equipment between late morning and late afternoon, and that's how I found out about ionospheric interference and the the correction service's ionospheric warning page which consistently reported high interference around these times

What is RTK in this context?

https://en.wikipedia.org/wiki/Real-time_kinematic_positionin...

This is super interesting! For data quality nerdery: "there's no such thing as a string (without an encoding)", "there's no such thing as a timestamp (without a timezone)", and apparently for geo-data:

There's no such thing as a location (without a relative, timestamped, chain of reference points).

eg: 38°53′52″N 77°02′11″W (the white house), but needs a timestamp (eg: continental drift, san andreas fault: https://geotripper.blogspot.com/2023/10/why-did-road-cross-s...)

..and if you're doing this RTK-stuff, you kindof need to know that "chain of custody": Here => There => GPS@time

With GPS, we've kindof lost a lot of surveying / map-reading / orienteering in the general population, but looking at the guy trying to map out where the lines in the parking lot are to sub-millimeter accuracy really points out that it's inherently a relative (and time-fixed) process where the local _relative_ positions might not change really appreciably at all, but relative to GPS, over decades there'd probably be some skew (which could be "corrected", but only if you kept that original "chain of custody" of your measurements).

RTK is really about correcting for momentary atmospheric conditions that lead to SLIGHTLY different propagation times for radio waves in order to get much more accurate measurements. The idea is that you take nearby fixed objects that are constantly recording their GPS position, and so over time their precision in their GPS fix goes up. When you hop on with your RTK, it will communicate with those nearby GPS stations and apply a correction based on what they measure vs. the position they know they're actually at.

What you're talking about is totally true though. And it's why defining land boundaries by GPS coordinates is not a good idea.

That's when we get into the wonderful world of coordinate systems. These are deeply involved with RTK, and not knowing about them can mean you get incorrect results even with the RTK, most correction services actually use specific localized coordinate systems, and even offer additional correction data when even that is not enough.

Interesting use by Google of everyone's android phone data to compute space weather info.

Do users who unknowingly contributed sensor data get a sticker or badge or anything? Reminds me of seti@home.

What else could you do with full control of a global botnet of high powered sensor packs like android phones?

Imagine if they all transmitted simultaneously in a manner that was phase synchronized at a particular destination…

What would you expect to happen?

Most current day cellphone antennas don't have phasing for any tuned directionality. There are hard limits to array size due to physics and phones are just very small compared to yhe wavelengths they use.

And then there is the general challenge of synchronizing the transmitter phase. There is only so much that can be done via GNSS.

If cellphone frequencies were not filled with cellphones, it could make for a neat radiotelescope on receive.

This would be more practical with cell towers I think, but again they have the same GNSS based timing

Ignoring phase synchronization concerns, a cell phone can transmit about 3W of power, so a million of them would be about equivalent to the 3MW of the HAARP transmitter. Frequencies are different, HAARP is in the MHz range, cell phones are GHz, so while I bet your cell phone array would have less effect on the ionosphere, I also bet it it would cook a mean hot pocket.

https://en.wikipedia.org/wiki/High-frequency_Active_Auroral_...

From https://research.google/blog/mapping-the-ionosphere-with-the...:

> Knowing the current ionospheric conditions allows a GPS receiver to reduce location error by several meters.

This is amazing

This is rather tangential, but I see from the map of Europe that monitoring stations are clustered in three nations - Italy, Portugal and Sweden (at least the southern part of the last, which is as far as the map covers.)

> Knowing the current ionospheric conditions allows a GPS receiver to reduce location error by several meters.

This is amazing

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