Can a low-cost ground magnetometer track Earth's geomagnetic variations?

A preregistered, 60-day test against the USGS Fredericksburg (FRD) magnetic observatory. Hypotheses, metrics, analysis code and success criteria were frozen and time-stamped by a third party before the test data existed.

Preregistration sealed on OSF

Test period

Day 15 of 60 · 23.4%

Start	2026-10-07 02:10 UTC (first data after the OSF seal)
Earliest end	2026-12-06 02:10 UTC — or later, until at least 12 geomagnetic storm windows are recorded

Integrity record

Independent time-stamps prove what was committed and when. The SHA-256 fingerprints identify the exact frozen documents: changing a single character changes the fingerprint.

OSF registration	https://osf.io/tqg3c
Sealed (UTC)	2026-10-07 02:00:35 UTC
SHA-256 · preregistration	0eb2c5dde7f413f3d256bc1ec7848bb440fe5fd38f03d67d19bcd946dc3c88fc
SHA-256 · analysis code	ec864faca86a23495d96b33840ae34f14dfa006ab2e7c81529a38b84a2d873ad
SHA-256 · SHA256SUMS.txt	44c5041110e5febbd516ef740bc9d3b38e98100a6ca3fd03af53883a871adb71
Public announcement	https://x.com/StormSentinelOr/status/2107653469368676529
Registration DOI	https://doi.org/10.17605/OSF.IO/TQG3C
Addendum 1 · thermal-correction sensitivity analysis (DOI)	https://doi.org/10.17605/OSF.IO/D2J73
Internet Archive · copy of the OSF registration	https://archive.org/details/osf-registrations-tqg3c-v1
Web archive · this page (2026-10-07 02:06 UTC)	https://web.archive.org/web/20261007020609/https://stormsentinel.org/
Web archive · record.json (2026-10-07 02:06 UTC)	https://web.archive.org/web/20261007020625/https://stormsentinel.org/record.json
Web archive · this page after sealing (2026-10-08 02:24 UTC)	https://web.archive.org/web/20261008022455/https://stormsentinel.org/?status=sealed
Web archive · record.json after sealing (2026-10-08 02:20 UTC)	https://web.archive.org/web/20261008022042/https://stormsentinel.org/record.json
Web archive · this page with Addendum 1 (2026-10-12 00:23 UTC)	https://web.archive.org/web/20261012002307/https://stormsentinel.org/
Web archive · record.json with Addendum 1 (2026-10-12 00:23 UTC)	https://web.archive.org/web/20261012002353/https://stormsentinel.org/record.json

How to verify: download the registered files from OSF and run sha256sum <file> (Linux/macOS) or certutil -hashfile <file> SHA256 (Windows). The result must match the fingerprints above. Machine-readable record: /record.json.

What is being tested

ReferenceGeomagnetic storm windows are defined only from the public USGS FRD record, never from our own sensors, so the test cannot be circular.

PredictionThe primary sensing axis shows more fluctuation inside storm windows than outside, with the direction of the effect fixed in advance.

Built-in controlInternal control channels, sharing the same acquisition chain and site, must not show the effect.

CommitmentThe result will be published whatever it is, including a negative or invalidated outcome.

Instrument log

Every physical change near the instrument is recorded here with its time. During the test period the instrument is not modified; any unavoidable intervention will be added below and declared as a deviation.

2026-10-12 00:06 UTCAddendum 1 registered on OSF (DOI 10.17605/OSF.IO/D2J73): adds a secondary thermal-correction sensitivity analysis, fixed before any test-period result. The registered analysis, its code and its decision rules are unchanged, and the addendum cannot change the verdict. SHA-256 of SHA256SUMS_addendum.txt: 522b093bd81f8208e439a1b9f0c91a9d107644129bca52643b768ebb7d94d14b.
2026-10-08 02:32 UTCHost-PC maintenance: the data-acquisition supervisor was restarted (a duplicate instance running since 2026-10-04 was removed). Data gaps: primary instrument 2 s, secondary instrument 3 s. Both instruments untouched; no effect on the 10-min analysis (segments split only at gaps > 30 min).
2026-10-08 01:40 UTCSecondary instrument: remote firmware update adding an internal temperature reading (once per minute); 12 s data gap at 01:40 UTC, plus a 5 s gap at 01:50 UTC when its data receiver was restarted. No physical access; primary instrument untouched. Deviation from the frozen-instrument statement for the secondary instrument only.
2026-10-07 02:00 UTCPreregistration submitted to OSF. Test period starts 02:10 UTC; instrument frozen until the end of the period.
2026-10-04 21:35 UTCMetal awning fully removed (DC step on all primary-instrument channels, transition about 2 min). Instrument left untouched from here on.
2026-09-23 13:32 UTCMetal awning partially moved away from the sensors (DC step visible on all primary-instrument channels).
2026-09-06 UTCSecondary instrument relocated.
2026-08-30 UTCSecondary instrument: mechanical adjustment.
2026-08-14 00:34 UTCMetal awning installed next to the sensor site.

Data sources

Reference magnetometer data: USGS Geomagnetism Program (FRD, public). Space-weather context: NOAA Space Weather Prediction Center. The instrument time series and analysis code will be deposited with a DOI at publication.