Document magnetometer siting guidance for ~10 nT-class citizen-hosted stations (literature and documentation gap)

[w2naf]

AI-assisted content notice: This issue was drafted with AI assistance (Claude, Anthropic, claude-fable-5) from a working reference file prepared 2026-08-20. It has not yet been fully human-reviewed. Citations were checked against published abstracts and full texts on 2026-08-20, but DOIs and details should be verified before any of this is used in formal documentation or publication.

Summary

There is no published siting specification for ~10 nT-class, citizen-hosted magnetometers, and PSWS documentation currently has no siting guidance to give a prospective host. Every citable siting standard (IAGA, INTERMAGNET, DOE) is written for ~0.1 nT-class observatory performance. Citing those criteria directly to a PSWS host over-constrains the site by roughly 30–100x relative to the instrument's actual noise budget and risks discouraging otherwise-viable installations.

The gap

A recent siting inquiry from a prospective DASI2 host surfaced four questions that we could not answer from any existing PSWS document:

1. Minimum distance from large metal objects, feed lines, and power lines.
2. Whether the magnetometer must be co-located with the HF receive antenna.
3. Whether elevation differences (tens of feet) matter.
4. Whether solar-charged battery power with a wireless data link is acceptable.

The honest answers exist, but they are scattered across observatory-practice literature written for a performance class two orders of magnitude more stringent than ours, plus institutional knowledge held by individual team members. Two structural problems follow:

• Literature gap: no peer-reviewed work establishes siting criteria appropriate to a ~3 nT resolution / ~10 nT working-budget instrument (Kim et al. 2024) deployed in amateur EM environments. The observatory standards frame the requirement correctly (site magnetic gradient, measurable at a candidate location) but at the wrong performance scale.
• Documentation gap: https://hamsci.org/mag_install does not currently give hosts a gradient-based siting framing, a mechanical-stability discussion, or a site-verification protocol. Each new host conversation re-derives the same guidance by email.

What documentation should cover

Drawn from the working reference; each point is defensible from the citations below or from first principles:

1. Distance from structures. Farther is better; the DOE guideline of 100 m (~330 ft) from substantial steel is the only published number. Static structures produce a baseline offset falling as 1/r³; the uncalibratable contamination comes from sources that move or switch (vehicles, garage doors, HVAC, well pumps, EV chargers, rotating antennas).
2. Elevation. The main-field vertical gradient is ~0.024 nT/m, so a 50 ft drop contributes a ~0.36 nT static offset, an order of magnitude below the 3 nT resolution. Elevation can be disregarded at host-site scales.
3. Antenna co-location. Not required. Keep ~10 ft or more from any structure that flexes in wind: for a vector sensor in a ~52,000 nT field, a 12 arcsec tilt produces a ~3 nT artifact (one full resolution element). Mechanical stability of the mount dominates over proximity to static non-magnetic structures.
4. Site verification protocol. Log 24–48 hours at the candidate location and compare against the nearest INTERMAGNET/SuperMAG station before committing to a permanent installation.
5. Off-grid solar power. Feasible; Mrozowski et al. (2024) met the INTERMAGNET one-second standard on a solar-powered node using shielded twisted-pair power runs, non-magnetic hardware, and ~1.5 m separation between sensor and power/compute modules. Their power-system lessons transfer to the RM3100; their orientation tolerance (scalar OPM) does not.

Open technical questions blocking complete guidance

• Maximum supported i2c cable length for the sensor run. Hosts need this number to order cable; it is currently unresolved.
• Minimum separation between a field-sited Raspberry Pi and the sensor before readings degrade. The Mrozowski et al. ~1.5 m figure is a starting hypothesis for a comparable compute load.
• Whether ongoing suburban-placement research (NJIT) can support a short methods paper establishing empirical siting criteria for this instrument class. That paper would fill the literature gap for the whole distributed-magnetometer community.

Starting-point citations

• Kim, H., Witten, D., Madey, J., Frissell, N., Gibbons, J., Engelke, W., Liddle, A., Muscolino, N., Visone, J., & Cao, Z. (2024). Citizen science: Development of a low-cost magnetometer system for a coordinated space weather monitoring. HardwareX, 21, e00580. https://doi.org/10.1016/j.ohx.2024.e00580 — defines the ~3 nT resolution and ~10 nT working budget that siting guidance should be scaled to.
• Jankowski, J., & Sucksdorff, C. (1996). IAGA Guide for Magnetic Measurements and Observatory Practice. IAGA, Warsaw. ISBN 0-9650686-2-5. https://www.iaga-aiga.org/publications/guides/ — canonical observatory siting reference; gives no universal distance figure.
• INTERMAGNET Technical Reference Manual, §2.2 Environment/Location. https://tech-man.intermagnet.org/latest/chapters/oneminuteimos/envlocation.html — frames the siting criterion as minimizing site magnetic gradient, the framing PSWS documentation should adopt.
• U.S. Department of Energy (2019). Geomagnetic Disturbance Monitoring Approach and Implementation Strategies. CESER. https://www.energy.gov/ceser/articles/geomagnetic-disturbance-monitoring-approach-and-implementation-strategies — federal (non-peer-reviewed) document containing the 100 m / steel-structure guideline.
• Bowen, T. A., et al. (2019). A network of magnetometers for multi-scale urban science and informatics. Geosci. Instrum. Method. Data Syst., 8, 129–138. https://doi.org/10.5194/gi-8-129-2019 — shows dominant urban/suburban contamination comes from large time-varying sources (e.g., DC rail), not nearby static structures.
• Soloviev, A., et al. Development and testing of a portable "noise-meter" for areal assessment of artificial magnetic noise at geomagnetic observatories. GI preprint gi-2019-18. https://gi.copernicus.org/preprints/gi-2019-18/gi-2019-18.pdf — precedent for empirical site surveys over fixed distance rules. (Cited from preprint; locate the final published version before formal use.)
• Mrozowski, M. S., et al. (2024). Distributed network of optically pumped magnetometers for space weather monitoring. Scientific Reports, 14, 28229. https://doi.org/10.1038/s41598-024-79841-x — published precedent for a solar-powered, remote-comms node meeting the INTERMAGNET one-second standard.
• Hartinger, M., et al. (2023). Global Networks of Ground-Based Magnetometers Enable Cutting-Edge Heliophysics Research, Education, and Space Weather Operations. Bulletin of the AAS, 55(3). https://doi.org/10.3847/25c2cfeb.abafe08b — community-level justification for dense distributed networks.

Proposed deliverables

1. A siting guidance document in this repository (and/or an update to https://hamsci.org/mag_install) written for PSWS hosts, using the gradient-based framing, the static-vs-moving-source distinction, the tilt-sensitivity argument, and the 24–48 hour verification protocol.
2. Resolution of the i2c cable-length and Pi-separation questions, with hard numbers hosts can order cable against.
3. Evaluation of whether the suburban-placement work supports a short methods paper on siting criteria for ~10 nT-class citizen-hosted magnetometers.

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