Raspberry Pi Magnetometer

Live Magnetometer Dashboard

Monitoring Earth's magnetic field from my backyard in Louisville, Colorado using an RM3100 magnetometer on a Raspberry Pi. Geomagnetic data from the USGS Boulder Observatory (~10 miles north of my house) is also plotted for comparison.

View the data in sensor-aligned magnetic coordinates (H, E, Z, F), or in geographic coordinates (X, Y, Z, F) rotated by the local magnetic declination (~7.8°).

About This Project

This station measures the tri-axial geomagnetic field in sensor coordinates. The sensor is mechanically aligned to approximate the magnetic NEZ frame: H (horizontal intensity toward magnetic north), E (magnetic east), Z (vertical, positive downward), and F (total field). Variations in these measurements can indicate geomagnetic storms and substorms caused by solar activity.

Coordinate Transformation

Geographic coordinates (X, Y) are computed from magnetic coordinates (H, E) using a 2D rotation by the local declination D ≈ 7.8°:

Z (vertical) and F (total field) remain unchanged by this rotation.

Installation

The magnetometer uses a PNI RM3100 magneto-inductive sensor with a noise floor of ~4 pT/√Hz at 1 Hz. I ordered the kit from HamSCI and followed their PSWS Ground Magnetometer installation guide.

The sensor is housed in a PVC pipe and buried vertically approximately 3 feet underground to provide temperature stability and isolation from electromagnetic interference. The sensor is oriented so that the H-axis points toward magnetic north, determined by rotating the assembly until the E component reads near-zero. A shielded CAT6 Ethernet cable runs underground to my shed, where the Raspberry Pi handles data acquisition and transmission to a cloud database.

Since the sensor is located in a residential backyard exposed to various sources of magnetic noise, I expect a resolution of 10–20 nT. The raw 1-second data exhibits a periodic fluctuation with a period of ~10–11 seconds and amplitude of approximately 10 nT. This is likely instrumental or EMI-related; it partially averages out at the 1-minute cadence but may still alias into spectral analyses.

Baseline Corrections

To compare the Raspberry Pi magnetometer readings with USGS Boulder Observatory data, baseline offset corrections are applied. These offsets account for differences in sensor calibration, local crustal magnetic anomalies, and the ~10-mile distance between the two sites.

The bias values were determined by calculating the median difference between the Raspberry Pi and USGS Boulder measurements over approximately 60 days of observations (November 2025 – January 2026):

• H: +490.7 nT
• E: ~0 nT (aligned during installation)
• Z: +3914.4 nT
• F: +3767.7 nT
• X: +486.2 nT
• Y: +66.6 nT

Note: These offsets absorb both sensor bias and real geophysical differences (crustal anomalies, local cultural noise) between the sites. This baseline alignment is appropriate for comparing variations (storms, substorms) but does not represent absolute calibration.

Assumptions & Limitations

• Declination-only rotation assumes the sensor Z-axis is truly vertical. Any tilt would mix horizontal and vertical components; no tilt compensation is applied.
• The sensor alignment to magnetic north was performed manually by minimizing the E component; small residual misalignment may exist.
• Offsets were computed from median differences and do not account for scale factors, non-orthogonality, or hard/soft iron effects.