1. What is the World Magnetic Model?

The World Magnetic Model (WMM) is a joint product of the United States' National Geospatial-Intelligence Agency (NGA) and the United Kingdom's Defence Geographic Centre (DGC). It represents the magnetic field of Earth and is used for navigation, attitude and heading referencing systems.

2. How Does the Calculator Work?

The calculator uses the WMM to estimate:

Where:

• \( latitude \) — Geographic latitude (-90° to 90°)
• \( longitude \) — Geographic longitude (-180° to 180°)
• \( altitude \) — Height above mean sea level (meters)
• \( date \) — Decimal year (e.g., 2023.5 for mid-2023)

Outputs: Magnetic declination (variation), inclination (dip), and total field intensity.

3. Importance of Magnetic Field Calculation

Details: Accurate magnetic field data is essential for navigation systems (compass corrections), geophysical surveys, satellite operations, and scientific research.

4. Using the Calculator

Tips: Enter coordinates in decimal degrees, altitude in meters, and year as decimal (e.g., 2023.5). The model is valid for 2020-2025 (WMM2020).

5. Frequently Asked Questions (FAQ)

Q1: Why does magnetic declination change over time?
A: Due to the movement of Earth's liquid outer core, which generates the magnetic field (secular variation).

Q2: How accurate is the WMM?
A: Typically ±30 minutes of arc for declination, but accuracy degrades in polar regions and during magnetic storms.

Q3: What's the difference between WMM and IGRF?
A: WMM is updated annually for precise navigation, while IGRF (International Geomagnetic Reference Field) is updated every 5 years.

Q4: Why include altitude in calculations?
A: Magnetic field strength decreases with altitude (approximately inverse cube law).

Q5: When is the next WMM update?
A: WMM is updated every 5 years (next in 2025), with annual updates in between.