The World Magnetic Model - Uses
The compass has been used for several thousand years to determine direction. Since magnetic north (to which a compass points) is at a different location than geographic north (North Pole), a more precise direction is achieved by knowing the angle (magnetic declination) between them. However, declination changes with location and time, and a geomagnetic model is often used to correct for it. Since the changes in geomagnetic fields are difficult to predict, timely model updates are required for navigational accuracy. The WMM satisfies all these criteria and is therefore widely used in navigation. Examples include, but are not limited to, ships, aircraft and submarines. Magnetometer based attitude (roll and pitch) control is commonly used in aircraft and satellites.
Do we need magnetic navigation when Global Position System (GPS) is available? GPS provides precise point location but only measures travel direction when in constant motion. A GPS receiver must collect several sets of latitude and longitude pairs to obtain direction. In addition, GPS signals may become blocked due to obstructions, adverse terrestrial and space weather, ionospheric conditions or being underwater. Hence, compasses complement GPS receivers to attain precise and immediate navigational headings for air, ground, and water-based systems. Electronic compasses and the WMM commonly co-exist in GPS receivers.
Antennas and solar panels
Antennas (e.g. satellite dish television) and solar panels often need to be precisely oriented for maximum performance. The WMM’s declination information for specific locations is often employed by companies to properly align solar panels and antennas.
While the traditional use of the WMM is for navigation, it is now acquiring new utilities in consumer electronic devices with built-in digital compasses. Some of the new generation “smart phones” and digital cameras take advantage of the WMM to estimate bearing. The availability of low-cost, small and energy efficient electronic compasses allow for magnetic direction in portable electronics. This new user group will significantly increase the demand for WMM models in the near future. This expansion will also bring the WMM to the everyday life of many people.
Airborne and marine magnetic surveys are used by oil and mineral exploration companies to detect magnetic signals from the Earth’s crust. These small amplitude signals (typically 100s of nT), must be separated from the large main magnetic field (typically 20,000 to 60,000 nT). Geomagnetic models are used by companies to extract these small magnetic signals from the survey records. A new application is the use of geomagnetic models for directional drilling. Oil wells are often drilled horizontally from a conveniently located platform. An electronic compass located behind the drill head (bit) provides the engineers with accurate orientation of the bit.