Present survey modes yield data from either very low altitudes (e.g. 500 feet a.g.l.) covering small areas (several hundred square kilometers) or very high altitudes (i.e. satellite orbits) covering the entire Earth. Because of limitations in the spatial wavelengths that can be obtained at the currently available altitudes, the mid-range wavelengths are suppressed or inaccessible, and these wavelengths would add important information to the magnetic modeling process. Consequently, there exists a need for national to continental scale surveys to be flown a high altitude. The desirable altitude range would be 40,000 to 80,000 feet. The higher altitudes allow greater flightline spacing and thus more rapid surveying.
A typical survey might be flown at 48,000 feet with 10 nautical mile flightline spacing. A flightline could range in length from 1000 to 3000 nautical miles depending upon the dimensions of a survey block. The preferred flight direction would be magnetic east/west. However, north/south and off compass point directions may become feasible with some research. Aircraft speed is not of concern for purposes other than increasing coverage. But, maneuvers must be held to the minimum required for staying online during data collection. Each flight would require a 30-minute compensation procedure over a magnetic base station or observatory.
The primary equipment needed would consist of at least one cesium magnetometer placed in a nose or tail stinger (as far as possible from the engines and other magnetic aircraft parts), and a standard quality tri-axial fluxgate magnetometer for compensation purposes. These would provide four 32-bit channels of data sampled at 1/10 second. Standard flight condition data would also be required, including: precise position, altitude, and attitude information. Tri-axial acceleration may also be useful.