Cesium vapor magnetometers are the type most widely used for aeromagnetic surveys and for base stations, whenever the highest resolution and/or cycling rates for measurement of the earth's magnetic field is required.
The output of a cesium sensor is essentially continuous in practice. Combined with the necessary electronics, it can operate at a resolution of up to 0.001 nT, at sampling rates of 10 readings per second or greater, throughout a range of 20,000 to 100,000 nT.
The magnetometers can be installed in fixed-wing aircraft or helicopters, in either "stinger" or "towed bird" configurations, and, in addition to measuring total magnetic field, can be used to make vertical, transverse and/or longitudinal gradient measurements by using two or more sensors.
A typical cesium magnetometer installation comprises some or all of the following subsystems:
- Orienting Gimbal
- Signal Processor and/or Compensator
Aircraft Motion and Attitude Sensors
The attitude and motion of the aircraft in flight, with respect to the Earth's magnetic field vector, is monitored by a three-component fluxgate magnetometer which is very sensitive to attitude changes.The outputs of this motion sensor are used to deconvolve the artificial anomalies created by the aircraft itself, from anomalies created by geologic variations.
With towed bird systems, CGG uses pitch, roll and yaw detectors in the bird to correct for geometric errors created as the bird departs from its assumed ideal flight orientation.
Navigation and Positioning
GPS brings a number of important benefits to aerial surveying. Firstly, the coordinates of the survey aircraft (horizontal and vertical) are provided on a continuous basis. This not only improves the quality of survey navigation and reduces its cost, it also simplifies data compilation and presentation by eliminating, to a large degree, the tedious and error-prone manual steps inherent in flight path recovery from film or video. Secondly, GPS provides a reusable positioning system. Surveys flown at different times in the same area may be precisely correlated in position, making it easy to repeat survey lines or to fly infill lines.