US Patent 7663373 Determining beacon location using magnetic field ratios

A method and system for identifying a location of a magnetic field source. A total magnetic field is measured during a calibration routine prior to a drilling procedure. During the drilling procedure, a magnetic field measurement is obtained. Using a ratio of the measured magnetic field and the calibrated field, a set of possible angles and distances is calculated. After the source is advanced a known distance, a second magnetic field measurement is obtained. A second ratio is calculated and a second set of possible angles and distances is calculated. The relative location of the source is then determined using the first set and second set of values, along with the known distance and a pitch angle of the source.