This magnetometer has been developed by C.S.F. (Compagnie Generale de Telegraphie Sans Fil) and C.G.G. (Compagnie Generale de Geophysique). The magnetic field is measured by an optical pumping sensor giving a frequency proportional to the field. A digital frequency-meter delivers a reading each second with a sensitivity of + or - one period (31.5 periods for one gamma).These readings are recorded on a magnetic tape recorder and on a analog TEXAS recorder. The digital data are processed on a 1620 IBM.During the flight a second magnetometer records the variation of the earth's field in a ground station located in the center of the area surveyed. The ground record data are subtracted from the airborne data.The following data obtained with this equipment are presented:Analog record with a sensitivity of one gamma for two mm.Restitution with 1620 IBM and CALCOMP of the magnetic record to an analog record with a sensitivity of one gamma for one cm.Isogam maps with a contour interval of one gamma and some intermediate contours at 0.5 gamma.