An airborne measurement
system borne by an aircraft, and comprising a plurality of conventional navigational-aid sensors generating data referred to as conventional data, at least one SPAD camera comprising a single-
photon avalanche diode matrix-array
detector and generating SPAD data comprising a first image and a second image of a scene to be observed, the
system comprising a
processing unit connected to the conventional sensors and to the at least one SPAD camera, the
processing unit being adapted to: choose, in accordance with a predetermined criterion and on the basis of the conventional data and / or of the SPAD data, a use of the conventional data which is referred to as the conventional mode, or a use of the SPAD data, and possibly comprising conventional data, which is referred to as the SPAD mode, and for the conventional mode, generate measurement information referred to as conventional information on the basis of conventional data, for the SPAD mode: determine, on the basis of the first image and of the second image, an
error band for the measurement of the horizontal position of the aircraft, called the protection
radius, generate measurement information referred to as reinforced information on the basis of at least SPAD data.