Abstract: For optical measurement of a distance between a hunter and a target, for instance between satellites, back-reflecting means are provided on the target. The hunter carries a source of substantially monochromatic light pulses and a solid state detector having a matrix of sensors. The matrix is read-out by transferring the contents of the sensors line per line or point per point at a predetermined frequency to an output memory. A time base triggers one pulse at a predetermined time selected for causing return of an echo from the target during read-out. The distance is derived from a determination of that line or that point which receives the echo, for two different transfer frequencies.