1. A system for estimating a motion of a first sensor during a time interval, said system comprising: a second sensor, said first sensor and said second sensor sensing a geo-location during said time interval, said first sensor computing a first target location error from sensing said geo-location, said second sensor computing a second target location error from sensing said geo-location; a data link interconnecting said first sensor and said second sensor, said data link transmitting said second target location error from said second sensor to said first sensor during said time interval; a processor at said first sensor for combining said first target location error and said second target location error in a first sensor observation model, said sensor observation model descriptive of said motion of said first sensor.