How? With two timing systems:  FTLRS Stanford chronometer ( temperature controlled)  Dassault Timers as a reference What conditions?  Very short time intervals: (internal cal. < 30 ns)  External calibration: (100 m to 300 m)  For satellites tracking: (400 km to km)  Time evolution (long-lasting effect ) F rench T ransportable L aser R anging S tation Chronometry accuracy estimation M.Pierron - D.Feraudy – M.Furia – F.Pierron – 0CA (Grasse) GEMINI – FTLRS staff FTLRS in Chania (Creta) Gavdos campaign – 04 to laser maintenance FTLRS in SanFernando (Spain) June 2004 Towards zero bias…

Rubidium Clock Steered to GPS Start Stop STANFORD Counter Start signal LASER Optical fiber START diode SPAD Signal Discriminator Card ECL NIM SPAD detector FILESFILES Stop signal Start signal Stop signal 10 MHz 2 DASSAULT Timers Return Pulse Laser Pulse On same events : Echo or noise Laser for start Photodiode for stop Without mutual perturbation In same Context : Start Distributor

Measurement results Roundtrip time from 15 to 55 ns close Internal calibration From 100 meters to 1 km close external calibration Few millimeters accuracy from 100 to 500 m Timing systems difference in ps to 5 km to km Calibration range Satellites range The best choice is when round trip time > 34 ns 25ps The difference between the 2 timing systems is less than 25 ps Variations can be accurately calibrated ~40ps in Crete Can explain part of data bias All this measurements are NOT time dependant

Very important to model the chronometry behavior at different ranges, and to processs the calibration value accordingly.CONCLUSION  Stanford Chronometer can achieve few milimeters accuracy during satellites tracking (from 400 to km).  Range near external calibration is easy to model. The correction to achieve for this external calibration can be tuned to 30/60 picos depending on the target’s range.  Values near internal calibration range are more difficult to evaluate, except when the roundtrip time is longer than 34 nanos. The difference between external and internal calibrations is about 50 picos (7.5 mm).