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How ? With two timing systems: FTLRS Stanford chronometer ( temperature controlled)

F rench T ransportable L aser R anging S tation Chronometry accuracy estimation M.Pierron - D.Feraudy – M.Furia – F.Pierron – 0CA (Grasse). FTLRS in Chania (Creta) Gavdos campaign – 04 to10 200 3 -. Towards zero bias …. What condition s?

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How ? With two timing systems: FTLRS Stanford chronometer ( temperature controlled)

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  1. FrenchTransportableLaserRangingStation Chronometry accuracy estimation M.Pierron - D.Feraudy – M.Furia – F.Pierron – 0CA (Grasse) FTLRS in Chania (Creta) Gavdos campaign – 04 to10 2003 - Towardszero bias… • What conditions? • Very short time intervals: (internal cal.< 30 ns) • External calibration: (100 m to 300 m) • For satellites tracking: (400 km to 10000 km) • Time evolution (long-lasting effect ) laser maintenance • How? With two timing systems: • FTLRS Stanford chronometer(temperature controlled) • Dassault Timers as a reference FTLRS in SanFernando (Spain) June 2004 GEMINI – FTLRS staff

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

  3. Measurement results 0 to 5 km 400 to 10 000km 100 90 80 100 Fewmillimeters accuracy from 100 to 500m 70 90 60 80 25ps 50 70 40 60 ~40ps in Crete Can explain part of data bias 30 50 Timing systems difference in ps 20 The difference between the 2 timing systems is less than 25 ps 40 10 30 Variations can be accurately calibrated 0 20 Satellites range Calibration range 10 0 2000 4000 6000 8000 10000 0 1 2 3 4 5 From 100meters to 1 km Roundtrip timefrom15 to 55 ns 100 90 80 70 60 50 The best choice is when round trip time > 34ns 40 30 20 10 close Internal calibration close external calibration 0 18 23 28 33 38 43 48 53 100 200 300 400 500 600 700 800 900 1000 All this measurements are NOT time dependant

  4. CONCLUSION Very important to model the chronometry behavior at different ranges, and to processs the calibration value accordingly. • Stanford Chronometer can achievefew milimeters accuracy during satellites tracking(from 400 to 10000km). • Range near external calibration is easy to model. Thecorrection 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).

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