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G. Stienne * S. Reboul J.-B. Choquel M. Benjelloun

SPACE REFLECTO 2013. Ground-Based Altimetry Using a Single-Receiver Single-Frequency GNSS Phase Ambiguity Resolution Technique. G. Stienne * S. Reboul J.-B. Choquel M. Benjelloun. Overview. System geometry Software receiver Signal processing architecture

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G. Stienne * S. Reboul J.-B. Choquel M. Benjelloun

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  1. SPACE REFLECTO 2013 Ground-Based Altimetry Using a Single-Receiver Single-Frequency GNSS Phase Ambiguity Resolution Technique G. Stienne* S. Reboul J.-B. Choquel M. Benjelloun

  2. Overview • System geometry • Software receiver • Signal processing architecture • Phase processing in open loops • Altimetrymeasurement • Ambiguityresolution • Experiments • Conclusion, prospectives

  3. System geometry: ground-based applications is the pathdifferencebetween the direct and the reflected signal

  4. Receiver architecture Direct signal RHCP Carrier replica (frequency, phase) Code and phase processing (DLL-POL) Code generator Pseudorange variations Sameoscillator for the digitizing Additional code delay(s) Carrier replica (frequency) Code generator Phase processing (POL) Reflected signal LHCP In open loops, phase measurements are angular

  5. Phase tracking: circular filter (linear evolution case) Filterdefined as the Kalmanfilter but with the Circular Normal von Mises distribution Predictionstep: Update step: with with and 11

  6. Phase tracking: circular change estimator When a cycle slip occurs (highdynamics, low Signal to Noise Ratios), itcanbedetected and its amplitude estimated via a GLR change estimatordefinedfollowingthe von Mises distribution. The estimations of (cycle slip position) and (cycle slip amplitude) are based on the inversion of (filter innovation)

  7. Ranging: code vs phase Both the code and the phase of a GNSS signal are periodic C/A code period: Phase period: Range periods: Phase ambiguity • GNSS codes are square signals. The observed code delays are piecewise constant. The samplingfrequencydefines the measurementsresolution. Rangingprecision: severalmeters. • The carrier iscontinuous, and so the phase delays. Rangingprecision: centimeter.

  8. Phase pseudoranging Pseudorange variations Replicated signal frequency Phase delaybetween the received signal and itsreplica Received signal frequency Local oscillatornoises Pseudorangeat t=0  ambiguity

  9. Phase altimetry Direct signal: Reflected signal: Choosencommon Common for a GNSS-R receiver Samereceiverclockerrors, atmosphericerrors, orbiterrors on bothsignals

  10. Pseudorangeat t=0 The pseudorangeat t=0 isobtained by dating the code using the data message Knownreception date Knownemission date (TLM) Received code 1 ms The telemetrywordemissionisdated, so the emission of each code periodcanbedatedwith the precision of the satellite atomicclock. The first code delay, , has to bepreciselyestimated in order to get a precisedatation at t=0.

  11. Precise estimation of Principle : averaging the code delaysobtained over the wholeacquired signal Method : Bringeachdelay back to the originusing the estimated phase variations Phase variations applied to each code delay Code delays

  12. Experiments : principle Graduations for accuratelyknownheight modifications

  13. Experiments : principle Several acquisitions (7 seconds) Preciselyknown variations on the antennaheightbetweentwo acquisitions First test: Constant height for the reflecting water The variations of shouldbeobserved Second test : Observation of several satellite footprints => samemeasuredheights

  14. Experiments : observedfootprints

  15. Experiments : results The heightis constant over time: good estimation of the phase On satellite 25, the water level variations differ by up to 20 centimeterfromwhatwasexpected The results on satellites 21 and 25 differ by up to 2 meters: wrong estimation of or with the signal of the satellite 21 or occurrence of a parasiticmultipath

  16. Conclusion & prospectives • Development of a mobile GNSS reflectometer • Short signal durations, no double difference • Robust and preciseheight variations estimations with 1 millisecond of coherentintegration • Stillimprecisions on altimetrymeasurementslinked to the phase ambiguityresolution • Need for more experiments in order to find the limits of the proposedambiguityresolution technique • Airborneexperiments Thankyou for your attention

  17. GPS L1 signal structure Modulation Emitted signal L1 carrier Multiplexing C/A code Data message Emitted signal : Received signal: Code delay Phase delay

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