1 / 29

A review of the transponder calibration activities in the frame of the GAVDOS project

A review of the transponder calibration activities in the frame of the GAVDOS project. Hausleitner , W. (1) , J. Weingrill (1) , F. Moser (1) , J.-D. Desjonqueres (2) , N. Picot (2) , S.P. Mertikas (3) (1) Austrian Academy of Sciences, Graz, Austria

carney
Download Presentation

A review of the transponder calibration activities in the frame of the GAVDOS project

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A review of the transponder calibration activities in the frame of the GAVDOS project Hausleitner, W.(1), J. Weingrill(1), F. Moser (1), J.-D. Desjonqueres(2), N. Picot (2), S.P. Mertikas(3) (1) Austrian Academy of Sciences, Graz, Austria (2) Centre National d’EtudesSpatiales (CNES), Toulouse, France (3) Technical University of Crete, Chania, Greece

  2. The GAVDOS Project • GAVDOS – Establishment of a European radar altimeter calibration and sea-level monitoring site for Jason, Envisat and EURO-GLOSS • Objectives • Establish an absolute sea-level monitoring and altimeter calibration permanent facility on the isle of Gavdos • Conduct tide-gauge measurements as well as direct altimeter transponder, Global Positioning System (GPS), Doppler Orbitography by Radio-positioning Integrated on Satellite (DORIS) and Satellite Laser Ranging (SLR) measurements for altimeter calibration • Deliverables • Jason absolute altimeter bias, Marine geoid, Sea level variations, local deformations / land displacements, etc. IWF/ÖAW GRAZ

  3. Gavdos Calibration Work • Calibration of satellite radar altimeters a Gavdos Cal/Val facility using three different methodologies (S.P. Mertikas, et.al. 2010) • Comparing sea level anomalies between the satellite and the in-situ observations • BIAS = SSH_altim – SSH_tide_gauge ≈18±5 cm • Relate measurements to the Mean Sea Level of CLS01_MSS • BIAS = SSH_altim – MSS_CLS01 – SLA_tide_gauge • Usage of a microwave transponder placed at the satellites ground-track • BIAS = ALT_altim – range_altim – H_TRP IWF/ÖAW GRAZ

  4. Microwave Altimeter Transponder • The principle of a microwave altimeter transponder is to receive, amplify and retransmit a satellite radar altimeter pulse. • The emitted pulse is received by the altimeter on-board the satellite again with the 2-way travel-time of the pulse giving the range between the satellite and the transponder • Technical specifications • Minimal distortion of the signal • High frequency stability • Frequency: 13.7 GHz • Bandwidth: 600 MHz • High amplification rate • Total gain: 77 dB • Stable instrument delay • Response delay: 13.24 ns IWF/ÖAW GRAZ

  5. TRP Location • Deployment on Gavdos at DIAS • Cross-over of Jason • 3 km apart of Envisat • ITRF2005 coordinates • GPS campaign by S. Mertikas (Nov. 2010) • Φ = 34°49‘17.2953“ • λ = 24°05‘27.6631“ • h = 251.5627 m IWF/ÖAW GRAZ

  6. TRP Site Setup • Housing • Aluminium frame enveloped with fabric • Cover plate from acrylic glass • Protection from wind, dust contamination, animals, etc. • Electrical Power Supply • 12 V car batteries • recharched by solar panels (2x50 W) • Modem Telecommanding • Watchdog timer (daily at 0.0h) • GSM/GPRS-modem for remote controlled TRP switch-on IWF/ÖAW GRAZ

  7. Ocean vs. Point Target Response IWF/ÖAW GRAZ IWF/ÖAW GRAZ

  8. The Transponder Principle cont‘d • OSTM Level-2 S-IGDR Data Files • 1 Hz / 20 Hz data • Ku / C-band waveforms • Latency: 2 days • Provided by CNES • (Envisat Picture) IWF/ÖAW GRAZ IWF/ÖAW GRAZ

  9. ENVISAT Calibration • Two years ENVISAT calibration campaign • TRP approx. 3km outside of footprint center • RA-2 set to Preset Loop Output (PLO) mode • RA2/MWR products analyzed • RA2_science_level-1b • RA2_average_waveforms • RA-2 instrument bias: 39.0±3.3cm (Cristea at.al., TGRS-20067-0032) IWF/ÖAW GRAZ

  10. Jason Calibration • Poseidon-2/3 instrument characteristics • Dual-band (C/Ku) pulse compression radar • 128 waveform samples • Frequency / PRF / t-res. = 13.575 GHz / 2060 Hz / 3.125 ns • Operation modes • Acquisition mode: Detects ocean returns and init. Tracking loops • Tracking mode: Nominal mode for the altimeter • Problem:The TRP signature is not visible in the waveform data • Because: ▶ J-Tracking is more sensitive to coast/land transitions generating loss of tracking resulting to a 1.5 sec data gap (desc. passes) ▶ Gavdos is small enough to keep tracking the sea shifting the TRP outside of the altimeter ranging window (asc. passes) • Calibration 2: Measures the transfer function of the internal receiver channel IWF/ÖAW GRAZ

  11. Cal-2 Calibration Data 32 Individual Calibrations 128 bins 0.153 s • Calibration-2 Mode • NO absolute epoch time available! • Dating of individual calibrations is known with 1s accuracy only 3.125 ns IWF/ÖAW GRAZ

  12. Calibration Processing Concept IWF/ÖAW GRAZ

  13. Cal-2 Calibration Configuration 5 sec calibrationwaveforms ±1s ±1s 11 sec data gap IWF/ÖAW GRAZ

  14. Data Screening • Pass 050 Cycle 018 IWF/ÖAW GRAZ

  15. Data Interpolation • Densification to 20 Hz rate (cubic spline interpolation) • Precise computation of point of closest approach (φ,λ) 11s Gavdos Crete φ λ IWF/ÖAW GRAZ

  16. Individual Calibration Analysis • Definition/Estimation of maximum power reflection by • 1)Maximum value of received energy • 2)Max. val. of Gaussian fit to return power • 3)Half ma. power at leading edge of Gaussian fit • 4)Centroid of received energy IWF/ÖAW GRAZ

  17. Individual Calibration Fitting IWF/ÖAW GRAZ

  18. Optimal Parabola Fit 32 Individual Calibrations 128 bins IWF/ÖAW GRAZ

  19. Power Vertex Adjustment • Alignment of PCA of orbit vertex of fitted parabola • Absolute time of PCA fromorbit • Absolute datingof bin #1 ofindivid. cal. #1 • Altimeter range command • Set for each calibration • Provided by CNES on a pass-per-pass basis • Ranging ambiguity IWF/ÖAW GRAZ

  20. Geophysical Parameters Range Wet Troposph. Dry Troposph. Ionosph. Sea State Bias DOY IWF/ÖAW GRAZ

  21. Range Correction  -2.49 m [m] [m] DOY IWF/ÖAW GRAZ

  22. Sea Surface Height IWF/ÖAW GRAZ

  23. Geophysical Correcitons IWF/ÖAW GRAZ

  24. Cal-2 Ranging Budget / Residual Calibration bin rangeAmbiguityAltimeter delayCoM Correction 33738.0881310718.858 -5.173 0.471 r -2.297-0.116-0.016 Dry troposphereWet (water vapour)Ionosphere TRP delay (electronic)TRP delay (geometric)Station marker eccentricitySlant range correction - 3.972 -1.477 -0.824 TRP ell.heightSolid earth tides 251.169 -0.0601344398.967 44.575 Geoid Ellipsoid Orbital heightResidual IWF/ÖAW GRAZ

  25. Outlook • Analysis of full set of Cal-2 passes • Limitednumber ofpassesavailable • Usage of precise orbits • Provided with a 60 days latency • DIODE DEM coupling mode • Usage of onboard digital elevation model for pre-definingthe altimeter tracking window • Transponder calibration withnominal tracking rate (51 ms) IWF/ÖAW GRAZ

  26. Figure Pool IWF/ÖAW GRAZ

  27. Geophysical Corrections Mean sea surface Solid Earth tide Geocentr. Ocean tide Pole tide height Inv. barom. height eff. HF fluctuations of SST IWF/ÖAW GRAZ

  28. Orbit SlantDistance Range_ku TRP Altitude SeaSurface SSH Ellipsoid IWF/ÖAW GRAZ

More Related