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Global altimetric marine gravity field mapping The impact of Cryosat-2

Global altimetric marine gravity field mapping The impact of Cryosat-2. Ole B. Andersen and L. Stenseng. Outline. Satellite altimetry – State of the art gravity Cryosat-2 (what it offers). Noise estimation (20 Hz vs 1 Hz) for Gravity DTU12 Beta. Altimetry – basic principles.

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Global altimetric marine gravity field mapping The impact of Cryosat-2

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  1. Global altimetric marine gravity field mappingThe impact of Cryosat-2 Ole B. Andersen and L. Stenseng

  2. Outline • Satellite altimetry – State of the art gravity • Cryosat-2 (what it offers). • Noise estimation (20 Hz vs 1 Hz) for Gravity • DTU12 Beta.

  3. Altimetry – basic principles Satellite orbit Altitude (H) Range (R) Sea surface Geoid Reference ellipsoid

  4. Gravity field Gravity field Gravity field sea mount The (mean) Sea surface height mimicks the geoid Gravity from MDT corrected MSS (= Geoid) Laplace 1 mGal -> Alongtrack heights differences need to be accurate to <1 cm Rule of Thumb: 1 cm Height difference over 10 km equals 1 mGal.

  5. State of the Art:

  6. Cryosat ”promises” Conventional DD Cryosat Factor of 2 onaccuracy over conventionalaltimetry Accuracy independent of Seastate: Jason-1: 1 Hz (altimnoise = 1.5 cm): 20 Hz = 6.4 cm C2 DD: 1 Hz (altimnoise = 0.75 cm): 20 Hz LRM = 3.2 cm (sqrtaveraging)

  7. C2 will improve Shortwavelength scale signal Bathymetry -> oceanography Long wavelength signal still in error.

  8. SAR-In ESA Level 2 Products. (20 Hz data) Identical profile 2011 / 2012 SAR LRM Hawaii

  9. 18 Hz Cryosat LRM SAR SAR-In >100 mGal 2011 V 2.1 2012 V 2.4 Large ”jumps” at mode shift SOUTH North

  10. DTU 2012 Beta Coastal regions heavily improved Including CRYOSAT LRM data - 30% more data. Currently investigating ESA L2 LRM vs NOAA LRM data. Including Retracked L1 CRYOSAT SAR and SAR-In data Has to solve for ”mode jumps first” Updating all existing GM data. Ocean tide correction updated to GOT 4.7 SSB correction updated (N/A for Cryosat-2) Dynamic Atmosphere updated from IB alone

  11. Retracking of Cryosat-2 • Level 1b SAR waveform (black) with fitted five parameter beta retracker with exponential tail (blue) and surface estimate (red). COG – Center of Gravity Level 1b SAR waveform (black) with fitted five parameter beta retracker with exponential tail (blue) and surface estimate (red). Green is cut off for leading edge Center of Gravity

  12. DTU12? Gravity

  13. DTU 2012 Beta Coastal regions heavily improved Preliminary testing using 1.6 years of NOAA C2 LRM Data

  14. Summary ESA L2 LRM are very good for marine gravity Processor upg (2.1-2.4) removes spikes and is better for SAR-In But increases noise for LRM Jumps between modes are clear and needs to be handled Current Cryosat 2 data are comparable to retracked GM altimetry Aims at releasing DTU12 at “20 years progress of altimetry” Jason-1 EOL Geodetic Mission ? . Will still be a fantastic asset for marine gravity up to the 66 parallel (no Arctic here).

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