Presentation on theme: "Global altimetric marine gravity field mapping The impact of Cryosat-2"— Presentation transcript:
1Global altimetric marine gravity field mapping The impact of Cryosat-2 Ole B. Andersen and L. Stenseng
2Outline Satellite altimetry – State of the art gravity Cryosat-2 (what it offers).Noise estimation (20 Hz vs 1 Hz) for GravityDTU12 Beta.
3Altimetry – basic principles Satellite orbitRange (R)Altitude (H)Emitting a electromagnetic pulse ... Simply by measuring the return timeh ellipsoidal heightH the altitude (or orbital distance) of the satellite above the reference ellipsoidR the range from the satellite to the surfaceSea surfaceGeoidReference ellipsoid
4Rule of Thumb: 1 cm Height difference over 10 km equals 1 mGal. sea mountGravity fieldThe (mean) Sea surface height mimicks the geoidGravity from MDT corrected MSS (= Geoid) LaplaceSlope of the sea surface ...1 mGal -> Alongtrack heights differences need to be accurate to <1 cmRule of Thumb: 1 cm Height difference over 10 km equals 1 mGal.
5State of the Art: 321.400 obs Mean Max Dev Note KMS02 0.44 49.38 Std Dev.Max DevNoteKMS020.445.1549.38DNSC08DTU100.393.913.8236.9136.89Double RetrackSS V12.10.625.7982.20GSFC 00.10.686.1489.91NTU010.796.1092.10SS V16.1SS V18.10.590.414.883.9645.2936.99Retracked ERS1+GSA
6Cryosat ”promises” Conventional DD Cryosat Factor of 2 on accuracy over conventional altimetryAccuracy independent of Sea state:Jason-1: 1 Hz (altim noise = 1.5 cm): 20 Hz = 6.4 cmC2 DD: Hz (altim noise = 0.75 cm): 20 Hz LRM = 3.2 cm (sqrt averaging)
7C2 will improve Shortwavelength scale signal Bathymetry -> oceanographyLong wavelength signal still in error.
101 Hz ”Noise”Entire profileNorth part (42->)L2 – Proc3.5 cm2.4 cm (no jumps)L2 – Proc2.8 cm3.1 cmRADS 2012
11ERS-1GEOSATERMCRYO-2Number893613698378312430Std All / Alongtrk8.9 (5.7)7.2 (4.8)5.2 (2.4)7.5 (5.7)
12Coastal regions heavily improved DTU 2012 BetaCoastal regions heavily improvedIncluding CRYOSAT LRM data - 30% more data.Currently investigating ESA L2 LRM vs NOAA LRM data.Including Retracked L1 CRYOSAT SAR and SAR-In dataHas to solve for ”mode jumps first”Updating all existing GM data.Ocean tide correction updated to GOT 4.7SSB correction updated (N/A for Cryosat-2)Dynamic Atmosphere updated from IB aloneStandardsDNSC08/DTU10DTU12 BetaDry troposphereECMWFWet troposphereRadiometerIonosphereAltimeterDynamic AtmosphereIB (1013 mbar)MOG-2D_IBOcean tidesGOT 00.2GOT4.7Sea State BiasBM4Non-PARAM
13Retracking 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 GravityLevel 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
15Coastal regions heavily improved DTU 2012 BetaCoastal regions heavily improvedPreliminary testing using1.6 years of NOAA C2 LRMDataAll > obsDTU12DTU10SAND 18EGM2008Purple (0-20 m DEPTH)3.013.303.693.20Dark Blue (20-50 m)2.793.422.80Light Blue ( m)3.223.273.523.23Green ( m)3.533.493.793.51Yellow ( m)4.334.304.35Red/Pink (>1000 m)4.834.824.694.85All3.723.814.093.83
16Summary ESA L2 LRM are very good for marine gravity Processor upg ( ) removes spikes and is better for SAR-InBut increases noise for LRMJumps between modes are clear and needs to be handledCurrent Cryosat 2 data are comparable to retracked GM altimetryAims 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).