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Cryosat Data Processing in Near Real Time for
Oceanographic Applications J. BENVENISTE -
ESA/ESRIN, Italy OZ. ZANIFE, B. SOUSSI - CLS,
France M. P. MILAGRO SERCO, Italy
1) Introduction
CryoSat is an Opportunity Explorer mission,
dedicated to answer one science question. The
focus of that science exploration is in the
cryosphere. For many reasons, including for
simplicity of the operations, CryoSat may acquire
data systematically all over the planet in the
classical altimeter mode, when it is not busy
exploiting the special SAR and SARin modes. This
means that classical altimeter data (in LRM mode)
would be acquired over the ocean. The current
CryoSat L2 LRM (Low Rate Mode) processing chain
does not address specialised ocean processing,
other than elevation, sigma C and sigma 0. Indeed
ocean processing was not included in the original
processing requirements. A review of the
available processing documentation confirms that
no specialised ocean processing is present other
than the above retracker derived parameters.
Specific additional processing steps needed to
add ocean processing to the LRM L2 chain is to be
encapsulated in a CFI software package developed
by CLS, under an ESRIN contract.
2) Users Requirement
2) CryoSat operating modes map
Well aware of the important user requirement for
radar altimeter data over the ocean, today
supplied by ERS-2, GFO, ENVISAT, TOPEX/Poseidon
and Jason-1, ESA set out to see how ocean data
could be exploited from the CryoSat mission and
to develop the necessary processing chain to
provide ocean data to users from the CryoSat
archive. The user requirements are also for fast
delivery CryoSat LRM data over the ocean, which
are the same as for the ENVISAT RA-2 FDMAR and
IMAR products (3 hours and 3 days latency,
resp.). The main user requirement for fast
delivery altimeter data is Improved sampling in
space and time (Cotton et al 2004, in the GAMBLE
report). The applications of fast delivery
CryoSat LRM data over the ocean are twofold sea
state and sea surface height. The users of such a
CryoSat FDMAR product are worldwide Met Offices,
the Navies, Groups supporting offshore and
coastal activities, Ocean circulation modelers
using altimetry data through assimilation (the
international GODAE Project). The required
latency for assimilation in meteorological models
and ocean battlefield models is 3 hours. The
required latency for assimilation in the GODAE
models is on the availability of the MOE orbit
(2-3 days). This means that the more data that
can be delivered in 3 hours the better. The 3
hour data and its complement disseminated several
hours later will be used for offshore
applications and assimilation in ocean models for
ocean circulation forecasting using enhanced
meteo fields and orbit solution. Today GODAE
users are served by DUACS (CNES), including
enhanced data from all flying radar altimeters.
Blue LRM (over oceans), Red SAR (over sea-ice),
Green SARin (over ice-sheets)
4) CryoSat ocean NRT processing chain scheme
3) Processing
Future enhanced LRM chain
Ocean processing functions needed to be added to
the original CryoSat ground processing to compute
significant wave height, wind speed and the
oceanographic corrections at 1 Hz. Operational
requirements for the CryoSat Near Real Time ocean
processing functionality, product generation,
dissemination and archiving were specified. The
ocean processor is an additional functionality of
the IPF2 LRM processor component of the CryoSat
Ground Segment, to be run in near real time. It
was developed under contract with CLS (F),
re-using and adapting the ocean retracker from
ENVISAT RA-2 with aim to generate a CryoSat FDMAR
product equivalent to the ENVISAT FDMAR product
to be supplied to the ENVISAT FDMAR and IMAR
users by ftp. After launch validation of the
product is planned
Existing LRM chain

• (- Surface discriminator
• Range and Corrections
• Retracking
• Slope correction
• Elevation
• Slope Doppler
• MSS and Geoid)

From internal buffer
4) Ocean NRT Product format
Group Field Descriptor Unit
time Time stamp 1 Hz and 20 Hz TAI µ-seconds
Location Latitude, Longitude 1 Hz and 20 Hz µ-degree
Counter and MCD Source Packet Counter and MCD -
Orbit Altitude of CoG above reference ellipsoid 1 Hz and 20 Hz mm
Orbit Instantaneous altitude rate mm/s
Range Ku-band ocean range 1 Hz and 20 Hz mm
Range Ku-band OCOG range 1 Hz and 20 Hz mm
Range Associated standard deviation and number of valid points  
Range corrections Doppler correction mm
Range corrections Delta Doppler correction mm
Range corrections Model dry tropospheric correction mm
Range corrections Model wet tropospheric correction mm
Range corrections Inverted barometer height mm
Range corrections High frequency atmospheric correction mm
Range corrections Model ionospheric correction on Ku-band mm
Range corrections Sea state bias correction on Ku-band mm
SWH Square of Ku-band Significant wave height 1 Hz and 20 Hz mm2
SWH Ku-band Significant wave height mm
SWH Standard deviation and number of valid points  
Backscatter Ku-band corrected ocean backscatter coefficient 1 Hz and 20 Hz dB/100
  Ku-band corrected OCOG backscatter coefficient 1 Hz and 20 Hz dB/100
  Associated standard deviation and number of valid points  
Off nadir angle off nadir angle of the satellite from platform data deg/104
Off nadir angle off nadir angle of the satellite from waveform data (TBC) deg2/104
Geophysical Mean sea-surface height mm
Geophysical Geoid height mm
Geophysical ocean depth/land elevation mm
Geophysical Total geocentric ocean tide height (solution 2) mm
Geophysical Long period tide height mm
Geophysical Tidal loading height (solution 2) mm
Geophysical Solid earth tide height mm
Geophysical Geocentric pole tide height mm
Geophysical Altimeter wind speed mm/s
Geophysical U-component of the model wind vector mm/s
Geophysical V-component of the model wind vector mm/s
Peakiness flags 20 Hz ku-band peakiness  
Flags Ku-band ocean retracking quality 20bits flags
Flags Corrections and geophysical flags flags
Flags Altimeter surface type flag flags
Flags Sea ice flag (TBC) flags
Delta Ocean CFI
To internal buffer