1

• CNES Toulouse involvement in Cryosat in-orbit
  mission
• Authors Service dAltimétrie et de Localisation
  Précise (SALP), CNES, TOULOUSE

CryoSat is the first Opportunity Mission of the
ESAs Earth Observation Envelope Programme.
CryoSat main mission objective is to measure the
thickness variations of sea-ice as well as
land-ice over a period of 3 years. This will be
achieved in combining the measurements made by
SIRAL, an interferometric radar altimeter, with a
very accurate determination of the satellite
orbit based on the DORIS system. The DORIS
system, developed by CNES together with IGN, is
able to provide precise orbit determination down
to a few centimetres. DORIS has successfully been
flown on various satellites (SPOT, TOPEX,
JASON-1, ENVISAT) demonstrating reliable and
highly accurate performance. In the frame of the
CryoSat development, ESA has acquired the latest
model of the DORIS instrument. And for the first
time, ESA is using Doris to provide onboard
services to the AOCS system (orbit and attitude
control). Concerning in-orbit operations, the
SALP CNES project has developed a specific
centre, SSALTO, and is responsible for the
maintenance of the on-board Diode DORIS navigator
and the DORIS ground beacon network, specific
Diode operations, expertise in support ESOC
operation team, as well as the processing of the
data generated by the DORIS instruments for
precise orbit determination. SSALTO is also
providing all the external auxiliary data to the
PDS L1b processing. ESA has developed the ground
segment of the CryoSat mission based on a close
interaction between the CryoSat project team and
SALP (Toulouse). Moreover, CNES has developed the
ESRIN Cryosat LTA dedicated to long-term
archiving for all mission products, off-line
reprocessing of SIRAL products and support to ESA
user services. At this end, it has to interface
with PDS (Payload Data System) for product long
term archiving, to report to centralised
facilities (OHS, MMC, RPF, MF), and serve users
requests. Its components are part of the SALP
Altimetry Mission Centre called SSALTO. The
DORIS/CRYOSAT and LTA projects team are rooted
in the Altimetry Division at CNES Toulouse to
guaranty that the development and the in-flight
and ground based operations are co-ordinated with
the other parts of the so-called  Altimetry
Mission Centre  SSALTO already including the
Envisat F-PAC. In conclusion, to fulfil needs of
the altimetric users community, CNES has set up a
system named SALP (for "Service dAltimétrie et
de Localisation Précise") with the following
objective to provide continuous series of
altimeter, orbitography and localization products
mainly generated with the altimeter payload
onboard Jason-1, ENVISAT, T/P, ERS and CryoSat
missions. CNES operations for both ENVISAT and
CryoSat are included in the SALP operations frame
work using SALP common components or dedicated
software and hardware developed in the context of
the ENVISAT or CryoSAT ground segments and which
will be used in order to fulfil ESA requirements.
From PDS Doris telemetry files to SSALTO all
products and aux data to LTA From SSALTO Doris
orbit products and SALP auxiliary files
KIRUNA PDS
ESOC Darmstad Flight Operations Segment
CNES Toulouse - SALP SOD, Long Term Archive
From ESOC WebTDRS, WebRMRecorded HK
Telemetry, Attitude data From SALP Command
requests Software upload files
ESRIN Frascati Multi mission catalog (OHS, MMC)
From ESRIN User orders From LTA Catalog
inventory updates Orders follow-up
SALP, the CNES ground segment for altimetric
missions

• With the successful launch of EnviSat and Jason-1
  missions, the scientists can have access to data
  gathered by at most as 5 altimetric missions. To
  ease data use, to enlarge the user community and
  to insure the data quality on the long term, a
  new ground segment (SALP) has been developed. For
  example, this system is used for the altimetric
  payload (RA2, MWR, Doris, LRA) onboard ENVISAT.
• SALP system is in charge of
• control of all DORIS instruments
• control and maintenance of the DORIS beacon
  network
• control of the Poseidon altimetric payload
  onboard TOPEX/POSEIDON, Jason-1,
• data processing from level0 to ephemeris files
  for all Doris data,
• data processing from level0 to level2 products
  for Jason-1 and TOPEX/POSEIDON missions,
• RA2 data processing from level1 to level2
  products for Envisat mission,
• high level product generation to merge all
  altimetric input data in an unique easy to use
  product,
• in depth control of the processing performed by
  systematic validation of all product
• in depth control of the Doris signal integrity
• Long term archive of all Jason-1, Doris data
• Long term archive of all ENVISAT RA2, MWR data
  (level 1B and higher)
• Long term archive of all CryoSat data

Control
Processing
SALP is involved in one way or the other in all
current altimetric missions. One key part of
those missions is the Doris system, onboard
Jason-1, T/P EnviSat and CryoSat. This system
allows to determine with a high accuracy the real
time position of the satellite. Processed off
line, the Doris measurements permit to compute
the satellite position with an accuracy of 2 to 3
centimeters.
Expertise
Data preservation
User Service
Service dAltimétrie et de Localisation Précise
2
Diode, a real time localisation service
Doris system

• Unlike the Global Positioning System (GPS), which
  beams signals from a constellation of satellites
  to Earth (or to other satellites in lower
  orbits), Doris uplinks signals to satellites.
  Collection of data on the satellite and at the
  SSALTO multi mission control and processing
  center makes the system particularly robust and
  is a definite advantage for distributing products
  in near-real time. It also facilitates the use of
  a single timing scale. An uplink system also
  allows the station network to be monitored
  remotely, thus significantly improving the
  quality.
• The Doris instrument is part of the satellite
  payload. It comprises an MVR receiver that
  measures radial velocity, an ultra stable
  oscillator which insure a datation accuracy of 1
  to 2 micro seconds, and an antenna. Every 10
  seconds, it measures the Doppler shift at two
  frequencies 400 MHz and 2 GHz (400 MHz channel
  being used to correct for the ionospheric
  effects).
• On ground, a network of 60 beacons emits signals.

• Since the launch of the Spot 4 satellite in
  January 1998, the Diode navigator has added
  real-time measurement processing capability for
  satellite navigation. Every 10 seconds, the
  onboard software determines the satellite
  position. Onboard Jason-1 and Envisat satellites,
  the position of the satellite is routinely
  determine within 50 centimeters in 3D (in normal
  conditions) with an accuracy of about 10 to 15
  centimeters on the radial axis. This allows real
  time or near real time delivery of precize
  altimetric data to the user community.
• Moreover, onboard CryoSat, ESA is using
  DORIS/Diode capabilities to provide onboard
  services to the AOCS system (orbit and attitude
  control)

LTA system

• The LTA system, part of CryoSat ground segment,
  will insure
• long term archiving of all CryoSat data
• upon ESA request, reprocessing of CryoSat data
  (for example at the end of the Kiruna
  operations).
• On demand user requests (the PDS being the
  nominal data distribution site during the CryoSat
  lifetime)
• This system has been designed using existing
  facilities already used for ENVISAT operations
  and part of the ground segment set up in place in
  Kiruna. Inside SALP system, this will allow in
  the future to develop higher level products as
  the one depicted below.

SALP Altimetric Products
SALP User Service aviso_at_cls.fr
www.aviso.oceanobs.com
study of ocean variability
marine meteorology, ocean-atmosphere gas tranfer
Ssalto/Duacs Along-Track Sea Level Anomalies
Along-Track Wind / Wave data
OSDR, RA2 WWV, Wind/Wave Media FTP Delay real
time, delayed-time Satellites Jason-1, T/P,
Envisat
NRT-SLA, DT-SLA Media FTP, DVD
Rom Delay near-real time delayed
time Satellites T/P, Jason-1, Envisat, GFO, ERS
geophysical studies, expert use
study of the general circulation
Gridded Wind / Wave data
Ssalto/Duacs Gridded Sea Level Anomalies
NRT-MWind and NRT-MSWH Media Live Access Server,
Opendap Delay near-real time Satellites T/P,
Jason-1, Envisat, GFO
NRT-MSLA, DT-MSLA Media FTP, DVD Rom, Live
Access Server, Opendap Images Delay
near-real time delayed time Satellites T/P,
Jason-1, Envisat, GFO, ERS independently and
merged
Ssalto/Duacs Gridded Absolute Dynamic Topography
NRT-MADT Media FTP, Live Access Server,
Opendap Images Delay near-real time
Satellites merged T/P, Jason-1, Envisat, GFO
Geophysical Data Records
IGDR, GDR Media FTP, DVD Rom Delay near-real
time delayed time Satellites T/P, Jason-1,
Envisat
Ssalto/Duacs Along-Track Absolute Dynamic
Topography
Geophysical sensor data
NRT-ADT Media FTP Delay near-real
time Satellites T/P, Jason-1, Envisat, GFO
SGDR, Waveforms Media DVD Rom Delay delayed
time Satellites T/P, Jason-1, Envisat
Service dAltimétrie et de Localisation Précise