The Jason 2 Mission:\
Monitoring Ocean Surface Topography from Space

**Yves Menard ^(1)^, Lee Fu^(2)^, François Parisot^(1)^, Said
Kaki^(2)^,\
Alain Ratier^(3)^, Robert Cheney^(4)^**

**(1) CNES, 18 Ave. Ed. Belin, 31401, Toulouse cedex, France**\
**(2) JPL, 4800 Oak Grove Drive, Pasadena, CA 91109, USA\
(3) EUMETSAT, Am Kavalleriesand 31, D-64295 Darmstadt, Germany\
(4) NOAA, 1315 East-West Highway, Silver Spring, MD 20910, USA**

**September** **16,** **2002**

**Presentation to** **EUMETSAT** **Scientific and Technical Group**

1.  **Contributing to the Space-Based Ocean Observatory**

*The oceans are a fundamental element in our planet\'s climatic system.
We should be able to monitor their conditions at all times, to describe
them, to understand them and forecast their changes.* The climatic
upsets we have experienced in recent years---like those related to \"El
Niño\" and \"La Niña\" events---gave us a sudden wake-up call to try to
better understand the « ocean machine » and its interaction with the
atmosphere. Scientists need in particular to examine the causes,
consequences, and \"predictability\" of oceanic changes because it is
now accepted that the ocean has a fundamental disruptive and regulating
role in the Earth\'s climate.

Our limited view of the ocean has become much sharper over the last
thirty years. Just a few decades ago, the thought that we could have a
continuous, real-time global view of the ocean seemed unrealistic; at
that time, only partial and intermittent *in-situ* data were available.
This is no longer the case, thanks to the many satellites that monitor
the Earth and its oceans, flying over the entire surface of the planet
in just a few days and measuring, with unparalleled accuracy, surface
temperatures, ocean color, wind speed and direction, and sea surface
topography.

The Franco-American satellite TOPEX/Poseidon (T/P) was launched in 1992
as a follow-up to SEASAT (1978) and GEOSAT (1985). Together with ERS-1
and ERS-2 (1991, 1995) and Geosat Follow-On (1998) it showed the wide
range of oceanographic applications that can be obtained from space.
Using very powerful radar altimetry technology, the sharp eye of this
satellite detects the slightest variation in sea level and provides
quick, synoptic, global, and regular measurements of ocean surface
topography (Chelton et al., 2001). Data gathered by T/P over all the
Earth\'s oceans every 10 days allow scientists to regularly draw up
charts of sea surface currents, follow their intra-seasonal to seasonal
variations, and observe the oceanic signatures of major climatic
anomalies, such as the 1997-99 El Niño/La Niña phenomena. This is
helping scientists better understand and describe the complex mechanisms
and interactions among the oceans\' different variability modes.

On December 7, 2001, the Jason-1 satellite was launched from the
Vandenberg site in USA to take over the T/P mission. This new satellite,
jointly developed by CNES and NASA as the previous one, was declared
operational 2 months after the launch and since then is delivering
geophysical data at a level of performance identical to T/P. Placed in
the same orbit as T/P, Jason-1 is working in tandem with its companion
T/P, still operational after 10 years of a brilliant career. On March 1,
2002, the ENVISAT satellite from ESA was launched by an Ariane 5 rocket
from Kourou. Onboard this multi-mission satellite, a radar altimeter is
running (Benveniste, 2002) to take over the ERS-2 altimetric mission
(still in operation). The orbit repeating at 35 days (instead of 10 days
for Jason and T/P) is sampling the ocean at a shorter spatial scale,
complementing the large scale vision of T/P.

With T/P and previous missions living up to expectations, satellite
altimetry has become an indispensable discipline in the development of a
new challenge, that of operational oceanography. In this regard, Jason-1
and ENVISAT are considered as precursors with the implementation of new
near-real time capabilities (for instance, Jason-1 delivers data to
users within 3 hours of observation). This challenge has been spurred on
by the success and interest generated by these altimetric missions in
research programs like WOCE (World Ocean Circulation Experiment),
TOGA-COARE (observing climatic anomalies in the tropical Pacific
region), and more recently CLIVAR (Climate Variability and
Predictability).

Progressing from research to applications and operational services is
always delicate. It demands first a permanent dialogue between
researchers and teams involved in operational system developments. This
close relation is essential to implement and update models and
assimilation tools in the operational centers. Another strong
requirement is to increase and maintain in a consistent way the
satellite based and in-situ observation networks and the data access
systems. The Global Ocean Data Assimilation Experiment (GODAE)
represents an international effort to address these different issues (N.
Smith, 2002). Several pilot experiments are already running in various
countries to prepare the demonstration phase of GODAE over 2003-2005.
High resolution 3D global description and forecast of the ocean will be
then routinely released by different centers around the world. The
MERCATOR and FOAM projects in Europe (Bahurel et al., 2002; Bell et al.,
2002), the ECCO project in US (Fukumori et al., 2002) are few examples
of such pilot experiments. Climate seasonal forecasts, ship routing,
ecosystem management, and coastal area activities, will widely benefit
from these new oceanic products. In the meantime, oceanic models will
reach increasing levels of performance and the global *in-situ*
observation network will be enhanced and maintained. The international
ARGO program will support around 3000 profiling floats over all the
oceans by 2005 (Roemmich et al., 2002).\
\
The satellite based observation systems also need to be maintained and
developed (Ratier, 2001; Kawamura, 2002). In this regard, spaceborne
altimetry programs are key elements of the global observation network
(Mitchum et al., 2001). They have to be consistent with the global and
long term observation strategy required for the GODAE objectives (Smith
and Koblinsky, 2001). In this regard, new altimetric missions have to be
decided soon in order to replace the current missions by 2006. In late
2001 CNES, NASA, Eumetsat, and NOAA exchanged letters indicating that
they intend to work together on a "Jason-2"mission (a new name for this
mission is currently under discussion; is it known generically in the
U.S. as the Ocean Surface Topography Mission, or OSTM, but in this paper
we will use the term Jason-2.)

**\
2. Jason-2 to take over the Jason-1 mission**

The main objectives of Jason-2 include the continuation of the T/P and
Jason-1 missions, based on the science and pre-operational returns of
these two missions (Menard and Fu, 2001) and the support in a timely
manner to the global and regional operational applications. As its
predecessors, Jason-2 will be placed onto a 66° orbit, at an altitude of
1336 km.. It will follow the same reference ground tracks, repeating
these tracks every 10 days. Performance and data delivery latency will
be the same as Jason-1 (Menard et al., 2000). Even if the operational
application objectives of the Jason-2 mission will take a growing place
with respect to previous missions, the research part will be still very
intense.

***2.1. Research topics cover many different fields**.*

Description of the mean circulation using altimetric sea level
measurements is essential to better understand its interaction with the
time-varying components and the involved mechanisms. It is also
important for initializing ocean models. The large accumulation of
altimetric data from the early missions through Jason-2 and follow-on,
along with high resolution marine geoid derived from space-borne
gravimetric measurements (CHAMP in 2000, GRACE in 2002, GOCE in 2005)
will provide significant contributions to a better understanding of this
"mean" ocean.

The ocean exhibits variability at different scales in time and space,
affecting significantly mass and heat transport, exchanges with the
atmosphere, and consequently the climate. Sea surface topography as
measured by altimetry has proven its usefulness to understand the
physics behind this variability (e.g. Fu and Chelton, 2001; Picaut and
Busalacchi, 2001). Model parameterization has been improved thanks to
these new findings. But there is still more to do. Apart from the
seasonal cycle, which leads to an increase or decrease in sea level in
each hemisphere, exceeding 15 cm in some areas, there are significant
variations from one year to the next which are not yet well understood.
The El Nino event, the North Atlantic Oscillation, the Pacific Decadal
Oscillation, the planetary waves crossing the oceans over periods of
months are among the mechanisms which need to be better characterized.
Because of the long period of these phenomena, very long time series of
altimetric observations are needed, requiring Jason-2 and follow-on
missions.

Mesoscale ocean variability is associated with shorter time and space
scales (typically 1 month/30 km) but it impacts significantly the energy
balance with the atmosphere. Western boundary turbulent currents and the
energetic whirlpools which they form play an essential role in moving
heat from low to high latitudes. But eddies are travelling over all the
oceans interacting with the lower frequency modes as well as with the
coastal currents, coast line, continental shelf, and bathymetry. This
eddy activity is now quite well characterized statistically, thanks to
the multi-year accumulation of altimetric data (Le Traon and Morrow,
2001). But we need to go one step further to decode this complicated
turbulent physics and to transcribe it better in the eddy resolving open
ocean and coastal models. Jason-2 (as Jason-1 and T/P) will provide
spatial resolution not optimized for such investigations (320 km at the
equator), but its contribution along with complementary missions (e.g.
ENVISAT and follow-on) will be essential.

At the other end of the ocean variability spectrum, the secular mean sea
level trend is a pertinent indicator of global warming. The unique
accuracy of T/P sea level measurements has demonstrated an unexpected
capability of recovering a global trend of about 2 mm/year (Nerem and
Mitchum, 2001). Nevertheless, this parameter has an extremely small
variation, at the limit of what can be observed even with systems as
efficient and accurate as T/P and Jason-1. Only long term time series
over several decades will decrease the error bar at a level consistent
with the small amplitude of the signal. The continuation of Jason type
missions is a unique way to fulfill this objective of great importance
and of general interest.

In the domain of tide modeling significant progress has been made thanks
to the altimetry, in particular T/P data (Le Provost, 2001). Several
models now are able to predict the main diurnal and semi-diurnal
components of ocean tides with an exceptional precision of 2 cm rms. But
investigations are continuing to track more subtle tide signals,
including long period components, coastal interactions, internal waves
generated by the tides, and tidal energy dissipation. All these issues
need absolutely the continuation of altimetric missions, including
Jason-2, to provide the appropriate space and time sampling of the sea
level.

Other domains will benefit from the Jason-2 mission. Estimates of wave
height and wind speed derived from the radar altimeter echos are two
parameters which are of great value for marine meteorology nd
climatology studies as well as operational sea-state forecasts (Lefevre
and Cotton, 2001). Investigations in the field of earth sciences, such
as research on marine geoid (Tapley and Kim, 2001), tectonics (Cazenave
and Royer, 2001), hydrology, ice (Zwally and Brenner, 2001), closed
seas, great lakes, and desert regions, will also greatly profit from the
continuation and the merging of high precision Jason-2 altimetric
measurements with other data sets.

***2.2 Operational Applications, predicting the ocean weather***

One of the major objective of the Jason-2 mission (\~2006 launch) will
be to support the transition from the ocean operational system
demonstration phase (the 2003-2006 GODAE time frame) to the ocean
routine operations. Operational activities can be divided into two
categories depending on the time-scale: the short range ocean forecast
(in which we can include coastal aspects) and the seasonal to long term
range ocean forecast.

**The seasonal ocean forecasting** is one of the most demanding and
ambitious objectives. Information on these time scales provided by
altimetry to the ocean models is essential, because the role of currents
is not yet well understood and well parameterized. Even if progress in
the related physics is expected within the next years, the near-real
time ocean state estimates derived from altimetric data and assimilated
continuously with other data sets into models is of great value
(Rienecker at al., 2002). This assimilation leads to a description and a
prediction of oceanic currents, temperatures, and salinity with a level
of precision that has never before been obtained. The question of longer
term predictions (interannual to decadal) is of importance, but research
in this field is just starting, so long term routine ocean forecasts
will not emerge in the near future. As mentioned previously, long time
series of accurate altimetric data (Jason-2 and follow-on) will help in
understanding this ocean long-period variability and its interaction
with short term modes (participating thus in the improvement of seasonal
forecasts).

One example of seasonal ocean forecast operated on a routine basis is
the one provided by NOAA. Since 1996, T/P sea level anomalies have been
assimilated each week in the NCEP Pacific Ocean model used to predict
ENSO (Miller et al., 2002). This processing is done in near-real time
thanks to the 2-day latency delivery of T/P interim geophysical data
(figure 1). In the meantime several groups around the world are working
on the coupling of ocean with atmosphere to develop seasonal climate
forecasting models. Such models will use as inputs the ocean analysis
and predictions released by ocean operational centers.

**The short range ocean prediction** has many applications of great
interest. Several global and regional models have been developed and run
in an experimental or pre-operational configuration, before entering the
operational phase (e.g. MERCATOR, FOAM, ECCO\...) (figure 2). They
provide high resolution, high frequency 3D products which depict and
forecast a few weeks in advance the very short scale nature of the ocean
signal, including current positions and intensity, position and scales
of eddies and thermal fronts (Hurlburt et al., 20002; Bahurel et al.,
2002; Bell et al, 2002; Pinardi et al., 2002). One issue which is
especially challenging is understanding the connection of the open ocean
with the coastal ocean and development of models capable of recovering
the sharpest details (Thompson et al., 2002). Because of the highly
turbulent characteristics of this short range signal and its non-linear
evolution, it is absolutely necessary to take advantage of global,
dense, and accurate observations. Altimetry is especially powerful for
monitoring in near-real time the mesoscale signal and adjusting
regularly the models. The derived products satisfy many applications
(e.g. marine safety, marine pollution, ship routing, navy needs, oil
drilling, coastal forecasts, fish stock management\...).

For instance, based on these products, links can be observed between the
marine environment, the rate of marine species reproduction, and their
life cycle (Griffin et al., 2002). Consequently, this is helpful to
better manage variations in fishing resources according to fishing
campaigns. Fishing industry management is a promising market for short
range mesoscale products (e.g. CLS CATSAT project, NOAA fishery service
forecasts). The offshore drilling oil industry is also interested in
those products because petrol companies are going further from the coast
and into deep water. Oil is brought to the surface through flexible
umbilicals to barges anchored above the site, and tankers then remove
the oil from these barges. Knowing the currents at the surface but also
at a depth of several hundred meters is very useful for this type of
operation sensitive to destructive eddies and fronts (Evensen,
communication at GODAE symposium, 2002). Navy forces need also for their
own needs specific forecasting and analysis of short range oceanic
state. Water masses, temperatures, currents, eddies, and the position of
fronts are essential information to help both surface and underwater
navigation (Jourdan et al., 2002; Smedstad et al., 2002).

Another field of activity is that concerning coastal areas where there
are many problems related to risk prevention and coastal development.
High resolution models require as an input high accuracy products in the
coastal band but also at the deep ocean boundary. One example is the
prevention of storm surges. They generate an abnormal increase in sea
level (up to few meters) caused by low pressure together with high winds
blowing from the sea toward land (amplified during hurricane situations)
which can be particularly devastating to the shoreline. Another example
is the trajectory monitoring and forecasting of drifting polluted
waters, ships, and objects lost at sea. The drift is a result of the
combined actions of a current pushed by the wind, tide, and coastal
currents and large-scale oceanic circulation. Its forecast is based on
dedicated oceanic models coupled with models describing the behavior and
changes of the drifting materials. In this domain too, altimetry
products have a key role to assess and to constrain frequently the
models, improving thus the forecasts (Daniel et al., 2002) (figure 3).

Meteorological centers run sea state forecast models to anticipate the
evolution of waves and swells, which are superimposed, on all parts of
the Earth, providing sailors and workers at sea with regular forecasts
and special weather updates when weather conditions deteriorate. Such
models (e.g. VAG at Météo-France, WAM at the ECMWF European Center)
benefit undoubtedly from real-time wave-height and wind speed altimetry
products such as those issued within 3 hours from ERS2, Jason-1, and
ENVISAT (Lefevre and Cotton, 2002).

**3. The Jason-2 System**

The Jason-2 mission will be conducted within a partnership extended to
four: the CNES and NASA space agencies, and the EUMETSAT and NOAA
operational agencies. This new program organization will reinforce the
transition of the Jason-2 mission towards operational applications.
Indeed, EUMETSAT and NOAA will be involved in the ground operations,
while CNES and NASA will have the project development responsibility.
CNES participation is placed within a national effort of developing the
operational oceanography. On the NASA side, this new project is part of
its EOS program. NOAA participation is linked to its existing satellite
ground system and its ocean applications programs. EUMETSAT will be
engaged through its first optional program to be approved mid-2003.

On a technical point of view, Jason-2 satellite (figure 4) will be as
identical as possible to Jason-1 (Escudier et al., 2000). Even if not
yet finalized, the organization should be close to the following:

CNES providing:

-   A new version of the PROTEUS multi-mission platform taking into
    account the\
    experience return of the past missions and the evolution of the
    electronic components,\
    - The dual-frequency radar altimeter Poseidon 3 adapted to new
    electronic components\
    and new engineering developments\
    - The Precise Orbit Determination System DORIS, a second generation
    miniaturized\
    version

NASA providing:

\- A GPS receiver to contribute in the precise determination of the
orbit of the satellite\
- A laser retro-reflector to complete the orbit tracking of the
satellite\
- A new generation radiometer to measure the water vapor content in the
troposhere and\
derive the appropriate radar path delay correction

As with Jason-1, Jason-2 should be launched by NASA using a Delta 2
Boeing rocket from the Vandenberg launch site in California. The ground
system will benefit from the T/P and Jason-1 heritage. In CNES, the data
processing, archiving and distribution will be part of the SALP (Precise
Localization and Altimetry Service) project.

NOAA has proposed to provide Earth terminals, the satellite operations
control center, and near real time data processing, archiving, and
distribution.

EUMETSAT should provide an Earth teminal and should be responsible for
near real time product processing, distribution, and user interface
support.

A science team selected by the four agencies will assist the project in
science algorithm development and further calibration and validation
activities.

In addition to this nominal payload (similar to Jason-1), NASA/JPL has
proposed to embark as a technological demonstration passenger, a new
radar altimeter imager called the Wide Swath Ocean Altimeter (WSOA).
This new concept of instrument uses two antennas separated by a 7-meter
mast and the interferometric technique to map directly under the
satellite and over a 200 km swath the dynamic sea surface topography
(Pollard et al., 2002). Because of its full coverage and high
resolution, such an instrument looks very promising for the users,
especially with regard to mesoscale and short scale applications. But
first, the technological feasibility and the performances need to be
assessed in orbit. Jason-2 may be an opportunity for such a
demonstration, assuming WSOA is compatible with the PROTEUS platform and
does not imply any additional risk to the core mission. Consequences of
this option for the nominal Jason-2 mission are presently being
evaluated by CNES and JPL project teams. The final decision about this
option will be taken by the four partners, mid-2003, after a careful
evaluation of the technical, budget and schedule impacts on the core
mission.

**4. Performances and Products**

The unique error budget of the T/P sea level measurements and derived
products explains for a large part the exceptional science return of
this mission. This high level performance has been due mainly to a
thorough optimization of the mission design, including a high technology
payload and satellite, and the choice of an orbit perfectly adapted to
the objectives of the mission. The T/P mission was quickly considered as
a reference for the whole users community. In particular for data
centers merging altimetric data sets issued from different satellites,
the contribution of T/P data set is essentially its high accuracy (Le
Traon et al., 2002). Soon after the launch of T/P, the scientists
recommended strongly to continue for the long term such a reference
mission. This is why Jason-1 and the next Jason-2 missions are designed
to have at least the same level of performances as T/P and the same
orbit, revisiting the same reference tracks. The first Jason-1
calibration/validation results presented at the 2002 Biarritz Science
Team meeting (Jason SWT, 2002) show that the final error budget should
be even better than the pre-launch specifications (table I).

Based on the heritage of the T/P and Jason-1 geophysical products (Blanc
et al., 2002; Benada et al., 2002), three types of Jason-2 products will
be delivered (table I):

-   As for Jason-1, the Operational Sensor Records (OSDR) will be the
    faster product delivered to the users. These products take advantage
    of the DORIS navigator and of the on-board processing capabilities
    to provide in a short delay of 3-5 hours the geophysical data,
    including the radar range, the wind speed, wave-height, the orbit,
    and the radiometer measurements. This product is essentially
    dedicated to marine meteorology applications. But, thanks to the
    exceptional performances of the DORIS navigator and further
    improvements in the on-board processing, applications in other
    domains, like short range ocean circulation monitoring, are
    expected.

-   The Interim Geophysical Data records (IGDR) are delivered within 3
    days to satisfy the near real time requirements of ocean prediction
    systems. Based on ground processing, they contain all the
    information needed to compute a sea level height as accurate as 5 cm
    at 1 Hz sampling along the track of the satellite. In the near
    future, the quality of the OSDR could be improved at a level of
    performances similar to IGDR which would allow production of a
    single OSDR/IGDR product in a delay of 3-5 hours.

-   The Geophysical Data Records are the final fully validated products
    offering the ultimate accuracy in the measurements of sea level,
    wave-height and wind speed. The present GDR Jason-1 error budget is
    expected to be improved thanks to up-coming adjustments in the
    processing algorithms which would benefit also to Jason-2 GDR
    products.

-   

**5. Schedule**

On a programmatic point of view, first discussions between the four
agencies started early in 2000, resulting in a co-signed letter for a
preliminary agreement on the Jason-2 program. The Memorandum of
Understanding is now being prepared for a program decision and an
expected signature in 2003. In the meantime, technical discussions are
going on to define in more detail the project components and the
respective contributions of each agency. Anticipated procurements and
studies on Poseidon, DORIS altimeter, and PROTEUS platform have been
initiated by CNES in order to meet the starting of the phase B
development end of 2002 and the starting of phase C/D mid 2003, and
consequently the targeted launch date, end of 2006. The satellite will
be designed for a 5 years mission.

Table I. JASON-1 PerformanceS AS A FUNCTION OF LATENCY and products.\
(This is for 1 Hz sampling along the satellite track)

  --------------------------- ---------- ----------- ----------- ----------
  Measurement                 3 hours    3 days      30 days     30 days
                              (OSDR)     (IGDR)      (GDR)       (goal)

  Range to surface (cm,       4.5        3.3         3.3         2.3
  corrected)                                                     

  Radial orbit height (cm)    \< 30      4.0 (2.5\*) 2.5 (2.0\*) 1.0

  **Sea-surface height (cm)** **N/A**    **5.0       **4.2       **2.5**
                                         (4.1\*)**   (3.8\*)**   

  Significant wave height     50         50          50          25
  (cm)                                                           

  Wind speed (m/s)            2          1.7         1.7         1.5
  --------------------------- ---------- ----------- ----------- ----------

\* Revised error, based on preliminary Jason-1 Cal/Val results (TBC)

# 

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Pollard B., E. Rodriguez, L. Veilleux, T. Akins, P. Brown, A.
Kitiyakara, M. Zawadski, S. Datthanasombat and A. Prata, The Wide Swath
Ocean Altimeter : Radar Interferometry for Global Ocean Mapping with
Centimetric Accuracy, IEEEAC paper n° 068, IEE, 2002

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System : The Operational Transition Issue, in «Observing he Oceans in
the 21^st^ Century, C.J. Koblinsky and N.R. Smith (Eds), GODAE and
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**Relevant** **Web sites**

http://[www-aviso.cnes.fr](http://www-aviso.cnes.fr/)\
[http://sealevel.jpl.nasa.gov](http://sealevel.jpl.nasa.gov/)\
http://[www.mercator.com.fr](http://www.jason.oceanobs.com/)

![](media/image1.wmf){width="4.3in" height="4.0256944444444445in"}

> Figure 1: T/P and Jason-1 are watching permanently\
> the tropical Pacific, detecting any sea level\
> anomaly which may be due to ENSO starting

![](media/image2.png){width="4.6in" height="4.030555555555556in"}

Figure 2: The MERCATOR system fed by T/P and Jason-1 data\
provides since January 2001, routine high resolution\
2 weeks forecast of the North Atlantic circulation

![](media/image3.png){width="3.0597222222222222in"
height="1.8784722222222223in"}

Figure 3: Three weeks forecast of the Lyria pollution in the
Mediterranean Sea (1993), by the Meteo-France MOTHY polluant drift model
(red star is the starting point, red diamonds are observations)\
on the right: with assimilation of MERCATOR yearly circulation and of
ERS1 and T/P data\
on the left: without assimilation (from Daniel et al., 2002)

Figure 4: The Jason-2/OSTM satellite ![](media/image5.png){width="5.8in"
height="3.332638888888889in"}