MONITORING OF CLIMATE CHANGE AND
MICROWAVE SATELLITE REMOTE SENSING
_ Introduction
_ Satellite altimetry
_ Passive remote sensing
_ Earth Exploration Satellite frequencies
Jean PLA
CNES, Toulouse, France
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
Jean PLA - CNES
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INTRODUCTION
• Climate change has now become a reality and the data
accumulated since for years show that the climate is warming
on a global scale
• Today, climatology relies increasingly on space technology.
Earth observation delivers series of precise, global
measurements matching the scale of planetary climate
phenomena.
• Remote sensing is the acquisition of physical data without touch
or contact. It is a form a vision but nothing new.  Focus on
the usage of the electromagnetic spectrum and of Earth
Observation satellites to monitor some aspects of climate
change.
• Importance of the ITU-R Radio Regulations to protect the Earth
Exploration Satellite frequencies.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
Jean PLA - CNES
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BACKGROUND
• A variety of satellites and ground systems are already in place:
meteorological, telecommunication, navigation and Earth
Observation.
• Space has become an increasingly important source of
information and an essential data-relaying infrastructure, a
resource in places in places in the world where ground-based
monitoring systems are not deployable.
• A number of scientific discoveries about climate change have
also been made thanks to space based data.
• Example: mission TOPEX/JASON in space altimetry: rise of the
mean sea level, ocean circulation (El niňo events)
• Future satellites to be launched: SMOS (Soil moisture, Sea
salinity) and MEGHA-TROPIQUES (cyclones, tropical rainfall)
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
Jean PLA - CNES
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SATELLITE ALTIMETRY: INTRODUCTION
• Seventy-one per cent of the planet’s surface is covered by
water and a key dimension to understanding the forces behind
changing weather patterns can only be found by mapping
variations in ocean surface conditions all over the world and by
using the collected data to develop and run powerful models of
ocean behaviour.
• Combining oceanic and atmospheric models  accurate
forecasts on both a short- and long-term basis.
• Coupling of oceanic and atmospheric models needed to take
the mesoscale (medium-distance) dynamics of the oceans 
weather forecasting beyond two weeks.
• The oceans are also an important part of the process of climate
change and a rise in sea levels all over the world is widely
recognized as potentially one of the most devastating
consequences of global warming.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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SATELLITE ALTIMETRY
TOPEX POSEIDON
JASON 1, 2
SATELLITES:
Measurements
● Distance between the
Satellite and the sea
● wave height
● wind speeds
ACCURACY: cm
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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SATELLITE ALTIMETRY
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Altimetry is a technique for measuring height. Satellite altimetry
measures the time taken by a radar pulse to travel from the satellite
antenna to the surface and back to the satellite receiver. Combined
with precise satellite location data, altimetry measurements yield seasurface heights.
TOPEX-POSEIDON launched on August 10, 1992, decommissioned
late 2005.
• Jason-1 satellite was launched on December 7, 2001.
• Jason-2 satellite was launched on June 20, 2008.
• Two altimeters belonging to the same family are now in
operation: tandem mission
•
Orbit :
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Altitude 1336 km, circular, non-sun-synchronous
66° inclination, global data coverage between 66°N and 66°S latitude
10-day repeat of ground track (±1-km accuracy)
coverage of 95% of ice-free oceans every 10-days
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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MEAN SEA LEVEL RISE
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Global mean Sea Level rise is one of the consequences of global
warming. Monitoring this level is an application of altimetry, and one of
the main issue in Environmental sciences of the 21st century.
It is quite difficult to separate the natural variability of the climate
from the warming effects. The measurements of the mean sea levels
are derived from a period of time of 15 years of satellite earth
observation: such a period of time is short. In addition to that, it is
necessary to indicate that human induced peturbation is added to the
natural climate variability.
Climate change signals can be detected only if they are greater than
the background natural variability. Detecting global climate change is
much more demanding than monitoring regional impacts.
Need to have a stable environnment and time series must be stable
and accurate.
The rise of the sea level is mainly a consequence of past climatic
events. The following figure shows that the rise is about 3,3 mm per
year, roughly 5 cm within 15 years.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
Jean PLA - CNES
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MEAN SEA LEVEL RISE
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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Map of sea level variation trends since 1992: regional trends
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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WHAT IS MAKING THE OCEANS RISE?
Mean sea level rise causes are better and better known. Comparison
between measurements coming from different techniques enables to
better specify the various contributions between water exchanges,
thermal expansions, etc. Other measurements enable to estimate ice
melting (glaciers and indlandsis), continental water storage variations,
etc.
Changes in water temperature impact sea level variations. As water
warms, it expands and its volume increases, causing levels to rise.
The quantity of salts in the water has also an influence on sea level,
since it changes the water density. The more salty the water, the
denser it is, and the lower the level.
Thermal expansion
1.6 +/- 0.5 mm/yr
Glaciers and ice caps
0.77 +/- 0.22 mm/yr
Greenland ice sheet
0.21 +/- 0.07 mm/yr
Antarctic ice sheet
0.21 +/- 0.35 mm/yr
Sum
2.8 +/- 0.7 mm/yr
Observed
3.1 +/- 0.7 mm/yr
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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El Niño Southern Oscillation - ENSO
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Better knowledge of ocean circulation is enabling us to better
understand and predict climate, especially natural catastrophes
such as El Niño. This phenomenon, caused by anomalous warm
water arrivals on the coast of Peru, brings severe weather
patterns, such as drought, flooding, and cyclones. It is now
possible to predict El Niño from ocean data.
Forecasting El Niño
– Since the 1990s, an in situ observation system has been set up in the
Pacific and new satellites have continuously scanned the global
ocean. Though we cannot avoid El Niño's whims, we can predict and
mitigate its impacts.
•
Impacts around the world
– Warm El Niños and cold La Niñas follow each other against the
backdrop of the ocean seasons. These surface temperature and sea
level anomalies in the intertropical Pacific affect climate worldwide.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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El Niño is behind rise in sea level
● The meteorological effects of El Niño 1997-1998
were felt worldwide, but it also contributed to
variations in mean sea level. Indeed, sea level
anomalies measured by Topex/Poseidon were over
20 centimeters in the equatorial Pacific when the
phenomenon was at its height (and as much as 30
centimeters off the coast of Peru). These anomalies
obviously had an effect on the global mean of sea
levels.
● El Niño not a consequence of the climate change
since it already exists, but could be amplified by the
warming climate effect.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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El Niño bulletin, latest news
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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OTHER MEASURED PARAMETERS THROUGH ALTIMETRY
• Estimates of wind and waves data from altimeter measurements
originate in analysis of the return from the sea surface.
• Accuracy of wind speed (m/s) : 1.5
• Satellite altimetry useful for ships: the knowledge of the sea
currents (derived from observed sea level variations) will allow
the ships to optimize their trip.
• Main practical applications of wind and wave data derived from
altimeter measurements: production of reliable atlases of
wind and wave climate. Commercial applications include
evaluation of wind and wave energy resource, and evaluation of
risks to shipping, marine structures and coastal defences. The
usage of the products from the project Ocean & Weather
Routing alows to save fuel for the ships and therefore and
has a positive impact on the environnment.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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SMOS
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Soil Moisture and Ocean Salinity (SMOS) mission is to globally
observe soil moisture and ocean salinity, two crucial variables for
modelling our weather and climate.
Salinity is fundamental in determining ocean density and hence
thermohaline circulation. Furthermore, ocean salinity plays a part in
establishing the chemical equilibrium, which in turn regulates the CO2
uptake and release.
Unlike sea surface temperature (SST) and sea level anomalies (SLA),
it has not yet been possible to measure salinity from space.
The SMOS instrument will be launched November 2009, and is
designed to provide temperature brightness (TB) data for 3–5 years.
The instrument is microwave radiometer using the frequencies in the Lband, corresponding to 1.4 GHz.
The satelite orbit, instrument design and dataprocessing prosedures is
designed to provide data every third day with a 35–50 km resolution.
The accuracy requirment of the ocean salinity observations has been
set to 0.1 practical salinity units (1 psu= 1g salt in 1kg of seawater),
every 10 days at 200 km spatial resolution.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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WATER CYCLE ON THE PLANET
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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SEA SALINITY
● Simulation, during the four seasons of the average salt
concentration within the ocean. This salinity eqauls
typically de 35 «units de practical salinity» (psu),
Which means that 35 gr. of salt are within 1 kg of water,
about 1 l.
● This value is modified through evaporation and
precipitations and is between 32 and 38 psu.
● The salinity is maximum at subtropical latitudes, where
the evaporation is not enough compensated by rain.
● The salinity is minimum around the equator, where
the rain is frequent, and also within polar regions,
mainly because of the icecap melting.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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Thermohaline circulation
• Once SMOS is launched, it is expected that SMOS will
investigate the coupling between SSS (Sea Surface
Temperature), the the North Atlantic Oscillation/Arctic Oscillation
and The Atlantic Thermohaline Circulation.
• The Atlantic Thermohaline Circulation (ATHC) is a dynamically
active component of the climate system, in particular on multiannual to decadal time scales. The heat and salt carried
northward across the Greenland-Iceland-Scotland (GIS) ridge
are substantial, and both quantities are of importance for the
water mass and ice distribution of the Nordic Seas and Arctic
Ocean, and possibly also the deep mixing and water mass
transformations taking place in the region.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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Thermohaline circulation
The quantity of salt within the ocean has an essential
impact on the behaviour of the overall thermolaline
(from thermos, « temperature », and halin, « salinity
») circulation. Within some deep areas of the oceans,
there is hot water, with salt. For instance, over the
west part of the Pacific ocean, the précipitation rate is
quite high and the water at the surface has a
moderate amount of salt. But, below 30 and 60
meters, there are areas having warmer waters (+1
°C). The salinity is therefore an essential factor on
the climate variability.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
Jean PLA - CNES
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Thermohaline circulation
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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SMOS satellite
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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Monitoring of cyclones and tropical rainfall
The MEGHA-TROPIQUES satellite to be launched 2009/2010,
is part of the Global precipation mission (GPM). It is a frenchindian MEGHA-TROPIQUES satellite devoted to the
atmospheric research. The data collected by the satellite will
allow to improve our knowledge on the water cycle contribution
to the climate dynamic in the tropical atmosphere and our
understanding of the processes linked to the tropical convection.
●provide simultaneous measurements of several elements of the
atmospheric water cycle: water vapour, clouds, condensed water in
clouds, precipitation and evaporation,
●measure the corresponding radiative budget at the top of the
atmosphere, ensure high temporal sampling in order to
characterise the life cycle of the convective system and to obtain
significant statistics.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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MEGHA-TROPIQUES
• MEGHA-TROPIQUES: to study the water and energy
cycle in the tropics associated to convection and will
perform the retrieval of rain, radiative budget and
water vapour. The main applications are as follows.
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Model data assimilation to improve weather forecast
General circulation models validation/improvement
Climate model validation/improvement
Risk assessment/management (floods, hurricanes)
• MADRAS passive microwave for rain/cloud estimates
operating between 19 to 157 GHz
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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MEGHA-TROPIQUES SATELLITE
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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Megha-Tropiques mission
To provide the following geophysical parameters:
Cloud condensed water content
Cloud ice content
Convective-stratiform cloud discrimination
Rain rate
Latent heat release
Integrated water vapour content
Radiative fluxes at the top of the atmosphere
Sea surface wind
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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MADRAS instrument (range: 18.7 GHz-157 GHz)
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Rain retrieval over Ocean is easier because all channels are useful.
Rain retrieval over Land is difficult because only higher frequencies are
useful, especially 89 GHz.
Tropical rain is VERY constrained by ice microphysics hence higher
channels.
157 GHz is innovative and VERY promising for rain over land.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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Microwave frequencies used for Earth Exploration Satellite: passive
at 1.4 GHz: soil moisture and sea salinity
(SMOS)
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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SENSITIVITY OF PHYSICAL PARAMETERS IN OCEANOGRAPHY AND
METEOROLOGY WITH RESPECT TO FREQUENCY AND THE
OPTIMUM CHANNELS: passive remote sensing
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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WINDOW AND SOUNDER CHANNELS: passive remote sensing
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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Frequencies for satellite active remote sensing
• For most of the EESS (active) sensors, the
operating frequency range is linked to the
geophysical parameters to be observed. For
instance, to enable measurement of clouds and
precipitation, the wavelength needs to be small
enough to reach the required sensitivity.
• For radar altimeters, the main frequencies used
are at 5.3 GHz, 13.65 GHz and also at 35.4-36
GHz.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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NEED OF FREQUENCY PROTECTION
• Spectrum management: to estimate the social and economic
value of different usage of spectrum. For scientific use: the
benefits of scientific use can be difficult to quantify as they can
relate to the society as a whole, may be difficult to foresee and
may be realised over a very long period of time
• Scientific use of spectrum: considerable societal value. Most
of the data retrieved from the use of the so-called “scientific
bands” are directly dedicated to the benefit of every citizen as
they relate in particular to meteorology, climatology,
environment, civil security and fundamental research.
• Human activity today: opportunity for interference to occur
to microwave sensing measurements. Simultaneous
concerns about global warming have heightened awareness of
possible risks to life.
• Reasonable balance between our reliance on emitting devices
and incomplete understanding of global climate changes needs
to be achieved.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
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CONCLUSION
• Climate change is a reality and it is probably one of the biggest
challenges in the history of humankind.
• Need of global data sets, coordinate climate analysis, modelling
and predictions  establish the correct climate state and to
create powerful modelling tools for climate prediction.
• Satellite Earth observation data from space plays a crucial role
in understanding the current state of the climate and how it may
evolve.
• Need for global information on key indicators of climate.
• Usage of Earth Observation satellites providing reliable data
sets is one element of the puzzle. Microwave frequencies are
essential and should be protected on a long term basis.
ITU Symposium on ICT and Climate Change, Quito, 8-10 July 2009
Jean PLA - CNES
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