2 Satellite Oceanography for Ocean
Forecasting
PIERRE-YVES LE TRAON
CLS Space Oceanography Division
2.1 Overview of space oceanography
This lecture aims at providing a general introduction to satellite oceanography in
the context of ocean forecasting. Satellite oceanography is an essential component
in the development of operational oceanography. Major advances in sensor development and scientific analysis have been achieved in the last 20 years. As a result,
several techniques are now mature (e.g. altimetry, infra-red imagery) and provide
quantitative and unique measurements of the ocean system.
We begin with a general overview of space oceanography, summarizing why it is
so useful for ocean forecasting and brietly describing sateUite oceanography techniques, before looking at the status of present and future missions. We will then
turn to sateUite altimetry, probably the most important and mature technique currently in use for ocean forecasting. We will also detail measurement principles and
content, explain the basic data processing, including the methodology for merging
data sets, and provide an overview of results recently obtained with TOPEXI
POSEIDON and ERS-l/2 altimeter data. Lastly, we will focus on real-time aspects
crucial for ocean forecasting. Perspectives will be given in the conclusion.
2.1.1 Why do we need satellites for ocean forecasting?
An ocean hindcastinglforecasting system must be based on the assimilation of
observation data into a numerical model. It also must have precise forcing data.
The ocean is, indeed, a turbulent system. "Realistic" models of the ocean are
impossible to construct owing both to uncertainty of the goveming physics and of
an initial state (not to mention predictability issues). Continuous observations are
required to drive the model towards a realistic state. Ocean forecasting therefore
caUs for an ocean observing system which should also include forcing data. Both
in-situ and satellite data are needed:
• The usefulness of in-situ data is limited by poor space/time coverage, and
access to remote regions (e.g. southem oceans) is often difficult. Conventional
techniques (ship measurements, ship deployment) also may not be suitable for
an operational system. Reliable, autonomous techniques have to be used. Such
techniques are already being used or starting to emerge (e.g. XBT, TOGNTAO,
PIRATA, profiling tloats such as P-ALACE or PROVOR) and promising new
techniques (e.g. gliders, acoustic tomography) are under development. Global
Forecasting
PIERRE-YVES LE TRAON
CLS Space Oceanography Division
2.1 Overview of space oceanography
This lecture aims at providing a general introduction to satellite oceanography in
the context of ocean forecasting. Satellite oceanography is an essential component
in the development of operational oceanography. Major advances in sensor development and scientific analysis have been achieved in the last 20 years. As a result,
several techniques are now mature (e.g. altimetry, infra-red imagery) and provide
quantitative and unique measurements of the ocean system.
We begin with a general overview of space oceanography, summarizing why it is
so useful for ocean forecasting and brietly describing sateUite oceanography techniques, before looking at the status of present and future missions. We will then
turn to sateUite altimetry, probably the most important and mature technique currently in use for ocean forecasting. We will also detail measurement principles and
content, explain the basic data processing, including the methodology for merging
data sets, and provide an overview of results recently obtained with TOPEXI
POSEIDON and ERS-l/2 altimeter data. Lastly, we will focus on real-time aspects
crucial for ocean forecasting. Perspectives will be given in the conclusion.
2.1.1 Why do we need satellites for ocean forecasting?
An ocean hindcastinglforecasting system must be based on the assimilation of
observation data into a numerical model. It also must have precise forcing data.
The ocean is, indeed, a turbulent system. "Realistic" models of the ocean are
impossible to construct owing both to uncertainty of the goveming physics and of
an initial state (not to mention predictability issues). Continuous observations are
required to drive the model towards a realistic state. Ocean forecasting therefore
caUs for an ocean observing system which should also include forcing data. Both
in-situ and satellite data are needed:
• The usefulness of in-situ data is limited by poor space/time coverage, and
access to remote regions (e.g. southem oceans) is often difficult. Conventional
techniques (ship measurements, ship deployment) also may not be suitable for
an operational system. Reliable, autonomous techniques have to be used. Such
techniques are already being used or starting to emerge (e.g. XBT, TOGNTAO,
PIRATA, profiling tloats such as P-ALACE or PROVOR) and promising new
techniques (e.g. gliders, acoustic tomography) are under development. Global