MONITORING THE OCEANS WITH SATELLITE ALTIMETRY TECHNIQUES
Demitris Delikaraoglou Nicholas Christou ^ and Mario Berube ^ ^
^ Canada Centre for Surveying, Geodetic Surveying Division, 615 Booth Street, Ottawa, Ontario, Canada K1A OE9
® University of New Brunswick, Department of Surveying Engineering, Fredericton, New Brunswick, Canada E3B 5A3
ABSTRACT
Satellite radar altimeter measurements provide a record of the elevation of the sea surface, the height of its waves and the
wind speed directly beneath the satellite. For the past three years, an altimeter onboard the United States Navy’s GEOSAT
satellite has used this technology to provide accurate information about the sea levels and ocean circulation patterns. These
observations provide directly an increadibly rich source of synoptic and global information enabling us to study ocean surface
variability on time and space scales unavailable in the past; to better understand the role of ocean circulation in past and future
climate; to provide accurate wave information for more efficient operation of commercial and naval vessels; and to produce
accurate predictions of tides, tide currents and surface winds which are essential to safe coastal navigation, resource exploration
and exploitation (e.g. fisheries and energy).
In the near future, planned altimetry systems such as those to be deployed in the early and mid-1990s onboard the SALT, ERS-1
and TOPEX/Poseidon satellites will vastly improve our ability to observe the detailed picture of the ocean’s circulation needed to
discern the subtle variations and weather patterns of the sea. This can be achieved by carrying out repeated observations which
would result in a series of topographical maps of the elevation of the sea surface. These maps would not only reveal the overall
behaviour of the sea surface, but also smaller changes and fluctuations. In the long term, satellite altimeter data will be combined
with the latest information regarding ocean density and with theories of ocean dynamics to produce for a first time accurate
models of how the global ocean circulation (from its surface to the seafloor) changes over time, and thus prove to be extremely
useful in detecting climatic changes and verifying model results. The critical step now in front of us is to bring the technology into
an operational environment where it will be used, along with data from other remote sensing satellite sensors for global climate
monitoring.
In preparation for these upcoming missions, application studies are being carried out at the Canadian Centre for Surveying to
develop an operational system for altimeter data analysis and processing. Unclassified data from the GEOSAT Exact Repeat
Mission are being used to develop new or revised algorithms and to produce trial products. This paper reviews these
developments, the results currently obtained from GEOSAT data, and the experiments planned for the upcoming missions.
KEY WORDS: Satellite Altimetry, Environmental Monitoring, Oceanic Studies
INTRODUCTION
To date techniques for observing the Earth from space have
evolved to the point that they can be exploited to achieve
an understanding of how the Earth’s atmosphere, oceans,
land and ice-covered regions function and interact as an
integrated system. The growing awareness to see the Earth
as one “system” has led to an initiative by NASA, the
European Space Agency (ESA), Canada and Japan to
establish a realistic and affordable overall strategy for Earth
observation. The major rationale for the future Earth
Observing System (Eos) program is founded on the
realization that major problems concerning
- the well-being of the environment and the increasing
evidence of climatic changes;
- the management of limited resources vis-à-vis the
increasing demand for these resources;
- the increasingly stringent operational constraints on
forecasting meteorological systems; and
- the understanding of the Earth’s geo-kinematics and
geophysics, gravity and magnetic fields, the relationships
of sea-level changes and climatology etc.
can only be addressed effectively by assessing the
importance/relevance of Earth observation to specific
interdisciplinary problems relevant to these issues.
In particular, the oceanic and polar regions of the Earth
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have become the focus of considerable attention in recent
years in connection with global climatic concerns, the main
reasons being that:
• Oceanic storage of heat can strongly influence the rate
and amount of greenhouse warming, and the oceans
themselves are major sinks for carbon dioxide. This
realization stresses the need for a better understanding of
the role of the oceans and ice cover in either modulating
or amplifying the warming trend;
• There is growing evidence that the polar regions play a
key role in the physical processes responsible for global
climatic fluctuations. In many instances, they might
even be the prime source of such fluctuations;
• Polar regions are now widely recognized as important
repositories of information on paleoclimates and the
causes of past climatic changes;
• There is mounting concern that systematic warming of
the polar regions and dramatic trends in ozone depletion
(believed to be a direct consequence of a man-induced
“greenhouse effect”) will alter the balance of the ice
masses and thus affect the global sea level with all the
attendant consequences in terms of flood control, surface
and groundwater level management and ecology;
• Field observations have now revealed a possible
