addition to observational capabilities from the polar
platforms, the Eos program will be supplemented by
moderate-cost Earth Probe missions, each of which will be
characterized by a choice of orbit and spacecraft design
capable of achieving a particular objective.
CANADIAN PLANS FOR Eos
Long-term Plans
There are currently a number of research initiatives within
various Canadian Government Departments aimed at
addressing the role of satellite observations to give a better
understanding of the Canada’s northern environment
including the land and ice components, and the surrounding
oceanic areas. Two major initiatives are particularly worth
mentioning:
(a) As an associate member of the European Space
Agency, Canada is a contributor to the ERS-1 mission.
Access to the ERS-1 data is a major reason for Canada’s
participation in the ERS-1 program. National requirements
for ERS-1 have been derived from a number of
requirements based on the extension of remote sensing
programs within various government departments (notably
Canada Centre for Remote Sensing (CCRS), Canada Centre
for Surveying (CCS) and the Geological Survey of Canada;
Atmospheric Environment Service (AES); and Fisheries
and Oceans), and interested industry and university groups.
The national objectives represent four major areas: oceans,
land resources, geology and ice, as well as specific
scientific and application priorities. Overall, Canada’s
highest priority is for regular guaranteed acquisition of
SAR imagery, as well as ERS-1 Radar Altimeter,
Scatterometer and Along Track Scanning Radiometer
sensor data. Canada plans to operate two ground stations
for acquisition of ERS-1 SAR image data, as well as global
low bit rate data such as altimetry. These data and fast
delivery products will be distributed to Canadian users
using national data networks.
(b) In a similar cooperative effort, an Eos interdisciplinary
program for use of a Cryospheric System (CRYSYS) to
monitor global change in Canada has recently completed its
definition phase (McNutt et al., 1988). At the time of this
writing, pending final NASA approval, CRYSYS will soon
enter its ten year-long execution phase (Simard et al.,
1990). There are several objectives for this work which
follow from the preparatory work for ERS-1 and Canada’s
own RADARSAT satellite programme; namely:
• to continue to develop and implement algorithms
necessary to extract geophysical information related to
the cryosphere, to validate the results of regional
models, and to use the regional information to initialize
and validate polar models;
• to maintain an extensive array of field sites in critical
areas;
• to access information from other related databases,
especially in Canada, so that a complete record of
information (including historical, operational and future
products) on cryospheric processes can be obtained; and •
• to use this information in models to examine the effects
of global change as manifested in cryogenic processes,
Figure 1 - Satellite Altimetry Mode Geometry
and to deliver this information for use, via the Eos Data
Information System (EosDIS), in the verification of
global climate models.
Current Developments in Satellite Altimetry
Satellite altimetry is a technique that uses a microwave
radar pulse sent from a satellite orbiting at a height of
approximately 1000 km (cf. Figure 1). This pulse interacts
with the sea surface and part of the incident radiation
reflects back to the satellite. The two-way travel time of the
pulse reflected from the ocean (or ice) surface is measured
with great precision, the equivalent of a few centimeters
(< 8 cm for the ERS-1 altimeter) in one-way path length.
From these observations, near-surface wind and significant
wave height can be determined from the power and the
shape of the returned signal. The marine geoid is recovered
by carefully editing the sea surface height data, and
correcting for time dependent phenomena such as ocean
currents, tides, and seasonal variations. In an inverse
procedure, the latter can also be extracted and studied.
Sea ice can be a problem when using satellite altimeter data
to recover precise geoid and gravity field information.
Nevertheless, special algorithms which utilize the altimeter
signal’s scattering signatures can yield information about
the presence of ice within the altimeter’s footprint, as well
as infer the position of ice shelf edges, ice-sheet averaged
surface gradients and thickness. During the ERS-1 mission,
large portions of the arctic areas overflown by ERS-1 will
be ice-free during late summer and early autumn. This
means the Canadian experiments scheduled then will
provide for the first time large amounts of much anticipated
altimetry data in the near-polar regions.
The altimetry measurements for oceanographic purposes,
useful for monitoring time-variable oceanic events of
interest to global environmental monitoring, pose quite
stringent requirements. For instance, measurements of
time-variable surface currents require observations with a
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