make optical observations and a data collecting system
to gather data. They are unique systems due to use of
on board sensors which combine features that are
specially designed to resolve the broad range of space
and time scales involved in the monitoring and
preservation of ecosystem.
The CBERS satellites will enhance and
complement the existing remote sensing systems in an
effort to improve our knowledge about the Earth
environment and resources. À unique characteristic of
CBERS is its multi-sensor payload with different
spatial resolutions and data collecting frequencies.
The Wide Field Imager - WFI has a ground
swath of 890 km which provides a synoptic view with
spatial resolution of 260m. The Earth surface is
completely covered in about 5 days in two spectral
bands: 0,66 mm (green) and 0,83 mm(near infra-red).
The high resolution CCD camera provides
images of a 113 km wide strip with 20m spatial
resolution. Since this camera has a sideways pointing
capability of + 32 degrees it is capable of taking
stereoscopic images of a certain region.In addition,
any phenomenon by the WFI may be "zoomed"by the
oblique view of the CCD camera with a maximum
time lag of 3 days.
The CCD camera operates in 5 spectral
bands: 0,51 - 0,73,4um (pan)
045 - 0,524m
0,52 - 0,594m
0,63 - 0,69um
0,77 - 0,89um
The two spectral bands of the WFI ((0,63 -
0,69 m and 0,77 - 0,89 4m) are also present in the
CCD camera to allow complementing the data of two
types of remote sensing images. A complete cycle of
the CCD camera takes 26 days.The spatial resolution
is 20m.
The Infrared Multispectral Scanner( IR-
MSS )operates in 4 spectral bands: 0,50 - 1,10
Adm(pan)
506
1,55 - 1,75 4m
2,08 - 2,35 um
10,40 -12,50
such as to extend the CBERS spectral coverage up to
the thermal infrared range. It images a 120km swath
with a resolution of 80 m (160 m in the thermal
channel). In 26 days one obtains a complete Earth
coverage that can be correlated with the images of :
CCD camera.
The CBERS includes a data collection
system for real-time retransmission of environmental
data gathered on the ground and transmitted to the
satellite by small autonomous stations. The data from
thousands of these stations located anywhere on Earth
are directed at the same time to processing centers and
to -users by means of transmissions in different
frequencies.
The CBERS satellite is composed of two
modules. The payload module houses the optical and
electronic systems used for Earth observation and for
data collecting. The service module incorporates the
equipment that ensures the power supply, the control,
the telcomunications and all other functions needed
for the satellite operation.
The 1100 W of electrical power needed to
operate the on-board equipment are obtained through
solar panels that are deployed when the satellite is in
orbit and that are continuously oriented towards the
sun by automatic control. To provide the stringent
pointing accuracy needed by the sensor systems that
will take high resolution images from a distance of
about 800 km, the satellite is equipped with a sensitive
attitude control system that is complemented by a set
of hydrazine thrusters which are also used in eventual
satellite orbit correction maneuvers. The internal data
used to monitor the satellite health are collected and
processed by a distributed computer system before
being transmitted to the Earth. An active and passive
thermal control system provides the appropriate
environment for operation of the'sophisticated on-boar
equipment.
CBERS has a sun-synchronous orbit at an
altitude of 778 km, completing about 14 revolutions
per day. The local solar time at the crossing of the
Equator is always at 10:30 A.M. thus providing the
same sola illumination conditions for comparing
images taken in different days.
It takes 26 days for the satellite to revisit the
same Earth location. This is the time necessary to
image the entire Earth with the CCD and the IRMSS
cameras that have narrow fields of view. On the other
hand, using the WFI camera which is able to take
images that are 900 km wide, the time required for
global coverage is 5 days.
The sideways pointing capability of the high
resolution CCD camera combined with the type of
satellite orbit provides stereoscopic vision capability
for given region with an interval of 3 days between the
two elementary images.
The CBERS satellites will be launched by
Chinese rockets of the Long March series from the
Shanxi Launch Site in China.The image receiving
stations and the processing centers in Brazil and in
China provide the main network for image reception.
Stations in other countries may be established to
extend the CBERS coverage potential.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
