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SPOT (Satellite Pour l'Observation de la Terre)
The SPOT (Satellites Pour lObservation de
la Terre or Earth-observing Satellites) remote-sensing programme
was set up by France in partnership with Belgium and Sweden. The
constellation of SPOT satellites in orbit makes it possible to observe
practically the entire planet in one day. Above 40° N. and S.
latitude any point whatsoever can be observed each day of the year,
whereas at the Equator itself a thin, approximately 250km-wide strip
(out of the 2,800 km separating the two adjacent SPOT satellite
orbits) remains inaccessible on any given day. Two stereoscopic
scenes can be acquired in tandem mode on the same day by using two
of the three satellites in the course of a 26-day cycle.
SPOT 1, 2 & 3
The first three satellites were identical
and their payloads consisted of two identical HRV (Visible High-Resolution)
optical instruments, data recorders (on magnetic tapes), and a system
for transmitting the images to the ground-based receiving stations
(downlink).
altitude: 822 km
inclination: 98 degrees
orbit: sun-synchronous polar
period of revolution: 101 minutes
repeat cycle: 26 day
| satellites : |
SPOT 1 |
(21/02/1986 - still operational) |
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SPOT 2 |
(21/01/1990 - still operational) |
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SPOT 3 |
(25/09/1993 - 14/11/1996) |
HRV sensors
Each HRV sensor can acquire the images in panchromatic mode (P mode:
a single wide band in the visible part of the spectrum) or multispectral
mode (XS mode: the green, red, and infrared bands of the electromagnetic
spectrum) indifferently. The two HRV sensors can function independently
or in tandem in either XS or P mode. Each of the two HRV instruments
can sweep a 60km-wide swath. They thus acquire 60km x 60km images.
The images spatial resolution is 10m x 10m for the panchromatic
images and 20m x 20m for the multispectral images.
The SPOT satellites optical instruments can make oblique observations
up to angles of 27° from the satellites vertical axis
by changing the direction of each optical instruments entry
mirror. These orientations are remote-controlled by the ground stations,
thereby making it possible to observe particular regions that are
not necessarily vertical to the satellite. In this way, the temporal
resolution is shortened from 26 to 4-5 days for the temperate zones.
|
Mode
|
Band
|
Spectral band |
Resolution
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| XS-multispectral |
XS1 |
0,50 - 0,59 µm |
20m x 20m |
| |
XS2 |
0,61 - 0,68 µm |
20m x 20m |
| |
XS3 |
0,79 - 0,89 µm |
20m x 20m |
| P-panchromatique |
PAN |
0,51 - 0,73 µm |
10m x 10m |
SPOT 4
The second most recent addition to the SPOT
family is an enhancement of the earlier versions. Its payload consists
of several sensors (two identical HRVIR (Visible & Infrared
High-Resolution) optical sensors and the VEGETATION sensor), data
recorders (on magnetic tapes), and a system for transmitting the
images to the ground-based receiving stations (downlink).
altitude: 830 km
inclination: 98 degrees
orbit: sun-synchronous polar
period of revolution: 101 minutes
repeat cycle: 26 days
satellite: SPOT 4 (24/03/1998 still operational)
HRVIR sensors
The HRVIR sensors are very similar to the HRV sensors of the previous
generation (same spatial resolution and possibility of orienting
the mirrors). However, they differ by:
the presence of an additional spectral band in the middle-infrared
band (1.58-1.75 µm);
the panchromatic (0.51-0.73 µm) bands being replaced
by the B2 (0.61-0.68 µm) band, which can function equally
well in 10m and 20m mode; and
onboard superimposition of all of the spectral bands.
|
Mode
|
Band
|
Spectral band |
Resolution
|
| Multispectral |
B1 |
0,50 - 0,59 µm |
20m x 20m |
| |
B2 |
0,61 - 0,68 µm |
20m x 20m |
| |
B3 |
0,79 - 0,89 µm |
20m x 20m |
| MIR |
1,58 - 1,75 µm |
20m x 20m |
| M - monospectral |
PAN |
0,61 - 0,68 µm |
10m x 10m |
VEGETATION Sensor
The VEGETATION programme is co-financed by the European Union, Belgium,
France, Italy, and Sweden and being conducted under the supervision
of the CNES (National Centre for Space Studies, France). The aim
of the VEGETATION instrument is to provide accurate measurements
of the main characteristics of the Earths plant cover. Practically
daily global coverage and a resolution of 1 kilometre make this
sensor an ideal tool for observing long-term regional and global
environmental changes.
VEGETATION works independently from the HRVIRs. It includes a wide-angle
radiometric camera operating in four spectral bands
(blue, red, near-infrared, and middle-infrared) at a resolution
of 1 km. Given its 2,250km swaths, this instrument is thus able
to cover almost all of the Earths dry land in just one day.
|
Band
|
Spectral band |
Resolution
|
| B0 |
0,43 - 0,47µm |
1165m x 1165m |
| B2 |
0,61 - 0,68 µm |
1165m x 1165m |
| B3 |
0,79 - 0,89 µm |
1165m x 1165m |
| MIR |
1,58 - 1,75 µm |
1165m x 1165m |
Several products are available, including daily
and ten-day synthesis products (at full resolution as well as 4km
and 8km reduced resolutions) for the geographical areas that the
user has defined as well as for complete global coverage. The VGT
images are processed and archived by the Belgian research institute
VITO. VITO
is also responsible for distribution in Belgium.
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SPOT 5
The main payload consists of high resolution
imaging instruments delivering the following product improvements
compared to Spot 4:
- dedicated instrument for along track stereo acquisition,
- higher ground resolution: 5 metres and 2.5 metres (instead of
10 m) in panchromatic mode,
- higher resolution in multispectral mode: 10 m (instead of 20 m)
in all 3 spectral bands in the visible and near infrared ranges.
The spectral band in the short wave infrared band (essential for
VEGETATION data) is maintained at a resolution of 20 m due to limitations
imposed by the geometry of the CCD sensors used in this band,
The field width of each instrument: 60 km, same as Spot 1, 2, 3
and 4.
The oblique viewing capacity of each instrument is maintained providing
rapid access to a given area.
The Spot 5 spectral bands are the same as those for Spot 4 (see
below). The panchromatic band does, however, return to the values
used for Spot 1-2-3 (0,51 - 0,73 µm). As requested by many
users, this ensures continuity of the spectral bands established
since Spot 1. Spatial resolutions are, on the other hand, improved
within the limits of technical feasibility as the field width of
each instrument will be also kept identical.
altitude: 832 km
inclination: 98 degrees
orbit: sun-synchronous polar
period of revolution: 101 minutes
repeat cycle: 26 days
satellite: SPOT 5 (04/05/2002 still operational)
HRG sensors
Two HRG (High Resolution Geometric) instruments are capable of generating
data at four resolution levels with the same 60 km swath:
- images in the SWIR band: 20 m
- multispectral images (green, red and near-infra-red): 10 m
- panchromatic images : 5 m
- supermode panchromatic images: 2.5 m
|
Mode
|
Band
|
Spectral band |
Resolution
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| Multispectral |
B1 |
0,50 - 0,59 µm |
10m x 10m |
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B2 |
0,61 - 0,68 µm |
10m x 10m |
| |
B3 |
0,79 - 0,89 µm |
10m x 10m |
| SWIR |
1,58 - 1,75 µm |
20m x 20m |
| M - monospectral |
PAN |
0,51 - 0,73 µm |
5m x 5m (or 2.5m x 2.5m) |
HRS sensors
This is an instrument with the ability to acquire stereopair images
simultaneously, a considerable advantage for the quality of digital
elevation model (DEM) production.
Characteristics
- spectral band: panchromatic
- resolution: 10 m, along the track sampling: 5 m
- imaging swath (centred on the satellite track): 120 km
- maximum scene length: 600 km
- viewing angle of the telescopes: _+ 20°
|
Mode
|
Band
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Spectral band |
Resolution
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| M - monospectral |
PAN |
0,51 - 0,73 µm |
10m x 10m |
VEGETATION 2 Sensor
The VEGETATION sensor remains unchanged in
comparison to the one installed onboard SPOT 4.
Data distributors
Spot Image
5 rue des Satellites
F - 31031 Toulouse cedex 4
France
Tel: +33 5 62 19 40 40
Fax.: +33 5 62 19 40 11
URL : http://www.spotimage.fr
VITO-Image processing
and archiving centre
Boeretang 200
B-2400 Mol
Belgium
Tel.: +32 14 33 68 07
Fax.: +32 14 32 27 95
URL: http://www.vgt.vito.be
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