SPOT (Satellite Pour l'Observation de la Terre)

The SPOT (Satellites Pour l’Observation 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

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 satellite’s vertical axis by changing the direction of each optical instrument’s 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.

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) band’s 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.

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 Earth’s 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 Earth’s dry land in just one day.

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.

HRV
Haarlem, The Netherlands
© CNES - Distribution Spot Image

HRV
Algeria
© CNES - Distribution Spot Image

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

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°

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