Characteristics - SPOT
There have been four SPOT (Satellite Pour l'Observation de la Terre) satellites launched since 1986, providing medium to high resolution of the Earth's surface. SPOT 1, 2 and 3 carried a multi-spectral (XS) and panchromatic (P) sensor on board. SPOT 4 was successfully launched in March 1998.
The SPOT satellites orbit at an altitude of 822km. SPOT scene sizes are typically 60km by 60km (vertical viewing) or 60km by 80km for oblique viewing. The optical imaging instruments (HRVs) are steerable to either side of the ground track - east to west - by up to 30 degrees.
| Satellite | Launch Date | Current State |
|---|---|---|
| SPOT 1 | 22 February 1986 | Decommissioned: 12/31/90 |
| SPOT 2 | 22 January 1990 | Still Operational |
| SPOT 3 | 26 September 1993 | After 3 years in orbit the satellite stopped functioning. |
| SPOT 4 | 24 March 1998 | Still Operational |
| SPOT 5 | Anticipating launch in late 2001/2002 |
Spectral Modes of Acquisition and Spatial Resolution for SPOT 1,2, and 3
"XS" multispectral mode
Imaging is performed in three spectral bands. The bands used are band B1 covering 0.50 to 0.59 m (green), band B2 covering 0.61 to 0.68 m (red) and band B3 covering 0.79 to 0.89 m (near infrared). By combining the data recorded in these channels, color composite images can be produced with a pixel size of 20 metres.
"P" panchromatic mode (SPOT 1, 2, 3)
Imaging is performed in a single spectral band, corresponding to the visible part of the spectrum without the blue. The band covers 0.51 to 0.73 m. This single channel imaging mode supplies only black and white images with a pixel of 10 m. This band is intended primarily for applications calling for fine geometrical detail. The swath width for these satellites is 60 to 80 km, depending on vertical viewing angle.
| Mode | Band | Micrometres | Uses | Resolution |
|---|---|---|---|---|
| Multispectral (XS) | 1 (Green) | 0.50-0.59 micrometres | Recommended for use in combination with other bands because of low contrast and sensitivity to haze | 20 metres |
| 2 (Red) | 0.61-0.68 micrometres | Best for showing roads and bare soils. This band heightens the contrast between vegetated and non-vegetated areas | 20 metres | |
| 3 (Near Infrared) | 0.79-0.89 micrometres | This band is used to evaluate vegetation biomass and separates water from vegetation. | 20 metres | |
| Panchromatic (P) | Not Applicable | 0.51-0.73 micrometres | This band is intended primarily for applications calling for fine geometrical detail | 10 metres |
Spectral Modes of Acquisition and Spatial Resolution for SPOT 4
"Xi" multispectral mode
The imaging is performed in four spectral bands: the same bands B1, B2, B3 as XS mode, plus a Short Wave Infrared band B4, covering 1.58 to 1.75 m. The pixel size is 20 metres.
M monospectral mode
Imaging is performed in the band B2 (0.61 to 0.68 m). Like the "P" mode of SPOT 1, 2, 3, this single channel spectral mode of acquisition provides only black and white images with a pixel of 10 meters. The swath width for these satellites is 60 to 80 km, depending on vertical viewing angle
| Mode | Band | Micrometres | Uses | Resolution |
|---|---|---|---|---|
| Multispectral mode (Xi) | 1 (Green) | 0.50-0.59 micrometres | Recommended for use in combination with other bands because of low contrast and sensitivity to haze | 20 metres |
| 2 (Red) | 0.61-0.68 micrometres | Best for showing roads and bare soils. This band heightens the contrast between vegetated and non-vegetated areas | 20 metres | |
| 3 (Near Infrared) | 0.79-0.89 micrometres | This band is used to evaluate vegetation biomass and separates water from vegetation. | 20 metres | |
| B4 (infrared) | Like the "P" mode of SPOT 1, 2, 3, this single channel spectral mode of acquisition provides only black and white images | 20 metres | ||
| Monospectral mode (M) | Band B2 | 0.61 to 0.68 micrometres | Like the "P" mode of SPOT 1, 2, 3, this single channel spectral mode of acquisition provides only black and white images | 10 metres |
Improvements of SPOT-5 compared to previous SPOT missions include:
- 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 20m due to limitations imposed by the geometry of the CCD sensors used in this band
- field width of each instrument: 60 km, same as SPOT 1, 2, 3, & 4
- As well, it will offer greater capability for cartographic applications and single-pass stereo imaging
The scenes held by Mimas are panchromatic images covering the land mass of the British Isles. They are isolated scenes captured over an extended time period and as such are unsuitable for analysis where change over time is an important factor. The intention has been to provide a complete set of images of the UK and Ireland for a range of applications which require consistent data quality over a wide coverage. The SPOT and Landsat libraries are also ideal sample datasets for remote sensing and image analysis teaching purposes. Some of the applications to which SPOT data is commonly applied are outlined in the next section.
