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Landsat satellite sensors are one of the most popular remote sensing systems, the imagery acquired from these are widely used across the globe.
NASA’s Landsat satellite programme was started in 1972. It was formerly known as ERTS (Earth Resource Technology Satellite) programme. The first satellite in the Landsat series Landsat-1 (formerly ERTS-1) was launched on July 23, 1972 .Since then five different types of sensors have been included in various combinations in Landsat mission from Landsat-1 through Landsat-7. These sensors are Return Beam Vidicon (RBV), the Multispectral Scanner (MSS), the Thematic Mapper (TM), the Enhanced Thematic Mapper (ETM) and the Enhanced Thematic Mapper plus (ETM+). Landsat ETM (or Landsat 6) was launched in 1993 but it could not achieve the orbit. Six year later in 1999 Landsat ETM+ (or Landsat 7) was launched and it is the recent one in the series.
Landsat ETM+ contains four bands in Near Infrared-visible (NIR-VIS) region with 30mx30m spatial resolution, two bands in Short Wave Infrared (SWIR) region with same resolution, one in Thermal Infrared (TIR) region with spatial resolution of 60mx60m and one panchromatic band with resolution. Its revisit period is 16 days.
SPOT (Systeme Pour l’Observation de la Terre) was developed by the French Centre National d’ Etuded Spatiales with Belgium and Sweden. The first satellite of SPOT mission, SPOT-1 was launched in 1986. It was followed by SPOT-2 (in 1990), SPOT-3 (in 1993), SPOT-4 (in 1998) and SPOT-5 (in 2002).
There are two imaging systems in SPOT-5- HRVIR and Vegetation. The HRVIR records data in three bands in VIS-NIR region with 10mx10m spatial resolution, one band in SWIR region with 20mx20m spatial resolution and one panchromatic band with 5mx5m resolution. The Vegetation instrument is primarily designed for vegetation monitoring and related studies. It acquires images in three bands in VIS-NIR region and in one band in SWIR region (all with 1000mx1000m) spatial resolution.
Advanced Very High Resolution Radiometer (AVHRR)
Several generations of satellites have been flown in the NOAA-AVHRR series. NOAA-15 is the recent in the series. The sensor AVHRR (Advanced Very High Resolution radiometer) contains five spectral channels two in VIS-NIR region and three in TIR. One thermal band is of the wavelength range 3.55-3.93 mm, meant for fire detection. Spatial resolution of AVHRR is 1100mx1100m. NOAA-AVHRR mainly serves for global vegetation mapping, monitoring land cover changes and agriculture related studies with daily coverage.
Indian Remote Sensing (IRS) Satellites
The Indian Remote Sensing programme began with the launch of IRS-1A in 1988. After that IRS-1B (1999), IRS-1C (1995) and IRS-1D (1997) was launched. IRS-1D carries three sensors: LISS III with three bands of 23.5mx23.5m spatial resolution in VIS-NIR range and one band in SWIR region with 70.5x70.5 m resolution, a panchromatic sensor, with 5.8mx5.8m resolution and a Wide Field Sensor (WiFs) with 188mx188m resolution. WiFS is extensively used for vegetation related studies.
ISRO’s IRS-P6 (RESOURCESAT-1) is very advanced remote sensing system. It was launched in 2003. It carries high resolution LISS IV camera (three spectral bands in VIS-NIR region) with spectral resolution of 5.8mx5.8m which has capability to provide stereoscopic imagery. IRS-P6 LISS III camera acquires images in VIS-NIR (3 spectral bands) and SWIR (one spectral band) with spatial resolution of 23.5mx23.5m. IRS-P6 AWiFS (Advanced Wide Field Sensor) operates in VIS-NIR (3 spectral bands) and SWIR (one spectral band) with spatial resolution of 56mx56m.