IRS
IRS-1D is the latest in a series of Indian satellites and was launched on the 29th September 1997, and carries an identical payload to the IRS-1C satellite, launched on the 28th December 1995. Both satellites carry three sensors:
- Linear Imaging Self-scanning Sensor (LISS III)
- Panchromatic (Pan)
- Wide Field Sensor (WiFS)
The IRS satellites orbit at an altitude of 817Km. IRS Pan scene sizes are typically 70Km by 70Km (vertical viewing) and LISS scenes are 140Km by 140Km. Pan sub-scenes are also available (23Km by 23Km). See sample imagery for a picture of Benghazi, Libya.
IRS Panchromatic
IRS Pan data is acquired over the visible green to near infra-red portion of the spectrum, and has 5.8 metre spatial resolution. However, compared to SPOT 1-4 10 metre Pan data, which has 256 grey levels, IRS Pan has only 64 grey levels. Therefore, the increased spatial resolution of the IRS imagery has to be balanced against the better depth of SPOT 1-4 data. Generally, IRS data is of higher quality in lower latitudes compared to higher latitudes due to a better sun angle.
IRS LISS III
The LISS III sensor has similar bands to SPOT XI. However, it does have a limitation regarding the reduced resolution of band 4 (Landsat equivalent band 5) which reduces the potential number of applications for this sensor.
A summary of the band information is contained in the table below.
| Band Width | Spatial Resolution | |
|---|---|---|
| Band 1 | 0.52 - 0.59μm (green) | 23 metres |
| Band 2 | 0.62 - 0.68μm (red) | 23 metres |
| Band 3 | 0.77 - 0.86μm (near infra-red) | 23 metres |
| Band 4 | 1.55 - 1.70μm (mid infra-red) | 70 metres |
