Download pdf of IRS chapter from Eurimage Products and Services Guide
The Indian Remote Sensing Satellite (IRS–1C) was successfully launched into polar orbit on December 28, 1995 by a Russian launch vehicle. Its payload was activated in the first week of January 1996. This satellite was followed by a similar one that was successfully launched into polar orbit on September 29, 1997 by a PSLV launch vehicle. Its payload was activated in mid-October 1997.
The primary objective of IRS satellites is to provide systematic and repetitive acquisition of data of the Earth’s surface under nearly constant illumination conditions. IRS–1C operates in a circular, sun-synchronous, near polar orbit with an inclination of 98.69°, at an altitude of 817 km in the descending node. The satellite takes 101.35 minutes to complete one revolution around the earth and completes about 14 orbits per day. The entire earth is covered by 341 orbits during a 24 day cycle. Successive orbits are shifted westward by 2820 km at the equator. IRS-1C and 1D have slightly different orbits (see below) and for this reason do not have the same reference system.
The mean equatorial crossing time in the descending node is 10.30 a.m. ± 5 minutes. The orbit adjust system is used to attain the required orbit initially and it is maintained throughout the mission period. The ground trace pattern is controlled within ± 5 km of the reference ground trace pattern.
Details of the three sensors are given in the Technical Summary table below.
During systematic operational data acquisition the tilt angle of the PAN sensor is set to either +2° or –2°, approximately. These settings guarantee full coverage of the entire area within 2 cycles (2*24/25 days).
The WiFS referencing scheme is based on LISS-III scene centres. Due to the large coverage of each WiFS scene there is an overlap of approximately 85% between adjacent WiFS passes.
Currently there are several receiving stations able to acquire IRS data over many parts of the world.
Eurimage, thanks to special agreements with SpaceImaging, can distribute data acquired by all the stations whose receiving cone is marked in red in the map below. For the scenes acquired by Neustrelitz (Europe coverage, yellow cone), Eurimage has an agreement with Euromap to sell this data only to Italian customers
IRS data are typically available processed as System Corrected. This means that the products are radiometrically and geometrically corrected to the user-specified parameters including output map projection, image orientation, and resampling kernel (see after).
Geometric Corrections include Earth rotation, Earth ellipsoid and map projection, satellite attitude and internal sensor distorsions.
From Euromap products are also available corrected only Radiometrically (not geometrically) for PAN and LISS-III.
System Corrected images can be produced with 2 different orientations: path oriented, displaying on the same rows the satellite acquisition scan lines, or map oriented, with north-up display.
From Euromap it is possible to have for LISS-III a synthetic blue band. Euromap has developed a model to derive a synthetic blue band on the basis of the 3 recorded LISS bands covering the green, red and near IR portion of the spectrum and a library of signatures. The resulting natural color renditions have proven to be of excellent quality and are particularly useful for the production of IRS PAN/LISS merged scenes. The blue band can be ordered as an option.
No atmospheric corrections are applied to the images.
Level 1G images, during the geometric correction, are resampled to a regular output grid. The resampling kernel specifies how the input pixels are sampled: how many and how they are weighted. The available algorithms are:
Nearest Neighbour: in the transformed geometry the radiometric value of the output pixel is set equal to the value of the nearest input pixel in the original geometry. This algorithm preserves at its maximum the original radiance values.
Cubic Convolution: in the transformed geometry the radiometric value of the output pixel is interpolated using the values of its 16 nearest neighbours in the original geometry. This algorithm produces a better looking image, but changes the original satellite radiometry.
UTM/WGS84 are available from all ground stations. For other options please contact Eurimage Customer Service.
IRS-P6 (RESOURCESAT-1) is intended to not only continue the remote sensing data services provided by IRS-1C and IRS-1D, both of which have far outlived their designed mission lives, but also vastly enhance the data quality. The 1360 kg satellite was launched into an 817 km polar Sun Synchronous Orbit by the eighth flight of India’s Polar Satellite Launch Vehicle (PSLV-C5). Systematic acquisitions by IRS-P6 began in January 2005.
IRS-P6 carries three cameras similar to those of IRS-1C and IRS-1D but with vastly improved spatial resolutions.
IRS-P6 also carries a Solid State Recorder with a capacity of 120 Gigabits.
The LISS-IV multispectral high-resolution camera is the prime instrument
of this sensor. LISS-IV is a three-band pushbroom camera of LISS-III heritage
(with the same VNIR spectral bands as LISS-3) with a spatial resolution of
5.8 m and a swath of 70 km. The optoelectronic module uses the three mirror
telescope optics (the same as that of the PAN camera of IRS-1C/1D) and 12,288
(12k) pixels linear array CCDs with each pixel of the size 7 µm x 7 µm.
Three such CCDs are placed in the focal plane of the telescope along with
their individual spectral filters. A prism splits the beam into three imaging
fields which are separated in the along-track direction. The projection of
this separation on ground translates into a distance of 14.2 km between the
B2 and B4 image lines. While B3 is looking at nadir, B2 is looking ahead
and B4 looking behind.
LISS-IV can be operated in one of two modes:
Multi-spectral (MS) mode: Data is collected in 3 bands corresponding to pre-selected 4096 contiguous pixels with a swath width of 23.9 km (selectable from the 70 km total swath). The 4 k detector strip can be selected anywhere within the 12 k pixels.
Mono mode: Data from the full 12 k pixels of any single band, corresponding to a swath of 70 km, can be transmitted. Nominally, Band 3 data are acquired in this mode.
In addition, LISS-IV features a ±26º cross-track steering capability, permitting a 5-day revisit cycle.
A medium-resolution multi-spectral camera, the instrument is identical to the LISS-III on IRS-1C/1D (lens modules, detectors, and electronics) in the three VNIR bands, each with a spatial resolution of 23.5 m. The resolution of the SWIR band is now also 23.5 m on a swath of 140 km. The optics design and the detector of the SWIR band are modified to suit the required resolution; B5 uses a 6,000 element Indium Gallium Arsenide CCD with a pixel size of 13 µm. The SWIR CCD is a new device employing a CMOS readout technique for each pixel, thereby improving noise performance. The VNIR CCD array features 6,000 elements for each band.
AWiFS is a wide-angle medium resolution (56 m) camera with a swath of 740 km (FOV=±25º) of WiFS heritage. The pushbroom instrument operates in three spectral bands which are identical to two VNIR bands (0.62 - 0.68 µm, 0.77 - 0.86 µm) and the SWIR band (1.55-1.70 µm) of the LISS-III camera. The AWiFS camera is realized using two separate optoelectronic modules which are tilted by 11.94º from nadir. Each module covers a swath of 370 km providing a combined swath of 740 km with a side overlap between them. The wide swath coverage enables AWiFS to provide a five-day repeat capability.
See IRS images in the Image Gallery
N.B.: Since the summer 2001 there is a regular error on the IRS-1D PAN sensor. Every second data column within the left half (array) of the left stripe has no information; it means that 50 % of the data remain available (within the original image data set). Euromap has developed an algorithm that is able to minimize this problem, but the effect is still clearly visible on all the stright lines within the landscape
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