The IRS Mission

Remote Sensing technology has evolved in India at a fast pace.  The country is undoubtedly the Asian leader in the field of commercial remote sensing.  India is presently pressing ahead with an impressive national programme aimed at developing more and more Earth observation satellites to meet the ever-increasing demands, which have been created with the use of this technology.

IRS-1A

• Launched in: March 17, 1988
• Out of service since: 1995
• Repeat Cycle: 22 Days
• Orbit Height: 904 Km
• Orbit Type: Sun Synchronous

Table 2 LISS II Sensor Bands

* Two LISS II cameras combined swath

IRS-1B

• Launched in: August 29, 1991
• Out of service since: 1996
• Repeat Cycle: 22 Days
• Orbit Height: 904 Km
• Orbit Type: Sun Synchronous

IRS-1C and IRS-1D
IRS-1C and IRS-1D are identical and were launched in December 1995 and September 1997, respectively, the latter by India's Polar Satellite Launch Vehicle (PSLV). They carry three cameras, Panchromatic Camera (PAN), Linear Imaging Self Scanner (LISS-III) and Wide Field Sensor (WiFS).

Table Pan, LISS-III, WiFS specifications

 IRS-P2

• Launched in: 1994
• Repeat Cycle: 24 Days
• Orbit Height: 817 Km
• Orbit Type: Sun Synchronous

Launched on October 15, 1994 from Sriharikota aboard the PSLV-D2. The 5-metre panchromatic data is especially useful for urban planning and mapping, the 25-metre multi-spectral data is good for natural resource planning; and the 180 metre wide-field data band has a 740 km swath and 5-day repeat coverage, which is excellent for large-area vegetation monitoring.

Table LISS II Sensor Bands

* Two LISS II cameras combined swath.

IRS P3
The IRS-P3 satellite was launched from Sriharikota using PSLV-D3 on March 21, 1996. IRS-P3 was put in a polar, sun-synchronous orbit at an altitude of 817 km with equatorial crossing time of 10:30 AM in the descending node. IRS - P3 has an X-ray astronomy and two remote sensing payloads, namely WiFS and MOS. The mission caters to oceanography applications. IRS-P3 WiFS is similar to IRS-1C WiFS but for the inclusion of an additional band in the Middle Infra-red (MIR) region. This sensor is primarily meant for vegetation dynamic studies while MOS is meant for ocean related studies.

Table IRS P3 WiFS Camera (Sensor Characteristics)

IRS P4 (OCEANSAT-1)
India entered an elite club of commercial satellite launching nations when their PSLV rocket blasted off from a southern seaport with two international payloads on May 26, 1999. This was the first time an Indian launch vehicle carried more than one payload. This was also the fourth successful launch of the PSLV in a row.

One of the launched satellites was OCEANSAT-1 (IRS-P4), which is the first Indian satellite dedicated fully for the study of oceans. It carries the Ocean Colour Monitor (OCM) and the Multi-frequency Scanning Microwave Radiometer (MSMR). The satellite is helpful in the study of oceanographic phenomenon such as sea temperature, sea surface height, rain over oceans and would be useful in measuring various ocean parameters.

IRS-P6 (RESOURCESAT-1)
The heaviest earth-observation spacecraft launched by ISRO so far, RESOURCESAT-1 was launched into an 817 km sun-synchronous polar orbit on board PSLV-C5 On October 17, 2003. It is the most advanced satellite built by ISRO, bringing continuity to the current IRS 1C and 1D programmes. RESOURCESAT-1 carries three sensors that deliver an array of spectral bands and resolutions ranging from 5.8 metres to 60 metres. Data products derived from RESOURCESAT-1 can be used for advanced applications in vegetation dynamics, crop yield estimates, disaster management support etc. In addition, RESOURCESAT-1 has 120 Gigabits of on-board memory that allows for out-of-contact imaging. Scheduled to last for five years, RESOURCESAT is the tenth spacecraft of ISRO in the IRS series.

Improved features
IRS-P6 has several improved features over its predecessors. These include availability of 5.8 m spatial resolution in 3 bands from LISS-IV camera, improved LISS III with MIR band information at 23.5 m resolution as other Visible and NIR bands. In addition, the AWiFS provides data in the same spectral channels as LISS-III at about 56m resolution with 10-bit radiometry, 5-day revisit and scene coverage of 740 km for regional studies. Unique to IRS-P6 is the availability of simultaneous multi-spectral data at 3 spatial resolutions from the same platform with scene coverage varying from 576 sq km to 1,9,600 sq km to 5,42,000 sq km.

Technology Experiment Satellite (TES)
TES was launched on board PSLV-C3 in October 2001. The satellite is intended to demonstrate and validate technologies that could be used in the future satellites of ISRO. TES carries a panchromatic camera with a spatial resolution of 1 m. Some of the technologies that are being demonstrated in TES are attitude and orbit control system using high torque reaction wheels; new reaction control system with optimized thrusters and a single propellant tank; light weight spacecraft structure; solid state recorder; X-band phased array antenna; improved satellite positioning system; miniaturized TTC and power system and, two-mirror-on-axis camera optics.

Dealing with the Data
Data from IRS satellites is received at the Earth Station of National Remote Sensing Agency (NRSA) at Hyderabad. A dedicated data reception facility forms the core of the acquisition chain. The data is processed after several stringent quality checks at various levels, and then supplied on user request on digital/ photographic media. Payload programming support for IRS-1C/1D data is being provided for the Ground Stations in several countries and places including Norman and Alaska in USA, Ecuador, Germany, Spain, Taiwan, S. Korea, Saudi Arabia, Abu Dhabi, Thailand, Myanmar, Iran and to some mobile stations. IRS-P4 data is being transmitted to stations in Korea, Germany and USA on request. IRS-P3 data is also being received at Germany and Spain.
Resourcesat-1: Technical specifications

NNRMS
Recognizing the need and importance of natural resources management in the country the Government of India had set-up the National Natural Resources Management System (NNRMS). NNRMS is an integrated approach for management of natural resources, optimally utilizing the advantages of conventional systems and the information derived through remote sensing. The Department of Science established five Regional Remote Sensing Service Centres (RRSSCs) in the country for speedy operationalization of remote sensing as an integral component of natural resources inventory, monitoring and management. A North East Space Applications Centre established at Shillong addresses the specific needs of the region.

RRSSCs enable the use of remote sensing technology at a reasonable cost to derive necessary information on various aspects related to natural resources. The RRSSCs provide facilities for digital image analysis and GIS to the users, provide support service to execute national projects and much more. Indian Institute of Remote Sensing at Dehradun under the aegis of NRSA provides a wide spectrum of training and educational courses in Remote Sensing applications.

Plans for the future

IRS-P5 (CARTOSAT-1)
IRS-P5 is planned for launch by PSLV in 2004-05. The satellite is primarily intended for advanced cartographic applications. It will have two panchromatic cameras with a spatial resolution of 2.5 m and a swath of 30 km each. These cameras are mounted with a tilt of +26 deg and -5 deg along the track with respect to nadir to provide stereo pairs of images needed for the generation of Digital Terrain Model (DTM)/Digital Elevation Models (DEM) globally.

The data products will be used for cartographic applications, cadastral mapping and updating, land use and other GIS applications. The satellite will be placed in a sun-synchronous polar orbit of 617 km. It will have a revisit capability of 5 days, which can be realised by steering the spacecraft about roll axis by +26 degrees.

CARTOSAT-2
CARTOSAT-2 will be an advanced remote sensing satellite with a panchromatic camera capable of providing scene-specific spot imageries for cartographic applications. The satellite will have high agility with capability to steer along and across the track up to ±45 degrees. It will be placed in a sun-synchronous polar orbit at an altitude of 630 km. It will have a revisit capability of 4 days. The panchromatic camera is designed to provide better than 1 m spatial resolution imageries with a swath of 10 km. It is planned for launch after CARTOSAT-1.

Radar Imaging Satellite (RISAT-1)
Radar Imaging Satellite (RISAT) mission envisages to support and augment the operational remote sensing programme by enhancing agricultural and disaster related applications. RISAT will have all-weather and day-night observation capability. It is slated for launch during 2006 with a mission life of 5 years. RISAT will carry a C-band Synthetic Aperture Radar (SAR) operating in multipolarisation, multi-modes (ScanSAR, Strip, and Spot modes). The satellite will provide spatial resolutions of 3-50 metre with swaths varying from 10 km to 240 km. The RISAT is expected to be launched into a polar sun-synchronous orbit of 609 km.

Acknowledgement
This article is adapted largely from Dhawal Kumar’s article at GIS Development.net.