Sunday, 28 July 2013

Touching the Skies: 25 years of Indian Remote Sensing Satellite System

"Taking the daring step of breaking into the elitist league of space programmes 25 years ago, with a purely development-based agenda, India is firmly at the forefront of earth observation today. Let’s take a look at the remarkable journey."

On April 26, 2012 PSLV C-19 roared into the skies from SHAR on the eastern shores of India carrying RISAT-1, the biggest of the Indian Remote Sensing Satellite Series (IRS) weighing in at nearly 2 tonnes and carrying a state-of-the-art Synthetic Aperture Radar. It represented a major milestone in the overall Indian Remote Sensing Satellite Programme. Planning for the IRS Programme had begun in the late 1970s and the first satellite of the IRS series, IRS 1A, a 1-tonne satellite carrying two CCD cameras, was launched from Baikanur, onboard a Russian
Vostok launcher on March 17, 1988. As the Programme completes 25 years, it is worthwhile to
recount the IRS Story, the story of one of the most successful programmes of Indian Space Research Organisation (ISRO).

The genesis
The story begins in 1969. Vikram Sarabhai, the father of Space Technology and Applications in
India, clearly saw the need for a remote sensing programme for an agricultural society like India.
This is what he said in his presentation of the “summary of the conference and recommendation
for initiatives” at the First UN Conference on Peaceful Uses of Outer Space at Vienna in 1969:

“When we came to Vienna, we thought that the areas of most immediate practical applications
would be communications, meteorology and navigation, in that order. But one of the most
striking things to emerge has been appreciation of the great potentiality of remote sensing devices, capable of providing large-scale practical benefits. One of the group discussions considered the cost effectiveness of these techniques, and it was pointed out that there is a high cost benefit ratio, which, for example, in cartography, can be as much as 18:1. The time has come to interest meteorologists, hydrologists, surveyors, agricultural specialists and other groups in such programmes. The chairman of the thematic session summarised the consensus that aircraft could initially be used because of their comparatively low cost. There is need, to begin
with, to understand problems of interpretation. Remote sensing cannot replace man on ground,
but can direct man’s efforts on ground to be more efficient.”

Sarabhai sowed the seed but did not live long enough to see the fruits as he passed away
in 1971. His successors in the Indian Space Research Organisation took the idea forward
through a series of steps which were to lead to the IRS Programme. These steps can be summarised into three categories. 

The first was a strategy to utilise opportunities that presented
themselves which could add to capacity building
. In remote sensing, these included an opportunity to develop a thermal scanner with CNES, launch opportunities for the Bhaskara series of satellites offered by the erstwhile Soviet Space Agency and the offer to become a Principal Investigator in the Landsat Programme. 

The second strategy was to pace technology by applications. Thus, right from the first aerial remote sensing surveys and Landsat data analysis, ISRO always had end users as equal collaborative partners. 

This led to a third strategy in the form of specific utilisation programmes for its satellites – first Bhaskara and then IRS. This strategy gave a focus to technology developers and opportunity to the user community to own the programme by providing a forum where they could voice their needs.

Following a series of experimental satellites like the Bhaskara launch on Vostok and RS-D1 and RS-D2 launched as experimental payloads on ISROs nascent SLV launcher programme, a committee
was formed by the late Satish Dhawan, the then Chairman ISRO, under the Chairmanship
of the late Dr T.A. Hariharan, a senior scientist handpicked by Dr Sarabhai from the Woods Hole
Research Laboratory, to come up with a blueprint for an operational Indian Remote Sensing satellite series. It included, among others, scientists like George Joseph, O.P.N. Calla, P.S. Goel and Y.S. Rajan who have since then become familiar names in the Space community. This committee, in its 1976 report ‘Future Indian Earth Resources Satellites’, recommended that ISRO should build a remote sensing satellite that could be launched with an Indian rocket. They felt that an optical Multi-spectral Scanner (MSS) similar to that carried by Landsat with a resolution of 100 metres would suffice for many Indian application needs. The committee also said an experimental optical sensor using the newly emerging Charge Coupled Devices (CCD) technology should also be flown as a back up to the MSS payload. Microwave payloads were also considered as important in view of the cloud cover problems during the major crop-growing season. The committee made a strong recommendation that those critical technology activities in the area
of sensors, spacecraft subsystems, data processing and data products are undertaken expeditiously for a possible 1982 launch.

Detailed consultations among the scientific and technical professionals in ISRO and outside
including the user community followed. The experience from Bhaskara and RS-D satellites and
other ISRO programmes like the Apple Communications Satellite proved valuable in the configuration of what was to become IRS-1. To get the end users involved in the process, a programme called the Joint Experiments Programme was launched in 1977 to develop a strong user community who could contribute to the programme by way of appplications development and inputs for the payload selection and design. Using Landsat imagery and imagery from ISRO’s airborne multispectral scanner (an indigenous offshoot of the thermal scanner developed with CNES), applications were developed for various areas like agriculture, hydrology, geology, geomorphology, land use, soil mapping and so on.

The launch
The IRS Programme was launched in late 1981 and its first project IRS was firmed up as a three
axis stabilised, sun synchronous satellite carrying two CCD cameras with resolutions of 70 m and
35 m in four spectral bands covering the visible and near IR parts of the spectrum. In 1982, the
project was cleared by the government and India made an announcement at the second United
Nations Conference on the availability of IRS data to the world community, especially the developing countries. Dr K. Kasturirangan was designated the project director and Dr George Joseph was the director for the development of the two CCD payloads. There would be two satellites IRS-1A and 1B and an engineering model 1E. IRS-1A would carry three Linear Imaging Self Scanning Sensors; one was LISS 1 with a resolution of 72.5 m and two others were LISS-2A and B with resolution of 36.25 m. The decision to drop the multispectral scanner and commit to a new technology, the Charge Coupled Device, for the sensors was path breaking. The only other satellite to opt for this technology was the French SPOT satellite launched in 1986. IRS-1A and SPOT-1 were thus contemporaneous, both leading the switch to this new technology.
In 1983, the National Natural Resources Management System (NNRMS) was set up by the
Departments of Space and Science and Technology. The NNRMS was the brainchild of Prof Satish
Dhawan and Prof M.G.K. Menon to prepare various government departments as well as educational
institutions to make the fullest use of the IRS system. As part of this, three major efforts were
launched in the areas of forestry, groundwater exploration and wasteland mapping. On March
17, 1988 IRS-1A took to the skies from Baikanur atop a Vostok rocket
. Early on the morning of March 18, the excitement of waiting for IRS-1A to ‘open its eyes’ was palpable at the Shadnagar earth station of the National Remote Sensing Agency. The satellite was controlled from the ISRO Tracking and Telemetry Station in Bangalore. Each event was relayed by voice from Bangalore to Shadnagar; acquisition of the spacecraft as it rose above the southern horizon and the series of operational commands followed by ‘payload on’. A big cheer went up as the first images of the southern peninsula of India came into view on the quick look display monitor. India had stepped into the age of operational remote sensing from space.

IRS-1B, incorporating improvements arising from the analysis of the performance of 1A, was launched on August 29, 1991 again onboard Vostok from Baikanur. By this time, the PSLV
launcher was ready for its first developmental flight. It was decided to make IRS-1E flight-worthy
and launch it on the first developmental flight, PSLV-D1 from SHAR. The LISS 2 cameras were
replaced by an experimental payload from the German Space Agency DLR, called the Monocular
Electro-Optic Stereo Scanner. Unfortunately, the only PSLV flight to fail happened to be the D1 and IRS-1E failed to orbit. [B]Two remaining developmental flights of PSLV were used to launch experimental IRS satellites. PSLV-D2 put IRS-P2, carrying two LISS-2 cameras, into orbit on October 15, 1994. 

On March 21, 1996, PSLV-D3 launched IRS-P3 which carried a Wide Field Sensor, WIFS. A two-band version of this was already launched on IRS-1C. The version on P3 had an additional shortwave IR band. WIFS was a low-resolution sensor with a very wide coverage resulting in repeat coverage every five days. This trade-off between and resolution and coverage
was dictated by the need for enhanced repeat coverage to monitor situations like drought and
flood and to be able to monitor crops over their growth stages. P3 also carried an experimental
sensor called Modular Opto-electronic Scanner, MOS from DLR for remote sensing of the oceans.
Thus while D2 established confidence in the PSLV launcher D3 was useful to try out experimental
sensors. A word on the ISRO satellite naming convention: the P designation was applied to
prototypes. Successful prototypes were renamed and started a new series like Oceansat, Cartosat and Resourcesat. Meanwhile, the operational series continued with the design of IRS-1C and 1D. LISS-1 was replaced with a two-band WIFS while LISS-2 was replaced by LISS-3 having a resolution of 23m. LISS-3 also added a shortwave IR sensor at 70m. A new sensor called PAN was a steerable panchromatic high resolution sensor providing a resolution of 6m. An onboard recorder was added to provide global data. These changes were the result of feedback from the Indian user community as well as the need to be competitive in the global market.

 Although not explicitly stated, IRS 1C was designed to be a global player. Its WIF camera was unique and later copied by SPOT in its SPOT 4 and 5 satellites.

 The LISS 3 was slotted between the Thematic Mapper of Landsat (30m) and XSHRV of SPOT (20m). It lacked the second shortwave IR band and thermal IR bands of the TM but scored over the three bands of XS-HRV. The LISS-3 is a versatile sensor and the workhorse for most applications. PAN was, till the launch of IKONOS in 1999, the highest resolution civilian camera.

Going global
The failure of Landsat 6 and the upheaval in the international remote sensing scene caused by
premature commercialisation of remote sensing data acquisition resulted in a situation where
the global user community was left with very few options. They could depend on an ageing
Landsat 5 satellite or an expensive French SPOT satellite. The commercial wing of the Department
of Space, Antrix Corporation, addressed this vacuum and floated enquiries for global partners
to receive and redistribute IRS data worldwide. An agreement with EOSAT was signed in 1994
and consultations began between EOSAT and ISRO engineers on the nitty gritty of data reception. The first international IRS reception system was inaugurated in 1995 at Norman, Oklahoma in the US. Reception began with IRS-1B data and preparations were started for the simultaneous commissioning of IRS-1C data reception at NRSA Hyderabad station and the EOSAT station at Norman. On December 28, 1995 IRS-1C took to the skies from Baikanur onboard the Molniya launcher. IRS-1D was launched on September 27, 1997 on board the first commercial flight of PSLV, PSLV-C1. From now on PSLV would be the workhorse launcher for IRS.

Ocean sensing
The IRS series, operational and experimental, concentrated more on land-based applications.
This is to be expected as the major driving force for remote sensing applications were land applications such as crop forecasting, forest management, land management and mineral exploration. A Department of Ocean Development was created in 1981 and soon attention turned to ocean sensing, perhaps catalysed by Dr A.E. Muthunayagam, Director of ISRO’s Liquid Propulsion Systems Centre, who took over as the Secretary of the Department of Ocean Development in 1994. The IRS programme responded with IRS-P4 which carried a new sensor called the Ocean Colour Monitor, OCM and a microwave sensor called the Multi-frequency Scanning Microwave Radiometer, MSMR. The OCM was used for studying the ocean colour to track ocean features like temperature, chlorophyll and pollution. The microwave sensors made a comeback at long last after the Satellite Microwave Radiometers, SAMIR on board Bhaskara 1 and 2; a hiatus of nearly 15 years. Also it is important to note that though the Hariharan Committee mentioned these sensors, it took time before an operational sensor emerged. IRS-P4 was launched on May 26, 1999. It was renamed Oceansat-1 and was followed by Oceansat-2 in September 23, 2009.

Tracing the terrain 
The next area to be addressed by the IRS Programme was the third dimension in geography — the terrain. IRS-1C and D carried steerable PAN cameras which could be used to image an area
from different directions to create a stereo pair, which could then be used by a photogrammetric
workstation to create a Digital Elevation Model of the terrain
. However, these were not dedicated for this purpose. To meet this requirement, IRS-P5, renamed Cartosat-1, carried two 2.5m resolution PAN cameras pointed fore and aft along the flight track. This ensured a complete stereo coverage of the country enabling users to create 3D models of any part of India or even the world. 

Another area covered by IRS is that of agile imaging at very high resolution. These are requirements of the security establishment as well as agencies like infrastructure and urban planning departments. This technology was first tried out on a Technology Evaluation Satellite (TES), which had 1m resolution and could be commanded to image a specific area. TES was launched on October 22, 1999

TES was followed by Cartosat-2 in January 10, 2007, Cartosat 2A on April 28, 2008 and Cartosat 2B on July 12, 2010.
The successors Meanwhile, IRS-1D was aging and required a replacement. This came in the form of Resourcesat. Resourcesat-1 was launched on October 17, 2003 and was a vast improvement beyond IRS-1C and D. In keeping with the ISRO naming policy, the first satellite was designated in the P category as IRS-P6. It carried an Advanced WIFS (AWIFS), which had a 740-km swath, 70m resolution and three bands, effectively bringing back LISS-1 resolution of IRS-1A and B with a very wide swath and therefore higher revisit. The workhorse sensor continued to be the LISS-3. Another new sensor was LISS-4, a multispectral upgrade of the PAN. Resourcesat-2 followed on April 20, 2011. The latest in the series of IRS satellites is RISAT-1 which in a sense completes the programme envisaged by the Hariharan Committee in 1976 by adding a Synthetic Aperture Radar to the constellation of sensors in space on board IRS satellites. 

Providing all-weather, day and night capability, RISAT-1 represents the acme of technological achievement. No other country in the world has such a huge constellation of operational satellites carrying a wide variety of sensors from the visible to microwaves and from 1m to 70m resolution.

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