1. Introduction

India demonstrated the ability of remote sensing for societal application by detecting coconut root-wilt disease from a helicopter mounted multispectral camera in 1970. This was followed by flying two experimental satellites, Bhaskara-1 in 1979 and Bhaskara-2 in 1981. These satellites carried optical and microwave payloads.^[1]

India's remote sensing programme under the Indian Space Research Organization (ISRO) started off in 1988 with the IRS-1A, the first of the series of indigenous state-of-art operating remote sensing satellites, which was successfully launched into a polar sun-synchronous orbit on March 17, 1988 from the Soviet Cosmodrome at Baikonur.

It has sensors like LISS-I which had a spatial resolution of 72.5 meters with a swath of 148 km on ground. LISS-II had two separate imaging sensors, LISS-II A and LISS-II B, with spatial resolution of 36.25 meters each and mounted on the spacecraft in such a way to provide a composite swath of 146.98 km on ground. These tools quickly enabled India to map, monitor and manage its natural resources at various spatial resolutions. The operational availability of data products to the user organisations further strengthened the relevance of remote sensing applications and management in the country.^[2]

2. IRS System

Following the successful demonstration flights of Bhaskara-1 and Bhaskara-2 satellites launched in 1979 and 1981, respectively, India began to develop the indigenous Indian Remote Sensing (IRS) satellite program to support the national economy in the areas of agriculture, water resources, forestry and ecology, geology, water sheds, marine fisheries and coastal management.

Towards this end, India had established the National Natural Resources Management System (NNRMS) for which the Department of Space (DOS) is the nodal agency, providing operational remote sensing data services.^[3] Data from the IRS satellites is received and disseminated by several countries all over the world. With the advent of high-resolution satellites new applications in the areas of urban sprawl, infrastructure planning and other large scale applications for mapping have been initiated.

The IRS system is the largest constellation of remote sensing satellites for civilian use in operation today in the world, with 11 operational satellites. All these are placed in polar Sun-synchronous orbit and provide data in a variety of spatial, spectral and temporal resolutions. Indian Remote Sensing Programme completed its 25 years of successful operations on March 17, 2013.^[2]

3. IRS Data Applications

Data from Indian Remote Sensing satellites are used for various applications of resources survey and management under the National Natural Resources Management System (NNRMS). Following is the list of those applications:

• Space Based Inputs for Decentralized Planning (SIS-DP)
• National Urban Information System (NUIS)
• ISRO Disaster Management Support Programme (ISRO-DMSP)
• Biodiversity Characterizations at landscape level- http://bis.iirs.gov.in
• Preharvest crop area and production estimation of major crops.
• Drought monitoring and assessment based on vegetation condition.
• Flood risk zone mapping and flood damage assessment.
• Hydro-geomorphological maps for locating underground water resources for drilling well.
• Irrigation command area status monitoring
• Snow-melt run-off estimates for planning water use in down stream projects
• Land use and land cover mapping
• Urban planning
• Forest survey
• Wetland mapping
• Environmental impact analysis
• Mineral Prospecting
• Coastal studies
• Integrated Mission for Sustainable Development (initiated in 1992) for generating locale-specific prescriptions for integrated land and water resources development in 174 districts.
• North Eastern District Resources Plan (NEDRP)- www.nedrp.gov.in

4. IRS Launch Log

The initial versions are composed of the 1 (A,B,C,D). The later versions are named based on their area of application including OceanSat, CartoSat, ResourceSat. Some of the satellites have alternate designations based on the launch number and vehicle (P series for PSLV).

5. IRS Data Availability

Data from IRS is available to its users through NRSC Data Centre and also through Bhuvan Geoportal of ISRO. NRSC data center provides data through its purchase process while Bhuvan Geoportal provides data in free and open domain.

6. Capacity Building for IRS and Other Remote Sensing Data

The capacity building programme of ISRO for IRS and other remote sensing applications is through Indian Institute of Remote Sensing (IIRS) Dehradun and UN affiliated Center of Space Science and Technology Education in Asia and the Pacific (CSSTEAP) Center located at Dehradun of Uttrakhand State in India.

7. Future IRS Launches

Following are the remote sensing satellites planned by ISRO to be launched next strengthening the fleet of IRS satellites and widening their applications:^[4][5]

• RESOURCESAT-3: A follow on to Resourcesat-2, it will carry more advanced LISS-III-WS (Wide Swath) Sensor having similar swath and revisit capability as Advanced Wide Field Sensor (AWiFS), thus overcoming any spatial resolution limitation of AWiFS. Satellite would also carry Atmospheric Correction Sensor (ACS) for quantitative interpretation and geophysical parameter retrieval. It slated to be launched during 2021.^[5][6]

• OCEANSAT-3: Oceansat-3 would carry Thermal IR Sensor, 12 channel Ocean Color Monitor, Scatterometer and Passive Microwave Radiometer. IR Sensor and Ocean Color Monitor would be used in the analysis for operational Potential Fishing Zones. Satellite is mainly for Ocean biology and sea state applications. It is slated to the launched aboard PSLV in January 2020.^[5]

• GISATs: GISAT-1 is planned for launch in May 2020 and GISAT-2 is planned for launch in August 2020.^[7] They are expected to provide images from geostationary orbit during disasters.