RISAT-1

RISAT-1 (Radar Imaging Satellite-1) is India’s first indigenous microwave remote sensing satellite, developed and launched by the Indian Space Research Organisation (ISRO). It is part of the RISAT (Radar Imaging Satellite) series, designed to provide all-weather, day-and-night Earth observation capabilities using advanced synthetic aperture radar (SAR) technology.
Launched on 26 April 2012, RISAT-1 marked a major technological achievement for India in radar imaging, enabling high-resolution monitoring of land, water resources, and agricultural conditions, even under cloudy or low-light conditions — limitations faced by optical imaging satellites.

Background and Development

Before the launch of RISAT-1, India relied mainly on optical and infrared satellites (such as IRS and Resourcesat series) for Earth observation. However, these satellites were ineffective during monsoons, cloudy weather, or nighttime.
To overcome this limitation, ISRO initiated the RISAT programme to develop satellites capable of radar imaging using microwave frequencies.

• The first satellite in the series, RISAT-2, was launched in April 2009, carrying an Israeli-built SAR payload as an interim measure for security and reconnaissance purposes.
• RISAT-1, developed indigenously by ISRO, followed in 2012, featuring India’s first home-built C-band Synthetic Aperture Radar (SAR).

This project represented a significant milestone in India’s pursuit of self-reliance in advanced radar imaging technology.

Launch Details

• Launch Date: 26 April 2012
• Launch Vehicle: PSLV-C19 (Polar Satellite Launch Vehicle)
• Launch Site: Satish Dhawan Space Centre (SDSC), Sriharikota, Andhra Pradesh
• Orbit: 536 km Sun-synchronous orbit (SSO)
• Mass: Approximately 1,858 kg
• Mission Life: Designed for five years (operational beyond expectations)

The PSLV-C19 launch was the 21st consecutive successful mission of the PSLV series, further strengthening India’s reputation for reliable and cost-effective space missions.

Technical Specifications

1. Satellite Platform: RISAT-1 was built on ISRO’s I-1K satellite bus, customised for radar payload requirements.
2. Payload: The primary instrument onboard is a C-band Synthetic Aperture Radar (SAR) operating at 5.35 GHz frequency.

• Capable of imaging in multiple modes, varying in resolution and swath width.
• Provides high-resolution data irrespective of weather or lighting conditions.

3. Imaging Modes:

4. Power System:

• Solar panels generating up to 2.2 kW of power.
• Equipped with onboard batteries for continuous operation.

5. Orbit Type:

• Sun-synchronous orbit (SSO) ensures consistent lighting conditions for imaging.
• Revisit period: 25 days, allowing frequent observation of the same area.

Objectives and Applications

RISAT-1 was developed primarily for agricultural, hydrological, and disaster management applications, though its high-resolution imaging also supports strategic and security purposes.
Key Objectives:

1. Provide all-weather imaging capabilities for remote sensing.
2. Monitor crop growth and assess agricultural output.
3. Track flood, cyclone, and landslide-affected areas.
4. Support forestry and soil moisture estimation.
5. Conduct geological and coastal zone mapping.
6. Aid in disaster response and resource management.

Major Applications:

• Agriculture: Crop acreage and yield estimation, soil moisture monitoring, irrigation planning.
• Disaster Management: Flood mapping, disaster relief planning, and post-disaster damage assessment.
• Water Resources: Monitoring reservoirs, river basins, and catchment areas.
• Forestry: Deforestation and biomass studies.
• Urban Planning: Infrastructure mapping and land-use analysis.

Significance

RISAT-1 represents a technological milestone for India in several ways:

1. All-Weather Capability:
   • The SAR payload enables imaging during monsoon, cloudy conditions, and nighttime, unlike optical sensors.
2. Indigenous Development:
   • First fully indigenous radar imaging satellite developed by ISRO, marking a leap in India’s radar technology.
3. Strategic Utility:
   • Enhanced India’s ability to monitor its borders, coastlines, and disaster zones effectively.
4. Agricultural Monitoring:
   • Played a crucial role in crop forecasting, supporting government programmes related to food security and rural planning.
5. Scientific Advancement:
   • Strengthened India’s expertise in microwave remote sensing, paving the way for advanced radar missions like RISAT-2B, RISAT-2BR1, and future Earth observation systems.

Successor Missions

RISAT-1 was the forerunner of a series of advanced radar satellites:

• RISAT-2B: Launched in May 2019, equipped with improved X-band SAR for high-resolution imaging.
• RISAT-2BR1: Launched in December 2019, enhanced surveillance and reconnaissance capabilities.
• RISAT-1A: Launched in February 2022 as a follow-on mission to RISAT-1, offering improved resolution and imaging performance.

Together, these satellites form a comprehensive radar imaging constellation for both civilian and defence applications.

Achievements and Legacy

• Successfully provided continuous Earth observation data for over seven years, exceeding its expected lifespan.
• Strengthened India’s disaster response capabilities, particularly in flood and cyclone management.
• Facilitated agricultural and environmental monitoring at both national and regional levels.
• Established India as a global leader in cost-effective radar imaging technology.