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Remote Sensing ​

Remote sensing is a crucial technology that involves collecting information about an object or an area from a distance, without physical contact. This process primarily involves measuring its reflected and emitted radiation.

Principles of Satellite Remote Sensing ​

The process of satellite remote sensing relies on several key principles:

  • Radiation Emission and Reflection: All surfaces on Earth either emit radiation based on their temperature or reflect incident radiation based on their reflective properties.
  • Remote Sensing Process: The technology involves the collection and recording of information about this emitted or reflected radiation at different wavelengths using sensors onboard satellites. This collected data is then used to determine various crucial parameters for diverse applications.

COMPONENTS OF REMOTE SENSING

  1. Energy Source or Illumination: This is the initial step, where an energy source illuminates or provides electromagnetic energy to the target. Sensors can be classified into two types based on their energy source:
    • Passive Sensors: These detect natural energy, such as sunlight, that is reflected or emitted by objects.
    • Active Sensors: These emit their own energy, like RADAR or LIDAR, and then measure the reflected energy.
  2. Interaction with the Target: The energy interacts with the target in various ways, including transmission, absorption, emission, scattering, and reflection. Reflection is the most common interaction for many remote sensing applications.
  3. Recording of Energy by the Sensor: The sensor collects and records the energy after it has been scattered, reflected, or emitted from the target.
  4. Transmission, Reception, and Processing: Once recorded, the data is transmitted to Earth-based stations for processing. This often involves converting the data into a digital format for storage and analysis.
  5. Interpretation and Analysis: The processed data is analyzed to extract information about the target, either visually or digitally using image processing techniques.

Based on the electromagnetic (EM) spectrum, remote sensing systems are often classified as:

  • Optical Remote Sensing: Detects radiation in the visible and infrared regions for studying vegetation, water bodies, and Earth imaging.
  • Thermal Infrared Remote Sensing: Focuses on measuring surface temperatures by detecting radiation in the mid-wave and long-wave infrared.
  • Microwave Remote Sensing: Includes active sensors like RADAR, capable of observing the Earth in all weather conditions, regardless of day or night.

Types of Remote Sensing Satellites and Their Orbits ​

Remote sensing satellites are generally launched into low Earth orbit (LEO), typically at altitudes ranging from 1000 to 2000 km, with a revolution period of 90 to 130 minutes. This means they complete approximately 16 cycles per day. They often use polar orbits, which are parallel to the Earth's polar axis, allowing for complete global coverage over time as the Earth rotates.

A special type of LEO is the Sun-Synchronous Orbit (SSO), where the satellite passes over the same latitude at roughly the same local solar time, ensuring consistent lighting conditions for Earth observation. These satellites are crucial for remote sensing, meteorology, and environmental studies.

KEY INDIAN REMOTE SENSING (IRS) SATELLITES AND THEIR FUNCTIONS

  • IRS-1A: India's first experimental remote sensing satellite, launched in 1988 with the help of USSR.
  • Resourcesat Series: Used for natural resource assessment and monitoring, including agriculture and forest surveys.
  • Oceansat Series: Dedicated to oceanographic studies, marine resource assessment, and monitoring parameters like chlorophyll concentration, sea surface temperature, and wind vectors.
  • Cartosat Series: Specialized in high-resolution Earth imaging for cartographic applications such as topographic mapping, urban planning, infrastructure development, and border security. Cartosat-1, launched in 2005, was the eleventh in the IRS Satellite Series. Cartosat-3, launched in 2019, is India's most advanced Earth observation satellite with a resolution of 30 cm.
  • RISAT Series (Radar Imaging Satellite): Uses Synthetic Aperture Radar (SAR) technology to monitor the Earth's surface day and night, in any weather condition, including through clouds. These are vital for national security, strategic surveillance, and disaster monitoring (e.g., floods and landslides).
  • HySIS (Hyperspectral Imaging Satellite): Aims at hyperspectral sensing for studying vegetation, urban areas, and land usage.
  • EMISAT (Electronic Intelligence Satellite): India's first electronic intelligence (ELINT) satellite, developed by DRDO and ISRO, capable of tracking and monitoring enemy radar systems and electronic communication.
  • SARAL: A joint venture of ISRO and CNES France for oceanographic study.
  • Megha Tropiques: A joint venture of ISRO and CNES France, for studying the water cycle in the tropical atmosphere.
  • EOS series: From 2020 onwards, IRS satellites were unified under the prefix EOS (Earth Observation Satellite), designed to provide high-quality images for resource management under all weather conditions.
  • NISAR (NASA-ISRO Synthetic Aperture Radar): A joint mission between NASA and ISRO, designed to map the entire globe in 12 days using L and S dual-band SAR, providing consistent data for analyzing changes in Earth's ecosystems, ice mass, vegetation, sea levels, groundwater, and natural hazards.

Applications of Remote Sensing ​

Remote sensing technology has a wide array of applications, significantly contributing to various sectors:

  • Natural Resource Management: This includes land-use and land-cover mapping, assessment of water resources, and surveys of forest and mineral resources.
  • Disaster Management: Remote sensing aids in forecasting and assessing natural disasters like droughts, floods, cyclones, and storms, as well as assisting in rescue operations.
  • Meteorology: It is used for weather forecasting, tracking storms, and monitoring atmospheric conditions.
  • Agriculture: Applications include crop acreage and production estimation, soil moisture assessment, and monitoring agricultural health.
  • Urban Planning and Development: Used for creating structural plans for cities and guiding urban development.
  • Environmental Studies: Essential for monitoring environmental changes, such as deforestation and rising sea levels, and for studying climate.
  • Surveillance and Reconnaissance: These satellites are extensively used for intelligence gathering, border security, and monitoring enemy troop movements. They act as "spies in the sky," picking up images of activities on the ground.
  • Telecommunication: Though communication satellites (like INSAT) are often geostationary, remote sensing satellites also contribute by gathering information relevant to communication infrastructure.
  • Geodesy: Used to determine the exact shape and dimensions of the Earth.

Indian Remote Sensing Program Development ​

India's remote sensing program began with the Bhaskara-1 satellite in 1979. The Indian Space Research Organization (ISRO), established in 1969, has been instrumental in developing space systems for remote sensing and various national tasks.

Challenges and Future Prospects ​

Challenges in remote sensing include resolution limitations, data quality, high costs, data accessibility, and lack of skilled personnel. Ethical concerns also exist regarding privacy, surveillance, and potential misuse of geospatial data.

Future prospects involve emerging technologies like hyperspectral imaging, LIDAR, and UAVs in remote sensing. India also aims to enhance its role in global geospatial services through private sector partnerships and initiatives like IN-SPACe.