Thermal Infrared Remote Sensing

1. Principles

Thermal Infrared Remote Sensing is based on the detection of naturally emitted electromagnetic radiation from objects, rather than reflected solar energy.
According to Planck's Radiation Law, all objects with a temperature above absolute zero (0 K) emit electromagnetic radiation.
For Earth surface features, the peak emission lies in the Thermal Infrared (TIR) region of 3–14 μm of the electromagnetic spectrum.
The amount of radiation emitted is primarily a function of surface temperature and emissivity.
Sensors measure the radiant energy flux density (W/m²), which is later converted to surface temperature using Stefan-Boltzmann's Law.

2. Radiation Properties in TIR

Emissivity (ε): Ratio of radiation emitted by a surface to that emitted by a perfect blackbody at the same temperature. Natural surfaces like water (ε ≈ 0.98) have high emissivity, while bare soils and metals have lower values.
Blackbody: An idealized object that absorbs and emits all incident radiation perfectly.
Graybody: Real-world objects that emit less than a blackbody but with emissivity less than 1.
Kirchhoff's Law: At thermal equilibrium, absorptivity = emissivity.
Stefan-Boltzmann Law: Total energy emitted (E) = σT⁴ (σ = Stefan-Boltzmann constant, T = temperature in Kelvin).
Wien's Displacement Law: The wavelength of maximum emission (λmax) shifts inversely with temperature (λmax = 2897/T).

3. Thermal Infrared Atmospheric Windows

The Earth's atmosphere selectively absorbs and transmits thermal radiation.
Absorption bands are caused mainly by water vapor (H₂O), carbon dioxide (CO₂), and ozone (O₃).
The atmospheric windows in the TIR region allow maximum transmission of radiation to space and to sensors.
- 3–5 μm window: Useful for high-temperature targets like volcanoes, forest fires, and engines.
- 8–14 μm window: Used for Earth surface temperature monitoring, land cover studies, and meteorology.
These windows are crucial because radiation outside them is strongly absorbed by the atmosphere and cannot be sensed effectively.

4. Satellites and Sensors for TIR

Landsat series:
- Landsat 5 TM (Band 6: 10.4–12.5 μm, 120 m resolution).
- Landsat 7 ETM+ (Band 6, 60 m resolution).
- Landsat 8 & 9 TIRS (Bands 10: 10.6–11.2 μm, Band 11: 11.5–12.5 μm, 100 m resolution).
ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer): 5 TIR bands (8.125–11.65 μm) with 90 m resolution.
MODIS (Moderate Resolution Imaging Spectroradiometer): Multiple TIR bands with 1 km resolution, useful for global monitoring.
ECOSTRESS (ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station): Measures plant water stress via surface temperature.
NOAA AVHRR (Advanced Very High Resolution Radiometer): Long-term monitoring of sea surface and land surface temperature.

5. Applications

Land Surface Temperature (LST): Monitoring urban heat islands, agricultural drought, and land use/land cover changes.
Geological Studies: Mapping geothermal activity, volcano monitoring, mineral exploration.
Hydrology: Detecting soil moisture, evaporation rates, wetland mapping.
Atmospheric Studies: Estimating cloud top temperature, greenhouse gas distribution.
Oceanography: Measuring Sea Surface Temperature (SST), monitoring El Niño and La Niña events.
Disaster Management: Detecting and monitoring forest fires, volcanic eruptions, thermal pollution.
Military & Surveillance: Night vision imaging, target detection using heat signatures.
Agriculture: Crop stress detection, irrigation management, evapotranspiration estimation.

Thermal Infrared Remote Sensing utilizes the natural emission of radiation in the 3–14 μm range, governed by physical radiation laws (Planck, Stefan-Boltzmann, Wien). With atmospheric windows (3–5 μm and 8–14 μm) providing clear observation, satellites like Landsat TIRS, ASTER, and MODIS make it possible to study environmental processes such as surface temperature, vegetation stress, urban heat islands, volcanic activity, and global climate dynamics.

Comments

Types of Remote Sensing

Remote Sensing means collecting information about the Earth's surface without touching it , usually using satellites, aircraft, or drones . There are different types of remote sensing based on the energy source and the wavelength region used. 🛰️ 1. Active Remote Sensing 📘 Concept: In active remote sensing , the sensor sends out its own energy (like a signal or pulse) to the Earth's surface. The sensor then records the reflected or backscattered energy that comes back from the surface. ⚙️ Key Terminology: Transmitter: sends energy (like a radar pulse or laser beam). Receiver: detects the energy that bounces back. Backscatter: energy that is reflected back to the sensor. 📊 Examples of Active Sensors: RADAR (Radio Detection and Ranging): Uses microwave signals to detect surface roughness, soil moisture, or ocean waves. LiDAR (Light Detection and Ranging): Uses laser light (near-infrared) to measure elevation, vegetation...

Energy Interaction with Atmosphere and Earth Surface

In Remote Sensing , satellites record electromagnetic radiation (EMR) that is reflected or emitted from the Earth. Before reaching the sensor, radiation interacts with: The Atmosphere The Earth's Surface These interactions control how satellite images look and how we interpret them. I. Interaction of EMR with the Atmosphere When solar radiation travels from the Sun to the Earth, four main processes occur: 1. Absorption Definition: Absorption occurs when atmospheric gases absorb radiation at specific wavelengths and convert it into heat. Main absorbing gases: Ozone (O₃) → absorbs Ultraviolet (UV) Carbon dioxide (CO₂) → absorbs Thermal Infrared Water vapour (H₂O) → absorbs Infrared Concept: Atmospheric Windows These are wavelength regions where absorption is very low, allowing radiation to pass through the atmosphere. Remote sensing depends on these windows. For example, satellites like Landsat 8 use visible, near-infrared, and thermal bands located in atmospheric windows. 2. Trans...

Platforms in Remote Sensing

In remote sensing, a platform is the physical structure or vehicle that carries a sensor (camera, scanner, radar, etc.) to observe and collect information about the Earth's surface. Platforms are classified mainly by their altitude and mobility : Ground-Based Platforms Definition : Sensors mounted on the Earth's surface or very close to it. Examples : Tripods, towers, ground vehicles, handheld instruments. Applications : Calibration and validation of satellite data Detailed local studies (e.g., soil properties, vegetation health, air quality) Strength : High spatial detail but limited coverage. Airborne Platforms Definition : Sensors carried by aircraft, balloons, or drones (UAVs). Altitude : A few hundred meters to ~20 km. Examples : Airplanes with multispectral scanners UAVs with high-resolution cameras or LiDAR High-altitude balloons (stratospheric platforms) Applications : Local-to-regional mapping ...

Government of Kerala Initiatives for Water Management

Kerala, with its abundant rainfall and network of rivers, faces a dual challenge of water scarcity and excess —seasonal droughts and monsoon floods. The state government has implemented various policies and programs to address these challenges through sustainable water conservation, management, and distribution practices . Below is a detailed breakdown of the major water management initiatives in Kerala. 1. Jal Jeevan Mission (JJM) – Kerala Implementation Objective: To provide functional household tap connections (FHTC) to all rural households by 2024. Focuses on source sustainability and community-led water resource management. Key Features: Water Quality Monitoring & Surveillance: Ensures supply of safe drinking water through real-time monitoring. Decentralized Approach: Implementation through gram panchayats and local self-governments (LSGs) . Recharge & Conservation Measures: Rainwater harvesting, groundwater recharge, and watershed development inte...

Vineesh V, Geography

Search This Blog