Solar Radiation and Remote Sensing

Satellite Remote Sensing

Satellite remote sensing is the science of acquiring information about Earth's surface and atmosphere without physical contact, using sensors mounted on satellites. These sensors detect and record electromagnetic radiation (EMR) that is either emitted or reflected from the Earth's surface.

Solar Radiation & Earth's Energy Balance

Solar Radiation is the primary source of energy for Earth's climate system. It originates from the Sun and travels through space as electromagnetic waves.
Incoming Shortwave Solar Radiation (insolation) consists mostly of ultraviolet, visible, and near-infrared wavelengths. When it reaches Earth, it can be:
- Absorbed by the atmosphere, clouds, or surface
- Reflected back to space
- Scattered by atmospheric particles
Outgoing Longwave Radiation is the infrared energy emitted by Earth back into space after absorbing solar energy. This process helps maintain Earth's thermal balance.

Electromagnetic Radiation (EMR) Spectrum

The EMR spectrum encompasses all types of electromagnetic radiation, ranging from gamma rays to radio waves. Remote sensing typically uses the visible, infrared, and microwave portions of the spectrum.

Different materials on Earth interact with different wavelengths in unique ways, which allows satellites to differentiate between water, vegetation, soil, urban areas, etc.

Interaction of EMR with Atmosphere and Surface

When solar radiation enters Earth's atmosphere and reaches the surface, it undergoes several interactions:

Absorption: Certain gases and materials absorb specific wavelengths of EMR, converting it into heat. For example, ozone absorbs UV, and water vapor absorbs infrared.
Scattering: Small particles and gases deflect radiation in multiple directions. Rayleigh scattering causes the blue sky, while Mie scattering is associated with dust and smoke.
Reflection: Some surfaces reflect incoming solar radiation back into the atmosphere. This reflection depends on the surface properties and is central to remote sensing.
Refraction: The bending of light as it passes through different media, affecting how radiation travels through the atmosphere.

Blackbody Concept & Earth

A Blackbody is an ideal object that absorbs all incoming radiation and re-emits it perfectly. Though Earth is not a perfect blackbody, the blackbody radiation laws (e.g., Planck's Law, Stefan–Boltzmann Law) help us understand Earth's emission of longwave radiation.

Albedo

Albedo is the fraction of incoming solar radiation that is reflected by a surface. Surfaces like snow have high albedo (high reflectivity), while forests or oceans have low albedo (high absorption).

This directly influences Earth's energy budget and is monitored using satellite remote sensing to assess climate change, land cover changes, etc.

Conceptual Link Summary

Solar Radiation from the Sun (mainly shortwave) enters Earth's atmosphere.
It interacts with the atmosphere and surface via absorption, scattering, reflection, and refraction.
Earth's surface emits longwave radiation, part of which escapes to space or is absorbed by greenhouse gases.
These interactions are governed by principles of the EMR spectrum and concepts like blackbody radiation.
Albedo quantifies the reflected portion of incoming solar energy.
All these energy exchanges and surface properties are measured and monitored by satellite remote sensing.

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Accuracy Assessment

Accuracy assessment is the process of checking how correct your classified satellite image is . 👉 After supervised classification, the satellite image is divided into classes like: Water Forest Agriculture Built-up land Barren land But classification is done using computer algorithms, so some areas may be wrongly classified . 👉 Accuracy assessment helps to answer this question: ✔ "How much of my classified map is correct compared to real ground conditions?" Goal The main goal is to: Measure reliability of classified maps Identify classification errors Improve classification results Provide scientific validity to research 👉 Without accuracy assessment, a classified map is not considered scientifically reliable . Reference Data (Ground Truth Data) Reference data is real-world information used to check classification accuracy. It can be collected from: ✔ Field survey using GPS ✔ High-resolution satellite images (Google Earth etc.) ✔ Existing maps or survey reports 🧭 Exampl...

REMOTE SENSING INDICES

Remote sensing indices are band ratios designed to highlight specific surface features (vegetation, soil, water, urban areas, snow, burned areas, etc.) using the spectral reflectance properties of the Earth's surface. They improve classification accuracy and environmental monitoring. 1. Vegetation Indices NDVI – Normalized Difference Vegetation Index Formula: (NIR – RED) / (NIR + RED) Concept: Vegetation reflects strongly in NIR and absorbs in RED due to chlorophyll. Measures: Vegetation greenness & health Uses: Agriculture, drought monitoring, biomass estimation EVI – Enhanced Vegetation Index Formula: G × (NIR – RED) / (NIR + C1×RED – C2×BLUE + L) Concept: Corrects for soil and atmospheric noise. Measures: Vegetation vigor in dense canopies Uses: Tropical rainforest mapping, high biomass regions GNDVI – Green Normalized Difference Vegetation Index Formula: (NIR – GREEN) / (NIR + GREEN) Concept: Uses Green instead of Red ...

Landsat 8 Band designation and Band Combination.

Landsat 8 Band designation and Band Combination. Landsat 8-9 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) Bands Wavelength (micrometers) Resolution (meters) Band 1 - Coastal aerosol 0.43-0.45 30 Band 2 - Blue 0.45-0.51 30 Band 3 - Green 0.53-0.59 30 Band 4 - Red 0.64-0.67 30 Band 5 - Near Infrared (NIR) 0.85-0.88 30 Band 6 - SWIR 1 1.57-1.65 30 Band 7 - SWIR 2 2.11-2.29 30 Band 8 - Panchromatic 0.50-0.68 15 Band 9 - Cirrus 1.36-1.38 30 Band 10 - Thermal Infrared (TIRS) 1 10.6-11.19 100 Band 11 - Thermal Infrared (TIRS) 2 11.50-12.51 100 Vineesh V Assistant Professor of Geography, Directorate of Education, Government of Kerala. https://www.facebook.com/Applied.Geography http://geogisgeo.blogspot.com

Change Detection

Change detection is the process of finding differences on the Earth's surface over time by comparing satellite images of the same area taken on different dates . After supervised classification , two classified maps (e.g., Year-1 and Year-2) are compared to identify land use / land cover changes . Goal To detect where , what , and how much change has occurred To monitor urban growth, deforestation, floods, agriculture, etc. Basic Concept Forest → Forest = No change Forest → Urban = Change detected Key Terminologies Multi-temporal images : Images of the same area at different times Post-classification comparison : Comparing two classified maps Change matrix : Table showing class-to-class change Change / No-change : Whether land cover remains same or different Main Methods Post-classification comparison – Most common and easy Image differencing – Subtract pixel values Image ratioing – Divide pixel values Deep learning methods – Advanced AI-based detection Examples Agricult...

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...

Vineesh V, Geography

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