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Decorrelation Stretching

Decorrelation stretching is an image enhancement technique used to improve color contrast in multispectral remote sensing images. It reduces the correlation between image bands and spreads out (stretches) their color values so that features become easier to see. It is mainly used to enhance true-color or false-color composite images . Why Is It Needed?  Remote sensing bands often have strong correlations . For example: Red and NIR bands both reflect strongly from vegetation Visible bands (R, G, B) reflect similarly from many surfaces Because of this correlation: Images look dull , low-contrast , or washed-out Important features become hard to distinguish Decorrelation stretching solves this by reducing band-to-band correlation and enhancing color differences. How Decorrelation Stretching Works  1. Identify the Correlation Between Bands Multispectral bands often show similar brightness patterns. This makes the composite image look flat. 2...
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Spectral Signature vs. Spectral Reflectance Curve

Spectral Signature  A spectral signature is the unique pattern in which an object: absorbs energy reflects energy emits energy across different wavelengths of the electromagnetic spectrum. ✔ Key Points Every natural and man-made object on Earth interacts with sunlight differently. These interactions produce a distinct pattern , just like a "fingerprint". Sensors on satellites record these patterns as digital numbers (DN values) . These patterns help to identify and differentiate objects such as vegetation, soil, water, snow, buildings, minerals, etc. ✔ Examples of Spectral Signatures Healthy vegetation → High reflectance in NIR , strong absorption in red Water → Strong absorption in NIR and SWIR , low reflectance Dry soil → Gradual increase in reflectance from visible to NIR Snow → High reflectance in visible , low in SWIR ✔ Why Spectral Signature Matters It allows: Land cover classification Chan...
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Fourier Transform in Remote Sensing

The Fourier Transform (FT) is a mathematical method used in remote sensing to break an image into its spatial frequency components . Think of it as changing the view of an image—from shapes and objects (spatial domain) to patterns and textures (frequency domain). Why Fourier Transform Remote sensing images contain patterns such as: smooth water bodies rough mountains sharp boundaries regular textures (agriculture fields) The Fourier transform helps us: Identify landscape changes Study surface texture (smooth, rough, periodic) Remove noise Sharpen or smooth images Detect repeated patterns (crop rows, sand ripples) 1. Spatial Domain This is the original image in terms of rows and columns (x, y). Here, pixel values represent brightness (DN values). 2. Frequency Domain After applying Fourier Transform, the image is represented in terms of spatial frequencies : Low frequencies → slow changes (smooth areas, water, sky) ...
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Optical Sensors in Remote Sensing

1. What Are Optical Sensors? Optical sensors are remote sensing instruments that detect solar radiation reflected or emitted from the Earth's surface in specific portions of the electromagnetic spectrum (EMS) . They mainly work in: Visible region (0.4–0.7 µm) Near-Infrared – NIR (0.7–1.3 µm) Shortwave Infrared – SWIR (1.3–3.0 µm) Thermal Infrared – TIR (8–14 µm) — emitted energy, not reflected Optical sensors capture spectral signatures of surface features. Each object reflects/absorbs energy differently, creating a unique spectral response pattern . a) Electromagnetic Spectrum (EMS) The continuous range of wavelengths. Optical sensing uses solar reflective bands and sometimes thermal bands . b) Spectral Signature The unique pattern of reflectance or absorbance of an object across wavelengths. Example: Vegetation reflects strongly in NIR Water absorbs strongly in NIR and SWIR (appears dark) c) Radiance and Reflectance Radi...
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Contour Lines

How to Read & Draw Contour Lines? These 5 rules will help you, Rule 1 - Every point of a contour line has the same elevation.  Rule 2 - contour lines separate uphill from downhill. Rule 3 - contour lines do not touch or cross each other except at a cliff. Rule 4 - Every 5th contour line is darker in colour.
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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 ...
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Rock system

India's rock record spans a vast geological time scale from >3.5 billion years to the present . Geologists classify India's rocks into four major rock systems : Archaean (oldest) Purana Dravidian Aryan (youngest) This classification is based on: Age of rock formation Mode of origin (igneous, sedimentary, metamorphic) Tectonic setting Presence of fossils Mineral resources 1. Craton An ancient, stable part of the continental crust (e.g., Indian Peninsular Craton). 2. Basement Complex The oldest crystalline rocks forming the foundation over which younger layers are deposited (Archaean rocks). 3. Orogeny Mountain-building phases affecting rock formation (e.g., Himalayan orogeny for Tertiary rocks). 4. Sedimentation Deposition of sediments by water, wind, or ice, forming sedimentary rocks. 5. Fossils Preserved remains of ancient life; indicate geological age and depositional environment. (Purana = unfossilifer...
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Territorial Conflicts – India and Pakistan, India and China, India- Bangladesh

Territorial conflicts are disputes where two or more countries claim sovereignty over a geographic region. These disputes typically arise due to: Historical claims Colonial-era boundary definitions Ethnic or cultural overlap Strategic and resource significance River dynamics and shifting landforms Key Concepts: 1. Boundary A legally established line separating the territories of two states. 2. Border / Frontier A broader zone of interaction and control around a boundary. 3. LOC (Line of Control) A de facto military control line (India–Pakistan in Jammu & Kashmir). 4. LAC (Line of Actual Control) A de facto border separating Indian and Chinese-administered territories. 5. Radcliffe Line The 1947 boundary line dividing India and Pakistan (later India and Bangladesh). 6. Enclave / Exclave Territorial pockets of one country surrounded by another (e.g., India–Bangladesh enclaves before 2015). 7. Riverine Boundary A border defined by...
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Drainage Regionalization

Drainage regionalization refers to the systematic classification of river systems based on common physical, hydrological, and geomorphological characteristics . In India, drainage is mainly categorized according to: Origin and river characteristics Direction of flow / discharge Size of catchment area Physiographic control and geological structure This framework helps understand: Water resource distribution Flood potential Landform development River behavior and environmental management Drainage Basin / Catchment Area The total area drained by a river and its tributaries. Example: The Ganga basin is India's largest, covering nearly 26% of the country. Watershed A smaller hydrological unit within a basin, separated by ridges or highlands. Perennial Rivers Flow throughout the year; fed by rainfall + snowmelt. Example: Ganga, Brahmaputra. Seasonal (Non-perennial) Rivers Flow mainly during the monsoon; dry up in summer. ...
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Biogeographical Zones of India

India's natural environment is divided into 10 biogeographical zones based on distinct biological communities , ecological conditions , geological history , and climatic variations . This classification, widely referenced in ecology and conservation, comes from the work of Rodgers and Panwar (1988) under the Wildlife Institute of India. These 10 zones are further subdivided into 27 biogeographic provinces . This system helps scientists understand: Species distribution Habitat diversity Ecosystem functions Conservation priorities 1. Biogeography The scientific study of the distribution of species, ecosystems, and biotic communities across space and time. 2. Biogeographical Zone A large geographical area separated from others by ecological, climatic, or physical boundaries. Each zone has unique plants, animals, and environmental conditions. 3. Biogeographic Province A smaller subdivision within a biogeographical zone that reflects finer ecologi...
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