Vineesh V, Geography

Carbon Cycle 

  🔹 What is Contrast Enhancement? Contrast enhancement improves the difference between light and dark areas of an image so that important features become more visible. It changes the Digital Number (DN) values (brightness values) of pixels to make the image clearer and easier to interpret. There are two main types of contrast enhancement: Linear (simple stretching or scaling of pixel values) Nonlinear (based on the statistical distribution of pixel values) Here, we focus on Nonlinear Contrast Enhancement methods. ⚙️ 1. Histogram Equalization 🔸 Concept: In this method, all pixel brightness values (DNs) are redistributed so that there are roughly an equal number of pixels for each possible brightness level. The result is a flatter histogram , meaning the image uses the full range of brightness values more evenly. 🔸 Purpose: To increase contrast in areas where pixel values are heavily concentrated (for example, dark or light regions). 🔸...

Image enhancement is the process of improving the visual quality and interpretability of an image. The goal is not to change the physical meaning of the image data , but to make important features easier to identify for visual interpretation or automatic analysis (e.g., classification, feature extraction). In simple terms, image enhancement helps make an image clearer, sharper, and more informative for human eyes or computer algorithms. Purpose of Image Enhancement To improve visual appearance of images. To highlight specific features such as roads, rivers, vegetation, or built-up areas. To enhance contrast or brightness for better differentiation. To reduce noise or remove distortions. To prepare images for further processing like classification or edge detection. Common Image Enhancement Operations Image Reduction: Decreases the size or resolution of an image. Useful for faster processing or overview visualization. Image Mag...

It is the process of removing the influence of the atmosphere from remotely sensed images so that the data accurately represent the true reflectance of Earth's surface . When a satellite sensor captures an image, the radiation reaching the sensor is affected by gases, water vapor, aerosols, and dust in the atmosphere. These factors scatter and absorb light, changing the brightness and color of the features seen in the image. Although these atmospheric effects are part of the recorded signal, they can distort surface reflectance values , especially when images are compared across different dates or sensors . Therefore, corrections are necessary to make data consistent and physically meaningful. 🔹 Why Do We Need Atmospheric Correction? To retrieve true surface reflectance – It separates the surface signal from atmospheric influence. To ensure comparability – Enables comparing images from different times, seasons, or sensors. To improve visual quality – Remo...

  Radiometric correction is the process of removing sensor and environmental errors from satellite images so that the measured brightness values (Digital Numbers or DNs) truly represent the Earth's surface reflectance or radiance. In other words, it corrects for sensor defects, illumination differences, and atmospheric effects. 1. Detector Response Calibration Satellite sensors use multiple detectors to scan the Earth's surface. Sometimes, each detector responds slightly differently, causing distortions in the image. Calibration adjusts all detectors to respond uniformly. This includes: (a) De-Striping Problem: Sometimes images show light and dark vertical or horizontal stripes (banding). Caused by one or more detectors drifting away from their normal calibration — they record higher or lower values than others. Common in early Landsat MSS data. Effect: Every few lines (e.g., every 6th line) appear consistently brighter or darker. Soluti...

A pandemic disaster is a global or widespread outbreak of an infectious disease that causes mass illness, death, and disruption of social and economic systems across multiple countries or continents. Terminology: Epidemic: Outbreak of disease in a specific community or region. Pandemic: Epidemic that spreads across countries or continents. Endemic: Disease constantly present in a region (e.g., malaria in parts of Africa). Outbreak: Sudden increase in disease cases in a limited area. So, a pandemic becomes a disaster when the disease's scale and impact overwhelm healthcare systems and disrupt societies. Conceptual Understanding Pandemic disasters are biological hazards , categorized under man-made or natural–biological disasters because they are caused by natural pathogens but spread or intensified by human actions such as globalization, urbanization, and poor public health infrastructure. Pandemic disasters sit at the intersection of ...