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Raster, pixel, dn , band

Raster data is like a big picture made up of small squares called pixels . Each pixel shows some information about a small part of the Earth's surface, like how hot, bright, or green that spot is. Pixels Pixels are the tiny squares in a raster image. Just like how your phone screen is made of pixels, a satellite image also has pixels. Each pixel tells us something about the place it covers. DN Values (Digital Numbers) Each pixel has a number inside it, called a DN value . This number tells us what's going on in that area — for example: A high number might mean a bright area, A low number might mean a dark area. It can also show things like temperature , elevation , or vegetation . Bands Some satellite images have one band (like black-and-white photos). Others have many bands , each showing a different kind of light: Red, green, and blue (like what we see with our eyes), Near-infrared (helps us see plants and vegetation), Thermal (shows ...

EMR Spectrum Remote Sensing

The Electromagnetic Radiation (EMR) Spectrum is like a set of invisible waves that carry energy. In remote sensing , satellites and sensors use these waves to collect information about the Earth —like forests, water, cities, clouds, temperature, and more. Just like how our eyes can only see visible light (like colors in a rainbow), sensors in remote sensing can "see" many more types of waves that humans can't.  Types of EMR Used in Remote Sensing: Type of Wave Wavelength What It's Used For Example Visible Light 0.4 – 0.7 micrometers To take normal satellite images Google Earth pictures Near-Infrared 0.7 – 1.0 µm To check plant health Green areas, farming Shortwave Infrared (SWIR) 1.0 – 3.0 µm To see moisture in soil and vegetation Drought or wetness studies Thermal Infrared (TIR) 8.0 – 14.0 µm To measure surface temperature Heat from buildings, forest fires Microwaves 1 mm – 1 meter To see through clouds and at night (radar) Flood detection, weather, disaster...

Atmospheric Window in Remote Sensing

The atmospheric window is like a "clear path" in the sky. It means certain parts of sunlight or energy (called electromagnetic radiation) can pass through the Earth's atmosphere without getting blocked . These "clear paths" are very helpful in remote sensing —when we study the Earth using satellites and sensors. Why are Atmospheric Windows Important? Just like how we can see clearly through a clean glass window, satellites can "see" the Earth clearly through these atmospheric windows. These windows help in: Taking clear pictures of land, water, and forests Measuring temperature of the Earth's surface Even looking through clouds using special types of energy! Types of Atmospheric Windows and What They Show Visible and Near-Infrared (VNIR) Window (0.4 to 1.0 micrometers) This is the light we can mostly see with our eyes Used to observe green plants, water bodies, and land cover Shortwave Infrared (SWIR) Window...

Remote Sensing Resolutions

When we use satellites or drones to take pictures of the Earth, we talk about different types of "resolutions." These help us understand how clear, detailed, and frequent those pictures are. There are four main types : 1. Spatial Resolution – How small can you see? It tells us the size of the smallest object we can see in the image. It depends on the pixel size . Smaller pixels = more detail. Example: If the resolution is 10 meters , each pixel shows a 10m × 10m area on the ground. Higher spatial resolution means you can see things like buildings and roads clearly. 🟩 Think of zooming in on Google Maps — more zoom = better spatial resolution. 2. Spectral Resolution – How many colours can you see? It tells us how many types of light (or wavelengths) the sensor can detect. Better spectral resolution means it can tell the difference between more materials (like water, soil, and vegetation). It's like being able to see not just red, g...

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 bala...

Radiation law

Remote sensing, four basic radiation laws help us understand how objects give off and interact with energy (electromagnetic radiation). These laws link an object's temperature , wavelength , and the amount of energy it gives off: 1. Planck's Law Every object that has a temperature (above absolute zero) gives off energy at all wavelengths. But how much it gives off at each wavelength depends on its temperature. This law explains the full energy pattern (spectrum) of a hot object. 2. Stefan-Boltzmann Law Hotter objects give off more total energy. The energy released increases quickly as temperature rises — to the fourth power of the temperature. 3. Wien's Displacement Law Hotter objects give off energy at shorter wavelengths (like blue light), while cooler objects emit at longer wavelengths (like red or infrared). So, the color (or wavelength) of maximum emission shifts based on temperature. 4. Kirchhoff's Law If an object absorbs energy well at a cert...

Basic Principles of Remote Sensing

Remote sensing is the science of collecting information about the Earth from a distance, usually using satellites or aircraft — without touching the surface.  Basic Principles of Remote Sensing Energy Source (Sun) ☀️ Everything starts with the Sun , which sends energy (light) to Earth. Interaction with Earth 🌳🏙️💧 This energy hits the Earth's surface — like forests, water, buildings — and gets: Reflected Absorbed Transmitted Sensors Detect the Energy 🛰️ Satellites or aircraft have sensors (cameras) that capture the reflected energy. Data Transmission 📡 The sensors send the collected data back to ground stations . Image Processing 💻 The raw data is processed into images or maps using computer software. Analysis 🧑‍💼 Scientists or analysts study the images to find out what's happening — like land use, vegetation health, urban growth, disasters, etc. Example: Imagine you're taking a photo of a city from an a...

Flight Planning Mission

1. Define the Purpose Decide why you're doing the mission: Mapping land use? Creating a 3D model? Surveying a building or farmland? 2. Choose the Area of Interest (AOI) Mark the exact area you want to cover on a map: Set boundaries (length & width) Use coordinates (lat/long) 3. Select the Camera and Drone Pick the right tools: Camera type (sensor size, resolution) Drone (range, stability, battery life) 4. Set Flight Parameters Plan how the drone should fly: Altitude (height) – affects image size and detail Overlap : Forward overlap (between photos in the same line) – usually 60-80% Side overlap (between photo rows) – usually 30-60% Speed – slow enough for clear photos 5. Calculate Flight Lines Create the path the drone will fly : Straight lines to cover the whole area Make sure the overlap is correct Consider wind and obstacles 6. Plan Ground Control Points (GCPs) Mark known ground...

Photogrammetry – Types of Photographs

In photogrammetry, aerial photographs are categorized based on camera orientation , coverage , and spectral sensitivity . Below is a breakdown of the major types: 1️⃣ Based on Camera Axis Orientation Type Description Key Feature Vertical Photo Taken with the camera axis pointing directly downward (within 3° of vertical). Used for maps and measurements Oblique Photo Taken with the camera axis tilted away from vertical. Covers more area but with distortions Low Oblique: Horizon not visible High Oblique: Horizon visible 2️⃣ Based on Number of Photos Taken Type Description Single Photo One image taken of an area Stereoscopic Pair Two overlapping photos for 3D viewing and depth analysis Strip or Mosaic Series of overlapping photos covering a long area, useful in mapping large regions 3️⃣ Based on Spectral Sensitivity Type Description Application Panchromatic Captures images in black and white General mapping Infrared (IR) Sensitive to infrared radiation Veget...

Photogrammetry – Geometry of a Vertical Photograph

Photogrammetry is the science of making measurements from photographs, especially for mapping and surveying. When the camera axis is perpendicular (vertical) to the ground, the photo is called a vertical photograph , and its geometry is central to accurate mapping.  Elements of Vertical Photo Geometry In a vertical aerial photograph , the geometry is governed by the central projection principle. Here's how it works: 1. Principal Point (P) The point on the photo where the optical axis of the camera intersects the photo plane. It's the geometric center of the photo. 2. Nadir Point (N) The point on the ground directly below the camera at the time of exposure. Ideally, in a perfect vertical photo, the nadir and principal point coincide. 3. Photo Center (C) Usually coincides with the principal point in a vertical photo. 4. Ground Coordinates (X, Y, Z) Real-world (map) coordinates of objects photographed. 5. Flying Height (H) He...