Magnetic field of the Earth

Geometric Correction

When satellite or aerial images are captured, they often contain distortions (errors in shape, scale, or position) caused by many factors — like Earth's curvature, satellite motion, terrain height (relief), or the Earth's rotation . These distortions make the image not properly aligned with real-world coordinates (latitude and longitude). 👉 Geometric correction is the process of removing these distortions so that every pixel in the image correctly represents its location on the Earth's surface. After geometric correction, the image becomes geographically referenced and can be used with maps and GIS data. Types 1. Systematic Correction Systematic errors are predictable and can be modeled mathematically. They occur due to the geometry and movement of the satellite sensor or the Earth. Common systematic distortions: Scan skew – due to the motion of the sensor as it scans the Earth. Mirror velocity variation – scanning mirror moves at a va...

Radar Sensors in Remote Sensing

Radar sensors are active remote sensing instruments that use microwave radiation to detect and measure Earth's surface features. They transmit their own energy (radio waves) toward the Earth and record the backscattered signal that returns to the sensor. Since they do not depend on sunlight, radar systems can collect data: day or night through clouds, fog, smoke, and rain in all weather conditions This makes radar extremely useful for Earth observation. 1. Active Sensor A radar sensor produces and transmits its own microwaves. This is different from optical and thermal sensors, which depend on sunlight or emitted heat. 2. Microwave Region Radar operates in the microwave region of the electromagnetic spectrum , typically from 1 mm to 1 m wavelength. Common radar frequency bands: P-band (70 cm) L-band (23 cm) S-band (9 cm) C-band (5.6 cm) X-band (3 cm) Each band penetrates and interacts with surfaces differently: Lo...

Unmanned Earth Resources Satellites

Unmanned Earth resources satellites are satellites equipped with remote sensing instruments used to collect images and environmental data from the Earth's surface without a crew onboard. They help monitor: land use vegetation soil and water resources climate oceans atmosphere natural hazards These satellites are grouped based on the type of radiation they measure and the sensors they carry. Five Groups of Unmanned Earth Resources Satellites Remote sensing satellites can be categorized into five main groups , based on the wavelengths they record and the type of environmental information they collect. First-Generation Earth Resources Satellites Wavelength region: Visible and Near-Visible (VNIR) ✔ Characteristics Use multispectral scanners Record reflected sunlight Mainly for land use, vegetation, and surface mapping ✔ Example Landsat series (Landsat 1, 2, 3) These were the first generation of Earth resource sate...

Unmanned Aerial Vehicles

Unmanned Aerial Vehicles (UAVs) —commonly called drones —are pilotless aircraft used as remote sensing platforms to acquire very high-resolution geospatial data . They fly at low altitudes (typically 50–300 m), enabling them to record centimeter-level details of the Earth's surface. UAVs are increasingly used in remote sensing because they offer on-demand data acquisition , flexible sensor deployment , and the ability to fly under cloud cover , making them ideal for scientific, environmental, and disaster applications. Characteristics ✔ 1. High-Resolution Data Acquisition UAVs can collect imagery with spatial resolutions up to <1 cm . Suitable for detailed mapping of vegetation, buildings, hazards, and micro-topography. ✔ 2. On-Demand and Rapid Deployment Can be launched quickly anytime data is needed. Extremely useful after floods, landslides, earthquakes , or in inaccessible terrain. ✔ 3. Operational Flexibility Able to fly: in rugged ...

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...

Vineesh V, Geography

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