Geometric Correction

Geometric Correction:

- Geometric correction is a critical process in remote sensing and digital image processing. It involves adjusting and aligning an image so that it accurately represents the Earth's surface in terms of scale, orientation, and spatial accuracy. This correction compensates for various geometric distortions and errors introduced during image acquisition and sensor characteristics, ensuring that the image can be used for precise geospatial analysis and mapping.

Source of Geometric Error:

- Geometric errors in remote sensing arise from various sources, including inaccuracies in sensor characteristics, platform movement, Earth's curvature, terrain relief, atmospheric conditions, and other factors. These errors can lead to distortions, misalignments, and inaccuracies in the positioning and representation of objects within an image.

Types of Geometric Error:

- Geometric errors can manifest in different ways, including:

1. Scale Error: Inaccurate representation of distances in the image.

2. Positional Error: Errors in the location of objects within the image.

3. Angular Error: Errors in the orientation or rotation of objects.

4. Distortion: Misrepresentation of object shapes or sizes.

5. Parallax Error: Discrepancies in object positions due to elevation differences.

6. Relief Displacement: Displacements of objects due to variations in terrain elevation.

7. Atmospheric Refraction: Errors due to the bending of light in the atmosphere.

8. Satellite Ephemeris Errors: Errors in satellite position data.

9. DEM Errors: Inaccuracies in the Digital Elevation Model used for terrain correction.

10. Time-Dependent Errors: Errors that change over time.

11. Resampling Error: Errors introduced during pixel value interpolation.

12. Control Point Error: Errors in the accuracy of ground control points.

Types of Geometric Correction:

- Geometric correction techniques are used to rectify or mitigate these errors. Common types include:

1. Image-to-Map Transformation: Matching control points to align the image with a map.

2. Rubber Sheet Transformation: Non-linear correction using polynomial functions.

3. Affine Transformation: Linear correction for basic distortions.

4. Projective Transformation (Homography): Correcting complex distortions, including perspective.

5. Orthorectification: Comprehensive correction accounting for terrain and Earth's curvature.

6. Bundle Adjustment: Simultaneous adjustment of multiple images for 3D mapping.

7. Sensor Model-Based Correction: Using detailed sensor models for correction.

8. Resampling: Interpolating pixel values after correction.

Each type of geometric correction is chosen based on the specific nature of the errors in the imagery and the desired level of accuracy for the application at hand.

Comments

Platforms in Remote Sensing

In remote sensing, a platform is the physical structure or vehicle that carries a sensor (camera, scanner, radar, etc.) to observe and collect information about the Earth's surface. Platforms are classified mainly by their altitude and mobility : Ground-Based Platforms Definition : Sensors mounted on the Earth's surface or very close to it. Examples : Tripods, towers, ground vehicles, handheld instruments. Applications : Calibration and validation of satellite data Detailed local studies (e.g., soil properties, vegetation health, air quality) Strength : High spatial detail but limited coverage. Airborne Platforms Definition : Sensors carried by aircraft, balloons, or drones (UAVs). Altitude : A few hundred meters to ~20 km. Examples : Airplanes with multispectral scanners UAVs with high-resolution cameras or LiDAR High-altitude balloons (stratospheric platforms) Applications : Local-to-regional mapping ...

Types of Remote Sensing

Remote Sensing means collecting information about the Earth's surface without touching it , usually using satellites, aircraft, or drones . There are different types of remote sensing based on the energy source and the wavelength region used. 🛰️ 1. Active Remote Sensing 📘 Concept: In active remote sensing , the sensor sends out its own energy (like a signal or pulse) to the Earth's surface. The sensor then records the reflected or backscattered energy that comes back from the surface. ⚙️ Key Terminology: Transmitter: sends energy (like a radar pulse or laser beam). Receiver: detects the energy that bounces back. Backscatter: energy that is reflected back to the sensor. 📊 Examples of Active Sensors: RADAR (Radio Detection and Ranging): Uses microwave signals to detect surface roughness, soil moisture, or ocean waves. LiDAR (Light Detection and Ranging): Uses laser light (near-infrared) to measure elevation, vegetation...

Model GIS object attribute entity

These concepts explain different ways of organizing, storing, and representing geographic information in a Geographic Information System (GIS) . They include database design models (ER model), data structure models (Object and Attribute models), and spatio-temporal representations that integrate location, entities, and time . Together, they help GIS manage both spatial data (where things are) and descriptive information (what they are and how they change over time) . 1. Object-Based Model (Object-Oriented Data Model) The Object-Based Model treats geographic features as independent objects that combine spatial geometry and descriptive attributes within a single structure. Core Concept: Each geographic feature (such as a building, road, or river ) is represented as a self-contained object that stores both: Geometry – location and shape (point, line, polygon) Attributes – descriptive properties (name, type, length, capacity) Unlike older georelational models , which stored spatial ...

Government of Kerala Initiatives for Water Management

Kerala, with its abundant rainfall and network of rivers, faces a dual challenge of water scarcity and excess —seasonal droughts and monsoon floods. The state government has implemented various policies and programs to address these challenges through sustainable water conservation, management, and distribution practices . Below is a detailed breakdown of the major water management initiatives in Kerala. 1. Jal Jeevan Mission (JJM) – Kerala Implementation Objective: To provide functional household tap connections (FHTC) to all rural households by 2024. Focuses on source sustainability and community-led water resource management. Key Features: Water Quality Monitoring & Surveillance: Ensures supply of safe drinking water through real-time monitoring. Decentralized Approach: Implementation through gram panchayats and local self-governments (LSGs) . Recharge & Conservation Measures: Rainwater harvesting, groundwater recharge, and watershed development inte...

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

Search This Blog