Geometric fundamentals of Photogrammetry; Elements of Vertical Photograph; Relief displacement, Image Parallax, Stereo model- Photo mosaics; Image interpretation Keys; Ground Control for Aerial Photography

1. Geometric Fundamentals of Photogrammetry

The geometric fundamentals of photogrammetry explain how 3D ground features are represented as 2D images using the principles of perspective geometry.

Perspective projection – Formation of an image from a single camera position.
Camera station (Exposure station) – Position of the camera during exposure.
Principal point – Centre of the photograph.
Principal axis – Line joining the camera lens and principal point.
Focal length (f) – Distance between the camera lens and image plane.
Scale – Ratio of image distance to ground distance.

Concept:
Photogrammetry uses camera geometry to measure distances, heights, and coordinates accurately.

2. Elements of Vertical Photograph

A vertical photograph is taken with the camera axis nearly perpendicular (90°) to the Earth's surface.

Key Elements

Principal point (PP)
Nadir point (NP)
Isocentre (IC)
Fiducial marks
Photo centre
Flight line
Scale
Overlap (Forward and Side overlap)

Concept:
These elements help determine image orientation and accurate mapping.

3. Relief Displacement

Relief displacement is the apparent outward movement of objects from the centre of a photograph due to differences in elevation.

Height (H)
Flying height (h)
Radial displacement
Photo centre

Concept:
Higher objects (buildings, trees, hills) appear displaced farther from the photo centre than lower objects.

4. Image Parallax

Parallax is the apparent shift in the position of an object between two overlapping photographs.

Absolute parallax
Differential parallax
Air base
Stereo pair

Concept:
Parallax is used to calculate the height and elevation of ground features.

5. Stereo Model

A stereo model is a three-dimensional (3D) view created by observing two overlapping aerial photographs.

Stereo pair
Binocular vision
Stereoscope
Base-height ratio

Concept:
The stereo model enables accurate measurement of terrain height, slope, and landforms.

6. Photo Mosaics

A photo mosaic is a composite image formed by joining several overlapping aerial photographs into one continuous image.

Types:

Uncontrolled mosaic
Semi-controlled mosaic
Controlled mosaic

Concept:
Photo mosaics provide a larger and continuous view for mapping and land-use studies.

7. Image Interpretation Keys

Image interpretation keys are the visual characteristics used to identify objects in aerial photographs or satellite images.

Tone/Colour
Texture
Shape
Size
Pattern
Shadow
Site
Association

Concept:
These keys help distinguish natural and human-made features accurately.

8. Ground Control for Aerial Photography

Ground control refers to accurately surveyed reference points on the Earth's surface used to correct and georeference aerial photographs.

Ground Control Points (GCPs)
GPS/GNSS
Coordinates
Georeferencing
Image rectification
Check points

Concept:
Ground control improves the positional accuracy of aerial photographs and ensures reliable photogrammetric mapping.

Comments

Thermal Infrared Remote Sensing

1. Principles Thermal Infrared Remote Sensing is based on the detection of naturally emitted electromagnetic radiation from objects, rather than reflected solar energy. According to Planck's Radiation Law , all objects with a temperature above absolute zero (0 K) emit electromagnetic radiation. For Earth surface features, the peak emission lies in the Thermal Infrared (TIR) region of 3–14 μm of the electromagnetic spectrum. The amount of radiation emitted is primarily a function of surface temperature and emissivity . Sensors measure the radiant energy flux density (W/m²) , which is later converted to surface temperature using Stefan-Boltzmann's Law . 2. Radiation Properties in TIR Emissivity (ε): Ratio of radiation emitted by a surface to that emitted by a perfect blackbody at the same temperature. Natural surfaces like water (ε ≈ 0.98) have high emissivity, while bare soils and metals have lower values. Blackbody: An idealized object th...

Atmospheric Window

The atmospheric window in remote sensing refers to specific wavelength ranges within the electromagnetic spectrum that can pass through the Earth's atmosphere relatively unimpeded. These windows are crucial for remote sensing applications because they allow us to observe the Earth's surface and atmosphere without significant interference from the atmosphere's constituents. Key facts and concepts about atmospheric windows: Visible and Near-Infrared (VNIR) window: This window encompasses wavelengths from approximately 0. 4 to 1. 0 micrometers. It is ideal for observing vegetation, water bodies, and land cover types. Shortwave Infrared (SWIR) window: This window covers wavelengths from approximately 1. 0 to 3. 0 micrometers. It is particularly useful for detecting minerals, water content, and vegetation health. Mid-Infrared (MIR) window: This window spans wavelengths from approximately 3. 0 to 8. 0 micrometers. It is valuable for identifying various materials, incl...

Radar image. Polarization in Remote Sensing

L band radars operate on a wavelength of 15-30 cm and a frequency of 1-2 GHz. L band radars are mostly used for clear air turbulence studies. S band radars operate on a wavelength of 8-15 cm and a frequency of 2-4 GHz. Because of the wavelength and frequency, S band radars are not easily attenuated. . Polarization refers to the direction of travel of an electromagnetic wave vector's tip: vertical (up and down), horizontal (left to right), or circular (rotating in a constant plane left or right). . a synthetic aperture radar (SAR) for high-resolution imaging. a radar altimeter, to measure the ocean topography. echo amplitude a wind scatterometer to measure wind speed and direction. Other types of radars have been flown for Earth observation missions: precipitation radars such as the Tropical Rainfall Measuring Mission, or cloud radars like the one used on Cloudsat. . RISAT-1 (SAR, ISRO India, 2012) RORSAT (SAR, Soviet Union, 1967-1988) Seasat (SAR, altimeter, scatterometer, US, 19...

Regional Geography, Systematic Geography, Idiographic, Nomothetic, Inductive and Deductive Approaches

T wo major ways of studying Geography : the Regional Approach and the Systematic Approach . It also explains the related ideas of idiographic vs. nomothetic and inductive vs. deductive reasoning , especially in the context of the Hartshorne–Schaefer debate . 1. Regional Geography: “All About One” Regional Geography studies one particular region in detail . A region is an area that has some degree of homogeneity (sameness) within its boundary but is also unique or different from other regions . For example, if we study Palakkad District , we may study: Relief and drainage Climate Soil Vegetation Agriculture Population Occupation Economy Culture Political characteristics The purpose is to understand the complete geographical personality of Palakkad and the relationships among its different features. Key concepts Region: A geographical area with identifiable characteristics and boundaries. Homogeneity: Si...

Discrete Detectors and Scanning mirrors Across the track scanner Whisk broom scanner.

Multispectral Imaging Using Discrete Detectors and Scanning Mirrors (Across-Track Scanner or Whisk Broom Scanner) Multispectral Imaging: This technique involves capturing images of the Earth's surface using multiple sensors that are sensitive to different wavelengths of electromagnetic radiation. This allows for the identification of various features and materials based on their spectral signatures. Discrete Detectors: These are individual sensors that are arranged in a linear or array configuration. Each detector is responsible for measuring the radiation within a specific wavelength band. Scanning Mirrors: These are optical components that are used to deflect the incoming radiation onto the discrete detectors. By moving the mirrors, the sensor can scan across the scene, capturing data from different points. Across-Track Scanner or Whisk Broom Scanner: This refers to the scanning mechanism where the mirror moves perpendicular to the direction of flight. This allows for t...

Vineesh V, Geography

Search This Blog