JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV REMOTE SENSING AND GIS Previous Question Paper (July - 2021 - R16)

Aerial photographs are classified based on the orientation of the camera axis at the time of exposure, the spectral sensitivity of the film, and the angular field of view. The primary types are as follows:

1. Based on Camera Axis Orientation:

• Vertical Photographs: Captured with the camera axis held as nearly vertical as possible. These are the most common type used for mapping and GIS applications because they provide a planimetric view of the terrain.
• Tilted Photographs: These occur when the camera axis is unintentionally inclined from the vertical by a small angle (usually less than 3 degrees).
• Oblique Photographs: Captured with the camera axis intentionally inclined at a significant angle. These are further divided into:
  • Low Oblique: The horizon is not visible in the photograph.
  • High Oblique: The horizon is visible, providing a wider view of the landscape but with significant perspective distortion.

2. Based on Spectral Sensitivity:

• Black and White (Panchromatic): Records the entire visible spectrum, providing high-contrast images suitable for general terrain analysis.
• Color (True Color): Uses three layers sensitive to blue, green, and red light, mimicking human vision for easier feature identification.
• Color Infrared (False Color): Records green, red, and near-infrared wavelengths. This is particularly useful for vegetation mapping, as healthy plants reflect high amounts of infrared light, appearing bright red on these images.

3. Based on Angular Field of View:

• Narrow-angle: Used for high-precision mapping where distortion must be minimized.
• Normal-angle: Standard coverage for general survey purposes.
• Wide-angle and Super-wide-angle: Capture a larger ground area per frame, which is efficient for large-scale mapping projects but introduces greater radial distortion toward the edges of the image.

Aerial photo interpretation is the process of examining photographic images to identify objects and deduce their significance. It relies on the analysis of image characteristics such as shape, size, tone, texture, pattern, shadow, site, and association to extract spatial and thematic information from the terrain.

Fundamentals of Stereoscopy:

Stereoscopy is the technique of viewing two overlapping aerial photographs (a stereopair) to perceive a three-dimensional model of the terrain. This is based on the principle of binocular vision, where the human brain combines two slightly different perspectives of the same object to perceive depth.

• Stereo-overlap: Aerial photographs are typically taken with 60% forward overlap. This ensures that every point on the ground is captured from two distinct camera positions, creating the necessary parallax.
• Parallax: This is the apparent displacement of an object's position in two images due to the change in the observer's position. The difference in parallax between two points is directly proportional to the difference in their elevations.
• Stereoscope: An optical instrument used to view the stereopair. It aligns the left and right images with the left and right eyes respectively, allowing the brain to fuse the two images into a single 3D model. Common types include pocket (lens) stereoscopes and mirror stereoscopes.

Applications of Aerial Photo Interpretation:

1. Geological Mapping: Identifying rock types, structural features like faults and folds, and mineral exploration through the analysis of landforms and drainage patterns.
2. Forestry and Agriculture: Estimating timber volume, classifying forest types, monitoring crop health, and mapping land use/land cover changes.
3. Urban Planning: Mapping infrastructure, monitoring urban sprawl, and assessing traffic patterns or land development projects.
4. Hydrology and Watershed Management: Delineating drainage basins, identifying water bodies, and studying flood-prone areas.
5. Environmental Monitoring: Assessing the impact of natural disasters, soil erosion, and desertification over time.

By combining the 3D visualization provided by stereoscopy with the systematic interpretation of image elements, professionals can derive accurate topographic and thematic data essential for large-scale mapping and resource management.