Describe photo-characteristics of, (i) aeolian landforms (ii) folded sedimentary rocks and (iii) forest cover.

(i) Photo-characteristics of Aeolian Landforms

Aeolian landforms, created by wind action, exhibit unique photo-characteristics due to their composition (primarily sand) and morphology. These characteristics vary depending on the specific landform type.

• Sand Dunes: These are characterized by their distinctive shapes – crescentic (barchan), linear, star, or parabolic. On aerial photographs, they appear as bright, reflective features due to the high albedo of sand. Shadows cast by the dunes accentuate their relief and shape. The slip face (lee side) appears steeper and darker due to shadow. Transverse dunes show a rhythmic pattern of ridges and troughs.
• Yardangs: These streamlined, wind-sculpted ridges are formed in arid regions. They appear as elongated, parallel ridges with a characteristic ‘whaleback’ shape. Their tonal contrast with surrounding terrain is often subtle, but their alignment with the prevailing wind direction is a key identifier.
• Loess Deposits: Loess, wind-blown silt, appears as a relatively featureless, bright-toned surface. Drainage patterns are often poorly developed due to the porous nature of the loess. Gullies and badlands topography can develop in loess deposits, creating a network of incised channels.

Drainage patterns in aeolian environments are often ephemeral or absent, further distinguishing them from areas with more consistent water flow.

(ii) Photo-characteristics of Folded Sedimentary Rocks

Folded sedimentary rocks display photo-characteristics related to their layered structure, relief, and weathering patterns. The visibility of these features depends on the degree of folding, rock type, and vegetation cover.

• Layering/Bedding: The most prominent characteristic is the visible layering of different sedimentary strata. These layers appear as tonal variations due to differences in rock composition and weathering resistance. On aerial photographs, bedding planes can be traced as linear features.
• Fold Geometry: Anticlines (upfolds) and synclines (downfolds) are identifiable by their characteristic arcuate shapes. Anticlines often exhibit radial drainage patterns, where streams flow outward from the crest of the fold. Synclines often have parallel drainage patterns.
• Differential Weathering: Different rock layers weather at different rates, creating variations in slope steepness and surface texture. More resistant layers form ridges, while less resistant layers form valleys.
• Jointing and Faulting: Fractures (joints) and breaks (faults) in the rock appear as linear features on aerial photographs. Fault scarps can be identified by their abrupt changes in elevation.

The presence of synclinal valleys and anticlinal ridges is a key indicator of folded sedimentary structures. The degree of folding (gentle, tight, overturned) influences the clarity of these features.

(iii) Photo-characteristics of Forest Cover

Forest cover exhibits distinct photo-characteristics related to its vegetation type, density, and health. These characteristics are crucial for forest monitoring and resource management.

• Tonal Variation: Different forest types have different tonal signatures. Coniferous forests (e.g., pine, spruce) generally appear darker than deciduous forests (e.g., oak, maple) due to their lower reflectance. Healthy vegetation reflects strongly in the near-infrared (NIR) portion of the electromagnetic spectrum, appearing bright red in false-color composite images.
• Texture: The texture of forest cover varies with its density and species composition. Dense forests have a smooth texture, while sparse forests have a rough texture.
• Shape and Pattern: Forest patches exhibit varying shapes and patterns depending on their origin and management practices. Natural forests often have irregular boundaries, while planted forests have more regular shapes.
• Drainage Patterns: Forests influence drainage patterns by intercepting rainfall and reducing runoff. Streams and rivers within forested areas tend to be more sinuous and have lower gradients.
• Shadows: Tall trees cast shadows, which can provide information about forest height and density.

Spectral indices like Normalized Difference Vegetation Index (NDVI) are commonly used to assess forest health and biomass. Changes in NDVI values can indicate deforestation, disease outbreaks, or other disturbances.

Landform/Cover Type	Key Photo-characteristics	Distinguishing Features
Aeolian Landforms	Bright tones, distinct shapes, limited drainage	Alignment with wind direction, rhythmic patterns (dunes)
Folded Sedimentary Rocks	Layering, arcuate shapes, differential weathering	Radial/parallel drainage patterns, visible bedding planes
Forest Cover	Tonal variation, texture, shape, drainage patterns	Spectral signatures (NDVI), shadow patterns