Skip to main content

Elements of Image Interpretation



When an analyst looks at an aerial photo or satellite image, they rely on visual interpretation keys to identify features. These include size, shape, shadows, tone, texture, pattern, association, and site context.

1. Size

  • Definition: The actual or relative dimensions of an object in the image.

  • Concept: By knowing the scale of the photo, the real-world size of features can be estimated.

  • Examples:

    • An airport runway (large and long) vs. a village road (short and narrow).

    • Comparing cars (small) with buses (larger).

  • Fact: Size alone is not enough, but it helps eliminate confusion between features.

2. Shape

  • Definition: The geometric form or outline of an object.

  • Concept: Many cultural (man-made) features have regular shapes (rectangles, circles, straight lines), while natural features are often irregular.

  • Examples:

    • Rectangular → buildings, fields.

    • Circular → water tanks, ponds, stadiums.

    • Irregular → rivers, forests.

3. Shadows

  • Definition: Dark areas cast by elevated objects when sunlight is at an angle.

  • Concept: Shadows provide information about the height, profile, and shape of objects.

  • Examples:

    • Tall buildings cast long shadows.

    • Trees can be identified by their crown shape and shadow.

  • Fact: Shadow length varies with time of day and season.

4. Tone (or Color in multispectral images)

  • Definition: The relative brightness or darkness of features, usually in gray scale (black, white, shades of gray) or color.

  • Concept: Different materials reflect light differently → gives distinctive tones.

  • Examples:

    • Water → dark tone.

    • Vegetation → medium to dark gray (healthy vegetation looks dark in infrared).

    • Sand or concrete → bright tone.

  • Fact: In multispectral imagery, tones are called spectral signatures.

5. Texture

  • Definition: The visual impression of surface roughness or smoothness.

  • Concept: Caused by the variation of tones within a small area.

  • Examples:

    • Rough texture → forests, urban areas.

    • Smooth texture → water bodies, grasslands, roads.

6. Pattern

  • Definition: The spatial arrangement of objects in the landscape.

  • Concept: Features often occur in recognizable arrangements.

  • Examples:

    • Parallel → crop fields, orchards, railway tracks.

    • Radial → road networks around a central city.

    • Grid pattern → urban planning with rectangular streets.

7. Association

  • Definition: The relationship of one feature with others nearby.

  • Concept: Certain features are commonly found together, helping identification.

  • Examples:

    • A school → sports field, playground, residential areas.

    • Railway station → railway tracks, warehouses, roads.

    • River → sand bars, floodplains, vegetation.

8. Site Context

  • Definition: The location of a feature in relation to its surroundings.

  • Concept: Position helps confirm identity of features.

  • Examples:

    • A reservoir is usually near a dam or river.

    • A lighthouse is near the coastline.

    • Farmlands are generally located in plains, not mountain tops.


  • Size → small vs. large objects.

  • Shape → geometric outline (rectangular, circular, irregular).

  • Shadows → indicate height/shape.

  • Tone → brightness/darkness (spectral signature).

  • Texture → roughness/smoothness.

  • Pattern → arrangement (linear, grid, radial).

  • Association → features found together.

  • Site context → surroundings/location clues.

👉 By combining these elements, analysts interpret natural features (rivers, forests, mountains) and cultural features (buildings, roads, cities) in aerial and satellite imagery.


Comments

Popular posts from this blog

Natural Disasters

A natural disaster is a catastrophic event caused by natural processes of the Earth that results in significant loss of life, property, and environmental resources. It occurs when a hazard (potentially damaging physical event) interacts with a vulnerable population and leads to disruption of normal life . Key terms: Hazard → A potential natural event (e.g., cyclone, earthquake). Disaster → When the hazard causes widespread damage due to vulnerability. Risk → Probability of harmful consequences from interaction of hazard and vulnerability. Vulnerability → Degree to which a community or system is exposed and unable to cope with the hazard. Resilience → Ability of a system or society to recover from the disaster impact. 👉 Example: An earthquake in an uninhabited desert is a hazard , but not a disaster unless people or infrastructure are affected. Types Natural disasters can be classified into geophysical, hydrological, meteorological, clim...

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...

geostationary and sun-synchronous

Orbital characteristics of Remote sensing satellite geostationary and sun-synchronous  Orbits in Remote Sensing Orbit = the path a satellite follows around the Earth. The orbit determines what part of Earth the satellite can see , how often it revisits , and what applications it is good for . Remote sensing satellites mainly use two standard orbits : Geostationary Orbit (GEO) Sun-Synchronous Orbit (SSO)  Geostationary Satellites (GEO) Characteristics Altitude : ~35,786 km above the equator. Period : 24 hours → same as Earth's rotation. Orbit type : Circular, directly above the equator . Appears "stationary" over one fixed point on Earth. Concepts & Terminologies Geosynchronous = orbit period matches Earth's rotation (24h). Geostationary = special type of geosynchronous orbit directly above equator → looks fixed. Continuous coverage : Can monitor the same area all the time. Applications Weather...

India remote sensing

1. Foundational Phase (Early 1970s – Early 1980s) Objective: To explore the potential of space-based observation for national development. 1972: The Space Applications Programme (SAP) was initiated by the Indian Space Research Organisation (ISRO), focusing on applying space technology for societal benefits. 1975: The Department of Space (DoS) was established, providing an institutional base for space applications, including remote sensing. 1977: India began aerial and balloon-borne experiments to study Earth resources and assess how remote sensing data could aid in agriculture, forestry, and hydrology. 1978 (June 7): Bhaskara-I launched by the Soviet Union — India's first experimental Earth Observation satellite . Payloads: TV cameras (for land and ocean surface observation) and a Microwave Radiometer. Significance: Proved that satellite-based Earth observation was feasible for India's needs. 1981 (November 20): Bhaskara-II launche...

Purvanchal Hills

The Purvanchal Hills are an eastern extension of the Himalayan system , bending southward from Arunachal Pradesh along the Indo-Myanmar border. They include a series of discontinuous hill ranges such as the Patkai Bum, Naga Hills, Manipur Hills, Mizo (Lushai) Hills, Barail Range, and the Meghalaya Plateau (Khasi, Jaintia, and Garo Hills) . They are geologically young fold mountains (Tertiary period) made of sedimentary rocks (sandstone, shale, siltstone) . Their structure is the result of the collision of the Indian and Eurasian Plates , which uplifted the Himalayan orogeny . Unlike the snow-clad Greater Himalayas, these hills are moderate in elevation (600–3000 m) , with dense forests, heavy rainfall, and humid climate . 1. Barail Range Location: Separates the Brahmaputra Valley (north) and Barak Valley (south) in Assam. Geomorphology: Tertiary folded ranges with elongated ridges and valleys. Drainage: Acts as a watershed between the Barak River and the Brahma...