DATA COLLECTION TECHNIQUES, IMAGE ANALYSIS/ VISUAL INTERPRETATION

BY

DR. UPASANA CHOUDHURY RESEARCH SCHOLAR

CENTRE OF EXCELLENCE ON LAND GOVERNANCE, ASSAM

Remote Sensing Technologies

• Earth Observation relies on a variety of tools, including satellites and airborne technology, which are continuously improving. This includes older satellites, newer ones like the Sentinels, very high-resolution satellites, airborne laser scanners, and drones. Handling this wide range of data and the large amount of information collected over time can be challenging. To manage this, RSS uses advanced IT systems like cloud computing and smart machine learning techniques to turn the data into useful information for better decision-making.

What is Remote Sensing?

• Remote: Something which is not exactly in contact or physical

contact, something which is far away.

• Sensing: Sensing means getting information, data or any input. For example Temperature, Pressure, an image or photograph

Natural Remote Sensing

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Information or

Knowledge

Analysis

Sensing /

Perceiving

Artificial Remote Sensing

Subject / Target

Sensing / Perceiving

Analysis

Extracting Information

Output

Satellite Image

Classified Satellite Image

How does a satellite sensor works

Satellites capture data in different spectral bands using specialized sensors called multispectral or hyperspectral imagers. These sensors are designed to detect and measure the electromagnetic radiation (light) that is reflected or emitted from the Earth's surface.

Electromagnetic Spectrum and Bands

• Electromagnetic Radiation: The Earth’s surface reflects sunlight and emits thermal radiation in various wavelengths,

spanning from visible light (what we see with our eyes) to infrared and beyond.

• Bands: The electromagnetic spectrum is divided into distinct wavelength ranges called "bands." Each band corresponds to a specific range of wavelengths, such as blue, green, red, near-infrared (NIR), and shortwave infrared (SWIR).

Cont…

Satellite Sensors

• Optical Sensors: Satellites are equipped with optical sensors that are sensitive to different parts of the electromagnetic spectrum. These sensors can be passive (detecting natural radiation from the sun) or active (emitting their own energy and measuring the reflection, like Lidar, Radar).
• Filters and Detectors: The sensor uses filters to separate the incoming light into different wavelength bands. Each band is then directed to a specific detector that is sensitive to that range of wavelengths.
• Digital Data Capture: As the satellite passes over the Earth, the sensors continuously capture data for each band. This data is recorded as digital numbers that represent the intensity of the radiation in each band.
• Combination into Composite Images: The data from the different bands can be combined into images (like True Colour or False Colour Composites) that highlight specific features of the Earth's surface.

Cont…

True Color Composition

image created using visible light, the same

way the human eye perceives colours in the environment. In this method, the three

primary colors—red, green, and blue

(RGB)—are combined to form an image

that closely resembles what one would see with the naked eye.

• When these bands are combined, the

resulting image displays natural colours. For

example, vegetation appears green, water bodies appear blue, and urban areas appear grey or white.

False Color Composition

• A True Colour Composite (TCC) is an • A False Colour Composite (FCC) uses a

combination of bands that are not in the visible

spectrum, or it assigns different visible bands to create an image where the colours do not match what would be naturally seen by the human eye. This is done to highlight certain features or characteristics of the terrain that may not be as

easily distinguishable in a True Colour

Composite.

• By altering the band assignments, FCCs can

enhance specific features. For instance, healthy

vegetation appears bright red, making it easier to

differentiate from other land cover types. Water bodies usually appear black or dark blue, and urban areas may appear in shades of blue or grey.

Pixels

LANDSAT 8 (GUWAHATI CITY, ASSAM)

• Landsat 8 images have 15-meter panchromatic and 30-meter multi-spectral spatial

resolutions.

• Landsat 8 (formerly the Landsat Data Continuity Mission, or LDCM) was launched on an Atlas-V rocket from Vandenberg Air Force Base, California on February 11, 2013

Sentinel 2A

• Sentinel satellite image data at 10 m spatial resolution. The Sentinel-2 satellite image data can support important farming and agriculture data to manage crop yields, production, health, and weather patterns. The high resolution spectral image data can provide critical information for monitoring crop health and growth, that can improve farming and agriculture production.

LISS IV (ALMORA CITY, UTTARAKHAND)

• LISS IV 5.8m spatial resolution
• ISRO - NRSC

PLEIADES (ALMORA CITY, UTTARAKHAND)

• European Space Agency
• Spatial Resolution : 0.5m

Visual Interpretation / Image Interpretation

• Image interpretation is defined as the act of examining images to identify objects and judge their significance.
• Image interpretation of remote sensing data is to extract qualitative and quantitative information from the photograph or image.
• It involves identification of various objects on the terrain which may be natural or artificial, consist of points, lines or polygon.
• An interpreter studies remotely sensed data and attempts detailed logical process to detect, identify, measure and evaluate the significance of environmental and cultural objects, pattern and spatial relationship.

Basic Principles Of Image Interpretation Images And Their Interpretability

• An image taken from the air or space is a pictorial presentation of the pattern of a landscape of earth surface.

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• The pattern is composed of indicators of objects and events that relate to the physical, biological and cultural components of the landscape.

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• Similar conditions, in similar circumstances and surroundings, reflect similar patterns, and unlike conditions reflect unlike patterns.

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• The type and amount of information that can be extracted is proportional to the

knowledge, skill and experience of the analyst, the methods used for interpretation and the analyst's awareness of any limitations.

SHAPE

• Shape refers to the general form, structure, or outline of individual objects. (depends on the object outline)
• Shape adjectives: Linear, Curvilinear, Circular, Elliptical, Radial, Square, Rectangular, Triangular, Hexagonal & Amorphous.
• Straight edge shapes typically represent urban or agricultural (field) targets, while natural features, such as forest edges, are generally more irregular in shape, except where man has created a road or clear cuts.
• Farm or crop land irrigated by rotating sprinkler systems would appear as circular shapes.

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Triangular Shape

Rectangular Shape

Pentagon

Curvilinear Shape

Curvilinear Shape (rice Field)

Radial Palm Tree

SIZE

• Size of objects in an image is a function of scale.
• It is important to assess the size of a target relative to other objects in a scene, as well as the absolute size, to aid in the interpretation of that target.
• For example, if an interpreter had to distinguish zones of land use, and had identified an area with a number of buildings in it, large buildings such as factories or warehouses would suggest commercial property, whereas small buildings would indicate residential use.

Automobiles: 15ft/Length, 6ft wide

Rail road

Trailer 45-50ft in length

Baseball Ground 90/60 ft

Diving Board 12 ft in length

Cars/ Air conditioning units length

PATTERN

• Pattern refers to the spatial arrangement of visibly discernible objects. Typically an orderly repetition of similar tones and textures will produce a distinctive and ultimately recognizable pattern.
• Orchards with evenly spaced trees, and urban streets with regularly spaced houses are good examples of pattern.

Systematic Triangular pattern

Curvilinear pattern

Random, Sinuous braided stream pattern

Systematic Linear row of potatoes

Radiating Road Pattern

TONE

• Tone refers to the relative brightness (hue) or colour of objects in an image. Generally, tone is the fundamental element for distinguishing between different targets or features. Variations in tone also allows the elements of shape, texture, and pattern of objects to be distinguished.
• The degree of darkness or brightness is the function of the amount of light

reflected from the feature, within the specific wavelength interval.

Elements of Image Interpretation - Tone

and Color

Jensen, 2007

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Green

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Red

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Near-infrared

Color composite RGB = green, red, near-

infrared

TEXTURE

• Texture refers to the arrangement and frequency of tonal variation in particular areas of an image. Texture (smooth or coarse).
• Rough textures would consist of a mottled tone where the grey levels change abruptly in a small area, whereas Smooth textures would have very little tonal variation. Smooth textures are most often the result of uniform, even surfaces, such as fields, asphalt, or grasslands. A target with a rough surface and irregular structure, such as a forest canopy, results in a rough textured appearance. (Texture is one of the most important elements for distinguishing features in radar imagery)

Coarse texture Avocado Field; Grass &

Road Smooth Texture

Pine: coarse Tex; waterlilies: intermediate

tex.

Pine logs: Coarse texture

Corn Field: coarse texture

Irrigation System: Mottled Texture

R. Mississippi: Variety of textures

SHADOW

• Shadow is also helpful in interpretation as it may provide an idea of the profile and relative height of a target or targets which may make identification easier.
• Shadows can also reduce or eliminate interpretation in their area of influence, since targets within shadows are much less (or not at all) discernible from their surroundings. Shadow is also useful for enhancing or identifying topography and landforms, particularly in radar imagery.

People & Benches

Arch of Glory, Vienna

Bridge Sign shadow

Pyramids of Giza

House

Shadow fall

SITE

• Site refers to the topographic or geographic location & is a particularly important aid in the identification of vegetation types. Site (location helps recognition)

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• Certain tree species would be expected to occur on well drained upland site. Also various tre species occur only in certain geographic areas.

ASSOCIATION

• Association takes into account the relationship between other recognizable objects or features in proximity to the target of interest (features that are normally found near others).
• Commercial properties may be associated with proximity to major transportation routes, whereas Residential areas would be associated with schools, playgrounds, and sports fields.

RESOLUTION

• Resolution depends on many factors but it always place a practical limit on interpretation, because some objects are too small or have too little contrast with their surroundings to be clearly scene on the image.

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• Image color, Condition of image also effects the success of image interpretation activities.

Thank You