GIS & REMOTE SENSING (KOE066)
Section-wise Detailed Answers – B.Tech Semester VI
SECTION A
(Attempt all questions – brief but descriptive answers)
Q1(a) Define Remote Sensing (RS)
Remote sensing is the science and technology of obtaining information about objects, areas, or phenomena on the Earth’s surface without making physical contact with them. It is achieved by detecting and measuring electromagnetic radiation that is reflected or emitted from the Earth and recorded by sensors mounted on satellites or aircraft. Remote sensing enables large-scale, repetitive, and systematic observation of the Earth.
Q1(b) Basic components of Remote Sensing
The remote sensing system consists of an energy source, which is usually the Sun or an artificial source such as radar. The energy travels through the atmosphere and interacts with the Earth’s surface. The reflected or emitted energy is then detected by sensors mounted on platforms like satellites or aircraft. The recorded data is transmitted to ground stations, processed, analyzed, and interpreted to extract meaningful information for various applications.
Q1(c) Define Sensors
Sensors are devices used in remote sensing to detect and measure electromagnetic radiation reflected or emitted from the Earth’s surface. They convert this energy into electrical signals that can be processed to form images or data products. Sensors may be passive, relying on natural energy sources, or active, generating their own energy such as in radar systems.
Q1(d) Concept of Contrast Ratio
Contrast ratio refers to the difference in brightness or radiance between an object and its background in an image. Higher contrast improves the ability to distinguish features, while low contrast makes interpretation difficult. Contrast ratio depends on surface properties, illumination conditions, atmospheric effects, and sensor characteristics.
Q1(e) Photogrammetry
Photogrammetry is the science of making measurements from photographs, particularly aerial photographs. It involves extracting quantitative information such as distances, elevations, and shapes of objects by analyzing overlapping photographs. Photogrammetry plays a vital role in mapping, surveying, and terrain analysis.
Q1(f) Satellite Remote Sensing
Satellite remote sensing refers to the collection of Earth observation data using sensors mounted on artificial satellites orbiting the Earth. It provides continuous and repetitive coverage of large areas and is widely used in meteorology, agriculture, environmental monitoring, disaster management, and urban planning.
Q1(g) Use of Microwave Remote Sensing
Microwave remote sensing uses long-wavelength electromagnetic waves and has the ability to penetrate clouds, rain, and vegetation. It is especially useful for all-weather and day-night observation. Applications include soil moisture estimation, ocean surface studies, topographic mapping, and military surveillance.
Q1(h) Define Spatial Data
Spatial data refers to information that describes the location, shape, and relationship of geographic features on the Earth’s surface. It includes coordinates, geometry, and spatial relationships and forms the core data type used in Geographic Information Systems.
Q1(i) Data Editing
Data editing in GIS involves checking, correcting, and refining spatial and attribute data to ensure accuracy and consistency. This process includes removing errors, filling missing values, correcting geometry, and validating data against defined standards.
Q1(j) Map Overlay in GIS
Map overlay is a GIS technique that involves superimposing multiple thematic layers to generate new information. It allows spatial analysis by combining data such as land use, soil type, and elevation to support decision-making in planning and resource management.
SECTION B
(Attempt any three – detailed explanations)
Q2(a) Applications of Remote Sensing and GIS in land and water resource management
Remote sensing and GIS play a crucial role in managing land and water resources by providing accurate, timely, and spatially consistent data. Satellite imagery helps in land-use and land-cover mapping, monitoring deforestation, soil erosion, and urban expansion. In water resources, RS is used for watershed management, groundwater exploration, reservoir monitoring, flood mapping, and drought assessment. GIS integrates spatial data from various sources to analyze resource availability, plan sustainable usage, and support policy decisions.
Q2(b) Types of aerial photographs and causes of low contrast
Aerial photographs are classified based on orientation and scale. Vertical photographs are taken with the camera axis nearly perpendicular to the ground and are used for mapping. Oblique photographs are taken at an angle and provide better perspective but less accurate measurements. Low contrast in aerial photographs may occur due to haze, atmospheric scattering, low sun angle, uniform surface reflectance, or poor sensor performance. Low contrast reduces image interpretability.
Q2(c) Difference between supervised and unsupervised classification
Supervised classification involves selecting training samples of known land-cover types and using them to classify the entire image. The accuracy depends on the quality of training data. Unsupervised classification, on the other hand, automatically groups pixels into clusters based on spectral similarity without prior knowledge. The analyst later assigns meaning to these clusters. Supervised classification generally provides better accuracy, while unsupervised classification is useful when ground truth data is limited.
Q2(d) Ground control for aerial photography
Ground control refers to accurately known reference points on the Earth’s surface used to relate aerial photographs to real-world coordinates. These points help in correcting distortions, determining scale, and ensuring positional accuracy. Ground control points are essential for photogrammetric mapping and accurate spatial analysis.
Q2(e) Principles, advantages, and limitations of Remote Sensing
Remote sensing operates on the principle that different materials interact uniquely with electromagnetic radiation. These interactions create spectral signatures that allow identification of surface features. Advantages include large-area coverage, repetitive observation, cost-effectiveness, and access to inaccessible regions. Limitations include dependence on atmospheric conditions, need for ground verification, and challenges in interpreting complex surfaces.
SECTION C
(Attempt any one part – long descriptive answers)
Q3(a) Spatial data models and their structures
Spatial data models define how geographic information is stored and represented in GIS. The vector data model represents features as points, lines, and polygons and is suitable for discrete features like roads and boundaries. The raster data model represents space as a grid of cells and is ideal for continuous data such as elevation and temperature. Each model has its own data structure, advantages, and applications. Vector models provide high precision, while raster models support complex spatial analysis.
Q3(b) Requirements of stereoscopic photographs
Stereoscopic photographs require overlapping images taken from different positions to create a three-dimensional view. Adequate forward overlap and side overlap are essential. The photographs must have similar scale, proper orientation, and consistent illumination. Stereoscopic viewing enables height measurement and terrain analysis.
Q4(a) Use of Remote Sensing in land and water resource assessment
Remote sensing techniques are widely used to assess and monitor land and water resources. Satellite data helps in mapping land degradation, vegetation cover, soil moisture, and water bodies. Temporal analysis enables monitoring of changes such as urban growth and seasonal water availability. These techniques support sustainable resource management and environmental protection.
Q4(b) Identification of training areas in photogrammetry
Training areas are representative sample regions selected for image classification. Proper identification requires homogeneous land-cover areas, accurate ground truth data, sufficient sample size, and spectral separability. Well-chosen training areas improve classification accuracy and reliability.
Q5(a) Principle of position determination using GPS
Global Positioning System determines position by measuring distances between a receiver and multiple satellites. Each satellite transmits time-coded signals. By calculating signal travel time, the receiver computes distances and determines its position through trilateration. GPS provides accurate location information for navigation, mapping, and surveying.
Q5(b) Data formats of satellite images
Satellite image data formats define how image information is stored and accessed. Common formats include raster formats such as GeoTIFF, IMG, and HDF. These formats store pixel values along with spatial reference information, enabling integration with GIS software.
Q6(a) Planning end lap and side lap in aerial photography
End lap and side lap refer to overlap between consecutive aerial photographs along and across flight lines. Proper overlap ensures complete coverage, stereoscopic viewing, and accurate mapping. Planning depends on terrain, scale, and camera specifications.
Q6(b) Energy interactions in atmosphere and Earth’s surface
Electromagnetic energy interacting with the atmosphere undergoes scattering and absorption. At the Earth’s surface, energy may be reflected, absorbed, or transmitted depending on material properties. Understanding these interactions is essential for interpreting remote sensing data.
Q7(a) Multispectral scanner, whiskbroom, and push-broom scanners
Multispectral scanners capture data in multiple spectral bands. Whiskbroom scanners use a rotating mirror to scan across the track, while push-broom scanners use a linear array of detectors to capture data along the track. Push-broom scanners provide higher radiometric resolution and are widely used in modern satellites.
Q7(b) Applications of different wavelength regions in Remote Sensing
Different wavelength regions serve different applications. Visible wavelengths are used for land-use mapping, infrared for vegetation and moisture analysis, thermal infrared for temperature studies, and microwave for all-weather observation. Selection of wavelength depends on the application and target characteristics.
