Past Year Questions: Time Concept, Remote Sensing, GIS, GPS & Photogrammetry

# Past Year Questions: Time Concept, Remote Sensing, GIS, GPS & Photogrammetry | Topic wise GATE Past Year Papers for Civil Engineering - Civil Engineering (CE) PDF Download

Question 1: A camera with a focal length of 20 cm fitted in an aircraft is used for taking vertical aerial photographs of a terrain. The average elevation of the terrain is 1200 m above mean sea level (MSL). What is the height above MSL at which an aircraft must fly in order to get the aerial photographs at a scale of 1:8000?    [2019 : 2 Marks, Set-ll]
(a) 3200 m
(b) 2600 m
(c) 3000 m
(d) 2800 m
(d)
Solution:

Given focal length = 20 cm
as we know scale of vertical photograph

its given as 1 : 8000

Question 2: An aerial photograph of a terrain having an average elevation of 1400 m is taken at a scale of 1:7500. The focal length of the camera is 15 cm. The altitude of the flight above mean sea level (in m, up to one decimal place) is _________.    [2018 : 2 Marks, Set-II]
Solution: h= 1400 m
Scale = 1 : 7500
f = 15 cm

Question 3: A square area (on the surface of the earth) with side 100 m and uniform height, appears as 1 cm2 on a vertical aerial photograph. The topographic map shows that a contour of 650 m passes through the area. If focal length of the camera lens is 150 mm, the height from which the aerial photograph was taken, is    [2018 : 2 Marks, Set-I]
(a) 800 m
(b) 1500 m
(c) 2150 m
(d) 3150 m
Solution:
A =100 x 100 m2
Area on photo, a = 1 cm2
Scale 1 cm =100
f = 150 mm
h = 650 m
Scale

Question 4: Two towers, A and B, standing vertically on a horizontal ground, appear in a vertical aerial photograph as shown in the figure.

The length of the image of the tower A on the photograph is 1.5 cm and of the tower B is 2.0 cm. The distance of the top of the tower A (as shown by the arrowhead) is 4.0 cm and the distance of the top of the tower B is 6.0 cm, as measured from the principal point p of the photograph. If the height of the tower B is 80 m, the height (in meters) of the tower A is _____.    [2017 : 2 Marks, Set-II]
Solution: For Tower A:
Relief displacement,
dA = 1.5 cm
rA = 4 cm, hA = ?

For Tower B:
Relief displacement,
dB = 2.0 cm, rB = 6 cm, hB = 80 m
Relief displacement

Question 5: The number of spectral bands in the Enhanced Thematic Mapper sensor on the remote sensing satellite Landsat-7 is    [2017 : 1 Mark, Set-I]
(a) 64
(b) 10
(c) 8
(d) 15
Solution: Total number of spectrum band in Enhanced
Thematic Mapper sensor = 8
Band 1 - Blue
Band 2 - Green
Band 3 - Red
Band 4 - Near Infrared (NR)
Band 5 - Shortwave Infrared (SWIR)
Band 6 - Thermal
Band 7 - Shortwave Infrared (SWIR)
Band 8 - Panchromatic

Question 6: A tall tower was photographed from an elevation of 700 m above the datum. The radial distances of the top and bottom of the tower from the principal points are 112.50 mm and 82.40 mm, respectively. If the bottom of the tower is at an elevation 250 m above the datum, then the height (expressed in m) of the tower is _____    [2016 : 2 Marks, Set-II]
Solution:

Given: H = 700 m, havg = 250
Relief distance,
d = q - r
= 112.5 - 82.40
= 30.1 mm

[where h is height of tower]

∴ h = 120.4 mm

Question 7: Optimal flight planning for a photogrammetric survey should be carried out considering     [2016 : 1 Mark, Set-II]
(a) only side-lap
(b) only end-lap
(c) either side-lap or end-lap
(d) both side-lap as well as end-lap

Question 8: The system that uses the Sun as a source of electromagnetic energy and records the naturally radiated and reflected energy from the object is called    [2016 : 1 Mark, Set-I]
(a) Geographical Information System
(b) Global Positioning System
(c) Passive Remote Sensing
(d) Active Remote Sensing
Solution: The sun provide a very convenient source of energy for remote sensing. The Sun’s energy is either reflected, as it is for visible wavelengths, or absorbed and then re-emitted, as it is for thermal infrared wavelengths. Remote sensing system which measure energy i.e., naturally available are called as passive remote sensing.

Question 9: The minimum number of satellites needed for a GPS to determine its position precisely is    [2016 : 1 Mark, Set-I]
(a) 2
(b) 3
(c) 4
(d) 24
Solution: At a minimum, four satellite must be in view of the receiver for it to compute four unknown quantity (three position coordinate and one for clock deviation from satellite time).

Question 10: The local mean time at a place located in Longitude 90° 40'E when the standard time is 6 hours and 30 minutes and the standard meridian is 82° 30' E is    [2010 : 1 Mark]
(a) 5 hours, 2 minutes and 40 seconds
(b) 5 hours, 47 minutes and 20 seconds
(c) 6 hours and 30 minutes
(d) 7 hours, 02 minutes and 40 seconds
Solution: Difference between standard meridian and the longitude of the given place
= 90° 40'E - 82°30'E = 8°10'
The longitude of the given place is more than the standard meridian. Hence the local mean time of the given place will be ahead of the standard time.

= 0 hours and 32 minutes and 0 seconds

= 0 hours and 0 minutes and 40 seconds
Time for a difference of 8°10' = 32 minutes and 40 seconds
Local mean time = standard time + 32 minutes and 40 seconds
= 6 hours and 30 minutes + 32 minutes and 40 seconds
= 7 hours 02 minutes and 40 seconds

The document Past Year Questions: Time Concept, Remote Sensing, GIS, GPS & Photogrammetry | Topic wise GATE Past Year Papers for Civil Engineering - Civil Engineering (CE) is a part of the Civil Engineering (CE) Course Topic wise GATE Past Year Papers for Civil Engineering.
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## FAQs on Past Year Questions: Time Concept, Remote Sensing, GIS, GPS & Photogrammetry - Topic wise GATE Past Year Papers for Civil Engineering - Civil Engineering (CE)

 1. What is the time concept in remote sensing?
Ans. The time concept in remote sensing refers to the temporal aspect of capturing and analyzing data from Earth's surface using remote sensing technology. It involves understanding how the temporal dimension impacts the interpretation of remote sensing data and how changes over time can provide valuable information about land cover, land use, and environmental conditions.
 2. How does remote sensing contribute to GIS?
Ans. Remote sensing contributes to GIS (Geographic Information System) by providing spatial data that can be analyzed, visualized, and integrated into GIS software. Remote sensing technologies, such as aerial photography and satellite imagery, capture data about the Earth's surface, which can be used as input for GIS analysis, mapping, and modeling. This data enhances the spatial accuracy and detail of GIS datasets, allowing for better decision-making in various fields, including urban planning, agriculture, and environmental management.
 3. What is the role of GPS in remote sensing?
Ans. GPS (Global Positioning System) plays a crucial role in remote sensing by providing accurate geospatial coordinates for ground control points and positioning sensors. By using GPS receivers, remote sensing platforms can precisely determine their location, which is essential for accurate georeferencing and registration of remote sensing data. GPS also enables real-time positioning and navigation of remote sensing platforms, allowing for efficient data collection and mapping.
 4. How does photogrammetry complement remote sensing?
Ans. Photogrammetry complements remote sensing by utilizing overlapping aerial or satellite images to reconstruct and measure the 3D geometry of objects and terrain. It involves analyzing the parallax shift between overlapping images to determine the elevation, size, and shape of features on the Earth's surface. Photogrammetry techniques, such as stereo image interpretation and digital elevation modeling, enhance the accuracy and detail of remote sensing data, enabling precise measurements and topographic mapping.
 5. How can remote sensing and GIS be used for environmental monitoring?
Ans. Remote sensing and GIS are powerful tools for environmental monitoring. Remote sensing data, such as satellite imagery, can be used to detect and monitor changes in land cover, vegetation health, water quality, and air pollution. These data can then be integrated into GIS software to analyze spatial patterns, identify hotspots of environmental degradation, and support decision-making for sustainable resource management. Remote sensing and GIS also enable the monitoring of natural disasters, such as floods and wildfires, by providing timely and accurate spatial information for emergency response and recovery efforts.

## Topic wise GATE Past Year Papers for Civil Engineering

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