CE 797: Digital Elevation Models Chapter 2

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Questions and Answers

What type of sensors are used in remote sensing methods?

Active and passive sensors mounted on various airborne and spaceborne platforms (correct)

Ground-based sensors only

Only passive sensors mounted on drones

Only active sensors mounted on satellites

Which electromagnetic spectrum radiations are used in optical remote sensing?

X-rays and infrared radiation

Visible light, near infrared, and shortwave infrared (correct)

Ultraviolet and gamma rays

Radio waves and microwaves

What is the main advantage of using stereo imagery in DEM production?

It allows extraction of geographic features in 3D (correct)

It speeds up the image acquisition process

It reduces the cost of imaging

It provides better color fidelity in images

How can stereophotogrammetry be performed?

Either manually or automatically Signup and view all the answers

What does the automated method in stereophotogrammetry calculate?

The parallax displacement of a large number of points Signup and view all the answers

Which of the following methods is NOT considered a part of remote sensing?

Traditional surveying techniques Signup and view all the answers

What type of imagery is primarily used to generate DEMs using stereophotogrammetry?

Stereoscopic images Signup and view all the answers

What is the role of Radar in remote sensing?

To measure elevations using active sensors Signup and view all the answers

What is the primary advantage of using PRISM (ALOS) and CARTOSAT-1 for generating DEMs?

Ability to produce DEMs at low costs Signup and view all the answers

What technique is commonly used to create high-resolution DEMs from UAV images?

Photogrammetry Signup and view all the answers

Which of the following is NOT a type of sensor that can be mounted on UAVs?

Traditional satellite sensors Signup and view all the answers

Laser altimetry is primarily used for what function?

Generating DEMs from reflected laser pulses Signup and view all the answers

Which statement accurately describes LiDAR aerial surveys?

They can create DEMs up to 70 m deep in clear waters. Signup and view all the answers

Which platform was used to produce the quasi-global ASTER GDEM?

Terra satellite Signup and view all the answers

What is a key characteristic of stereo pairs used in remote sensing?

They can show the same area from multiple angles. Signup and view all the answers

What is often the cost of generating DEMs using PRISM and CARTOSAT-1?

Less than $10/km2 Signup and view all the answers

What principle underlies airborne optical sensing of bathymetry?

The total amount of radiative energy reflects water depth. Signup and view all the answers

What kind of water conditions are required for airborne optical sensing methods?

Clear waters only. Signup and view all the answers

How is water depth determined in the echo sounding method?

By measuring the time lag of sound pulses in water. Signup and view all the answers

Which of the following is NOT a type of echo sounding system?

Thermal detection Signup and view all the answers

What can be created using airborne optical sensing approaches?

Digital Elevation Models (DEMs) of shallow seafloors. Signup and view all the answers

What is the main purpose of using stereo pairs of images in photogrammetry?

To construct a stereo model and compute coordinates Signup and view all the answers

Which of these satellite platforms can be used to generate Digital Elevation Models (DEMs)?

Pleiades 1A Signup and view all the answers

What is the primary resolution of the ASTER VNIR sensor used for generating DEMs?

15 m Signup and view all the answers

How does the vertical accuracy of DEMs generated from ASTER images compare to the pixel resolution?

It is less than 20 meters Signup and view all the answers

What limitation is associated with the use of very high resolution images like Quickbird and IKONOS for detailed studies?

High acquisition costs Signup and view all the answers

What does the term 'stereo correlations' refer to in photogrammetry?

Matching images taken from two different positions Signup and view all the answers

Which statement about the resolution of the IKONOS satellite is true?

It provides 2-5 m resolution Signup and view all the answers

What is the purpose of reconstructing the geometric parameters in the context of stereo photography?

To create a reliable stereo model of the object Signup and view all the answers

What does LiDAR primarily generate from point measurements?

Digital Surface Models (DSM) Signup and view all the answers

What is the attainable vertical coordinate accuracy of LiDAR for well-defined target surfaces?

3 cm Signup and view all the answers

Which method describes the SAR technique that utilizes phase-difference measurements?

InSAR Signup and view all the answers

What are the four techniques that can be applied to produce DEMs using SAR?

Polarimetry, clinometry, interferometry, stereoscopy Signup and view all the answers

Which type of SAR mode uses two flights over the target area?

Two-pass mode Signup and view all the answers

In the context of LiDAR, what does a Digital Terrain Model (DTM) represent?

The bare earth surface without any objects Signup and view all the answers

What is the average cost range of LiDAR per square kilometer?

300 to 800 US$/km2 Signup and view all the answers

What is one of the common uses of SAR-based DEMs?

Medium to small-scale mapping of large areas Signup and view all the answers

Remote sensing methods use active and passive sensors mounted on airborne platforms such as planes and ______.

drones Signup and view all the answers

The optical EM spectrum includes visible light, near infrared, and ______ infrared radiations.

shortwave Signup and view all the answers

Radar Altimetry and Lidar are examples of ______ remote sensing methods.

non-imaging Signup and view all the answers

Stereophotogrammetry is utilized to produce DEMs from stereo pairs obtained by ______ remote sensing.

optical Signup and view all the answers

The primary advantage of stereo imagery is the ability to extract geographic features in ______.

3D Signup and view all the answers

In stereophotogrammetry, an operator uses a stereoplotter to move two dots together until they appear as one lying just at the ______ of the ground.

surface Signup and view all the answers

The automated method in stereophotogrammetry calculates the ______ displacement of a large number of points.

parallax Signup and view all the answers

Lidar (light detection and ranging) uses active sensors with ______ electromagnetic energy.

optical Signup and view all the answers

A stereopair of radar image coordinates can be computed using stereo __________.

correlations Signup and view all the answers

Automated photogrammetric generation of __________ can be done by processing digitized stereo pairs.

DEMs Signup and view all the answers

Various optical satellite sensors like Quickbird and IKONOS have resolutions ranging from __________ to 5 m.

2-5 m Signup and view all the answers

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) carries __________ channels.

15 Signup and view all the answers

The VNIR sensor allows generation of DEMs with a pixel resolution of __________ m.

15 Signup and view all the answers

DEMs generated from ASTER images have a vertical accuracy less than __________ meters.

20 Signup and view all the answers

Satellite stereo images from platforms like SPOT and __________ can be utilized to generate DEMs.

ALOS Signup and view all the answers

High acquisition costs of __________ images hinder their application in detailed studies.

very high resolution Signup and view all the answers

The __________ sensor has been utilized for generating DEMs with various resolutions using stereo images.

Pleiades 1A/1B Signup and view all the answers

The pixel resolution of ASTER images ranges from 15m to __________ m.

90 Signup and view all the answers

PRISM (ALOS) and CARTOSAT-1 have a resolution of ______ m.

2.5 Signup and view all the answers

UAVs are increasingly used for ______ sensing.

remote Signup and view all the answers

Laser altimetry, also known as ______, uses laser pulses to measure distances.

LiDAR Signup and view all the answers

Demonstrated by UAV photogrammetry, a key advantage is its ______ alternative to traditional methods.

low-cost Signup and view all the answers

DTM-based solutions from LiDAR can be applied to ______-scale mapping.

large Signup and view all the answers

Satellite laser altimetry contributes to the generation of Digital Elevation ______.

Models Signup and view all the answers

Aerial surveys using LiDAR can create high-resolution DEMs of both land surfaces and the ______.

seafloor Signup and view all the answers

Images from the Terra satellite contributed to the production of the quasi-global ______ GDEM.

ASTER Signup and view all the answers

UAVs can be equipped with various sensors, such as ______ band cameras.

visible Signup and view all the answers

Laser altimetry emits laser pulses that are reflected from the ______ surface.

ground Signup and view all the answers

LiDAR point measurements render Digital Surface Models (DSM), which contains information on all objects of the Earth’s surface, including buildings and ______.

trees Signup and view all the answers

The large one-pass spaceborne SAR interferometer was based on two similar radar satellites, TerraSAR-X and ______.

TanDEM-X Signup and view all the answers

Satellite radar altimetry is used to calculate heights on the earth by sending out short pulses of ______ energy.

microwave Signup and view all the answers

Through sophisticated algorithms and final manual editing, the landscape elements are removed and a Digital ______ Model (DTM) is generated.

Terrain Signup and view all the answers

SAR is a group of active remote sensing techniques where the SAR antenna transmits electromagnetic radiation at ______ frequencies.

microwave Signup and view all the answers

An example of a mission that carries a radar altimeter is the Jason-2 Ocean Surface Topography ______.

Mission Signup and view all the answers

SAR-based DEMs are utilized in medium- and small-scale mapping of large ______.

areas Signup and view all the answers

Applications of satellite radar altimetry include calculating the height of land, ocean, and ______ water bodies.

inland Signup and view all the answers

Synthetic Aperture Radar Interferometry (InSAR) is mostly used for detecting changes in ______ heights.

topographic Signup and view all the answers

InSAR utilizes phase-difference measurements derived from two radar images, which can be obtained by one-pass or ______ collection modes.

two-pass Signup and view all the answers

The InSAR technique was applied in the Shuttle Radar Topography Mission to prepare several Global DEMs with different ______.

resolutions Signup and view all the answers

The average costs of LiDAR range from ______ to 800 US$/km2 depending on the required point density.

300 Signup and view all the answers

To produce DEMs, four SAR techniques can be applied: interferometry, stereoscopy, ______, and clinometry.

polarimetry Signup and view all the answers

The one-pass mode of InSAR utilizes two SARs, but only one of them, the primary antenna, ______ pulses.

transmits Signup and view all the answers

The attainable elevation accuracy with LiDAR can be in the order of ______ cm for well-defined target surfaces.

3 Signup and view all the answers

Study Notes

Remote Sensing Methods

Active and passive sensors are used in remote sensing, mounted on airborne platforms (planes, drones) or spaceborne platforms (satellites, shuttles).
The electromagnetic (EM) spectrum utilized includes optical (visible, near infrared, shortwave infrared) and microwave.
Optical imageries from overlapping images are processed for DEM generation through stereo photogrammetry; radar imageries also support this process.
Non-imaging methods such as Radar Altimetry and LiDAR involve active sensors for elevation measurements.

Stereophotogrammetry Method

Stereophotogrammetry uses stereo pairs from optical remote sensing to generate DEMs.
Manual stereophotogrammetry requires operators to visually match images through a stereoplotter; automated methods calculate parallax displacement using instruments.
It enables 3D extraction of geographic features like buildings and roads.
DEM generation can use satellite images from platforms like SPOT, QuickBird, and ALOS, with varying resolutions.

Satellite Sensors for DEM Generation

Optical satellite sensors include Quickbird (2-5 m), Pleiades (1 m), WorldView2, and ASTER (15-30 m).
ASTER, launched in 1999, provides 30 m resolution free DEM data via Earthdata web service.
High-resolution satellite data is costly; PRISM (ALOS) offers a cheaper alternative with 2.5 m resolution at lower costs.

UAVs in Remote Sensing

Unmanned Aerial Vehicles (UAVs) are increasingly utilized, equipped with various sensors like visible band and laser scanners.
UAVs present a cost-effective alternative for high- and very high-resolution DEMs.

LiDAR Method

LiDAR (Light Detection and Ranging) uses active sensors to emit laser pulses and measure reflected light for elevation calculation.
Available in aerial and satellite forms, LiDAR generates high-resolution DEMs, including DSMs and DTMs.
LiDAR provides high accuracy, typically around 3 cm, with costs ranging from 300to300 to 300to800 per km².

Synthetic Aperture Radar (SAR) Method

SAR is an active remote sensing technique using microwave frequencies to produce DEMs.
Techniques include interferometry, stereoscopy, polarimetry, and clinometry; interferometric SAR (InSAR) is most widely used.
InSAR was essential for the Shuttle Radar Topography Mission (SRTM), producing various resolution global DEMs (up to 1” resolution).

Airborne Optical Sensing for Bathymetry

Uses passive remote sensing to estimate water depth from radiative energy reflected by the water column.
Effective only in clear waters for creating DEMs of shallow seafloors, aiding navigation safety.

Echo Sounding Method

A hydrographic sonar technique for determining underwater topography by transmitting sound pulses and measuring time lag.
Types of echo sounding include single-beam, multibeam, and side-scan systems to accurately assess water depth.

Remote Sensing Methods

Utilizes active and passive sensors on airborne (planes, drones) and spaceborne platforms (satellites).
Light and microwave portions of the electromagnetic spectrum are employed.
Optical methodologies involve visible light, near infrared, and shortwave infrared radiations for imagery acquisition.
Radar imagery uses microwave EM for elevation data generation.
Non-imaging remote sensing includes Radar Altimetry and Lidar.

Stereophotogrammetry Method

Classical approach for producing Digital Elevation Models (DEMs) using stereo image pairs garnered from optical remote sensing.
Can be performed manually (with stereoplotter) or automatically (using instruments for correlation).
Stereo imagery allows 3D feature extraction, useful for analyzing geographic elements like roads and structures.
Satellite stereo images can come from platforms like SPOT, Ikonos, and ALOS, with various sensors offering different resolutions.

Satellite Sensors for DEM Generation

High-resolution sensors: Quickbird (2-5 m), Pleiades (1 m), WorldView (1-2 m).
ASTER provides medium resolution (30 m) free DEM data with accuracy under 20 m from 15 m resolution images.
Recent technologies reduce costs of high-resolution data collection to less than $10/km².

Unmanned Aerial Vehicles (UAVs)

Drones increasingly utilized for remote sensing, providing various sensor options (visible, multispectral, thermal).
Offer a cost-effective alternative to traditional aerial surveying methods.

Laser Altimetry (LiDAR) Method

Active remote sensing technique using laser pulses for terrain measurement.
Produces high-resolution Digital Surface Models (DSM) and Digital Terrain Models (DTM) through point cloud data.
Vertical accuracy of LiDAR can reach 3 cm.
Cost of LiDAR varies from $300 to $800/km² based on point density requirements.

Synthetic Aperture Radar (SAR) Method

Active technique transmitting microwave radiation for DEM generation.
SAR operates on moving platforms and produces medium resolution topography maps.
Common techniques include interferometry, stereoscopy, polarimetry, and clinometry.
InSAR utilized for notable missions like the Shuttle Radar Topography Mission (SRTM) to generate various global DEMs.

Satellite Radar Altimetry Method

Measures Earth's heights with microwave energy pulses, correcting for atmospheric variations.
Example: Jason-2 mission uses advanced radar altimeter for ocean surface monitoring and marine gravity analysis.
Effective in capturing land and water height data, addressing challenges such as sparse ship track data for submarine topography.

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Description

Explore the concepts surrounding Digital Elevation Models (DEMs) as covered in Chapter 2 of CE 797. This quiz will focus on the applications of DEMs in GIS and their integration with remote sensing methods. Test your understanding of key principles and techniques in civil engineering related to digital elevation.