Geographic Information Systems Lecture 15
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Questions and Answers

What is the primary advantage of using aerial and satellite images?

  • They provide reliable information without touching the environment. (correct)
  • They can only cover small spatial areas.
  • They generate data records that expire quickly.
  • They require physical contact with objects.

What does reflection of electromagnetic radiation involve?

  • The passing of radiation through a material.
  • The emission of radiation from a surface.
  • The bouncing off of radiation from a surface. (correct)
  • The absorption of energy into heat.

Which of the following best describes irradiance?

  • The ratio of radiance to the amount of light striking a surface.
  • The radiation incident on a surface. (correct)
  • The light reflecting off a surface.
  • The rate at which electromagnetic radiation is emitted.

What characteristic is significantly high in the spectral signature of vegetation?

<p>High reflectance in infrared (IR) spectrum. (A)</p> Signup and view all the answers

What does orthogonal aerial photography achieve?

<p>Combines air photo characteristics with map quality. (B)</p> Signup and view all the answers

Which aspect of digital air photo imagery is mentioned as lacking?

<p>Value attribute table. (A)</p> Signup and view all the answers

What defines frequency in the context of wavelengths?

<p>Number of wavelengths passing a point per unit time. (A)</p> Signup and view all the answers

What are the types of digital raster data resolution?

<p>Spatial, spectral, radiometric, and temporal resolution. (A)</p> Signup and view all the answers

What is the main difference between block and focal neighborhood analysis?

<p>Block analysis moves to entirely new sets of cells. (D)</p> Signup and view all the answers

Which of the following defines a zonal function?

<p>Applying operations based on defined regions within an area. (B)</p> Signup and view all the answers

What do Digital Elevation Models (DEMs) represent?

<p>A 3D representation of terrain attributes. (C)</p> Signup and view all the answers

How is slope defined in terrain analysis?

<p>Change in elevation over horizontal distance. (A)</p> Signup and view all the answers

What does flow accumulation represent in GIS analysis?

<p>The number of upstream cells draining into a cell. (C)</p> Signup and view all the answers

What role does terrain analysis play in GIS?

<p>It interprets topographic features using slope and aspect data. (D)</p> Signup and view all the answers

Which of the following best describes aspect in terrain analysis?

<p>Directional measure of the slope's incline. (A)</p> Signup and view all the answers

What advantage do aerial and satellite images offer in geographic analysis?

<p>They allow for the capture of topographic features over large areas. (C)</p> Signup and view all the answers

What does the spectral aspect of remote sensing refer to?

<p>The number and width of spectral regions recorded (B)</p> Signup and view all the answers

How is NDVI calculated and interpreted?

<p>NDVI = (NIR-RED)/(NIR+RED), Higher values indicate denser vegetation (A)</p> Signup and view all the answers

What are false-color composite images primarily used for?

<p>To enhance the contrast between features of interest and the background (D)</p> Signup and view all the answers

What distinguishes hyperspectral imaging from multispectral imaging?

<p>Hyperspectral imaging generally has hundreds of spectral bands with narrow bandwidths (B)</p> Signup and view all the answers

Which statement accurately describes passive and active sensors in remote sensing?

<p>Passive sensors cannot function at night (B), Passive sensors depend solely on reflected sunlight for data acquisition (D)</p> Signup and view all the answers

What is LiDAR and how is it classified?

<p>Light Detection And Ranging; an active sensor (C)</p> Signup and view all the answers

What does the concept of 'return' refer to in elevation data collection?

<p>It indicates the total light collected by the sensor (D)</p> Signup and view all the answers

Why might NDVI values become less useful at high biomass levels?

<p>They saturate and do not distinguish differences in dense vegetation (B)</p> Signup and view all the answers

Flashcards

Neighborhood Analysis

Analyzing data by looking at the characteristics of a specific area around a given point or cell.

Zonal Function

An operation on data that is applied to different areas (zones) with unique attributes or identifiers.

Terrain Analysis

Studying the characteristics and features of land surfaces using GIS

Digital Elevation Models (DEM)

A digital representation of the elevation points on a surface.

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Slope

The steepness of a land surface, calculated as the change in elevation over a horizontal distance.

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Aspect

The direction a slope faces.

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Flow Direction

Determines the pathways of water flow based on the steepest descent.

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Aerial/Satellite Images

Images of Earth's surface from sources above the ground, used often in analysis of the Earth.

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Aerial Images

Photographs taken from aircraft capturing a wide view of the earth's surface.

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Satellite Images

Images captured by satellites orbiting Earth, providing broader coverage and long-term data.

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Reflection (Radiation)

When light bounces off a surface, like a mirror reflecting sunlight.

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Absorption (Radiation)

When a material takes in radiation, converting it to heat.

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Transmitted Radiation

Light passing through a material without being reflected or absorbed, like sunlight through a window.

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Wavelength

The distance between two consecutive peaks or troughs in a wave pattern.

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Frequency

The number of waves passing a point in a specific time.

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Spectral Signature

The unique pattern of how an object reflects light at different wavelengths.

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NDVI

A measure of vegetation density calculated from near-infrared (NIR) and red (RED) light reflectance. Higher values (closer to 1) indicate denser vegetation, while lower values (closer to -1) represent less vegetation or non-vegetated areas.

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False-color composite images

Images where different spectral bands are assigned to red, green, and blue channels, creating a visual representation that highlights specific features of the land surface.

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Hyperspectral imaging

A technique that captures data across hundreds of very narrow spectral bands, providing detailed information about the composition of objects.

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Multispectral imaging

A technique that captures data across a few broader spectral bands, providing information about key features of the land surface.

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Passive sensor

A remote sensing sensor that relies on energy from the sun to collect data.

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Active sensor

A remote sensing sensor that emits its own energy source to collect data.

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LiDAR

A remote sensing technology that uses laser light to measure distances and create 3D models of the Earth's surface. It's an active sensor.

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First Returns in LiDAR

The first reflections of laser pulses from objects like treetops or buildings, used to measure canopy height.

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Last Returns in LiDAR

The final reflections of laser pulses from the ground surface, even below vegetation canopies, used to determine ground level elevation.

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Study Notes

Lecture 15: Neighborhood Analysis and Zonal Functions

  • Neighborhood analysis uses a "moving window" to evaluate cells within a defined area.
  • Output from a moving window operation is based on the cell at the window's center.
  • Focal analysis evaluates cells one at a time, creating overlapping neighborhoods.
  • Zonal functions apply operations to defined regions or zones.
  • Zonal analysis uses defined areas of interest (like a country) to summarize data points like total population.
  • It employs a zonal statistics tool for data summarization.

Lecture 15: Terrain and Terrain Analysis

  • Terrain analysis interprets topographic features like slope, aspect, and viewshed.
  • Terrain is where water flows, lakes form, and land is affected by floods.
  • Terrain analysis examines how terrain features influence various aspects, such as soil moisture and food production.
  • Terrain analysis is conducted through Geographic Information Systems (GIS)

Lecture 15: Terrain Models

  • Models used for terrain analysis include elevation contours, digital elevation models (DEMs), triangular irregular networks (TINs), 3D point clouds, and LiDAR.

Lecture 16: Aerial and Satellite Imagery

  • Aerial imagery is taken from aircraft.
  • Satellite imagery is taken from satellites.
  • Both provide advantages in observing environments without physical contact. These methods provide reliable information about physical objects and long spatial coverage.

Lecture 16: US Terrain Data

  • USGS and NOAA/FEMA use high-resolution LiDAR, particularly in coastal areas.

Lecture 16: DEM Derivatives

  • DEM derivatives (slope, aspect, curvature, flow direction) are calculated using neighborhood analysis.

Lecture 16: Slope and Aspect

  • Slope is the change in elevation over a horizontal distance (rise over run).
  • It's measured in percent or degrees.
  • Aspect is the direction a slope faces.

Lecture 16: Flow Direction, Accumulation, and Watersheds

  • Flow direction follows the steepest downhill path.
  • Flow accumulation counts upstream cells that drain into a specific cell.
  • Watersheds include all cells that drain into a single outlet.

Lecture 17: Raster Data Resolution

  • Spatial resolution of raster data is the size of the instantaneous field of view.
  • Temporal resolution is how often data is acquired.
  • Radiometric resolution describes the sensitivity of detectors to small brightness differences.
  • Spectral resolution measures the number and width of spectral regions the sensor records.

Lecture 17: NDVI

  • Normalized Difference Vegetation Index (NDVI) is calculated using near-infrared (NIR) and red (RED) reflectance.
  • Higher NDVI values indicate denser vegetation.
  • NDVI values below a threshold might represent non-vegetated areas.

Lecture 17: False-Color Composite Images.

  • False-color composite images combine different bands of imagery.
  • This is used to highlight characteristics of land surfaces.

Lecture 17: Hyperspectral Imaging

  • Hyperspectral data have hundreds of narrow spectral bands.
  • Multispectral data have fewer, wider spectral bands. This is a key difference between the data types.

Lecture 17: Sensors

  • Passive sensors use energy from the sun.
  • Active sensors use their own energy source, like LiDAR.

Lecture 17: LiDAR

  • LiDAR, or Light Detection and Ranging, uses lasers to measure distance.
  • LiDAR data is an active remote sensing technology.

Lecture 17: "Return"

  • "Return" calculations, like First and Last Returns, allow for obtaining elevation data accurately.

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Study Guide 4 (Lectures 15-17) PDF

Description

Explore key concepts from Lecture 15 on Neighborhood Analysis and Terrain Analysis within Geographic Information Systems. This quiz covers focal analysis, zonal functions, and the interpretation of terrain features such as slope and aspect. Test your understanding of how these analyses influence data summarization and decision-making.

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