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Remote Sensing > Midterm > Flashcards

Midterm Flashcards

1
Q

What is Remote Sensing?

A

A technology, science, and art of observing, measuring and analyzing an object without touching it.

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2
Q

Frequency

A

the number of energy peaks passing a fixed point in space per unit time

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3
Q

Scattering

A

unpredictable diffusion of radiation by particles

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4
Q

MIE

A

the type of scattering caused when particles are of equal size to the wavelength and is significant in overcast conditions

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5
Q

Rayleigh

A

type of scattering that makes the sky blue and causes haze in an image; caused by particles smaller than the wavelength

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6
Q

Wavelength

A

distance from one energy wave peak to the next peak

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7
Q

Transmitted

A

energy that passes through the target

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8
Q

Data Acqusition

A

recording of energy variations from the earth’s surface features

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9
Q

Absorption

A

effective loss of energy to constituents

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10
Q

Data Analysis

A

examining data using various viewing and interpretation devices

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11
Q

Reflected

A

energy leaving the target

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12
Q

Spectral Signature

A

the typical energy graph of a target with respect to wavelength

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13
Q

Spectral Reflectance

A

measurement of the ratio of energy reflected and energy incident

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14
Q

GPS

A

Global Positioning Systems

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15
Q

Irradiance

A

the incoming radiation to the target

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16
Q

Atmospheric Windows

A

the wavelength ranges in which the atmosphere is transmissive of energy

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17
Q

Incident

A

energy arriving at the target

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18
Q

Non-selective

A

type of scattering caused by particles being larger than the wavelength (as in fog or clouds)

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19
Q

GIS

A

Geographic Information Systems

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20
Q

Radiance

A

brightness of energy at the sensor

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21
Q

Shutter

A

part of a camera that controls the duration of light exposure on the film

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22
Q

Monochromatic

A

CCD sensors cover each photosite with a blue, green or red filter.

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23
Q

Colour

A

our eyes can discriminate more shades of this than grey values

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24
Q

Subtractive

A

when you mix red, green and blue together, you get black

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25
Q

Infrared Film

A

a type of film that is sensitive to visible and near infrared

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26
Q

Photodiode

A

two dimensional arrays of light sensing solid-state devices for image acquisition

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27
Q

Diaphragm

A

part of a camera that controls the diameter of the lens opening

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28
Q

Haze Filter

A

colour film uses this type of filter to eliminate atmospheric scatter

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29
Q

Focal Length

A

the distance from the lens at which parallel light rays are focused to a point

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30
Q

Birds Eye View

A

aerial photography gives us this type of of view so we get the big picture of an area

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31
Q

The part of the electromagnetic spectrum that our eyes are most sensitive to.

A

Green

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32
Q

extremely hot objects can be photographed with color IR using this principle

A

Black Body

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33
Q

Exposure

A

this feature of a camera is determined by irradiance at that point multiplied by the exposure time

34
Q

Additive

A

When you mix red, green and blue together you get white.

35
Q

False Colour

A

the colour used so that we see infrared radiation

36
Q

Negative

A

an image that is the reverse tone of rendition

37
Q

a film camera that is most commonly used

A

Extra Wide

38
Q

Photogrammetry

A

the science and technology of obtaining spatial measurements and other geometrically reliable derived products from photographs

39
Q

Name Platforms

A

Satellite - high altitude spaceborne Shuttle - low altitude spaceborne Plane - high altitude airborne Helicopter - low altitude airborne Land/Street - terrestrial (ground observation)

40
Q

Geostationary Satellite

A

-rotates with the earth -weather reports -strays over one location on the ground

41
Q

Polar Orbiting/Synchronous Satellite

A

-stays on the sunny side of the earth at all times -large solar panels to absorb energy -goes around earth in a circle -crosses the equator at the same time everyday

42
Q

Passive Satellite

A

-one way ranging - only receives data. -can be geostationary or polar orbitting

43
Q

Active Satellite

A

-sends energy and receives -2 way ranging -only polar orbitting

44
Q

Spatial Resolution

A

the size of the pixel projected onto the ground

45
Q

Name the Spatial Resolutions

A

Land Sat - 30m x 30m Aster - 10m x 10m Quickbird - 30cm x 30cm

46
Q

Spectral Resolution

A

how much of the electromagnetic spectrum can the sensor differentiate between

47
Q

Panchromatic Image

A

Black and White photo

48
Q

Panchromatic Resolution

A

one large band to create a grayscale image. Takes B,G and R, and puts it into one band.

49
Q

Multispectral Resolution

A

2 or more bands that create separate images (eg: eyes)

50
Q

Hyperspectral Resolution

A

many narrow continuous bands

51
Q

Temporal Resolution

A

-need more than one image -time period between acquisitions controlled by: -when energy is available -position in orbit -when the flight goes over it.

52
Q

Radiometric Resolution

A

the ability of the sensor to decipher between EM energy acquired (%)

53
Q

Unprojected Coordinates

A

Latitude and Longitude (degrees)

54
Q

Projected Coordinates

A

1) Cylinder 2) Cone 3) Plane (all in decimal places)

55
Q

Electromagnetic Energy? Provide 3 examples

A

a form of energy emitted and absorbed by charged particles which exhibits wave-like behavior as it travels through space. i.e. X-rays, visible light and gamma rays are types of electromagnetic energy

56
Q

How do “scattering” and “absorption” differ?

A

Scattering is the unpredictable diffusion of radiation by particles. Scatter can cause haze in imagery. Absorption is the effective loss of energy to constituents. Absorption may occur at given wavelengths creating spectral response patterns. Remote sensing data acquisition is limited to ‘atmospheric windows’ where energy is not absorbed by the atmosphere.

57
Q

How does the atmosphere affect spectral response patterns?

A

The atmosphere affects the “brightness” or radiance recorded over any given point on the ground. It attenuates or reduces the energy reflected off of a ground object. As well path radiance, (radiation emitted or scattered into the sensor from the atmosphere) modifies the energy reaching the sensor.

58
Q

Name four characteristics of an ideal remote sensing system

A

An ideal remote sensing system would include a:

unifom energy source. This source would provide energy over all wavelengths, at a constant, known, high level of output. real-time data processing and supply system. Reference data would not be needed during analysis

Non-interfering atmosphere. Atmosphere does not distort image Supersensor. Sensitive to all wavelengths, accurate, detailed and economical

Multiple data users. Experts who understand information generation, and how to interpret and apply them

Series of unique energy-matter interactions at the earth’s surface. If every material emitted and/or reflected energy in a unique known way

59
Q

What are the four different types of resolution? Describe each of them

A

1) Spatial – size of pixel projected onto the ground
2) Spectral – How much of the EM spectrum can the sensor differentiate between
3) Temporal – need more than one image. Time b/w acquisitions; shorter = greater resolution
4) Radiometric – How well the sensor can decipher between EM energy acquired. How many greys can it determine? Differentiate b/w pixel values of 58, 62 or become 60 if poor resolution

60
Q

What is the difference between passive and active sensor

A

Passive sensors have one-way ranging. Can only receive or give data. In GIS passive sensors only receive data (do not emit wavelengths). Eyes are passive sensors

Active sensors have two-way ranging and both send and receive data. i.e. flash camera

61
Q

Describe a geo-stationary satellite and a sun-synchronous satellite

A

Geo-stationary satellites rotate with the earth thus staying over one location on the ground

Sun-synchronous/ Polar orbiting satellites stay on the sunny side of Earth at all times. They go around the earth and cross the equator the same time every day.

62
Q

List the advantages of aerial photography over on-the-ground observations

A

Advantages of aerial photography:

  • Improved vantage point
  • Capability to stop action unlike our eyes
  • Permanent recording of existing conditions
  • Greater spectral sensitivity, film can ‘see’ twice the EM range our eyes can
  • Increased spatial resolution and geometric fidelity, can magnify images for greater detail, and can obtain accurate measurements of distances, heights, volumes, directions etc using measurements and reference points
63
Q

List the types of films and explain each of them. What are the advantages and disadvantages of each film type?

A

Black and white IR – film that is sensitive to visible, UV and Infrared energy

Colour IR – Advantage to colour film is that the human eye can discriminate more shades of colour than grey

Black and White Panchromatic – film that is sensitive to all wavelengths of visible and UV light

64
Q

List three types of filters used in aerial photography

A

Absorption filters – i.e. yellow absorption filters absorb blue and transmit green and red which combine so yellow is all one can see through the filter. This reduces atmospheric haze in aerial photos. Such filters may be used to block/absorb the visible spectrum creating an image of the IR spectrum distinguishing fake turf from real grass despite both look green.

Antivignetting filters improve uniformity of exposure Colour compensating filter – used on aged film to compensating if the IR layer of the film loses sensitivity faster than the other layers.

65
Q

What are the three types of aerial cameras?

A

Single-lens frame cameras – Most used, low distortion, high image quality

Panoramic cameras – Camera views through a narrow slit and ‘scans’ an area. Greater detail than frame cameras, cover a large area but geometrically distorted

Digital cameras – record data with sensors (i.e. CCD) rather than film. Images are available immediately, can be uploaded onto a computer without scanning, can be copied indefinitely without losing image quality, memory devices can be erased and reused, positional data with GPS can be recorded along with image data,

66
Q

What is the difference between vertical and oblique photography?

A

Oblique photography: An aerial photograph taken with the axis of the camera held at an angle between the horizontal plane and the vertical plane perpendicular to the ground. A low oblique image shows only the surface of the earth; a high oblique image includes the horizon.
Vertical photography: An aerial photograph taken with the camera lens pointed straight down.

67
Q

If a 1 km stretch of highway covers 4 cm on an air photo, what is the scale of the photo?

A

If 1km = 4cm, Scale is 1cm = 250m, 1/25,000 or 1:25,000

68
Q

If a camera’s focal length length is 152mm, and the plane’s altitude Above Ground Level (AGL) is 7600m what is the scale of a photo?

A

Scale = (Camera Focal length)/(flying height abover terrain) 152mm/7,600,000mm, scale is 1:50,000

69
Q

What is the difference between a small scale versus a large scale photo?

A

Small scale 1:50,000 vs. Large scale 1:1000. Large scale shows ground features larger and thus is the smaller ratio. In small scale images a larger area is covered in smaller detail

70
Q

What can aerial photography be used for in environment assessments?

A

Aerial photography can be used for agricultural problems, forest and rangeland monitoring, watershed management, wildlife monitoring, natural resource planning, production statistics, biodiversity and climate change assessment, environmental impact assessment, emergency response planning, landfill monitoring, permitting and enforcement, and natural disaster mitigation.

71
Q

Choose an application of aerial photography and describe it.

A

Forestry Application of Aerial Images
Forestry is concerned of the management of forests for wood, water, wildlife, and recreation. Visual image interpretation can be used to identify tree species, study harvested areas, timber cruising and forest damage assessments.
Timbered areas are easily seen on satellite images with dark areas denoting trees, light areas showing stumps and grass and mottled areas showing the forest at an intermediate regrowth stage.
Timber cruising involves analyzing a tree or stand of trees to determine the volume of timber that might be harvested. Highly skilled interpreters are needed to measure tree-crown diameter, height, and volume etc. of an area.
Tree damage and disease can be detected from med-large scale images. Fungal, viral and bacterial infections, air pollution (smog, sulfur dioxide) animal damage (beavers, deer), fire, frost, moisture stress, soil salinity, storms, nutrient imbalance etc.
Other applications include forest land appraisal, monitoring logging and reforestation, planning and assessing the application of herbicides or fertilizers, assessing plant health in forest nurseries, mapping “forest fuels” to assess for fire potential, planning fire suppression activities, assessing potential slope failure and soil erosion, forest roads, monitoring re-growth in fire lanes and inventorying forest recreation resources.
Success in these applications relies on high quality reference data to aid in interpretation, as well as the collaborative use of aerial, satellite and conventional ground methods of observation.

72
Q

Suppose a city bus in an aerial photography is 3 cm and you know a bus is 20m in length in real life, what is the scale what is the scale of the photograph? If you measure the width

A

Scale of photo: 2000cm/3cm then 1cm = 6.67m, 1:667
Width = 0.5cm x 6.67m/cm = 3.335m Area = (3.335m)(20m) = 66.7m2

73
Q

A camera equipped with a 156-mm-focal-length lens is used to take a vertical photograph from a flying height of 3780m above mean sea level. If the terrain is flat and located at an elevation of 1500m, what is the scale of the photograph?

A

Scale = 0.156m/(3780m-1500m) = 1:14,615

74
Q

For the photo shown in the figure, assume that the relief displacement for the tower “d” is 3.01mm, and the radial distance from the center of the photo on top of the tower is “r” is 59.43mm. If the flying hright “H” is 1550m above the base of the tower, what is the height of the tower?

A

d = rh/H

d = relief displacement
r = radical distance
h = height above datum
H = flying height above datum

d = 3.01mm
r = 59.43mm
H = 1550000mm
h = ?

h = dH/r = (3.01mm x 1550m)/59.43mm = 78.5m

75
Q

Describe what a GCP is. What are the standards in determining one?

A 
#26 GCP= Ground Control Points
 They are points as road interception, building, corner of a lake; it depends on the spatial resolution of the image.
76
Q

What are the three techniques used to enhance images? Describe

A

3 techniques
• Contrast Manipulation (grey-level thresholding, level slicing, and contrast Stretching)
• Spatial Features Manipulation (spatial filtering, edge enhancement, and Fourier analysts)
• Multi-image manipulation (vegetation components, intensity hue-saturation (HIS)

77
Q

What is Digital Image Processing?

A

Digital Image Processing is a collection of computerized techniques for manipulation digital image for information extraction

78
Q

What are the major steps of Digital Image Processing?

A

1. Pre-Processing:
a. Image Rectification
b. Image Restoration
c. Image Calibration/ or noise removal
2. Processing and Analyzing
a. Image enhancement
b. Image Classification
3. Post-Processing
a. Data Merging and GIS integration
b. Biophysical Modeling
c. Image transition and compression
4. Presentation

-Map, Table, Report

79
Q

What are the sources of distortions in an image?

A

Sources, Altitude, Attitude, velocity of the sensor platform, earth curvature, relief displacement, atmospheric refraction.

80
Q

What are the steps in geometric correction using GCP’s??

A

–Collection of well distributed ground control point.

  • Transformation equation.
  • Correction of GCP’s location based on RMS error.
  • Selection of a suitable resampling technique.
  • Evaluation of accuracy.
81
Q
A

Remote Sensing (1 decks)

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