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Digital Mapping > Lecture 5: Remote Sensing > Flashcards

Lecture 5: Remote Sensing Flashcards

1
Q

What is remote sensing?

A

The measurement of physical, chemical, and biological properties of objects without direct contact

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2
Q

What does remote sensing measure?

A

the amount of electromagnetic radiation reflected, emitted, or scattered from objects

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3
Q

What is Electromagnetic Radiation (EMR)?

A
  • A form of energy
  • Wave-like behavior as it travels through space
  • Travels at speed of light
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4
Q

What is a wavelength?

A

The length of one wave cycle

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5
Q

What is frequency?

A

number of cycles of a wave passing a fixed point per unit of time, normally measured in hertz (Hz) equivalent to one cycle per second.

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6
Q

What is visible light?

A

The light, which our eyes can detect.

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7
Q

What is the range of visible light?

A

0.4 to 0.7μm (longest wavelength = red, shortest = violet)

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8
Q

What is the range of Infrared (IR) light (wavelength)?

A

0.7 to 100 μm

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9
Q

Range of Thermal IR?

A

3.0 to 100 μm

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10
Q

What is Thermal IR?

A

EMR that is emitted from the Earth’s surface in the form of heat (Temperature of object)

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11
Q

What is Infrared (IR)?

A

Solar-generated EMR that has been reflected from an object

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12
Q

Particles and gases in the atmosphere cause radiation to do what?

A

Scatter

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13
Q

What are the 3 types of scattering?

A

Rayleigh scattering
Mie scattering
Non-selective scattering

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14
Q

What is Rayleigh Scattering?

A

Occurs when particles are very small compared to the wavelength of the radiation (air molecules)
Causes shorter wavelengths of energy to be scattered much more than longer wavelengths

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15
Q

Why is the sky blue?

A

shorter blue wavelength are scattered more than longer visible wavelengths.

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16
Q

Why is sunset/sunrise red?

A

Radiation travels further through atmosphere at dawn/dusk leaving more of the longer red wavelengths to penetrate the atmosphere

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17
Q

What is Mie Scattering?

A

Occurs when the particles are just about the same size as the wavelength of the radiation (pollutants, brownish smog phenomena)

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18
Q

What does mie scattering affect?

A

longer wavelengths than those affected by Rayleigh scattering

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19
Q

When does Mie Scattering Occur?

A

lower portions of the atmosphere where large particles are more abundant, dominates when cloud are overcast

20
Q

What is non selective scattering?

A

when the particles are much larger than the wavelength of the radiation (water droplets, large dust particles)

21
Q

What does non-selective Scattering cause?

A

fog and clouds to appear white to our eyes because blue, green, and red light are all scattered in approximately equal quantities (blue + green + red light = white light)

22
Q

What is absorption?

A

Causes molecules in the atmosphere to absorb energy at various wavelengths

23
Q

What is transmission?

A

Radiation passes through a target

24
Q

What is reflection?

A

Radiation bounces off the target and is redirected

25
Q

What is a sensor?

A

measure and record energy reflected or emitted from a target, must be on stable platform

26
Q

What happens to radiation that is not absorbed or scattered in the atmosphere?

A

It can reach and interact with the Earth’s surface

27
Q

What is passive remote sensing?

A

Measure energy that is naturally available(e.g. Reflected sun’s energy as it is for visible wavelengths)

28
Q

What is active remote sensing?

A
  • Provides its own energy source for illumination
  • Measures energy that is emitted from a device and reflected from a target
  • Can use wavelengths not provided by the sun(e.g. microwaves/ requires power for energy)
29
Q

Name some platforms for sensors

A

Ground based platforms
Aerial platforms(airplane, etc.)
Platforms in space

30
Q

What is a geostationary orbit?

A
  • Satellite revolves at speeds that match the rotation of the Earth
  • View the same part of Earth at all times
  • Weather/communications satellites are usually geostationary
31
Q

What is a near polar orbit?

A
  • Satellite follows lines running between the North and South poles
  • Allow satellites to cover most of Earth’s surface over a certain period of time
  • Most remote sensing satellites are in near-polar orbits
32
Q

What is a swath?

A

area covered by the satellite on the surface of the Earth

33
Q

What is spacial resolution?

A

“higher resolution“ or “sharper“ image

34
Q

What are the four types of Resolution in Remote Sensing?

A

Spatial
Spectral
Radiometric
Temporal

35
Q

What is spacial resolution?

A

The size of the smallest possible feature that can be detected, limited by pixel size(smallest object cannot be smaller than a pixel)

36
Q

What does higher spacial resolution do?

A

see smaller objects

37
Q

What is Spectral resolution?

A
  • ability of a sensor to define small electromagnetic wavelength intervals
  • intervals are called bands or channels
  • higher the spectral resolution, the narrower the wavelength range for a particular band
    Blue + Green + Red= Black and white
    Blue|Green|Red = in color
38
Q

What is Radiometric Resolution?

A

Sensor sensitivity to the magnitude of the electromagnetic energy
- The higher the radiometric resolution of a sensor, the more sensitive it is to detecting small differences in reflected/emitted energy

39
Q

What is Temporal Resolution?

A
  • How often we capture an image of the same place on earth

- Higher temporal resolution -> more frequent images of the same place

40
Q

What is a revisit period?

A

the length of time it takes for a satellite to complete one entire orbit cycle

41
Q

How is Electromagnetic energy detected photographically?

A

uses chemical reactions on the surface of light-sensitive film to detect/ record energy variations

42
Q

How is Electromagnetic energy detected electronically?

A
  • Any pictorial representation that records the electromagnetic energy
  • Most images are now captured using electronic sensors -> digital images
43
Q

Name some Remote sensing systems

A
  • Geostationary Operational Environmental Satellite(GOES)
  • Landsat
  • Digital Globe
44
Q

Analysis of remote sensing imagery involves what?

A

The identification of various features/ phenomena

defined in terms of the way they reflect/emit radiation

45
Q

What is the simplest form of remote sensing imagery analysis?

A

Visual interpretation

46
Q

Name the Elements of Visual interpretation

A 
Shape
Tone/Color
Size
Texture
Pattern
Shadow

Digital Mapping (5 decks)

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