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Basics Flashcards

1
Q

What is remote sensing

A

Using remote observations to make inferences about the state of an object

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2
Q

Why is it remote?

A

Sensors are not in direct physical contact with objects being measured

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3
Q

What is earth observation

A

Remote sensing when the object are the Earth’s varied environments

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4
Q

Who took the first aerial photo and when was it taken?

A

Daguerre and Niepce in 1826

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5
Q

When was photograph first used for topographic mapping

A

1840

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6
Q

First use of balloon to make photographs of large areas

A

1858

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7
Q

First aerial photograph from Airplane

A

1909 over Italy

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8
Q

When was radar for ship detection developed

A

1900 - 1925

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9
Q

When was First color and IR photography taken?

A

Mid 1930s

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10
Q

When was high resolution radar system (SAR) developped?

A

Mid 1950s

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11
Q

Date of early experiments of classification of vegetation types

A

1956

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12
Q

When were multispectral imagers first developped?

A

1960s

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13
Q

When did the CIA’s Corona satellite program begin?

A

1960

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14
Q

When was the first Landsat satellite launched?

A

1972

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15
Q

When was the first civilian SAR satellite launched?

A

1978

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16
Q

List 5 reasons to use remote sensing.

A
  1. Ease of access, 2.Archiving,
  2. global observation,
  3. repeatability
  4. calibrated observation
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17
Q

List 3 fundamentals of an RS system

A
  1. A sensor.
  2. A measurable signal / source.
  3. An interaction with the target object.
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18
Q

List 4 examples of measurable signals.

A
  1. Electromagnetic radiation
  2. Acoustic waves
  3. Gravity field
  4. Magnetic field
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19
Q

What is another term used for electromagnetic radiation?

A

Light

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20
Q

What can determine the spacing distance from your target object?

A

Field of view

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21
Q

Give an example of a hand held platform

A

Ground penetrative radar

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22
Q

Which is further from the surface of the earth, CubeSat, ISS or GPS satellites?

A

GPS

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23
Q

Whit is Electromagnetic Radiation (physics)

A

Time varying oscillating electric and magnetic fields. They mutually induce each other so that they propagate through space from one location to another

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24
Q

Equation for frequency

A

F=Speed of light/ wavelength

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25
Q

Wavenumber equation

A

1/wavelength (also frequency/ speed of light)

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26
Q

Speed of light

A

2.998 * 10^8 m/s

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27
Q

Do wavelengths vary across a spectrum?

A

Yes, of course..

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28
Q

Electric field interacts strongly with matter, what 4 factors influence this?

A

Size of particle and wavelength.
Also atomic and molecular fabric.

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29
Q

Does EM more energy?

A

Yes

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30
Q

Do radio waver penetrate the earth atmosphere?

A

yes

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31
Q

Do microwaves penetrate the earth atmosphere?

A

No

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32
Q

Do infrared waves penetrate the earth atmosphere?

A

No

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33
Q

Do visible wavelengths penetrate the earth atmosphere?

A

Yes

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34
Q

Do ultraviolet waves penetrate the earth atmosphere?

A

No

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35
Q

Do W-rays penetrate the earth atmosphere?

A

No

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36
Q

Do Gamma rays penetrate the earth atmosphere?

A

No

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37
Q

Is light a wave or a particle?

A

Both! It exhibits typical wave properties (interference patterns, Doppler effect..)
It is also a particle travelling in straight lines between interactions

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38
Q

What is passive sensing?

A

Senses a naturally occurring signal

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39
Q

What is active sensing?

A

Generating its own signal.

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40
Q

What is spectral radiant emittance?

A

energy

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41
Q

What is black body radiation?

A

reasearch¨***

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42
Q

What kind of radiation do we emit?

A

Thermal Infrared

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43
Q

What does the sun emit?

A

Visible radiation

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44
Q

What process affects radiation as it crosses the atmosphere?

A

Absorption

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45
Q

What is used to measure the earth’s surface temperature?

A

Atmospheric Infrared Sounder (AIRS) on the NASA Aqua satellite

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46
Q

What wavelength do the earth’s emissions peak at?

A

In the thermal infrared

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47
Q

What wavelength do the sun’s emissions peak at?

A

Visible

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48
Q

Give 2 examples of active sensors

A
  1. GPS
  2. Radar altimeter satellite
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49
Q

How can you strip back a tree layer using Lidar?

A

By observing the change in signal

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50
Q

List 8 measurable quantities in light.

A

Energy, intensity, back-scatter, amplitude, radiance, time, phase and polarisation

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51
Q

What is the equation for the energy of a photon

A

E=h*f

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52
Q

in E=h*f, what is h?

A

h is Plank’s constant

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53
Q

What is power and its equation

A

Power = E/t, the amount of energy per unit of time
(unit of power is a watt)

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54
Q

What is the unit for a watt

A

Joules per second

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55
Q

What is irradiance?

A

power of radiation on one side of a surface per unit area (Irradiance = Power/ Unit area)

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56
Q

List 3 trajectories of radiation

A
  1. upwelling/ surface leaving
  2. downwelling/ Incident
  3. total solar
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57
Q

What is the radiance equation?

A

Radiance = (energy / (second * area * angle))

58
Q

What is the Emmittance equation

A

E = W/m^2

59
Q

What is trilateration?

A

It’s when you use three GPS satellites (GPS/ GALILEO/ GLONASS) to provide the specific location of something.

60
Q

WHat technique is used to make DEMs

A

Altimetry

61
Q

What did the Shuttle Radar Topography Mission (SRTM) do?

A

Synthetic Aperture Radar Interferometry (InSAR)
I think … double check this.

62
Q

What is DInSAR

A

Differential Synthetic
Aperture Radar
Interferometry

(maps earthquakes)

63
Q

What is polarisation?

A

Research this

64
Q

What is radar cross polarisation?

A

Transmit radar horizontally and receive vertically (and vice versa)
It weakens the returning signal.

65
Q

What does HV cross polarsation radar help detect

A

targets on the water surface

66
Q

What can Radar cross polarisation help differentiate in agriculture?

A

grain crops from broad leaf crops

67
Q

what wavelengths does passive remote sensing focus on?

A

Visible, Near Infra Red, Short Wave Infra Red

68
Q

What wavelengths does visible fall between?

A

390 - 700 nm

69
Q

What wavelengths does NIR fall between?

A

700 - 1000nm

70
Q

What wavelengths does SWIR fall between?

A

1000 - 2500nm

71
Q

What are the three object interactions with the EM spectrum?

A
  1. Reflected
  2. Absorbed
  3. Transmitted
72
Q

What are the 3 methods you can use to measure energy reflected from a surface?

A
  1. Spectroradiometer
  2. multispectral imager
  3. hyperspectral imager
73
Q

What is the red edge?

A

It’s the wavelength where there is a lot of absorption in vegetation (700 nm)

74
Q

what is spectral resolution?

A

It’s the instrument’s resolution

75
Q

List the 5 pros of hyperspectral imaging

A
  1. higher res leads to better characterisation/ classification
  2. detects features too small to be detected by multispectral
  3. Uses alternative techniques for data anaylises (beyond spectral ratio)
  4. Use of radiative transfer models can help us better understand high spectral resolution
    from earth surface objects and develop improved techniques for analysis
  5. Pushes us away from traditional approaches, E.g. image analysis – limitations in 3-band
    colour display
76
Q

List the main pro of multipsectral imaging

A

it’s cheaper than hyperspectral

77
Q

List 4 cons of multipsectral imaging.

A
  1. loss of potentially useful info
  2. crude spectral characterization of the reflectance properties of earth surface objects
    using multispectral approaches
  3. Doesn’t allow us to better define something about the object of interest
  4. can limit classification
78
Q

What effects can the atmosphere have on energy?

A

Aerosols absorb energy at different wavelengths

79
Q

What are the 4 main EO applications for forests?

A
  1. Resource management
  2. Protection/ prosecution
  3. disaster management/ recovery
  4. Climate science
80
Q

3 main challenges in EO being used to monitor forests

A
  1. Highly dynamic (seasonal)
  2. Complex (3D, different types)
  3. Remote and large
81
Q

What is a Vegetation Index (VI)?

A

A spectral transformation of two or more bands

82
Q

Why are Vegetation Indexes used?

A

They enhance the contribution of vegetation properties and allow reliable
spatial and temporal inter-comparisons of terrestrial
photosynthetic activity and canopy structural variations.

83
Q

NDVI equation

A

NDVI = (NIR – Red) / (NIR + Red)

84
Q

Narrow-band ratio approach

A
  1. A form of data reduction
  2. Use the data to select narrow-bands in apparent features of interest
  3. Use these as the basis of indices (e.g. ratios) to correlate against (bio)physical
    parameters
  4. Can use a correlation matrix approach to test every possible ratio
85
Q

Smoothing

A

Mathematical functions applied to VI time series data… revise this

86
Q

List types of matter which emit EM

A

Gases, clouds, dust and molecules, solid/ liquid surfaces (all matter emits thermal radiation

87
Q

What is Wien’s law?

A

The Wien’s displacement law states that the wavelength at which the blackbody emission spectrum is most intense varies inversely with the blackbody’s temperature.

88
Q

Describe what this equation is saying λm = 2897 / T

A

λm is the wavelength at which the peak emissions intensity occurs, T is temperature of the blackbody

89
Q

What is an easy way to remember Wien’s law?

A

the hotter the object the shorter the wavelengths of the maximum intensity emitted

90
Q

What is emissivity?

A

the ratio of energy radiated to that of a perfect emitter (blackbody)

91
Q

What is the emissivity scale?

A

0-1

92
Q

What is the IR emissivity of ground and water bodies?

A

0.9 - 0.99

93
Q

What is the IR emissivity of gases, aerosols and clouds?

A

0.0 - 1.0 (it depends on the optical path)

94
Q

What is the Microwave emissivity of land surfaces?

A

~0.9

95
Q

What is the Microwave emissivity of the ocean?

A

~0.5 (depends of wavelength and sea state)

96
Q

What are the two main influences of emissivity?

A

wavelength and geometry

97
Q

What is brightness temperature?

A

the temperature an object would need to bee for the radiance from it to match the actual radiance observed

98
Q

What is Kirchhoff’s law?

A

efficient absorbers are efficient emitters. The emissivity is proportional with the asborption

99
Q

I f a surface absorbs 80% of the spectral radiance incident on it, what is its emissivity?

A

0.8

100
Q

what is transmission

A

allowing to pass through

101
Q

Give an example of a large transmitting medium

A

the atmosphere

102
Q

What is transmittance

A

the fraction transmitted

103
Q

List 5 types of reflection

A

Specular, quasi-specular, lambertian, quasi lambertian, complex

104
Q

What does a perfectly rough surface do to the angle of reflection?

A

it destroys any memory of the angle of incident radiance. The outgoing radiance is the same from any viewpoint. It is known as isotropic reflected radiance or lambertian

105
Q

Give an example of a lambertian surface

A

paper, snow

106
Q

What kind of reflection is there on real surfaces?

A

it is somewhere betwee specular and lambertian

107
Q

What can affect the amount of reflection you receive

A

The viewing angle and the incidence angle

108
Q

How do rough surfaces appear in SAR imagery?

A

It appears bright because the microwave energy is reflected to the satellite

109
Q

How do smooth surfaces appear in SAR imagery?

A

dark because the microwave energy is reflected away from the satellite

110
Q

What is a benefit of SAR satellites

A

they can operate at night

111
Q

Give two common uses of SAR satellites

A

Monitoring ships and oil spills

112
Q

What is diffuse or hemispheric reflectivity?

A

It is the average reflectivity over all possible incidence angles

113
Q

What are spectral signatures?

A

The trajectory of the line across the spectrum or the individual spectral response of the target

114
Q

What does scattering do?

A

It changes the direction of radiation without absorbing its energy. this attenuates the direct beam and introduces diffuse illumination

115
Q

What are the two measures of scattering?

A

The amount of scattering and the angular distribution of the scattered radiance

116
Q

What scatters in the atmosphere?

A

molecules (Rayleigh scattering), aerosols and water droplets

117
Q

Why is the sky blue?

A

It is blue because shorter wavelengths scatter more than longer ones

118
Q

What colour is chlorophyll bloom?

A

in Green

119
Q

What is the instantaneous field of view?

A

it represents the ground area or angle, viewed by the sensor at a given instant in time

120
Q

What does the instantaneous field of view determine?

A

It determines the spatial resolution (setting the lower limit fro the level of spatial detail that can be represented in a digital image)

121
Q

What are the two values of of instantaneous field of view?

A

along-track and across-track

122
Q

pixel size is not resolution

A
123
Q

Look into Advanced Very High Resolution Radiometer pixel geometries

A
124
Q

What is nadir?

A
125
Q

Radiometric resolution

A

where each grid cell contains a single number

126
Q

How many possible values does a 6 bit image have?

A

2^6

n bit image has 2^n values

127
Q

What is a digital number

A

the number a grid cell contains

128
Q

what is the radiance equation including digital number (DN)

A

radiance = gain*DN+bias

129
Q

What is orbital period?

A

the time it takes for a satellite to circle the earth

130
Q

What are the three types of satellite orbit?

A

geostationary, geosynchronous, sun-synchronous

131
Q

What is a geostationary orbit?
And what is its use and spatial coverage

A

same location above Earth, used for weather and telecommunication, limited spatial coverage (25/30% of the earth’s surface), mid-latitude only (<55°)

132
Q

What is a geosynchronous orbit?
And what is its use and spatial coverage

A

same rotation period as the earth

133
Q

What is a sun-synchronous orbit?
And what is its use and spatial coverage

A

passes every location at same time - ensures illumination, global coverage, polar orbit (most EO satellites are geosynchronous)

134
Q

What influences the temporal resolution

A

swath width and orbit type

135
Q

what is a common tradeoff in terms of resolution

A

spatial, spectral and temporal resolutions, can’t have it all yet (tech developments and decrease of costs decrease the need for trade offs)

136
Q

What is the landsat repeat period

A

16 days

137
Q

What are the benefits of the Tropical Rainfall Measuring Mission?

A

Has a low inclinaison (35°) and a larger swath, making it useful for following weather patterns.

138
Q

Landsat 7 bands

A

Band 1 - deep blues and violets
Band 2-3-4 visible blue green and red
band 5 - NIR
Band 6-7 - SWIR
Band 8 - panchromatic layer
Band 9 - almost all energy absorbed by atmosphere
Band 10 - 11 - thermal IR (TIR)

139
Q

natural composite image numbers

A

4 - 3 - 2

140
Q

false colour composite

A

543 (NIR, R, G)

141
Q

WHat band highlights fire?

A

Band 6
composite 653

142
Q
A

PPRS (8 decks)

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