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Remote Sensing Final > Final > Flashcards

Final Flashcards

1
Q

Electromagnetic Energy - Properties

A

1) Wavelength
2) Amplitude
3) Phase
4) Frequency

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2
Q

Radiant Energy

A 
Q = h * v
Q = Radiant Energy
h = Planck's constant
v = Frequency
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3
Q

Radiant Flux

A

Rate of transfer of the energy

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4
Q

Radiant Flux Density

A

The amount of energy entering or leaving an object

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5
Q

Blackbody

A

A hypothetical entity that absorbs all radiation

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6
Q

Kirchhoff’s Law

A

For blackbodies the emissivity = absorption = 1
Perfect reflection emissivity = 0

e= emissivity = M/ Mb
where:
• M = emitted radiation of the real object
• Mb= emitted radiation of the blackbody @the same temperature of the real object

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7
Q

Stefan-Boltzmann Law – emitted radiation

A

Mb = sT^4

Mb = Total emitted radiation in Watts/m2 (a radiant flux density)
s= Stefan-Boltzmann constant (5.67 10-8 W/m2/K4)
T = Absolute body temperature [K]
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8
Q

Wien’s Displacement Law - Peak of Exitance

A

lmax= 2898/T

lmax= wavelength
T = Absolute body temperature [K]
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9
Q

Kirchhoff + Stefan-Boltzmann

A

For real material we use the concept of emissivity (e) to the blackbody law in order
to relate the actual radiance of a real body (greybody) at temperature T

M = esT4
M = Total emitted radiation in Watts/m2 (a radiant flux density)
s= Stefan-Boltzmann constant (5.67 10-8 W/m2/K4)
T = Absolute body temperature [K]
e= emissivity
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10
Q

Brightness Temperature

A

The temperature of the equivalent blackbody that would give the same radiance at the wavelength under consideration

Typically used in thermal and passive microwave RS

For sufficient long wavelengths Tb~eT

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11
Q

Infrared

A 
Near Infrared (NIR) 0.7-1.3 μm
Mid Infrared (MIR) 1.3-7.0 μm
Far Infrared (TIR) 7-1000 μm
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12
Q

NIR

A

Sensitive to plant’s health
Similar to VIS
Essentially solar radiation reflected from the earth’s surface

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13
Q

Mid Infrared/SWIR

A

Soil moisture applications and veg water content
Detecting plant stress and burnt area
Can detect active fires

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14
Q

Far Infrared/LWIR

A

Thermal Infrared

surface temperature, evapotranspiration, heat fluxes, etc.

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15
Q

Interaction of EM Radiation

A

Absorbed
Transmitted
Reflected

“Conservation of Energy”

Sum to 1

Divide by the incident to = the proportion of 1

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16
Q

Scattering

A

Depends on Wavelength, Size Particles, # of Particles, Depth of the Atmosphere

Function of: radiation wavelength, particle size

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17
Q

Rayleigh Scattering

A

-When the molecule diameter is smaller
than the wavelength
- Primarily caused by 02 and N2
- Scattering happens through absorption and re-emission
- Responsible for blue skies and red sunsets

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18
Q

Mie Scattering

A
  • Caused by larger particles with diameters approximately equal to the radiation wavelength EX. water vapor, dust, smoke
  • Causes pretty sunsets
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19
Q

Absorption

A

When the atmosphere absorbs radiation

Caused by: Ozone and oxygen <300nm
Carbon dioxide 13-17.5 um (MIR & TIR)
Water vapor 5.5-7um and 27um

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20
Q

Reflection

A

Product of: surface roughness, # of leaves, geometry of incident, viewing angle

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21
Q

Specular Reflection

A

When an object is smooth all (or almost all) of the radiation is reflected in one direction

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22
Q

Diffuse Reflection

A

Also called Lambertian

When a surface is rough energy is reflected in every direction

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23
Q

Bidirectional Reflectance Distribution Function (BRDF)

A

Ratio of reflected radiance to the incident irradiance of a flat surface

Describes the optical behavior of a surface with respect to angles of illumination and observation -> Hence BIdirectional (and wavelength)

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24
Q

Volume Scattering

A

Scattering occurring within the medium as the EMR transmits from one medium to another

EX inside of snow, between the snow particles

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25
Q

Albedo

A

The directional integration of reflectance over ALL sun and view angles and sun spectrum (VIS and NIR)

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26
Q

Atmospheric Correction

A

Converts measurements from description of earth-atmosphere system to of the earth’s surface

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27
Q

Dark Pixel Method

A

Minimum Digital Number value is assumed to be atmospheric distortion and subtracted from all pixels

Atmospheric Profile - Other method of Atmospheric Correction

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28
Q

Spectral Reflectance: Vegetation

A
  • Low reflectance in VIS due to chlorophyll absorption
  • depends on plant health, greater jump healthier plant
  • High reflectance in NIR due to leaf scattering
  • Lower reflectance in NIR w/ dips due to water absorption
  • Changes because of health, physiology, and structure
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29
Q

Vegetation Indices

A
  • The Red Edge is foundational

- Measure “greenness”

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30
Q

Simple Ratio Index

A

NIR/Red

Larger value = healthier veg (no upper bound)

Smaller value = Not veg

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31
Q

NDVI

A

(NIR-Red)/(NIR+Red)

-1 to 1
1 = Healthy veg
-1 = water
<0.1 = Not veg

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32
Q

NBR

dNBR

A

(NIR-SWIR)/(NIR+SWIR)

PrefireNBR-PostfireNBR

-Sensitive to water, high severity pixels may be water, mask water before

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33
Q

Enhanced Vegetation Index (EVI)

A

Stabilizes aerosol influence on NDVI

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34
Q

Spectral Reflectance: Water

A

Low Reflectance in VIS, drops off in NIR and SWIR

Distribution of reflectance can be used to infer water contents

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35
Q

Normalized Difference Water Content

A

2 Types: (NIR-SWIR)/(NIR+SWIR) - for veg in drought conditions
-1 to 0 = bright surface w/ no water
1 = water!
(green-nir)/(green+nir) - for flood water/level changes
<0.3 = No water

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36
Q

Spectral Reflectance: Snow

A
  • Tough to distinguish from clouds -> different signatures in MIR -> cloud reflectance(x) of cloud type
  • High in VIS, decreases in NIR, dark on SWIR
  • Varies with grain size -> volumetric scattering
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37
Q

Normalized Differenced Snow Index

A

(R550-R1640)/(R550+R1640)

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38
Q

Spectroscopy

A

The study of how radiated energy and matter interact

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39
Q

Spectrometry

A

Deals with the measurement of a specific spectrum

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40
Q

All materials reflect, absorb or emit photons in ways characteristic of their
molecular makeup

A
41
Q

Multispectral Imagers

A
  • Record incoming reflected or emitted EMR at a few wide and separated wavelengths
  • Typical band width is 100s of nm
  • Discrete bands
42
Q

Hyperspectral Imagers

A
  • Records EMR at a series of very narrow and contiguous bands
  • band width is typically 10s of nm
  • Continuous spectrum
43
Q

Data Cube

A

-How hyperspectral data is presented
Compiled from hyperspectral data, when a spectrometer collected bands as narrow as 1nm to create an image with as many bands as acquired channels

44
Q

Hyperspectral data

A
  • Typically very noisy
  • Bands are averaged to limit noise
  • Wider wavelength ranges increase SNR
45
Q

Digital Image

A

2-D array of pixels

-Each pixel has an intensity value and location address from its row and column reference

46
Q

Digital Number

A

Represents a physical quantity such as solar reflectance in a pixel

  • Pixel values are coded as Digital Numbers of Brightness Values
  • Stored with binary digits that must be converted to real numbers
47
Q

Natural Color Model

A

Pros: It’s what our eyes would see
Cons: Blue region subject to atmospheric scattering, Instruments collect radiation across the spectrum

48
Q

False Color Images

A

Cons: They look fucked up and weird
Pros: Can see things invisible to our eyes normally

49
Q

Color Infrared Image

A

Shows living vegetation and water bodies very clearly

50
Q

Landsat

A
  • 30m Spatial Res
  • 16 Day Temporal Res
  • Operational Land Imager, ETM+, Thermal IR Sensor
  • 8 has 9 bands
51
Q

MODIS

A
  • 250m-1 k spatial
  • aqua and terra orbit every day
  • 36 bands
  • Moderate Resolution Imaging Spectroradiometer
52
Q

AVHRR

A
  • 1km spatial
  • 4 satellites, 16 images a day
  • 6 bands
  • cloud and surface, land water boundaries, snow and ice, night cloud mapping
  • Advanced Very High Resolution Radiometer
53
Q

ASTER

A
  • Dead satellite (02-09)
  • 15 to 90m spatial
  • surface temperature, emissivity, reflectance, and elevation
54
Q

VIIRS

A
  • Visible Infrared Imaging Radiometer Suite
  • 1km spatial resolution
  • daily or bidaily temp res
  • Many bands
55
Q

Hyperspectral Sensors

A

Mostly airborne

Very few satellites

55
Q

Hyperspectral Sensors

A

Mostly airborne

Very few satellites

56
Q

Hyperspectral Sensors

A

Mostly airborne

Very few satellites

57
Q

Hyperion

A

Hyperspectral spaceborne sensor
Dead Sensor (00-17)
30m spatial, 242 bands

58
Q

Spectral Mixing

A
  • Assumes linear mixing of various fractional land covers to form the actual measured reflectance
  • Finds the best fitting surface fractions of endmembers
59
Q

LiDAR Distance Formula

A

Distance = (t*c)/2

t = elapsed time
c = speed of light
60
Q

Characteristics of emitted and returned LiDAR pulses

A

timing of pulses, wavelength, and angles

61
Q

Key Elements of Airborne LiDAR

A

1) GPS Unit
2) Inertial Measurement Units (position of aircraft)
3) Infrared or Green laser
4) Ground Control Points

62
Q

LiDAR Observations

A

Range Distance and Intensity (fraction of photon returned)

63
Q

LiDAR Return Types

A

Primary Returns - from the first object a pulse contacts

Secondary Returns - from the portion of a pulse that passes through a porous surface (tree canopy), 5 max

64
Q

LiDAR: Waveform Return

A
  • records the power of the pulse received as a function of time
  • Can show more info than discrete returns
  • Typically have larger footprints
65
Q

Processing LiDAR Data

A

Gathered as a zigzag

Must be resampled, gridded, and single shots are interpolated

66
Q

LiDAR Applications

A

Mapping aboveground biomass
Forest heights
Power line mapping

67
Q

Thermal Region Wavelengths

A

3.5-20um, typically 8-13um
Emitted, not reflected
3-5um lots of absorption in CO2
8-13um very little absorption in Ozone

68
Q

Thermal RS Theory

A
  • All objects above 0K emit radiation
  • Intensity and spectral composition depends on the material and its temperature
  • Observed radiance is a function of actual temperature and emissivity
  • Little atmospheric scattering
  • Some restrictions due to atmospheric absorption
69
Q

Emissivity

A

Dependent on:
Physical properties of surface: water content, density, color, roughness, compaction
-wavelength, surface temperature, and angle of observation
-Polarization dependent

70
Q

Brightness Temperature

A

The temperature of the equivalent blackbody that would give the same radiance at the wavelength under consideration

  • Always lower than absolute temperature
  • If emissivity of an object is know, then absolute temp can be derived from the radiation an object emits
  • If emissivity is not known, then only brightness temp can be known
71
Q

Thermal Inertia

A

Determined by thermal conductivity, thermal diffusivity, and thermal capacity
-Objects with higher inertia will have a smaller diurnal range in temperature

72
Q

Thermal RS: Example Sensors

A

GOES
Landsat 8
AVHRR
Ecostress

73
Q

Thermal RS: Applications

A

Soil moisture, land surface temp, mineral mapping, ET, forest fires, Sea Surface Temperature, cloud structure

74
Q

Microwave EM Spectrum Region

A 
1mm-1m
W band (3mm) to P band (75cm)
75
Q

Weather Radar Microwave

A

Use K band or S band

76
Q

GPS Microwave

A

L-band

77
Q

Soil Moisture

A

L band

78
Q

Penetration Depth Of Microwaves

A

X band, C band, L band (Deepest penetration)

79
Q

Polarization

A

Horizontal and vertical plane of EMR

80
Q

Passive Microwave RS

A

Focuses on detecting and monitoring emissivity and temperature changes
Radiometer
Energy is very low so footprint must be very large

81
Q

Active Microwave RS

A

Detects and monitors changes in reflectivity and backscatter

Radar

82
Q

Dielectric Constant

A

water content, has an inverse relationship with emissivity

83
Q

3 Dominant Source of Microwave Radiation

A

1) Earth’s Surface
2) Atmosphere
3) Extraterrestrial

84
Q

Rayleigh Jean’s Expression

A
  • Substitutes for Plank’s function at higher wavelengths
  • Integration over microwave region shows a linear relationship with temperature
  • At polarization, brightness temp/MWR is a product of physical temp * emissivity
85
Q

Radiative Transfer Model

A

Relative emissivity to soil moisture

86
Q

AMSR-E 2

A

Advanced Microwave Scanning Radiometer
Earth Observing
Currently orbiting

87
Q

SMOS

A

Soil Moisture Ocean Salinity

L band

88
Q

SMAP

A

Soil Moisture Active Passive

Really only passive

89
Q

GPM

A

Global Precipitation Measurement

6-36km res

90
Q

Microwave Polarization Difference Index

A

(Tbv-Tbh)/(Tbv+Tbh)

91
Q

Radiative Transfer Models

A

Similar to MPDI, but needs more info. on temperature, microwave roughness, vegetation opacity, and scattering albedo

92
Q

Snow Water Equivalent

A
  • Snow depth from PMW is inaccurate
  • Dry snow scatters
  • Wet snow absorbs and emits
93
Q

Active Microwave RS

A

Can have finer spatial resolution
More random noise
Distortion and shading issues

94
Q

Backscatter

A

Indicates how much energy is scattered and reflected back to a sensor from a target object
Depends on: Composition (roughness), Polarization, wavelength, Viewing angle
-Increases with soil moisture and surface roughness

95
Q

Validation

A

Accuracy
Precision
Stability

96
Q

Sources of Error

A

1) Sensor Limitations
2) Method of Analysis
3) Landscape Complexity
4) Verification Process

97
Q

Validation Steps

A

1) Design your sampling strategy
2) Collect reference data
3) Extract Information
4) Compare
5) Analyze the causes

98
Q

GRACE

A

Gravimetry satellite detects elevation changes and areas of high gravity generally

Remote Sensing Final (1 decks)

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