Basics Flashcards
1
Q
What is remote sensing
A
Using remote observations to make inferences about the state of an object
2
Q
Why is it remote?
A
Sensors are not in direct physical contact with objects being measured
3
Q
What is earth observation
A
Remote sensing when the object are the Earth’s varied environments
4
Q
Who took the first aerial photo and when was it taken?
A
Daguerre and Niepce in 1826
5
Q
When was photograph first used for topographic mapping
A
1840
6
Q
First use of balloon to make photographs of large areas
A
1858
7
Q
First aerial photograph from Airplane
A
1909 over Italy
8
Q
When was radar for ship detection developed
A
1900 - 1925
9
Q
When was First color and IR photography taken?
A
Mid 1930s
10
Q
When was high resolution radar system (SAR) developped?
A
Mid 1950s
11
Q
Date of early experiments of classification of vegetation types
A
1956
12
Q
When were multispectral imagers first developped?
A
1960s
13
Q
When did the CIA’s Corona satellite program begin?
A
1960
14
Q
When was the first Landsat satellite launched?
A
1972
15
Q
When was the first civilian SAR satellite launched?
A
1978
16
Q
List 5 reasons to use remote sensing.
A
- Ease of access, 2.Archiving,
- global observation,
- repeatability
- calibrated observation
17
Q
List 3 fundamentals of an RS system
A
- A sensor.
- A measurable signal / source.
- An interaction with the target object.
18
Q
List 4 examples of measurable signals.
A
- Electromagnetic radiation
- Acoustic waves
- Gravity field
- Magnetic field
19
Q
What is another term used for electromagnetic radiation?
A
Light
20
Q
What can determine the spacing distance from your target object?
A
Field of view
21
Q
Give an example of a hand held platform
A
Ground penetrative radar
22
Q
Which is further from the surface of the earth, CubeSat, ISS or GPS satellites?
A
GPS
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
24
Q
Equation for frequency
A
F=Speed of light/ wavelength
25
Wavenumber equation
1/wavelength (also frequency/ speed of light)
26
Speed of light
2.998 * 10^8 m/s
27
Do wavelengths vary across a spectrum?
Yes, of course..
28
Electric field interacts strongly with matter, what 4 factors influence this?
Size of particle and wavelength.
Also atomic and molecular fabric.
29
Does EM more energy?
Yes
30
Do radio waver penetrate the earth atmosphere?
yes
31
Do microwaves penetrate the earth atmosphere?
No
32
Do infrared waves penetrate the earth atmosphere?
No
33
Do visible wavelengths penetrate the earth atmosphere?
Yes
34
Do ultraviolet waves penetrate the earth atmosphere?
No
35
Do W-rays penetrate the earth atmosphere?
No
36
Do Gamma rays penetrate the earth atmosphere?
No
37
Is light a wave or a particle?
Both! It exhibits typical wave properties (interference patterns, Doppler effect..)
It is also a particle travelling in straight lines between interactions
38
What is passive sensing?
Senses a naturally occurring signal
39
What is active sensing?
Generating its own signal.
40
What is spectral radiant emittance?
energy
41
What is black body radiation?
reasearch¨***
42
What kind of radiation do we emit?
Thermal Infrared
43
What does the sun emit?
Visible radiation
44
What process affects radiation as it crosses the atmosphere?
Absorption
45
What is used to measure the earth's surface temperature?
Atmospheric Infrared Sounder (AIRS) on the NASA Aqua satellite
46
What wavelength do the earth's emissions peak at?
In the thermal infrared
47
What wavelength do the sun's emissions peak at?
Visible
48
Give 2 examples of active sensors
1. GPS
2. Radar altimeter satellite
49
How can you strip back a tree layer using Lidar?
By observing the change in signal
50
List 8 measurable quantities in light.
Energy, intensity, back-scatter, amplitude, radiance, time, phase and polarisation
51
What is the equation for the energy of a photon
E=h*f
52
in E=h*f, what is h?
h is Plank's constant
53
What is power and its equation
Power = E/t, the amount of energy per unit of time
(unit of power is a watt)
54
What is the unit for a watt
Joules per second
55
What is irradiance?
power of radiation on one side of a surface per unit area (Irradiance = Power/ Unit area)
56
List 3 trajectories of radiation
1. upwelling/ surface leaving
2. downwelling/ Incident
3. total solar
57
What is the radiance equation?
Radiance = (energy / (second * area * angle))
58
What is the Emmittance equation
E = W/m^2
59
What is trilateration?
It's when you use three GPS satellites (GPS/ GALILEO/ GLONASS) to provide the specific location of something.
60
WHat technique is used to make DEMs
Altimetry
61
What did the Shuttle Radar Topography Mission (SRTM) do?
Synthetic Aperture Radar Interferometry (InSAR)
I think ... double check this.
62
What is DInSAR
Differential Synthetic
Aperture Radar
Interferometry
(maps earthquakes)
63
What is polarisation?
Research this
64
What is radar cross polarisation?
Transmit radar horizontally and receive vertically (and vice versa)
It weakens the returning signal.
65
What does HV cross polarsation radar help detect
targets on the water surface
66
What can Radar cross polarisation help differentiate in agriculture?
grain crops from broad leaf crops
67
what wavelengths does passive remote sensing focus on?
Visible, Near Infra Red, Short Wave Infra Red
68
What wavelengths does visible fall between?
390 - 700 nm
69
What wavelengths does NIR fall between?
700 - 1000nm
70
What wavelengths does SWIR fall between?
1000 - 2500nm
71
What are the three object interactions with the EM spectrum?
1. Reflected
2. Absorbed
3. Transmitted
72
What are the 3 methods you can use to measure energy reflected from a surface?
1. Spectroradiometer
2. multispectral imager
3. hyperspectral imager
73
What is the red edge?
It's the wavelength where there is a lot of absorption in vegetation (700 nm)
74
what is spectral resolution?
It's the instrument's resolution
75
List the 5 pros of hyperspectral imaging
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
List the main pro of multipsectral imaging
it's cheaper than hyperspectral
77
List 4 cons of multipsectral imaging.
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
What effects can the atmosphere have on energy?
Aerosols absorb energy at different wavelengths
79
What are the 4 main EO applications for forests?
1. Resource management
2. Protection/ prosecution
3. disaster management/ recovery
4. Climate science
80
3 main challenges in EO being used to monitor forests
1. Highly dynamic (seasonal)
2. Complex (3D, different types)
3. Remote and large
81
What is a Vegetation Index (VI)?
A spectral transformation of two or more bands
82
Why are Vegetation Indexes used?
They enhance the contribution of vegetation properties and allow reliable
spatial and temporal inter-comparisons of terrestrial
photosynthetic activity and canopy structural variations.
83
NDVI equation
NDVI = (NIR – Red) / (NIR + Red)
84
Narrow-band ratio approach
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
Smoothing
Mathematical functions applied to VI time series data... revise this
86
List types of matter which emit EM
Gases, clouds, dust and molecules, solid/ liquid surfaces (all matter emits thermal radiation
87
What is Wien's law?
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
Describe what this equation is saying λm = 2897 / T
λm is the wavelength at which the peak emissions intensity occurs, T is temperature of the blackbody
89
What is an easy way to remember Wien's law?
the hotter the object the shorter the wavelengths of the maximum intensity emitted
90
What is emissivity?
the ratio of energy radiated to that of a perfect emitter (blackbody)
91
What is the emissivity scale?
0-1
92
What is the IR emissivity of ground and water bodies?
0.9 - 0.99
93
What is the IR emissivity of gases, aerosols and clouds?
0.0 - 1.0 (it depends on the optical path)
94
What is the Microwave emissivity of land surfaces?
~0.9
95
What is the Microwave emissivity of the ocean?
~0.5 (depends of wavelength and sea state)
96
What are the two main influences of emissivity?
wavelength and geometry
97
What is brightness temperature?
the temperature an object would need to bee for the radiance from it to match the actual radiance observed
98
What is Kirchhoff's law?
efficient absorbers are efficient emitters. The emissivity is proportional with the asborption
99
I f a surface absorbs 80% of the spectral radiance incident on it, what is its emissivity?
0.8
100
what is transmission
allowing to pass through
101
Give an example of a large transmitting medium
the atmosphere
102
What is transmittance
the fraction transmitted
103
List 5 types of reflection
Specular, quasi-specular, lambertian, quasi lambertian, complex
104
What does a perfectly rough surface do to the angle of reflection?
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
Give an example of a lambertian surface
paper, snow
106
What kind of reflection is there on real surfaces?
it is somewhere betwee specular and lambertian
107
What can affect the amount of reflection you receive
The viewing angle and the incidence angle
108
How do rough surfaces appear in SAR imagery?
It appears bright because the microwave energy is reflected to the satellite
109
How do smooth surfaces appear in SAR imagery?
dark because the microwave energy is reflected away from the satellite
110
What is a benefit of SAR satellites
they can operate at night
111
Give two common uses of SAR satellites
Monitoring ships and oil spills
112
What is diffuse or hemispheric reflectivity?
It is the average reflectivity over all possible incidence angles
113
What are spectral signatures?
The trajectory of the line across the spectrum or the individual spectral response of the target
114
What does scattering do?
It changes the direction of radiation without absorbing its energy. this attenuates the direct beam and introduces diffuse illumination
115
What are the two measures of scattering?
The amount of scattering and the angular distribution of the scattered radiance
116
What scatters in the atmosphere?
molecules (Rayleigh scattering), aerosols and water droplets
117
Why is the sky blue?
It is blue because shorter wavelengths scatter more than longer ones
118
What colour is chlorophyll bloom?
in Green
119
What is the instantaneous field of view?
it represents the ground area or angle, viewed by the sensor at a given instant in time
120
What does the instantaneous field of view determine?
It determines the spatial resolution (setting the lower limit fro the level of spatial detail that can be represented in a digital image)
121
What are the two values of of instantaneous field of view?
along-track and across-track
122
pixel size is not resolution
123
Look into Advanced Very High Resolution Radiometer pixel geometries
124
What is nadir?
125
Radiometric resolution
where each grid cell contains a single number
126
How many possible values does a 6 bit image have?
2^6
n bit image has 2^n values
127
What is a digital number
the number a grid cell contains
128
what is the radiance equation including digital number (DN)
radiance = gain*DN+bias
129
What is orbital period?
the time it takes for a satellite to circle the earth
130
What are the three types of satellite orbit?
geostationary, geosynchronous, sun-synchronous
131
What is a geostationary orbit?
And what is its use and spatial coverage
same location above Earth, used for weather and telecommunication, limited spatial coverage (25/30% of the earth's surface), mid-latitude only (<55°)
132
What is a geosynchronous orbit?
And what is its use and spatial coverage
same rotation period as the earth
133
What is a sun-synchronous orbit?
And what is its use and spatial coverage
passes every location at same time - ensures illumination, global coverage, polar orbit (most EO satellites are geosynchronous)
134
What influences the temporal resolution
swath width and orbit type
135
what is a common tradeoff in terms of resolution
spatial, spectral and temporal resolutions, can't have it all yet (tech developments and decrease of costs decrease the need for trade offs)
136
What is the landsat repeat period
16 days
137
What are the benefits of the Tropical Rainfall Measuring Mission?
Has a low inclinaison (35°) and a larger swath, making it useful for following weather patterns.
138
Landsat 7 bands
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
natural composite image numbers
4 - 3 - 2
140
false colour composite
543 (NIR, R, G)
141
WHat band highlights fire?
Band 6
composite 653
142
