Chipperfield Flashcards
(175 cards)
1
Q
How many nations have signed the Antarctic Treaty?
A
29, with 53 operating
2
Q
Who funded CryoSat?
A
European Space Agency
3
Q
How many member states does the ESA have? Name one not in the EU
A
23, Canada
4
Q
How is Brexit affecting Earth Observations?
A
UK is being frozen out of the Galileo Program (GPS equivalent) and the Copernicus Project
5
Q
How much does CryoSat cost?
A
3p per European Citizen per Year
6
Q
What is the British Antarctic Survey’s minimum limit for sea ice work? and Finland?
A
60cm thick, 20cm thick
7
Q
How thick is sea ice and how thick are the Greenland Ice Sheet and Antarctic Ice Sheet?
A
Sea ice is on average 1.8m thick. Greenland is 2km thick, Antarctica is 3-4km thick.
8
Q
What are the two main advantages that Radar Imagery has over Visible Imagery?
A
Radar can penetrate and through cloud and can function at night
9
Q
Who funds LandSat?
A
NASA
10
Q
What was the name of the first Infrared Imaging Instrument in Space and when was it launched?
A
TIROS-N, 1978
11
Q
What was the first satellite that carried a radar altimeter and an imaging radar and when was it launched?
A
SeaSat. 1978
12
Q
When was the first recorded year that the entire Greenland Ice Sheet melted out?
A
2012
13
Q
What determines the period of a satellites orbit?
A
The altitude of its orbit
14
Q
What is special about a satellite orbiting at 36,000km?
A
It takes exactly 24 hours to orbit the Earth and can have a geostationary orbit.
15
Q
What are geostationary satellites often used for? (2 things)
A
Communications, routine weather monitoring
16
Q
Describe polar orbits. (3 Points, including inclination and purpose)
A
- Perpendicular to Earth’s equator
- Passes close to both north and south poles with an inclination of just less than 90.
- pass over the entire surface of the earth so useful for weather or observing the whole planet
17
Q
Where are the upper boundaries of troposphere and stratosphere?
A
Top of troposphere is ~12km, top of stratosphere is ~50km
18
Q
Where is the ozone layer?
A
In the stratosphere
19
Q
What is the altitude of the ISS?
A
Altitude of ISS is ~350km
20
Q
How high is Low Earth Orbit and how long is the orbital period of satellite here?
A
LEO is ~750km, orbital period is 1/15 day
21
Q
How high is High Earth Orbit and how long is the orbital period of a satellite here?
A
36,000km, 24 hours
22
Q
What is the radius of the Earth?
A
~6370km
23
Q
Describe a sun synchronous orbit.
A
-Passes over the any point on Earth at the same local (solar) time every day of the year
24
Q
Describe precession of orbits including what the rate of precession depends on.
A
- The process of naturally rotating with respect to background stars because Earth is oblate. Near polar orbits are affected the most.
- 360 degrees of precession in one year means a sun synchronous orbit
- Rate of precession depends on satellite altitude and inclination
25
Give some examples of HEO satellites over the equator
Meteosat-5, GMS-5, GOES-8, GOES-9
26
What can't geostationary satellites observe and why?
Cannot observe the poles due to curvature of the earth
27
Describe Passive Sensors
- Measure electromagnetic radiation emitted by the Earth or by the Sun via interaction with the surface/atmosphere.
- most satellite instruments are passive and rely on external source of illumination
28
Describe Active Sensors. Give 2 examples
-instruments generate their own radiation and record the reflection of this back from the observed object. RADAR and LIDAR
29
Describe RADAR in terms of satellites, give an example
Active Sensors; Radio Detection and Ranging; Use microwave radiation and measure time for signal to be returned. Sentinel 1A and 1B carry SAR.
30
Describe LIDAR in terms of satellites, give an example
Active Sensors; Light Detection and Ranging; use visible radiation such as lasers to emit a monochromatic beam of light and measure return signal. ICESat carries LIDAR
31
Describe limb viewing, and what it is used for, give an example instrument.
Looks tangentially through the atmosphere, good vertical resolution, used for atmospheric profiles, limb scanning bottoms out at 6km due to high water vapour content of clouds. SCIAMACHY on ENVISAT uses limb and nadir
32
Describe nadir viewing, what it is used for
Looks directly down through the atmosphere. good horizontal resolution. Used for all surface observations, used for HOE observations, useful for lower atmosphere. SCIAMACHY on ENVISAT uses both limb and nadir viewing
33
What are the two classifications of limb viewing? Describe both and draw
- Limb Emission: active sensing using IR or microwaves, can be ground based.
- Limb Absorption (Occultation); passive sensing using UV/vis/near IR from external sources (sun or other stars, earth's atmosphere), can be ground based
34
At what altitude does limb viewing bottom out and why?
~6km due to excessive water vapour in troposphere from clouds
35
Give examples of instruments that use limb and nadir viewing
SCIAMACHY on ENVISAT (atmospheric composition), OMPS (ozone)
36
Give an example of an instrument that takes atmospheric observations by nadir viewing and how it operates.
Total Ozone Mapping Spectrometer (TOMS), in LEO, measures ozone by back scattered radiation, measures only total ozone and thickness and can't create profiles
37
Give an example of a satellite that takes atmospheric observations by limb viewing and describe how it operates
Microwave Limb Sounder (MLS) on Upper Atmosphere Research Satellite (UARS). Measures ozone, ClO etc by microwave emission, can operate without sunlight. Can create profiles of atmosphere
38
What are the three variables when measuring Electromagnetic Radiation?
Wavelength, Frequency and Amplitude
39
What does the Stefan-Boltzmann Law define?
the relationship between the total emitted radiation and temperature
40
Write the Stefan Boltzmann Law and define the terms.
- W=σT^4
- W is energy emitted
- σ is Stefan-Boltzmann Constant (5.67x10^-8 watt m^-2 K-4
- T is temperature in K
41
How are frequency and wavelength related? Give the Law and define terms
As wavelength get shorter, frequency increases (c=λv);
c is speed of radiotion in a medium and is constant
-λ is wavelength (m)
-v is frequency (Hz)
42
Give the equation to relate the energy of a photon to its frequency and define terms.
- Q=hv
- Q is radiant energy
- h is Planck's constant
- v is frequency
43
What happens to the total energy emitted and wavelength of peak emission when the temperature of an object is increased.
Temp increase = total energy increase = decrease in wavelength
44
What happens to the total energy emitted and wavelength of peak emission when the temperature of an object is decreased.
Temp decrease = reduction in total energy = longer wavelength
45
What is a black body?
A hypothetical object which behaves in an idealised manner and absorbs all radiation and emits none. Emissivity of 1
46
What does the Stefan Boltzmann Law say?
Hot black bodies emit more radiation than cold black bodies
47
What does the Beer Lambert Law describe?
The absorption of radiation passing through a medium
48
Write the Beer Lambert Law and define terms
Itr = Io e^(-k c l), where -Itr is energy transmitted
- Io is initial energy
- k is aborption coefficient
- c is concentration of the absorber
- l is path length
can be Itr = Io e^(-k ca)
-ca is column amount of absorber if concentration varies hugely
49
Define scattering of radiation
the redirection of radiation by particles in atmosphere, not absorbed and can be in any direction
50
Define extinction of radiation
Extinction = absorbtion + scattering
51
Define absorption of radiation
A particle in the atmosphere absorbs radiation and increase in energy
52
What are the 3 basic types of scattering in the atmosphere?
Rayleigh
Mie
Large Particle scattering
53
Where does rayleigh scattering occur?
Upper atmosphere, 9-10km.
54
What causes the blue colour of the sky and red sunsets?
Rayleigh Scattering
55
What causes Rayleigh scattering?
Particles that have smaller radii than incident wavelength (molecules in the atmosphere)
56
in Rayleigh scattering, is red or blue light scattered more and by what degree? Why?
Blue is scattered 4 times more as scattering increases with shorter wavelengths
57
Why can't UV wavelengths be used for surface observations?
Rayleigh scattering of higher UV wavelengths distorts images
58
At what height does Mie scattering occur?
Lower atmosphere (0-5km)
59
What causes Mie scattering?
Particles with similar diameter to incident wavelength (dust, pollen, smoke etc)
60
the absorption of which radiation results in changes electron arrangement in a gas molecule?
UV
61
the absorption of what radiation results in changes of the vibration of a molecule?
Infrared
62
The absorption of which radiation causes changes in the rotation of gas molecules?
Microwave
63
What are the 4 major atmospheric windows for radiation that are weakly absorbed?
Ultraviolet and visible, Near Infrared, Thermal Infrared and Microwave
64
What is 'retrieval' in terms of satellites?
The process of converting raw radiances into more meaningful quantities such as temperature or gas concentration
65
What do satellites directly measure?
Spectral radiances: the flux of electromagnetic radiation per unit area in different wavelength intervals
66
What are atmospheric sounding channels and how are they chosen?
They are specific wavelengths that have very strong absorbance and so little or no contribution from the surface.
67
What are surface sensing channels and how are they chosen?
Specific wavelengths that are in the IR and microwave atmospheric windows and have little or no absorbance in the atmosphere so no atmospheric contribution
68
What are surface sensing channels used for?
To obtain information on the surface temperature of earth and quantities that influence surface emissivity (wind over ocean, vegetation over land)
69
How long does a single satellite mission usually last for?
Around 5 years, so long term trends need careful calibration between different missions
70
Why are clouds important? 3 points
- Close connection with meteorology
- Important in the transfer of radiation to the atmosphere
- interfere with the measurement of other properties
71
How much solar radiation is reflected and absorbed by clouds?
20% and 3%
72
Name an example of a passive cloud measuring instrument
Moderate Resolution Imaging Spectroradiometer (MODIS). MeteoSat Second Generation (MSGs)
73
What happens to cloud top temperature and pressure with altitude?
Cloud top temperature decreases with increasing altitude, as does pressure
74
Name 3 things that can cause issue with cloud observations
- Aerosols in the atmosphere
- Multi-layer clouds
- Clouds over ice/snow
75
What was the first LIDAR in orbit?
LITE (LIDAR In-space Technology Experiment) on Space Shuttle.
76
Name 3 things LITE could measure
- stratospheric/tropospheric clouds and aerosols
- the height of the planetary boundary layer (PBL)
- stratosphere temperature and density between 25-40km altitude
77
What is CALIPSO? (in terms of sensors etc)
COmbines active LIDAR instrument (CALIOP) with passive IR and visble imagers. Part of the A-Train
78
What is the A-Train constellation?
A chain of complementary satellites that observe clouds and aerosols etc. including CALIPSO, AURA, PARASOL, AQUA, CLOUDSat and OCO
79
Identify four advantages to satellite observations.
- the most inaccessible places can be reached quickly
- many phenomena (ENSO etc) require global measurements
- Several parameters can be measured simultaneously
- remote sensing facilities facilitate analysis of long time series, and can be cheaper per measurement over time
80
What does the weighting function vary with (1) and depend on (2)?
- varies with wavelength
- depends on absorption coefficient of the gases absorbing/emitting at this wavelength
- the concentration of these gases in the atmosphere
81
What is the weighting function?
It describes the region (altitude) of the atmosphere from which the radiation principally originates from
82
Explain limb onion peel observations, draw it.
The atmosphere is divided into layers, and lines of observation got through only the topmost layer, then the 2 topmost layers etc. This allows profiling for the entire height of observations as the influence of upper layers on lower layer observations can be discounted.
83
Identify 4 problems with satellite measurements
-Measurements are always indirect
-the EM signal is often affected by more than just the quantity to be measured
-Additional assumptions and models are needed for the interpretation of the measurements
-measurement area can be huge
validation of measurements is often a major task
-estimation of errors is often difficult
-observation are often affected by cloud cover
84
What causes supraglacial lakes to drain?
Increasing water pressure forces open crevasses or moulins in lake bottoms
85
What is the typical area of a supraglacial lake and how long would one of this size take to drain?
~6km^2 and ~1.5hours with a faster flow rate than Niagara Falls
86
What is the effect of a draining supraglacial lake on ice flow velocity?
Potential to increase ice flow velocity for a short period, potential to open a permanent connection between surface and base of glacier
87
What observations are required in order to monitor supraglacial lakes?
- Lake Area (seasonal evolution and longer term trends)
| - Lake Depth (volume of water in lake and reaching glacier bed)
88
What are the types of Optical Remote Sensing?
Panchromatic, Multispectral
89
Describe Panchromatic Remote Optical Sensing
Detects radiation over a single, broad waveband, black and white image, no spectral/colour information
90
Describe multispectral optical remote sensing
detects radiation over, multiple narrower wavebands (e.g. green waveband shows vegetation, while near IR shows heat). can create a true or false colour image from different wavelengths
91
In which region of Greenland are supraglacial lakes most common and why?
In the SW as it is fairly flat and relatively warm. Too cold in the N, topography is too steep in SE
92
What 'shape' is the pulse of a radar?
Top Hat shaped, with no power, up to a constant power, then off to no power
93
What does the leading edge of a radar pulse echo correspond to?
the first interaction with the surface, can be used to estimate roughness
94
What does a steep leading edge on a pulse echo signify?
Smooth surface
95
How is a rough surface represented in a pulse echo signal?
As a shallow leading edge
96
What does the trailing edge of a pulse echo correspond to?
The scattering properties of the surface (and so penetration)
97
What does a rapid tailing off in a radar pulse echo's trailing edge signify?
Scattering is only from the surface and there is no penetration.
98
What happens to a radar pulse echo when there is penetration and scattering at depth?
Slow tailing off in trailing edge
99
What happens when a radar is fired at the ocean?
All is either reflected back at the surface or absorbed, none is scattered at depth meaning a rapid tailing off of the trailing edge
100
What can happen when a radar is fired at an icesheet?
Some radiation penetrates the surface is scattered at depth, causing a slow tailing off of the trailing edge
101
How can satellite radars view snow accumulation layers?
Each layer will scatter the radar echo in its own way and each can be seen on the echo pulse
102
Give 4 variables that satellite radar altimeters enable us to monitor
Sea level rise, ocean waves, lava flows and ice sheet growth or loss
103
What can wave height measured by satellite be used for?
As a proxy for measuring windspeed
104
Why is it important to monitor tides around ice shelves?
Ice shelves float on the ocean and so rise and fall with the tides making it difficult to investigate changes in ice shelf thickness
105
Why is ice area not a useful parameter for studies of climate change?
Ice area does not correlate with Ice mass, for example a glacier can surge and double its area but mass remains constant
106
Why does it appear that the Antarctic Ice Sheet is growing?
Increased precipitation (snowfall)
107
What do we need to know in order to use changes in ice volume to predict sea level change?
Accurate densities of ice, firn and snow
108
How does one estimate ice density? (3 points)
- In-situ measurements
- estimate using a regional climate model
- compare to known patterns of ice flow and snowfall
109
Give 2 advantages of Satellite Radar Altimetry (SRA) in terms of ice monitoring
- comprehensive cover of Greenland Ice Sheet and 2/3 of Antarctic Ice Sheet
- Mass changes can be easily inferred from volume changes
110
Give 4 major disadvantagges of Satellite Radar Altimetry (SRA)
- instrument failure over high or rugged slopes
- missing data from highest latitudes (central Antarctica)
- low spatial resolution (~10km)
- variations in the depth of radar penetration of the snow surface
111
What are the main processes for loss of ice from ice shelves? (2)
Calving and ocean driven melting at their base
112
What are the 2 inputs for ice shelves?
Glacier Influx and snow accumulation
113
Why are ice shelves important to thermohaline circulation?
They supply cold, fresh water, and if the production of this shuts down, it could impact on the northern European climate.
114
Why are ice shelves sensitive indicators of changes in climate?
They are exposed to both the oceans and atmosphere and implies an equilibrium has been reached between ocean, atmsphere and grounded ice sheet.
115
What may happen if an ice shelf collapses?
Rapid acceleration of discharge from grounded ice upstream
116
Do ice shelves contribute significantly to sea level rise on melting?
No, as they are already floating
117
Why is it difficult to measure ice shelf mass balance? (2)
- Mass loss/gain due to basal freezing/thawing is almost unknown
- Ice shelves float and so surface elevation changes are only a fraction of total ice thickness change
118
What is the name of the ice that is above the waterline when a shlef or block is floating?
Freeboard
119
What does ice mass loss mean for the surface lowering of an ice shelf?
Surface lowering is ~1/9 of total thinning
120
What does snow mass loss mean for the surface lowering of an ice shelf?
Surface lowering is ~2/3 of the total thinning
121
What area has been lost from Antarctic Peninsula Ice Shelves each year since 1980?
300km^2
122
What is the radar equation? Define terms
R=1/2cT
c = speed of light
T = is time
123
What is the geoid?
The hypothetical reference level used to describe a surface close to mean sea level where gravity is constant. Can be used as a reference for surface elevation changes.
124
Give 5 things bathymetry is important for
- Seafloor depth
- Submarine geology (plate tectonics, undersea volcanoes etc)
- Oceanography
- Inertial Navigational Systems (GPS etc)
- Marine Engineering
125
What does a rough bottom mean for ocean mixing rate?
Rough bottom means faster ocean mixing
126
Where does the least ocean mixing occur?
Over smoother sea floors
127
What is the main advantage of satellite bathymetry over ship bathymetry?
Ship based surveys are expensive and time consuming for relatively little data at very high resolution
128
At what height would mean sea level be if only under the influence of Earth's gravitation and rotation?
The Geoid, which varies by ~100m around the earths surface
129
Why does the geoid have an irregular shape?
Due to spatial variation in distribution of mass within the Earth.
130
What influences mean sea level on a ~100s of m scale?
Earth's Geoid
131
What influences sea level on a 1000s of km scale?
Variations in crust, mantle and core
132
What influences sea level on a 10s of m scale?
Sea floor topography
133
How much can persistent currents contribute to mean sea level?
~1m
134
Why are Synthetic Aperture Radar useful for the military? 2 points
Can see through cloud and can operate at night to build images
135
How large does an object need to be to be detected by electromagnetic radiation?
Needs to be larger than the wavelength of the radiation
136
At what part of the EM spectrum do most SARs operate?
In the microwave frequencies
137
Why are TV and radio stations able to broadcast long distances?
Earth's atmosphere is transparent to EM radiation with wavelengths between 1mm and 20m, which includes radio and microwaves
138
What kind of weather may start to interfere with microwave radiation?
Hailstorm if hailstones are larger than ~1mm
139
Why will snow in lower latitudes be more detectable than polar snow when using microwave technology?
Snow at lower latitudes is denser than polar snow as it contains more moisture
140
At what microwave band do most SARs operate?
Ku band (2.8-1.7cm)
141
At what angle do imaging radars operate?
25-30degrees. This illuminates a wider area than a nadir.
142
Why does a SAR system need to have a higher power than a simple radar altimeter?
Most of the energy a SAR emits is scattered away and lost, with only a small portion coming back to the instrument to be measured
143
What is special about the shape of the echo of a SAR?
It resembles the terrain as the closest part of the ground will be the echo that is received first
144
What is lost when using a SAR over a radar altimimeter?
The ability to range to a target
145
Describe a synthetic Aperture Radar (SAR). Draw Diagram
A side looking radar system which utilises the flight path of the platform to simulate an extremely large antenna or aperture., allowing the generation of remotely sensed images with very fine spatial resolution.
146
How is across track resolution achieved in a SAR? Draw diagram
The beam is divided into across track resolution cells, the closest cell is reflected first etc etc.
147
How is along track resolution achieved in a SAR? Draw diagram
SAR transmits frequency modulated burst of energy acorss a range of angles along the flight path, as satellite moves forwards, the target is illuminated in multiple bursts. These can be stacked to form an image
148
How much would a typical SAR satellite and a typical radar altimeter cost?
SAR: 300-400million Euro
RA: 50-60million
149
What kind of system is a SAR?
Active microwave system operating by looking sideways
150
What is radar speckle?
Signal distortion caused by complex scattering in a radars echo, makes radar images appear noisy
151
Do rough or smooth surfaces appear brighter in SAR images? Why?
Rough surfaces appear brighter as smooth surface reflect more microwave radiation away from the sensor
152
Why can snow surface appear darker than smoother ice surfaces in SAR imagery?
Microwaves can penetrate through snow so backscatter intensity is less
153
Describe foreshortening in terms of SAR. Draw Diagram
As SARs are side looking, taller object scan appear closer the sensor in slant range and so slope can be shortened
154
Describe the shadowing effect in terms of SAR. Draw Diagram
As SARs are side looking when a mountain peak is too tall, it can over shadow the leeward side of its slope
155
Describe layover in terms of SAR. Draw Diagram
Layover occurs when the radar beam reaches the top of a tall feature before it reaches the base.
156
Give an example of a SAR,
TerraSAR
157
Give two examples of SAR applications
Oil Spills (oil changes scattering properties of ocean); Hurricanes windspeeds (ocean surface is whipped up and made rougher)
158
What does InSAR mean? What is it for?
Synthetic Aperture Radar interferometry, used for measuring tiny movements in the Earth's surface from space
159
What observable property of an EM wave does InSAR use?
The Phase
160
Describe how InSAR uses SAR images
Two SAR images of the same area taken at separate times produce an interference pattern related to surface movement and elevation during the time interval
161
What causes a phase shift between 2 SAR images taken at different times (2 points).
- The change in location of the satellite
| - a change in the surface
162
List 7 applications of InSAR
Earthquakes, Land Subsidence (Jubilee Line in London, Las Vegas), Landslides (lead up to sudden events), Permafrost, Oil and Gas, Volcanoes, Ice Flow
163
Name 3 case studies of InSAR use in glaciology
Russel Catchment Glaciers, Greenland; Antarctica Mass Budget; rapid retreat of Pine Island grounding line
164
What are the 5 components of the interferometric phase in InSAR?
Geometry, topography, atmosphere, noise, deformation (motion)
165
What has InSAR told us about Russel Catchment Glaciers in Greenland?
Ice flows faster overall in colder years.
166
Why is rate of ice movement faster in colder years than warmer years in Greenland?
Evolution of drainage network from narrow high pressure cavities to wide low pressure channels reduces pressure under glacier and leads to cessation of sliding
167
What is a problem with using InSAR to measure glacier velocity?
InSAR only accounts for surface velocity and glacier velocity normally reduces with depth
168
Why is the accuracy of the mass budget technique limited in Antarctica when using InSAR?
While InSAR velocity data is very accurate, Snowfall and thickness errors are common as data is very sparse.
169
What has InSAR told us about the Antarctic Mass Budget?
The main losses are from the Amundsen Sea sector which accounts for 17% of the area but 72% of mass loss)
170
How can InSAR be used to measure location of ice sheet grounding lines? What needs to be cancelled out?
Grounding lines are the junction between floating ice that moves with ocean tide and grounded ice that does not, this can be seen using double or quadruple interferometry. Topography, lateral motion of the ice need to be cancelled out so left with differential tidal motion
171
Name 8 things that can be monitored on the Earth's surface from satellites
- Global elevation and change
- Sea floor bathymetry
- Ocean tides/Sea Level
- Sea Ice Thickness
- Earthquakes
- Subsidence/Uplift
- Subglacial/supraglacial lakes
- Ice flexure
172
How are crossover points used to determine height changes?
2 satellite altimeters tracks cross each other and height can be determined in tracks to give an idea of 3D shape. Crossing points are closely spaced at high latitudes and widely spaced at the equator
173
Name 2 ways over determining elevation change using satellite altimeters
Crossover points and repeat track
174
Explain why true surface of ice and snow may appear lower in spring than in autumn when in fact it is the other way around. Draw diagram
In spring, winter snow lies on top of ice and can be penetrated by radiation, so the radiation is scattered at the ice surface. In winter, the snow has compacted into firn and radiation scatters from the top of the firn. Scattering horizon moves up while true surface moves down
175
What wavelengths of light are in the visible spectrum?
blue is at ~0.4μm to red at ~0.7μm
