Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Geog319RmSns > Altimetry > Flashcards

Altimetry Flashcards

1
Q

Spaceborne altimeter

A
  • System consisting of: Satellite, active nadir-facing sensor, orbit determination system, and data processing system
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Radar altimeter

A
  • Radar pulse

- Ku-band (13.575 GHz) or Ka-band (35.75 GHz)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Laser altimeters

A
  • Laser pulse
  • Infrared (1064nm) or green (532nm) light
  • ICESat GLAS (2003-2010): both
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

MOLA

A
  • Mars Orbiter Laser Altimeter

- 1997-2006

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Current missions

A
  • Sentinel-3 ESA
  • Jason-2 and 3, NASA/CNES/EUMETSAT/NOAA
  • Saral-AltKA, ISRO
  • HY-2, China Academy of Space Technology
  • Cryosat-2, ESA
  • All radar altimeters, ICESat-2, a laser altimeter will launch in 2017
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Altimetry

A
  • Technique for measuring height
  • Measures time taken by pulse to travel from satellite antenna to the surface and back to satellite receiver, elapsed time is proportional to the altimeter height
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Satellite altimeters provide height estimates accurate to within?

A
  • A few cm

- Complex surfaces w/ a single footprint (tens to hundreds of meters for satellite) make height estimates more difficult

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Time and Range

A
  • Time: Distance from satellite to a target surface found by measuring the satellite-to-surface round-trip time of a radar pulse
  • Range: Time is converted to satellite-to-surface range
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Altimeter Height, halt

A
  • halt = (speed of light*time delay)/2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Surface height measurement

A
  • Difference btwn sat’s position on orbit w/ respect to an arbitrary reference surface and the range
  • Reference surface can be the Earth’s centre, or a rough approx. of the Earth’s surface (reference ellipsoid)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are 2 examples of other measurements besides surface height that can be captured with an altimeter?

A
  • Signal backscatter

- Waveform

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What can signal backscatter be used to measure?

A
  • Windspeed over ocean
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Dual-frequency altimeters emit in how many frequencies and what does this allow for?

A
  • 2 frequencies
  • Allows for comparison btwn return signals, which generates interesting results (ex. atm effects like rain rate over ocean)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Altimetry requires lots of information to be able to use data. What are some error sources in altimetry?

A
  • 2 key factors in data processing:
  • Satellite position (exact lat, long, and altitude relative to geoid)
  • Atm effects: interface by water vapour and particles that changes signal speed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How can atm effects be determined?

A
  • By using supporting instruments flown on same mission
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Sea Level/Ocean height is measured relative to what?

A
  • A reference ellipsoid
  • Variations in height used to infer processes about currents and weather (short-term) or overall rises in sea-level (long-term)
17
Q

What is the Globally averaged sea level change (MSL) from 1901-2010

A
  • Increased 19cm overall, 3mm/yr since 1993
18
Q

What are the 2 major contributors to sea level rise?

A
  • Melting of perennial ice (glaciers, ice sheets, and permafrost), which drains water from land to the oceans (approx. 50%)
  • Thermal expansion of the oceans (approx. 50%)
19
Q

What is the major ice type that is currently the largest contributor to sea level rise?

A
  • Glaciers and small ice caps, followed by Greenland ice sheet and Antarctic Ice sheet
20
Q

What are factors that must be considered in context of ice sheets melting?

A
  • Land subsidence
  • Ocean dynamics
  • Gravitational and rotational changes
21
Q

What will play a key role on the observation and mitigation of the predicted large rise in sea level in the coming decades?

A
  • Altimetry
22
Q

Which satellite missions have been used to create elevation models of major ice sheets>

A
  • Altimeter data from ICESat (2003-2010) and Cryosat-2 (2010-present)
23
Q

What platform type is sea ice thickness measured from?

A
  • Not space
  • Instead it is estimated using archimedes principle where basically the height at which ice is floating above water line is related to thickness
  • Satellite altimetry is used
24
Q

Freeboard measurement

A
  • Detection of ice and open water allows for freeboard
  • Freeboard is floating height above water
  • Then freeboard used to estimate thickness
25
Q

Radar freeboard, and factors

A
  • Not sam as ice freeboard due to differences in penetration depth of radar signal
  • Factors: Snow wetness/melt, snow salinity (brine from sea ice), snow layering
  • Error in ice thickness due to salinity can be 25-80%
26
Q

In addition to radar penetration depth, what are other sources of error in sea ice thickness estimates?

A
  • Assumptions of density of sea ice (not pure ice so variations in ice, air, brine volume fractions affect density spatially and temporally)
  • Variations in sea surface height due to geoid and ocean dynamics mean regular calibration needed
  • Snow loading depresses the sea ice freeboard, making it lower than if volume were devoid of snow
27
Q

What are other applications to altimetry?

A
  • Geodesy and gravity anomalies
  • Tsunamis
  • Large scale ocean circulation patterns, tides, cyclones
  • Climate, el niño
  • Lake and river level monitoring
  • etc.
28
Q

Cyro-Vex 2017 and Can/UK research program

A
  • Dedicated ice remote sensing and validation experiment april-june 2017
  • Validation of cryosat, saral-alitka, and other satellites w/ focus on resolution of sea ice thickness retrieval errors

Geog319RmSns (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions