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Geog319RmSns > Radar > Flashcards

Radar Flashcards

1
Q

Spatial Resolution

A
  • Ground size of the smallest recording it

- Smallest area on the ground that can be seen or resolved by a sensor

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2
Q

Spectral Resolution

A

The number and dimension of electromagnetic wavelength intervals to which a remote sensing instrument is sensitive

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3
Q

Temporal Resolution

A
  • Revisit frequency for a particular area on the Earth’s surface
  • Dependent on swath and orbit
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4
Q

Radiometric Resolution

A
  • The sensitivity of a remote sensing instrument to differences in electromagnetic energy
  • Signal vs. noise
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5
Q

RADAR: acronym and description

A
  • RAdio Detection And Ranging
  • Active Remote sensing
  • Transmitter sends pulse of microwave energy of specific frequency and polarization
  • Antenna receives energy scattered back to radar (echo)
  • Receiver/system records the intensity (strength of echo) and the time delay (range)
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6
Q

Active remote sensing

A

Pulse, Echo, and Range

  • Echo also called Backscatter
  • Similar to acoustic but with microwaves and not sound
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7
Q

What are the 3 classes of radars used in EO? And what are other radar types?

A

1 - Imaging Radar (SAR)
2 - Scatterometer
3 - Altimeter
Other - Side-Looking Airborne Radar (SLAR) used in surveillance, and meteorological radar

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8
Q

How many frequencies are in one band of radar?

A
  • Radar transmits and receives one frequency i.e. band
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9
Q

Time delay

A
  • clock how long it takes a signal/pulse to return (echo)
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10
Q

Where did the technology, and therefore the terminology for radar originate?

A
  • Military based

- Terms non-sensical to confuse spies during war times

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11
Q

What are 4 of the most important bands for RS w/ Radar?

A
  • L (1 - 2 GHz)
  • C (4 - 8 GHz)
  • X (8 - 12 GHz)
  • Ku (12 - 18 GHz)
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12
Q

Single-pol

A
  • HH, VV, HV, or VH
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13
Q

Dual-pol

A
  • HH and VV, HV and HH, or VV and VH
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14
Q

Quad-pol

A
  • HH and VV and HV and VH
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15
Q

Polarimetric

A
  • Quad-pol and phase info
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16
Q

Synthetic Aperture

A
  • Forward motion of craft, combined w/ sensor’s ability to store the location of a target enables synthesis of a larger effective aperture (i.e. antenna length) and finer resolution
  • Synthesizes a larger antenna w/o having to install a really big antenna
17
Q

Imaging Radar: SAR

A
  • Can be controlled by user needs
  • Instrument can be set to run in a background mode
  • B/c source energy is controllable, SAR’s have selectable beam modes
18
Q

Beam mode

A
  • Vary based on spatial resolution and swath coverage
  • Beam and swath and spatial resolution is inter-related, therefore can be controlled
  • Controllable energy = same amount of energy but transmitted over larger/smaller area
  • Vary beam so swath is smaller and spatial res increases
  • Increase swath for large coverage = decrease spatial res
19
Q

What is the benefit of being able to run in background mode?

A
  • Instrument can last longer before it runs out of power
20
Q

Name some examples of Beam modes on Radarsat-1

A
  • Fine, 8m,
  • Standard, 30m
  • Wide, 30m
  • ScanSAR Narrow, 50m
  • ScanSAR Wide, 100m
  • Extended High, 18-27m
  • Extended Low, 30m
21
Q

What is the trade-off involved w/ varying swath?

A
  • Trade-off w/ spatial res
  • High spatial res with narrow swath
  • Ex. 45km swath = 8m vs. 500km swath = 100m res
22
Q

What are Constellations

A
  • Multiple identical EO satellites that are separated in orbit
  • Enhances re-visit freq for instruments that otherwise have small swath
  • Increases temporal res
  • More efficient monitoring based on temporal resolution for change detection
  • Maximizes coverage
  • Not exclusive to SAR, becoming more common
23
Q

Constellation example

A
  • Sentinel-1 SAR mission
  • Launch 2014
  • Sentinal-1A and 1B
  • 2 Satellites on one orbit plane, spaced 180 degrees apart
  • 12 day orbit w/ 6 day repeat freq
  • Revisit frequency 3 days at equator, <1 day at high latitudes (Europe 2 days)
24
Q

Radarsat Constellation Mission (RCM)

A
  • SARs
  • Launch 2018
  • 3 sats, 1 orbit plane
  • Spaced 120 degrees apart
  • Approx. 4 scenes/day at polar, 1/day at equatorial
25
Q

Scatterometer

A
  • Side-looking, non-imaging radar used to measure backscatter quantitatively at low resolution and over large swaths
  • Spatial res = low, several km, swath = several hundred km, comparable to radiometers
  • Regular data acquisition, not controllable like SAR
  • BS data can be mapped to grid and visualized like an image
  • Ex. Wind speed retrieval from NASA’s QuikScat satellite scatterometer
26
Q

Why use scatterometers if they have such poor fixed spatial res?

A
  • Ability to form Earth surface images w/ increased temp res b/c of large swath like a radiometer but w/ active tech
  • Good for large areas
27
Q

Radar Altimeters

A
  • Precise nadir measurements of distance from the satellite to the surface from time delay
  • Infer topography
  • Know height of sensor and time of signal to calc elev at surface
  • Ex. Ice-sheet height change over time
28
Q

3-polarization colour overlay

A
  • HH = Red
  • HV = Green
  • VV = Blue
  • Overlay and different polar combos highlights different features
29
Q

Which platforms can provide distance baed on the time it takes a signal to return?

A
  • SAR

- Scatterometers

30
Q

What is the overarching goal of EO?

A
  • Development of relationship btwn image measurements and geophysically useful information
  • Ex. Forest biomass, SWE, Soil moisture, Sea-ice type
31
Q

What needs to be considered when using Radar?

A
  • What measurements radar provides
  • What geophysical parameters these measurements can provide
  • Whether they can be provided by radar alone, in combination w/ other radars or other sensor types such as optical, or other data sources
32
Q

What are the simplest things SARs and scatterometers provide info about? How?

A
  • Structure
  • Roughness and Texture
  • Wetness
  • Distance (range) info
  • Mainly by providing BS intensity and polarization information
33
Q

Scattering Mechanisms

A
  • Microwave interactions w/ Earth materials and BS are described by scattering mechanisms
  • Surface (specular, water)
  • Double Bounce (2 objects, very bright return)
  • Volume (snow, veg)
34
Q

What are scattering mechanisms and BS affected by?

A
  • System Parameters (Incidence angle, resolution, frequency, polarization)
  • Target Parameters (Target geometry, surface roughness, electrical properties i.e. moisture)

Geog319RmSns (15 decks)

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