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CONS 127 > Active Remote Sensing > Flashcards

Active Remote Sensing Flashcards

1
Q

Passive Remote Sensing

what we’ve have been doing so far

A

Passive remote sensing measures energy that is naturally emitted

o Typically from the sun
o And reflected off of targets/surfaces

slide 6

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2
Q

Active Remote Sensing

slide 6

A
  • Active sensors provide their own energy source (for illumination)
  • A sensor emits a form of radiation that is directed towards a target in a
    particular area
  • The radiation that is reflected back from the target is then detected and
    measured by the sensor
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3
Q

Passive vs. Active Remote Sensing

A

Passive
* Energy is naturally emitted from
the sun
* This energy is reflected off the
surface of the Earth
* Reflection of this energy is
measured by a sensor

Active
* Instruments produce their own
energy (radiation)
* Energy travels towards a target
and is reflected
* Sensor detects and measures
this reflected radiation

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4
Q

Active Remote Sensing: Advantage

A
  • Weather independent specifically for
    RADAR
  • Sunlight independent
    -Survey at anytime of day
    -Control energy emitted
  • Can penetrate vegetation, soil,
    ice and snow only RADAR
  • Information on surface layers and
    structure

LiDAR cannot penetrate throughsurfaces

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5
Q

Active Remote Sensing: Disavantages

A
  • Limited spectral information
  • Complicated analysis
  • Costly
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6
Q

Why would active remote sensing have limited spectral information?

IMPORTANTTTTT

A

with passive sensors we are able to measure reflectence for a wide number of spectrum bands

we can measure reflectence of:
* visible red,blue,green light,
* near infared light,
* shortwave infared light
* ,etc

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7
Q

Three Types of Active Remote Sensing

A
  1. RADAR – uses high frequency radio / microwaves
  2. LiDAR – uses a laser light beam (often VIS or NIR)
  3. SONAR – uses sound waves
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8
Q

RADAR (RAdio Detection And Ranging)

A

Radar works with different wavelengths in the microwave part of the spectrum, by:

  1. Transmitting a microwave (or radio) signal towards a scene
  2. Receiving the portion of transmitted energy backscattered from the scene
  3. Observing the strength (detection), orientation and time delay (ranging) of the return signals- we can determine how far away the sensor is

o We mostly discuss detection in this class

btw microwaves is a subcategory of radio waves

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9
Q

Why Use RADAR?

A
  • Active microwave energy penetrates clouds and serves as an all-
    weather remote sensing system
  • Coverage can be obtained** at user-specified times, even at night**
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10
Q

Three factors govern the response of the backscatter/reflection: RADAR

A

1.Surface roughness

-Corner reflector:strong detection/signal going to be sent back from the sensor/backscatter

-Specular reflection: the signal might be sent to the opposite direction/away from the sensor

-Diffuse Reflection: they have energy bouncy around all directions

2. Dielectric properties
:
increse in dielect properties will result in a larger ammount of backscatter/gretatter detection

chemical makeup of materials and their condectivity

3.Moisture content

an increse in moisture content will result in increse of backscater recived by the radar signal

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11
Q

RADAR Bands

IMPORTANT : band size and ground penetration (how small or how big)

A
  • X smallest band ( smallest ground penetration)
  • C small band (small ground penetration
  • L Large (large ground penetration)
  • P Largest bands(Largest ground Penetration)
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12
Q

Scattering

A

ScatteringGeneral Rule: choose the wavelength that approximates the objects of interest

  • Smaller target: X-band
    o Example: rain droplets
  • Medium target: C-band
    o Example: leaves
  • Larger target: L & P-band
    o Example: branches and tree trunks
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13
Q

RADARSAT 1 and 2

canadian remenber?

A
  • First operational civilian RADAR satellite launched in November 1995
  • RADARSAT 2 Launched In Dec** 2007**
  • both use a C-band
  • Spatial resolution from 8 - 100m
  • Can see through clouds and very good at detecting sea ice and snow
  • Covers polar regions daily
  • Temperate zones every 3 days; Tropical zones every 5 days
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14
Q

3rd RADARSAT is the
RADARSAT Constellation

A
  • third RADARSAT
  • 3 Identical smaller satellites
  • 3-8m pixel
  • quicker in producing an image because there a 3 satelittes instad of 1
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15
Q

Why is RADAR particularly suitable for a country like Canada?

A
  • canada is very high latitude country, with a lot of artic areas, during winter there is not a lot of sunlight which can make it difficult to collect data

but with radar we can collect images at any time of the day even in darkness

  • there is also a lot of snow in canada , RADAR is particular good at detecting and mesuring snow and ice cover
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16
Q

RADAR Applications

A

* Ice mapping: ex: Antartic , good to have this because we can see the impact of climate change

  • Oil spills
  • Ground penetrating RADAR for archaeology
17
Q

RADAR Applications: Oils spill

A
  • Camarthen Bay, Wales, a super tanker, ran aground on rocks on February 15, 1996, releasing crude oil
  • Oil floats on water, suppressing
    oceanic capillary waves, and creating
    a surface that is smoother than the
    surrounding water
  • Easily detectable day or night by RADAR at any weather conditions
18
Q

Ground Penetrating RADAR: Archeology

A

ex:

  • Geophysical archaeological study at several Viking Age and medieval sites in West Jutland, Denmark
19
Q

LiDAR( Light Detection And Ranging)

A
  • Sends a pulse of laser light
    o A laser is a narrow beam of light
    o All with the same wavelength
  • Thus, not all weather system
    o User picks wavelength

42;22

20
Q

What do you think are the most common types of electromagnetic

waves (i.e. wavelengths) used in LiDAR for environmental
applications?

A
  • Near Infraed energy

sometimes visible green light

because of the strong reflectence of near infared light by vegetation

21
Q

LiDAR
Technologies:

A
  1. Laser ranging
    * Measures distance to targets(from the sensor/sitelite)
    * we can determine that by how long it takes for the pulse to get to the target and back
  2. Positioning (GPS)
    * To determine geographic location and height of sensor
  3. Inertial Measurement Unit (IMU)
    * To determine precise orientation/angle of sensor
    * to make sure the target is determined with precise acuracy
22
Q

LiDAR: How it works

A
  • LiDAR system emits pulse of laser light
    o Times how long it takes that pulse to travel to target, bounce off that target,
    and return to the sensor
    o Using the speed of light, calculates how far that target is from the sensor
  • Using the precise location (GPS) and orientation (IMU) of the sensor:
    o Calculates where that target is in** 3D space**
23
Q

LiDAR

A

Lidar system emits thousands to millions of pulses per second

o Each one of these pulses typically has 1(closer to sensor) – 5 (further from sensor) return measurements

o this is a lot of data that Results in very high resolution 3D data

LiDAR dosnt penetrate through surfaces like RADAR does, but it does allow us to have structural information below the top of canopies because of the gaps in thees canapies

52:52. 56;00

24
Q

Applications of LiDAR

A

Two types of information can be derived from LiDAR that we will
discuss in class:

  • Terrain Data
    -In the form of Digital Elevation Models (DEMs)
  • Structural Information of Vegetation
    -in the form of point clouds
25
Q

Digital Elevation Models

A

are grids where each cell has a number that represents the elavation of the ground in that cell/pixel

26
Q

LiDAR: Forest Structure

A
  • LiDAR is an excellent tool for
    measuring forest structure
  • Lidar can be used to gather a
    tremendous amount of detail
    relating to forest structure and the
    vertical organization of plant biomass.
27
Q

LiDAR: Forest Structure

A

(pole/sapling/new three)
* Not structurally complex
* Very dense canopy

(old forest)
* Structurally complex
* Lots of canopy gaps

28
Q

LiDAR Applications

A

The 3-D information capable from Lidar systems allows for a wide
breadth of environmental applications, to name a few:

  • Habitat mapping (wildlife and vegetation)
  • Resource management
  • Community planning
  • Environmental disasters (predictions and response)
  • Biomass mapping
  • Forest growth models
  • Storm impacts
29
Q

SONAR(Sound Navigation and Ranging)

A
  • Transmits a sound signal
  • The signal propagates towards an object of interest
  • The signal is then reflected by the target or object and is recorded by a receiver
  • Some SONAR signals we can hear, and others are at such a high frequency we cannot
30
Q

Applications of SONAR

A
  • Submarines use SONAR to detect other vessels
  • Fishing boats use SONAR to locate schools of fish
  • Oceanographers use SONAR to map the contours of the ocean floor

-By measuring the return strength of the “echo” we can measure ocean depth, and surface material

  • Some animals use BioSONAR or echolocation to see
    ex:Bats, dolphins, etc.
31
Q
A

CONS 127 (19 decks)

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