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Active Remote Sensing > Topic 5: LiDAR > Flashcards

Topic 5: LiDAR Flashcards

1
Q

what does LiDAR stand for

A

Light detection and Ranging

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2
Q

what is an INS

A

Inertial navigation system
- measures acceleration and gyroscope of device.

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3
Q

LiDAR Data

A

X,y,z
- intensity

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4
Q

what is LITE

A

LiDAR in space technology experiment
first detailed view of vertical structure of cloud and aerosol form surface through middle atmsophere

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5
Q

how is data typically collected in lidar

A

sensors are flown on aerial platforms

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6
Q

what are some applications of LiDAR

A

DTM
Geology
Forestry
Oceanography
Glacier mapping

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7
Q

what is a Laser

A

focus coherent beams of light energy with very little divergence.

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8
Q

how does LiDAR use lasers

A

sends pulses of light to a target and the reflected light which returns is measured

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9
Q

single return

A

if all the incidence energy is reflected from a solid object

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10
Q

multiple returns

A

when some light passes through canopy and hits multiple objects resulting in multiple returns. Similar to Volumetric

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11
Q

what is PRF

A

pulse repetition frequency
has been increasing with advancements in technology
increased PRF results in greater accuracy

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12
Q

what is a DTM

A

Digital terrain model shows elevation of the bare earth

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13
Q

what is a DEM

A

digital elevation models are used to create DTM and DSM, database containing elevation points

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14
Q

what is a DSM

A

digital surface model showing the elevation of all features on a landscape. contains trees, buildings, and other structures above ground

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15
Q

methods of creating DEM’s

A
  • in-situ surverying (expensive)
  • interferometric SAR (errors with veg)
    Photogrammetry (less accurate than LiDAR)
    -LiDAR
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16
Q

what are the two main wavelengths of LiDAR

A

Infared
blue-green

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17
Q

Blue-green wavelength uses

A

bathymetric

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18
Q

NIR wavelength uses in LiDAR

A

terrestrial topographic mapping

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19
Q

discrete return LiDAR system

A

records X,Y,Z and intensity
intensity from amplitude of returned signal

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20
Q

how does multiple returns work

A

A signal can have multiple returns if it interacting with a complex surface (tree canopy) part of the single will be returned, resulting in lower intensity in each returns than if it was all one return.

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21
Q

discrete return LiDAR system

A

records multiple returns into descrete levels
intenisty of pulse range through multiple returns

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22
Q

what is one downside of multiple returns

A

increased the size of datasets significantly

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23
Q

Full Waveform LiDAR

A

records the entire waveform of the return laser pulse, very high precision
results in extremely high data volumes

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24
Q

two types of LiDAR sensors

A

1.Profiling
2. imaging
they differ in how swath data is collected

25
Q

Profiling Lidar

A

Nadir facing. an echo profile along the flight path of sensor recorded

26
Q

Imaging LiDAR

A

directing pulses over a swath beneath the platform traveling
- extended echo profile
- mos common in areal LiDAR systems

27
Q

are spaceborne LiDARS Profiling or Imaging?

A

Profiling, like

28
Q

swath width, vs footprint

A

swath with is the width of the footprint. footprint usually oval.

29
Q

how do height and swath width relate

A

greater heigh, greater swath width. opposite true

30
Q

how is footprint measured

A

diameter

31
Q

how does height and footprint relate

A

greater height, greater footprint. OT. based on divergence

32
Q

rough footprint size of airborne Lidar

A

0.2m - 0.9m

33
Q

rough footprint size of spaceborne LiDAR

A

13m

34
Q

swath pattern is determined by…

A

scanning mechanism
- profiling
- imaging
also a function of point density

35
Q

what are the three main data processing techniques for LiDAR

A

-filtering
-classification
- interpretation

36
Q

what is LiDAR FIltering

A

removing unwanted data, removal of partial returns in order to keep first and last returns

37
Q

what does a first return represent

A

DSM

38
Q

what does a Last return represent

A

DTM

39
Q

what the difference between first and last return represent

A

Height Model (eg. CHM)

40
Q

what is a filtering algorthrim

A

something that is used to separate point clouds

41
Q

what is a CHM

A

canopy Height model (DSM-DTM)

42
Q

what is the goal of classsification

A

-find specific structure after filtering
-appling class labels

43
Q

LiDAR classification can be based on..

A

elevation, slope or intensity

44
Q

ways to enhance LiDAR imagery

A

combine it with Optical to improve interpretation

45
Q

interpolation

A

used to fill in between areas of no data for DTM

46
Q

what is the goal of interpolation

A

to correct a smooth, accurate continuous dataset from descrete points

47
Q

what are the two common methods for Interpolation

A
  1. inverse distance weighting
  2. Spline
    - other methods are based on nearest Neighbour
48
Q

Inverse Distance Weighting (IDW)

A

interpolation method
weights are assigned to to known values within a neighbourhood
- useful for locationally dependant vairables
-trends not accounted for,
Can create Duck Egg pattern

49
Q

Spline

A

an interpolation method
- piece-wise
- smooth cuves are locally fitted to set a data points using polynomial functions
- quick DEM creation
- small scale features retained
- creates an uncharcteristically smooth surface

50
Q

LAS file format

A

standard for storing point cloud data

51
Q

benefits of LAS file format

A

available software
datasets easily transferable
eliminates need for proprietary software

52
Q

what are three wavelength dependent applications of LiDAR

A
  • atmospheric applications
  • bathymetry
  • vegetation surface
53
Q

differential measurement of LiDAR

A

different LiDAR wavelengths are measured to note differneces

54
Q

what is Differential Absorption LiDAR (DIAL)

A

where intensity of returns at different wavelengths are used to Infer Atmospheric Properties.

55
Q

NASA’s Airborne topographic mapper is used for

A

measuring thinning ice sheets

56
Q

what is 3DEP

A

3D Elevation Profile
- generates LiDAR PC and DEMs

57
Q

what is Terrestrial Laser scanner

A

ground based version of a Airborne LiDAR
- short ranged scanning
- photorealistic 3D mapping

58
Q
A

Active Remote Sensing (4 decks)

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