Topic 5: LiDAR

Question 1

what does LiDAR stand for

Answer 1

Light detection and Ranging

Question 2

what is an INS

Answer 2

Inertial navigation system
- measures acceleration and gyroscope of device.

Question 3

LiDAR Data

Answer 3

X,y,z
- intensity

Question 4

what is LITE

Answer 4

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

Question 5

how is data typically collected in lidar

Answer 5

sensors are flown on aerial platforms

Question 6

what are some applications of LiDAR

Answer 6

DTM
Geology
Forestry
Oceanography
Glacier mapping

Question 7

what is a Laser

Answer 7

focus coherent beams of light energy with very little divergence.

Question 8

how does LiDAR use lasers

Answer 8

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

Question 9

single return

Answer 9

if all the incidence energy is reflected from a solid object

Question 10

multiple returns

Answer 10

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

Question 11

what is PRF

Answer 11

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

Question 12

what is a DTM

Answer 12

Digital terrain model shows elevation of the bare earth

Question 13

what is a DEM

Answer 13

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

Question 14

what is a DSM

Answer 14

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

Question 15

methods of creating DEM’s

Answer 15

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

Question 16

what are the two main wavelengths of LiDAR

Answer 16

Infared
blue-green

Question 17

Blue-green wavelength uses

Answer 17

bathymetric

Question 18

NIR wavelength uses in LiDAR

Answer 18

terrestrial topographic mapping

Question 19

discrete return LiDAR system

Answer 19

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

Question 20

how does multiple returns work

Answer 20

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.

Question 21

discrete return LiDAR system

Answer 21

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

Question 22

what is one downside of multiple returns

Answer 22

increased the size of datasets significantly

Question 23

Full Waveform LiDAR

Answer 23

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

Question 24

two types of LiDAR sensors

Answer 24

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

Question 25

Profiling Lidar

Answer 25

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

Question 26

Imaging LiDAR

Answer 26

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

Question 27

are spaceborne LiDARS Profiling or Imaging?

Answer 27

Profiling, like

Question 28

swath width, vs footprint

Answer 28

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

Question 29

how do height and swath width relate

Answer 29

greater heigh, greater swath width. opposite true

Question 30

how is footprint measured

Answer 30

diameter

Question 31

how does height and footprint relate

Answer 31

greater height, greater footprint. OT. based on divergence

Question 32

rough footprint size of airborne Lidar

Answer 32

0.2m - 0.9m

Question 33

rough footprint size of spaceborne LiDAR

Answer 33

13m

Question 34

swath pattern is determined by...

Answer 34

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

Question 35

what are the three main data processing techniques for LiDAR

Answer 35

-filtering -classification - interpretation

Question 36

what is LiDAR FIltering

Answer 36

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

Question 37

what does a first return represent

Answer 37

DSM

Question 38

what does a Last return represent

Answer 38

DTM

Question 39

what the difference between first and last return represent

Answer 39

Height Model (eg. CHM)

Question 40

what is a filtering algorthrim

Answer 40

something that is used to separate point clouds

Question 41

what is a CHM

Answer 41

canopy Height model (DSM-DTM)

Question 42

what is the goal of classsification

Answer 42

-find specific structure after filtering -appling class labels

Question 43

LiDAR classification can be based on..

Answer 43

elevation, slope or intensity

Question 44

ways to enhance LiDAR imagery

Answer 44

combine it with Optical to improve interpretation

Question 45

interpolation

Answer 45

used to fill in between areas of no data for DTM

Question 46

what is the goal of interpolation

Answer 46

to correct a smooth, accurate continuous dataset from descrete points

Question 47

what are the two common methods for Interpolation

Answer 47

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

Question 48

Inverse Distance Weighting (IDW)

Answer 48

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

Question 49

Spline

Answer 49

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

Question 50

LAS file format

Answer 50

standard for storing point cloud data

Question 51

benefits of LAS file format

Answer 51

available software datasets easily transferable eliminates need for proprietary software

Question 52

what are three wavelength dependent applications of LiDAR

Answer 52

- atmospheric applications - bathymetry - vegetation surface

Question 53

differential measurement of LiDAR

Answer 53

different LiDAR wavelengths are measured to note differneces

Question 54

what is Differential Absorption LiDAR (DIAL)

Answer 54

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

Question 55

NASA's Airborne topographic mapper is used for

Answer 55

measuring thinning ice sheets

Question 56

what is 3DEP

Answer 56

3D Elevation Profile - generates LiDAR PC and DEMs

Question 57

what is Terrestrial Laser scanner

Answer 57

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