LIDAR

What type of remote sensing is LIDAR?

It is a form of active remote sensing

What does LIDAR stand for?

Light Detection and Ranging

What is LIDAR?

It measures wavelengths in UV, Visible and NIR. Measures the time different between the emissions and reflection. Has a variable time of flight, can fly any time of the day, can get info on terrain and topographic data

What are some things LIDAR cannot do?

Cannot do aerial photography, cannot collect information in all types of weather and cannot see through objects. If the Sun can't get past then LIDAR will not either.

Why can LIDAR fly regardless of the time of the day but weather matters?

Different weathers change the way light is reflected as it as higher chances of hitting raindrops or clouds causing interference and reflectance of the wrong objects. It also does not rely on the Sun for energy as it is active form of RS

What happens when the laser is pulsed on LIDAR?

- The transmitter generates an optical pulse
- Pulse is reflected off of an object and returns to the receiver
- A high counter measures the time from the start pulse to the return pulse
- Time measurement is converted to a distance

Can multiple returns be measured for each pulse?

Yes

What does the distance tell us when measured with the LIDAR system?

Distance to the target and position of the airplane tells us the elevation and location of object

What is terrestrial LIDAR used for?

It is a ground-based LIDAR system used for close-range and high accuracy areas.

What are some characteristics of terrestrial LIDAR?

results are within mm and cm, either mobile or static, can rotate 360º

What is GLAS stand for?

Geoscience Laser Altimeter System

What does GLAS do?

It was the the first instrument for global observations. It looks particularly at Ice, Cloud and Land Elevation

What does ATLAS stand for?

Advanced Topographic Laser Altimeter System

What does ATLAS do?

It also measures the elevation for ice, cloud and land elevation. Its laser pulses 10,000 times per second and each pulse will have about 20 trillion photons.

How many photons from ATLAS make it to the Earth's surface?

Only about a dozen photons will hit the Earth's surface and go back to the satellite.

What does GEDI stand for?

Global Ecosystem Dynamics Investigation W

What are some characteristics of GEDI?

It's on board with ISS, it has full waveform LIDAR (will gave the shape of the object) and is a 2 year mission.

What is Airbone LIDAR?

It uses a scanning mirror that has high accuracy which is better than DEM which we get with optical

What are the three components of the LIDAR system?

Laser, Scanning system and detector, and navigation and positioning systems

What does the laser do?

It has a wavelength that is dependent upon the platform. Such as blue-green lasers are used for water penetration and topographic LIDAR is 1964 nm which is eye-safe.

What does the scanning system and detector consist of?

Scanning mirror, ranging unit, receiver optics and photodetector.

What are the three different types of scanning mirrors?

Oscillating mirror, rotating mirror, nutating mirrorW

What does the oscillating mirror do?

As the plane is moving so is the mirror which gives the Z-shaped pattern also called sinusodial.

What does the rotating polygon mirror do?

It gives parallel lives

What does the nutating mirror do?

Provides a ground pattern and eliptical pattern

Explain the navigation and positioning system.

- Inertial navigational measurement unit (IMU) continuously records the aircraft altitude vectors (orientation)
- IMU is looking at the movements of the place, such as, pitch/yaw/roll
- High-precision airborne GPS which records the 3-D position of the aircraft

What are the 4 things that are collected in a LIDAR scan?

Two-way travel time (range), position and orientation of platform, scan angles and attributes

What is two way time travel (range)?

Captures the distance only and no indication of the the direction or position

What is the position and orientation of platform?

Recorded at regular intervals. Such as every second or minute etc.

What does scan angle do?

Direction of the laser beam as it scans across - should be collected within 15º of nadir

What does attributes mean in LIDAR scan?

Return number and number of returns. Intensity/strength of reflected return which is generally weak

How many returns does a LIDAR pulse have?

Three forms of returns

What happens in the 1st return?

It determines the height of the object and is usually from local relief (i.e. treetops)

What happens in the intermediate or 2nd return?

Returns the branches or understories. More returns are here as it hits all the secondary objects

What happens at the last return?

It is the bare-earth return and it does not always have to be the ground

What does the signal look like on
(a) Multiple objects
(b) Sloped Surface
(c) Flat Surface

(a) Multiples of elongated and smaller signals
(b) Elongated signal
(c) Smaller signal

What is the energy that is returned to the sensor affected by?

The backscatter/angle of incidence, reflectivity of target's laser wavelength, and number of distinct targets within the laser footprints

What is the intensity level that is returned?

Maximum intensity level

What are different elevation models?

Digital elevation models, digital surface models, canopy height model

What is DEM?

Bare earth models of the surface of the Earth using only ground returns

What is DSM?

Contains elevation information about features such as landscape, vegetation buildings and other structures

What is the canopy height model?

It gives the true height of topographic features on the ground. AKA normalized digital surface model (nDSM)