LiDAR Weather Radar + Synthetic Aperture Radar (SAR)

LiDAR

Light detection and ranging

Laser at the 905 nm (near-ir) wavelength

Each time the laser is pulsed:

Laser generates an optical pulse

Pulse is reflected off an object and returns to the system

receiver

One pulse can have multiple returns.

High-speed counter measures the time of flight from the

start pulse to the return pulse

Time measurement is converted to a distance

Multiple returns can be measured for each pulse

Simultaneous Localization And Mapping (SLAM)

Is the computational problem of constructing or updating a map of an unknown environment while simultaneously keeping track of your location within it.

Think of it as creating a map without knowing where you are and keeping track of your location, without possibly the use of GPS!

RADAR

◦ RAdio Detecting And Ranging

◦ A radio wave is sent out in a direction

◦ It bounces off something and comes back to the source

◦ Measure the time required to go out and back

◦ ½ the time multiplied by the speed of light equals the distance (speed of light = 3 × 108 m/sec)

Active sensing

Radar and LiDAR is ACTIVE is because it illuminates its target with a signal then receives data back from that target

• ex. taking a photo with flash

Passive sensing

Most Infra Red is PASSIVE because it depend on emitted energy from the object. (LiDAR = Active)

 EO (visible imagery) flown on drones is passive

• ex. taking a photo on your phone

Radar Uses

 Study thunderstorms from a distance

 Target detection & tracking

 Terrain mapping

 Foliage mapping

 Bird/Insect migration studies

 Change detection

Radar information

Weather radar “return signals” generally are from precipitation sized particles.

Synthetic Aperture Radar (SAR)

Areas with a lot of reflected energy show up white

Areas with little or no reflected energy show up black

The aircraft movement is used to simulate a larger antenna than actually exists

Smooth Surfaces

Oil slick can be seen on the water because there is a difference in radar reflection and absorption between oil and water even when they are both smooth on the surface

Change Detection

Always 2 photos