Lidar vs Radar: The truth about technology that powers self driving cars.

 

Lidar also called Laser Radar is an acronym for Light Detection and Ranging. Lidar is basically an active remote-sensing technique that uses laser waves to measure a three-dimensional distance between the object and the sensor.

Radar is the short form of Radio Detection and Ranging. Radar is an Object detection technique that uses electromagnetic waves to determine the location, direction and velocity of moving objects.

Well, to compare lidar vs radar, let us first understand what Lidar is?

 

What is Lidar? 

 

Lidar is a remote sensing technique that uses light waves to measure,  distances between objects and is also used in the 3-D mapping of Objects as well as Earth terrain. Lidar works on very simple principle.

Laser rays are emitted from a laser transmitter, which hits the ground and gets reflected back to a specialized receiver. Time taken by laser waves to travel from transmitter to receiver is recorded. Based on this Time recorded, Variable distance measurements are calculated.

Lidar - working principle of lidar

Distance = (Time taken x Speed of light) / 2

A typical airborne Lidar sensor mounted on moving platform such as Satellites, Aeroplane, Cars etc. also consists of an Inertia measurement unit and GPS Tracking system.

GPS Tracking system gives the exact location of the instrument that is carrying the Lidar sensor. Inertia measurement unit consists of Gyroscopes and accelerometers which helps in determining proper orientation – pitch, roll and yaw of the lidar sensor.

There are primarily two types of Lidar sensors- Topographic Lidar and Bathymetric Lidar.

 

Applications of Lidar

 

It was in 1971 that Lidar came into limelight when it was first used in an Apollo mission by NASA to accurately map the distance between the Lunar Module and surface of the moon.

Since then, Lidar has found its applications in many areas such as Remote-sensing Satellites, Self-driving cars, Agricultural analysis, Air pollution monitoring, Topographical and forest cover mapping etc. 

Lidar in Remote-sensing satellites:  Today, Majority of advanced Earth Observation satellite systems are equipped with active remote sensing Lidar sensors. Lidar sensors were first included in ICESat (Ice Cloud and Elevation Satellite – 2003), that was equipped with GLAS- a space-based Lidar sensor.

GLAS Lidar sensors can precisely map Ice sheet cover in Antarctic glaciers and can  Monitor different types of Clouds and Aerosol particles present in the atmosphere.  

Lidar in Self-driving cars: Lidar sensors mounted on Artificially Intelligent Self-driving Cars gives them the ability to sense nearby objects. Therefore Lidar sensors are also termed as ‘ Eye of Self-driving cars’.

These sensors can precisely track velocity and direction of moving objects such as cars, bicycles, trucks, and even pedestrians. These sensors rotate steadily in all directions, sweeping the surroundings with the light pulse.

Apart from these, Lidar sensors can effectively scan stationary objects such as traffic signals, traffic signs etc.  Lidar sensors can also accurately calculate the distance of moving objects up to 300 metres.

Lidar in Topographical mapping: Lidar sensors are mounted on an aeroplane to conduct Topographic mapping of the surface of the earth. These Lidar sensors use near-infrared light waves(1000 nm) for topographical mapping and water penetrating green light waves (530 nm) for hydrographic mapping.

Lidar is also used in Forestry management. Laser waves emitted from lidar are powerful enough to penetrate thick forest canopies.Therefore Airborne Lidar systems are used in the monitoring of forest vegetation cover. The 3-dimensional aspect of lidar makes it highly suitable for mapping of complex terrains such as mountains, Cliffs and rivers.

 

Difference between Lidar and Radar

Lidar vs Radar

 

 

What is Radar?

 

Radar

 

Radar is an Object detection technique that uses Radio waves to detect Motion, Speed and direction of incoming objects such as aircraft, missiles, ships, and spacecraft etc.

Unlike Lidar, Radar transmits electromagnetic radio waves to detect the exact location of an object from the Radar scanner.

Radar Sensors emits radio waves through an antenna assembly which rotates steadily in all four directions. The Echo of radio waves that are reflected back from an object is received by the radar scanner.

By measuring the exact time taken for radio waves to reach the receiver, the location, speed as well as the direction of objects are calculated.    

If you are wondering that why do radar uses Radio waves and not Light waves, here’s your answer.

Radio waves are used in radar because they possess very high wavelength and easily gets reflected from faraway objects without being distorted, which helps in determining the exact location, speed and direction of far away objects. Modern-day radars possess the effective range of up to 100 miles.

EM Spectrum

 

Electromagnetic Spectrum

 

Applications of Radar

 

Radars in Air traffic control: Air traffic controllers use precision radar sensors which can detect incoming aircraft from all directions. Radars are primarily used to detect the location, speed, and direction of incoming aircraft approaching towards the airport.

With the help of radars, Air traffic controllers can safely control the movement of aircraft near the airports. Radars are also used in the monitoring of weather and environmental conditions in the vicinity of the airport. Apart from controlling air traffic, Secondary Radars are also used in controlling the ground vehicular movement of aircraft. 

Radars in Ship navigations: Marine radars are used in sea vessels to detect nearby ships and land barriers. Marine radars help in effective navigation of the ships when the ship is passing through congested waters.

Marine radars have a very high range as they are placed in tall masts. Marine radars also act as anti-collision devices and warn the captain of the ship if any other sea vessel in manoeuvring too close. 

Doppler Radar: If you are amazed at how those guys at weather forecasting agencies accurately predict the conditions of the atmosphere, then here’s your catch,

Thanks to weather radars popularly termed as Doppler Radar. Doppler radars are used in weather and precipitation forecasting. Doppler radar uses doppler effect to determine the velocity, motion and type (snow, rain, hail etc.) of precipitation. Today, most of the developed countries such as United States, France, Canada etc. have an interconnected network of Doppler radars throughout the country.

 

So, now probably you might have learned the difference between lidar vs radar, Don’t forget to share it.

 

Image Credits:

Electromagnetic Spectrum: https://commons.wikimedia.org/wiki/File:BW_EM_spectrum.png

Featured image: https://commons.wikimedia.org/wiki/File:Uber_Self_Driving_Volvo_at_Harrison_at_4th.jpg