What Is Lidar?
by Marshall Honorof, TechNewsDaily Staff Writer
June 18 2013 04:40 PM ET
Whether you need to map out a landscape or discover an ancient city, lidar — an advanced application of laser technology — is probably your best bet.
Recently, a global team of researchers using lidar technology discovered the lost city of Mahendraparvata underneath the temples of Angkor Wat in Cambodia. The unobtrusive scanning method allowed researchers to unearth an entire network of streets and city blocks without harming the priceless structures above.
Although lidar uses sophisticated technology, there's nothing mysterious about how it works, or why it presents so many opportunities for researchers of all stripes.
What is lidar?
Lidar is an acronym that stands for "light detection and ranging," although its name may originate from a combination of "light" and "radar." A lidar device is usually attached to an airplane or helicopter, and then flown above an area that scientists wish to study.
A lidar device sends out pulses of laser light over an area of interest, while a scanner and a GPS receiver interpret the data and assemble it into a detailed 3D map. The targeted area reflects the light, and depending on how long it takes, the scanner and the receiver can calculate the shape and elevation of the target.
What is the difference between lidar and radar?
Although lidar and radar have similar names, the two scanning methods function in very different ways.
Radar ("radio detection and ranging") devices broadcast radio waves to bounce off of objects. When a radar dish or antenna receives "pings" from distant bodies, it can calculate an object's distance, size and rough trajectory with fair accuracy.
The wavelengths in radar scanning are much longer than those in lidar. This means that radar scans do not need a particular target, and can sweep a wide area over a very short amount of time. As a practical example, a policeman could set up a radar system to determine which cars are speeding, or use a lidar device to determine if a car in question is speeding.
What is lidar used for?
Lidar's primary function is for scanning and mapping either geographic regions or man-made objects. When creating topographic maps, lidar uses infrared light over land, and visible green light to penetrate water and depict seafloors.
As with the city of Mahendraparvata, archaeologists can use lidar to scan beneath vegetation, and even existing structures, to see long-standing features that have been covered by plants or erosion. Alternatively, if plants are of interest, lidar can create forest maps accurate enough to estimate an entire ecosystem's biomass.
Aiming lidars skyward can help meteorologists determine the weather and astrophysicists detect minerals on the surface of foreign planets, like Mars, through lidar tech in rovers and landers. Robotic vehicles and other autonomous devices use lidar to navigate, while architects and engineers can scan structures with lidar in order to recreate them or examine their stresses under real-world conditions. [See also: 10 Technologies Poised to Transform our World]
Who invented lidar?
Lidar does not have one specific inventor. It came into being in the early 1960s in the United States, alongside the widespread use of lasers in military applications. The National Center for Atmospheric Research used it to research weather patterns in clouds. As the technology became cheaper and more widely available, industries from farming to law enforcement adopted it.
How accurate is lidar?
The accuracy of lidar depends on a number of factors, including scanning distance and the brand of scanner used. According to Airborne 1, one of the foremost lidar mapping outfits in the United States, lidar scanners that attach to airplanes or helicopters can generally scan with an accuracy of about 2 centimeters (0.79 inches) at an elevation of 4,000 feet (1,219 meters). At this elevation, a lidar device can generally scan an area in intervals of 4.5 feet (1.4 m). Favorable flying conditions and more advanced GPS models can improve these numbers, while obstructions and old equipment can hinder its accuracy.
Lidar is one of the most versatile technologies available, and with any luck, it hasn't uncovered its last lost city.
More
The following tutorials on radar remote sensing originate from the Canadian Centre for Remote Sensing (CCRS). Navigate your way through the tutorial matter by using the sub-sections displayed in the menu on the left in the CCRS webpage.
Please note that the use of this material is strictly for non-commercial purposes. When refering to it, the RSAC should be duly acknowledged.
What is the difference between radar and lidar?
Radar (radio detection and ranging) and Lidar (light detection and ranging),
Radar:- Radar units transmit radio waves at a designated frequency that reflect off of a moving target vehicle and return to the unit.The difference between the transmitted frequency and the return frequency is called the Doppler frequency or Doppler shift, which is used to determine the target vehicle's speed. The greater the shift received by the unit, the greater the speed.
Lidar:-Lidar (light detection and ranging), on the other hand, sends out a laser beam. The initial bursts of light allow the lidar unit to determine the distance to the target vehicle.
both Radars and Liars are used to measure the speed of vehicles but many officers prefer to use radar in fastest mode to easily obtain the speed of the motorcycle.
LIDAR does take slightly longer than receiving a reading using radar.
Both are failed in the heavy traffic situations.
Radar:- Radar units transmit radio waves at a designated frequency that reflect off of a moving target vehicle and return to the unit.The difference between the transmitted frequency and the return frequency is called the Doppler frequency or Doppler shift, which is used to determine the target vehicle's speed. The greater the shift received by the unit, the greater the speed.
Lidar:-Lidar (light detection and ranging), on the other hand, sends out a laser beam. The initial bursts of light allow the lidar unit to determine the distance to the target vehicle.
both Radars and Liars are used to measure the speed of vehicles but many officers prefer to use radar in fastest mode to easily obtain the speed of the motorcycle.
LIDAR does take slightly longer than receiving a reading using radar.
Both are failed in the heavy traffic situations.
Even More
Radar and LiDAR
If you have worked your way through the Satellites and sensors tutorial of the CCRS, you will have
read about LiDAR and radar under the 'Other sensors' topic. LiDAR and radar are
both active remote sensing techniques, in other words they both send out a
signal which bounces or scatters off ground surface features in different ways.
The backscattered or reflected signals are received by the sensor which make up
the remote sensing image data. The links below will guide you through a number
of tutorials that focus on radar and LiDAR. Extra useful links are provided in
the right-hand margin of this apge.
Radar
Radio Detection and Ranging (radar) remote sensing is based on microwaves. Although the most common use of radar remote sensing is in active mode, passive radar remote sensing techniques also exist. A big advantage of radar remote sensing is that the longer wavelength microwave radiation can penetrate through cloud cover, haze, and dust, which makes it very useful in areas that are continuously covered in cloud or are otherwise not easily acquired by optical remote sensing tecniques.The following tutorials on radar remote sensing originate from the Canadian Centre for Remote Sensing (CCRS). Navigate your way through the tutorial matter by using the sub-sections displayed in the menu on the left in the CCRS webpage.
LiDAR
Light Detection and Ranging (LiDAR), also referred to as airborne laser scanning (ALS), is a relatively new remote sensing technique that allows the measurement of relative heights of (objects on) the ground surface. This technique is widely applied for canopy height retrieval or mapping digital elevation models of the ground surface. The following links will guide you through a series of tutorials on LiDAR remote sensing. The material presented in these tutorials was provided by the Remote Sensing Applications Centre (RSAC) and was adapted with permission for the UK forestry context.Please note that the use of this material is strictly for non-commercial purposes. When refering to it, the RSAC should be duly acknowledged.
