LiDAR data overview

Dr. Keiko Saito

Global Facility for Disaster Reduction and Recovery (GFDRR)

3D height profile

LiDAR (Light Detecting And Ranging)

• Laser emitted from sensor onboard aircraft to measure the distance between the sensor and the nearest object on the earth’s surface

Aerial photograph draped on LiDAR data

1. Flying at high altitude for collections over a large area

2. Flying at low altitude for collection in e.g. a transportation corridor

3. Mobile collection for high accuracy mapping of a wide area

4. Terrestrial LiDAR

Four LiDAR capture techniques

1. Flying at high altitude for collections over a large area (e.g. state wide flood risk mapping)

Accuracy for these are 9.25 to 18.5 cm vertically. 20 cm – 1 m horizontal accuracy.

Fixed wing Aircraft flying at between altitude 400 to 2500 m. Sensor performance requires the altitude to be no more than 2500m. Flight line length is also limited due to the IMU.

Requires ground differential GPS stations. Two or more stations during a flight.

The correction data can be obtained from •virtual reference stations (VRS), continuous•operating reference stations (CORS), •national geodetic survey (NGS) points, or •established points that are referenced to a network

Base stations should be located with a certain radius of the aircraft at any given time.

Four LiDAR capture techniques

2. Flying at low altitude for collection in a transportation corridor e.g. road surveys, rail line surveys, transmission surveys, and pipeline surveys, use of low altitude collection (helicopter)

•The sensors can be flow as low as 50 m above the target and as high as 800 m.

•The sensors operate at much higher repetition rates

•Point sample spacing is much higher, at20-100 points per meter.

•Several base stations should be set up for corridor mapping projects along the corridor.

Four LiDAR capture techniques

3. Mobile collection for high accuracy mapping of a wide area

The sensors are mounted on a van or vehicle, rail car, boat. Sensor is rotated 360 deg.

DMI to provide velocity info as well as IMU for inertia.

The sensors operate at1550 nm, newest sensors.

Distance from target few meters to 200 meters.

Point sample spacing is much higher, 1000-4000 points per meter.

Seeking accuracy of 1-3 cm.

Need more rigorous base stations, always within 10 km of the sensor.

Need to consider traffic when planning for the survey.

Four LiDAR capture techniques

4. Terrestrial LiDAR

The sensor is stationary. Used to map very specific areas of interest i.e. a tunnel, bridges,

Inexpensive compared to other systems. High detail in a short amount of time.

Four LiDAR capture techniques

Example (1) FEMA Flood plain maps: point sample spacing of 1.4 meters

Need to achieve accuracy of 0.5 m horizontally and 15-18.5 cm vertically2 foot contour specification

Example (2) Electricity utility companies and contractors will have to collect 20-40 points per meter in order to properly map power lines

The denser and higher the accuracy required, helicopters are used. But fixed wing aircraft are increasingly being used for these as well. Helicopter can fly a alower altitude, hence can collect denser data with higher accuracy.

For engineering grade Information required by, for example, transportation engineers, mobile mapping lidar is used. Provided that adequate ground control points are utilised for high accuracy data calibration.

Scale and point density depends on the project.

Example: Koshimura et al, (2011) Tsunami

• Example: Inomata et al (2009) Flood risk modeling sensitivity to DEM resolution

図-2 Laser Profiler（左上），ALOS PRISM（右上），ASTER（左下），SRTM（右下）の標高縦断図

Inomata et al, (2009), A study on accuracy of satellite based topographical data and its applicability to flood inundation simulation,

GEBCO global bathymetry data

(from website)

•The General Bathymetric Chart of the Oceans (GEBCO) is made up of an international group of experts in ocean mapping. We develop and make available a range of bathymetric data sets and data products.

•It operates under the joint auspices of the Intergovernmental Oceanographic Commission (IOC) (of UNESCO) and the International Hydrographic Organization (IHO).

• Products produced (downloadable free of charge) include:

the GEBCO_08 Grid (at 30 arc-second intervals – still beta version) and GEBCO One Minute Grid (at one arc-minute intervals) a global set of digital bathymetric contours the GEBCO Gazetteer of Undersea Feature Names the GEBCO Digital Atlas the GEBCO world map

Global dataset

Bathymetry overlaid with a land map

LiDAR usage

• LiDAR can be used for flood, tsunami, landslide modeling

• The horizontal spacing of the DEM data used as input to the models has an effect on the results..

• “USGS National Elevation Dataset (NED) is critical to identifying and modeling geologic features such as water drainage channels and basins, watersheds, peaks and pits, and land movements such as avalanches.

NED is used to create relief maps, 3-D visualizations, to classify land cover and to geometrically correct data from satellite or aircraft sensors (orthorectification). The fire community, natural resource managers, urban planners, conservationist, emergency responders, communication companies to name a few all rely on these elevation datasets.”

• IF the data can be shared between different departments of the government. (Licensing, legal framework, ownership, open data, cost)

The cost of acquiring LiDAR data

• LiDAR is 40% less expensive than classic photogrammetric collection. Less time to collect and process data too.

• Cost of hiring the sensor for X number of days, the specialists to man the sensor, in the case of airborne LiDAR, the pilot and specialist’s time, the aircraft, fuel, post-processing of the data to make it into a useable format.

• Following the Haiti earthquake in 2010, GFDRR acquired LiDAR data for the Port au Prince area. The cost was in the region of 200,000 USD. H

What Type of LiDAR Data Do I Really Need?

✓ Accuracy requirements for data.✓ Extraction requirements — do you just need points, orlinear features, too?✓ End products you’ll require. Do you need a triangulatedsurface, a classified LAS, and/or GIS features?

Thank you for your attention!

For questions, please contact ksaito2@worldbank.org