2010 LiDAR Project. GIS User Group Meeting June 30, 2010

Transcription

1 2010 LiDAR Project GIS User Group Meeting June 30, 2010

2 LiDAR = Light Detection and Ranging Technology that utilizes lasers to determine the distance to an object or surface Measures the time delay between transmission and reflection of a pulse What is LiDAR?

3 Acquisition Parameters Airborne GPS utilized to know exactly where plane is when data are captured Calibration using GPS base stations on ground Test strips within project area, usually in airport Survey points where CORS tower available using high-grade GPS units Every flight flies over the test strip at beginning & end of flight Foundation for instrument calibration Orthophotography has specific parameters, which are different than LiDAR specs Usually cannot capture both orthos & LiDAR at the same time For a project covering a small area, it might be possible to acquire orthos and LiDAR at the same time Not much survey data needed for field acquisition LiDAR has a more flexible acquisition time Could be captured in day or night Could capture LiDAR data in either spring or fall because sun angle does not matter Leaf-off conditions (budding OK) Based on product specifications, i.e. bareearth or tree canopy analysis Weather Conditions Clouds have to be higher than plane Cannot capture in rainy or foggy conditions Flight Mission Typically use 20% overlap Normalize overlap areas Irregular areas, not traditional blocks

4 LiDAR Acquisition ARRA Grant through USGS SEMCOG submitted on behalf of the 4 counties in the region that did not have LiDAR Woolpert selected vendor LiDAR captured during ortho flight window Leaf-off conditions

5 LiDAR Specifications 1.5-meter point spacing Each point includes: Point number X coordinate Y coordinate Z coordinate Intensity value Hydrology enforcement Products Include: Raw data: bare earth and reflective surface data in.las format Digital Elevation Model DSM (reflective surface), ArcGIS 9.2 format Intensity images, ArcGIS 9.2 GRID format

6 LiDAR Applications Rim heights (manholes) determined by creating small surface model of surrounding LiDAR points (Baltimore County) DEM supports future ortho flights Breaklines Use LiDAR to create intensity surfaces and view in 3D to create breaklines Contours in sync with LiDAR data Cost effective Contours Cartographic representation of LiDAR-derived contours can be strange Breaklines & smoothing techniques can improve contour display Building footprints (polygons) extracted using COTS in-house (Morris County, NJ) Could detect changes as small as 6 m2 (example: deck additions) Vegetation Mapping & Analysis No confusing shadows LiDAR provides height, shape, & intensity Combination of multi-spectral imagery & LiDAR provides additional classification detail Forestry & Biomass Determine tree height & volume Using combination of hyperspectral imagery (120 bands of data) and LiDAR, location & health of Ash trees were determined

7 Examples July 2001 September 15, 2001 Aerial Views and Maps of the WTC - LIDAR A laser-based imaging instrument, known as LIDAR (light detection and ranging), provided elevation data of the Ground Zero site. It enabled emergency managers to assess damage through the smoke. The LIDAR data was used to determine changes in the rubble pile and to create 3-D digital elevation models that demonstrated the extent of the destruction.

8 Contours & Slope Examples Contours made from full-resolution LiDAR on the top and a rasterized version of the thinned set on the bottom. The result, while obviously not cartographic quality, still represents a significant improvement. Slope made from full-resolution lidar is on the top and slightly thinned and rasterized is on the bottom.