Change Analysis using LiDAR

Landfill Investigation
Blacktown City Council in the fast-growing western suburbs of the Sydney Metropolitan area, has been dealing with the problems of unchecked and sometimes unauthorised landfill or excavation in the local government area. These activities change the drainage system and affect floodplain characteristics, which are of concern to engineers undertaking hydrologic/hydraulic modelling for flood studies and development planning.

LiDAR and Orthophotography
Blacktown City Council surveyors and engineers utilised an innovative approach for detecting and measuring landfill using LiDAR (also known as Airborne Laser Scanning) over different time periods. In 2001, an airborne LiDAR survey was undertaken by AAM to create a base data set and digital terrain model (DTM). Extensive field survey was undertaken to verify the accuracy and ability of the LiDAR data to define the terrain surface, with particular emphasis along watercourses.

Aerial photography was also acquired to create a visual record at the same time, to support investigations. In 2006 a LiDAR survey was repeated for the entire LGA, thus creating the third successive set of surface data after the completion of the major road and engineering works in the M7 Motorway corridor and adjacent areas.

Isopach analysis (refer image below) was used in the comparison of the DTM’s and in mapping the differences as areas of variation, like a contour map or elevation model. The change in the terrain surface is represented as a height above or below the baseline 2001 derived surface. Any change greater than the threshold is apparent in the GIS layer when integrated with roads and property boundaries.

This project demonstrated that surveying and spatial science technologies can be used to effectively measure, monitor and report the impact of unauthorised landfilling activities on floodplains over large areas. The project demonstrated that the methodology developed a fast and accurate means to assess potential sites. Useful and accurate evidence was gathered to support Council officer’s claims for resolution and/or prosecution.

To read the expanded case study, click here (PDF - 0.3MB).

For more information on LiDAR, click here.