Traditional orthoimagery of downtown Toledo, Ohio.
If your department’s invested in aerial mapping and/or light detection and ranging (LiDAR) data acquisition, it’s already paid for a wealth of information that can be manipulated far beyond the traditional uses: topography for engineering design, for example, or reassessing property values.
Using the information that’s already been gathered, a GIS/remote sensing specialist can create 3-D digital surface models and identify application-specific characteristics with near-term ROI potential. Depending on the type and extent of the information you need, this service can be provided for an additional $10,000 to $500,000.
Public entities that conduct remote sensing can take the next step and employ a technique called feature extraction that has virtually limitless possibilities for civil improvements. The four most common are mapping impervious surfaces, land cover, tree species/woodland area, and solar-power potential.
How data’s gathered
The data acquisition process combines aerial 2-D photogrammetry and 3-D LiDAR to build an extremely precise dataset, complete with the necessary components to successfully perform feature extraction.
To avoid obstructions, the base dataset is usually collected after leaves have fallen, when there’s little cloud cover, and when the sun is at a minimum 30-degree angle.
Using aircraft equipped with multispectral, four-band (RGB and near-infrared) digital cameras, and LiDAR sensors, aerial technicians capture surface features at altitudes from 2,400 to 10,000 feet. From there, remote sensing specialists “train” software programs to perform data analysis geared toward project objectives. When the software processing’s complete, GIS technicians review the output data for completeness and accuracy and may manually make minor adjustments as necessary.
Using impervious surface data
Mapping impervious surfaces provides a comprehensive overview of all impervious surfaces, including roads, sidewalks, and parking lots in commercial, residential, and industrial zones throughout an entire stormwater assessment area.
Cities and counties use these maps to institute a fair, equitable billing system (see “Truth in stormwater billing,” Public Works, September 2010, page 45), sometimes recouping their original investment through more accurate stormwater revenues.
Another potential application: Use building outlines to update parcel zoning maps.
Using land cover data
The same area of downtown Toledo with building outlines (purple), paved surfaces (dark grey), tree canopies (dark green), grasses (light green) and open scrub land/bare surface area (orange) extracted.
Auditors faced with aging or non-existent land cover maps use feature extraction to provide modern land use assessments of a city or county.
A GIS/remote sensing specialist can extract and “crunch” surface features to identify woodlands, tillable farmland, bodies of water, waste areas, urban regions, and pastures (for livestock, animals, or produce orchards).
Another potential application: Vernal pool identification. Vernal pools serve as habitats for many native species, and they are often an integral part of larger ecosystems. Identifying vernal pools helps DOTs plan highways and roadways without harming the environment.