Mapping methods using airborne sensors
Vessel-based mapping capabilities can be supplemented in nearshore and shallow coastal areas with airborne sensors such as laser altimetry, hyperspectral and thermal imaging. Where the water is shallow or otherwise un-navigable, the airborne sensors provide an opportunity to map without direct impact to sensitive resources.
Aerial photography is the traditional airborne mapping method, requiring
hands-on operator interpretation and mapping. New sensors, imaging systems,
and advances in computing have expanded airborne mapping methods to include
quantitative measurements and water-penetrating sensors that facilitate
feature discrimination and objective change evaluation. Investigators at
the St. Petersburg Coastal and Marine Science Center use airborne sensors to map nearshore, shallow, and inaccessible tidal areas (http://coastal.er.usgs.gov/remote-sensing/index.html). Complete geographic coverage, little or no direct impact, high resolution, and multiple sensors/bands are some of the advantages of airborne mapping methods.
- Laser altimetry, often referred to as Lidar (Light Detection and Ranging) is a scanning airborne laser technology (http://coastal.er.usgs.gov/lidar/). Lidar acquires laser pulse returns to detect features of the earth surface or beneath shallow water (http://gulfsci.usgs.gov/tampabay/data/1mapping/lidar/). The surface elevations or depths derived from laser altimetry can supplement existing maps with detail not typically available.
- Hyperspectral, multi-spectral, and thermal Infrared imagery can provide improved maps of aquatic and terrestrial features with project-specific band selection and computer post-processing of the imagery. Submerged habitats, bathymetry and wetlands can be mapped with hyperspectral imagery (http://pubs.usgs.gov/of/2007/1382/).
Read the related USGS Fact Sheet "Mapping and Vessel-Based Capabilities"