Due to the growing need for precision DEM data, Aero-Metric is developing an archive of elevation data to complement our extensive historical and current film library. For example, over one billion data points covering more than 500,000 acres are included in the Anchorage Division's DEM archive.
HOW LIDAR WORKS
Lidar is an acronym for Light Detection And Ranging. It is a rapidly emerging technology for determining the shape of the ground surface plus natural and man-made features. By merging laser ranging, GPS positioning, and inertial attitude technologies, Aero-Metric offers airborne laser mapping to directly measure the shape of the earth's surface beneath the aircraft's flight path. This elevation data is generated at the rate of thousands of points per second, with absolute vertical accuracies of up to 15 cm. After hitting the tree-canopy the laser beam finds a hole between the foliage and reaches the ground. The returns are registered and a dataset is created instantly.
LIDAR PRODUCTS
Primary products derived from the raw lidar data include:
Intensity Image - When lidar data is collected, the instrument also measures the intensity of the returned light. The image is a 0-256 gray-scale measurement of the reflectance amplitutde of the light pulse. This captured information creates an orthorectified image that is comparable with a coarse photograph. Colors can be assigned to the elevation levels.
Digital Elevation Models - When lidar data is collected using four returns, DEMs may be classified various ways depending on client interests. The most common classification is bare-earth; another is vegetation. Because there may be more than one return in vegetation which allow a look at the undergrowth, data may be classified as first, second, third or last returns, and bare-earth. Many above-ground features may be classified separately. Most often used are the first and last returns. The first will show the highest features such as the tree canopy, buildings etc. The last return is generally assumed to be ground level. This data set will provide valuable accurate data on the surface of the earth.
TIN: Triangular Irregular Network - From the collected points a TIN is built. The more data included in the process, the more detailed this model will be.
3-D Models - When overlaid with aerial photography, a detailed representation of the area in natural colors can be created. The model can be rotated and viewed from all angles as well as lit in a multitude of ways. It can also be edited to virtually implement designs and calculate or illustrate the results and consequences of engineering projects.
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