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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, Air Survey
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.
Let us help you plan your next LIDAR project and share with
you the value of this exciting technology.
LIDAR
Survey Points, Cross Section
This
slide shows a side view and
cross-section of power lines. Clearly visible are the transmission
lines, the utility pole and the guy wires. The cross section
shows the three suspended transmission lines.
Gold = ground; Red = first pulse return, and White= vegetation.
Intensity
Image
When
LIDAR data is collected, the instrument also captures the
light intensity that is returned. It creates an image that
is comparable with a coarse black and white photograph.
Painted
Relief
In the
elevation dataset, each pixel value is proportional to the
elevation. When each pixel value is assigned a specific color,
the image will display as "painted relief". In general,
blue is used to indicate low areas and red for the highest
point.
LIDAR
Return Points
Bare-earth DEM
Three
primary products derived from the raw LIDAR data include a
first-return file and two classifications from the last return
data.
1) The first-return file is a combination of all data classes
received from the first-return of each laser pulse.
2)
the bare-earth file is the data from only the last return
of each pulse and attributed to the ground surface, and
3)
the classification file, including everything from the last
return of each laser pulse (vegetation, structures, etc.)
except the ground elevations.
First-return DEM
Ffirst-return DEM
This
image shows a rendering of the first-return. Colors indicate
elevation values. Blue represents low areas, purple the higher
elevations.
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LIDAR
technology offers one of the most accurate, expedient
and cost-effective ways to capture wide-area elevation
information to produce highly detailed Digital
Elevation Models (DEMs).
LIDAR
data sets contain vast amounts of information.
Buildings, trees and power lines are individually
discernible features. This data is digital and
is directly processed to produce detailed bare
earth DEMs at vertical accuracies of 0.15 meters
to 1 meter. Derived products include contour maps,
slope/aspect, three-dimensional topographic images,
virtual reality visualizations and more.
LIDAR
data can be seamlessly integrated with other data
sets, including orthophotos, multispectral, hyperspectral
and panchromatic imagery. LIDAR is combined with
Geographic Information System (GIS) data and other
surveying information to generate complex geomorphic-structure
mapping products, building renderings, advanced
three dimensional modeling/earthworks and many
more high quality mapping products.
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How
LIDAR Works
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. 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 ground level. This data
set will provide valuable accurate data on the
surface of the earth.
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Ground
Points & Cross sections
This
screen capture shows the ground returns, in gold,
and cross sections at random locations. The fist-
return points are shown in white.
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TIN:
Triangular Irregular Network
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From
the collected points a TIN is built . The more data
included in the process, the more detailed this model
will be. Software allows for the application of shaded
color overlays, each color corresponding with the
particular elevation.
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Digital
Elevation Models
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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, lit
in a multitude of ways, edited to virtually implement
designs and calculate and illustrate the results and
consequences of engineering projects.
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AIR SURVEY
45180 Business Court
Dulles, Virginia 20166-6706
Phone: (703) 471-4510
Toll Free: 1 800 272-6299
Fax: (703) 471-6810
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