9-11 Nov. 1999
that is large enough to
such markets require the
ties provided by laser
le from other survey
us economic factors to
ita products. Potential
hed client-base with the
laser altimetry survey
ble price. Due to the
he technology to the
markets are still being
, laser altimetry can be
| competitive technology
methods. | For many
is currently deployed in
onal sensors including
cameras, hyperspectral
al, laser altimetry is best
sensing toolbox that can
oducts produced, either
1 other sensor systems.
ithin a field survey can
n project specific goals
ual client has particular
xpect to be met, laser
ns without support from
, in certain applications,
g, laser altimetry offers
h any other technology.
applications is provided
utelius, 1997; Gutelius,
apping is a rapid, cost-
h-density elevation data
ping applications. The
oraphic surveys to be
reduced cost compared
mapping in the forestry
rcial areas investigated.
| topography beneath the
oth the forestry industry
rate information on tree
ormation that is difficult
iques. Airborne laser
itellite imaging, can
1 the tree canopy as well
of the data allows the
yzed and classified as
"IMs of the bare ground
ative tree heights to be
‘om the research sector
' return laser pulse to
Blair and Hofton, 1999)
s the technology gains
acceptance in the commercial sector. Consequently, airborne
laser mapping is an extremely effective technique for forestry
companies when compared to photogrammetry or extensive
ground surveys.
Coastal Engineering: Beach mapping or similar surveys of
coastal regions are another area where airborne laser technology
offers state-of-the-art type performance with significant
advantages over existing survey techniques. Since traditional
photogrammetry is difficult to use in areas of limited contrast,
such as beaches and coastal zones, an active sensing technique
such as laser altimetry offers the ability to complete surveys that
would be too costly using other methods. In addition, highly
dynamic environments such as coastal zones often require
constant updating of baseline survey data. Airborne laser
mapping offers a cost-effective method to do this on a routine
basis. It is also used for mapping and monitoring of shore
belts, dunes, dikes and coastal forests.
Corridor or Right-of-Way Mapping: Airborne laser mapping
allows rapid, cost-effective, accurate mapping of linear
corridors such as power utility right-of-ways, gas pipelines, or
highways. A major commercial market is mapping power line
corridors to allow for proper modeling of conductor catenary
curves, sag, ground clearance, encroachment and accurate
determination of tower locations. For example the use of data
acquired through airborne laser surveys can be combined with
simultaneous measurements of air and conductor temperature
and load currents to establish admissible increases in load-
carrying capacity of power lines.
Flood Plain Mapping: Accurate and updated modeling of
flood plains is critical both for disaster planning and insurance
purposes. Airborne laser mapping offers a cost-effective
method of acquiring the topographic data required as input for
various flood plain modeling programs. As part of its Map
Modernization Plan, the Federal Emergency Management
Agency (FEMA) in the U.S. is currently performing an
assessment of advanced technologies including laser altimetry
for possible use in the preparation of National Flood Insurance
Program (NFIP) maps and related products. FEMA has
recently released guidelines which present specifications that to
be used for the application of laser altimetry systems for
gathering the data necessary to create digital elevation models
(DEMS), digital terrain maps, and other NFIP products.
Urban Modeling: Accurate digital models of urban
environments are required for a variety of applications
including telecommunications, microclimate modeling, wireless
communications, law enforcement and disaster planning. An
active remote sensing system such as a laser offers the ability to
accurately map urban environments without some of the
disadvantages of other technologies.
Disaster Response and Damage Assessment: Major natural
disasters such as hurricanes or earthquakes stress an emergency
response organization's abilities to plan and respond. Airborne
laser mapping allows timely, accurate survey data to be rapidly
incorporated directly into on-going disaster management efforts
and allows rapid post-disaster damage assessments. It is
particularly useful in areas prone to major topographic changes
International Archives of Photogrammetry and Remote Sensing, Vol. 32, Part 3W14, La Jolla, CA, 9-11 Nov. 1999
during natural disasters; areas such as beaches, river estuaries
or flood plains.
Wetlands and Other Restricted Access Areas: Many
environmentally sensitive areas such as wetlands offer limited
ground access and due to vegetation cover are difficult to assess
with traditional photogrammetry. Airborne laser altimetry
offers the capability to survey these areas. The technology can
also be deployed to survey toxic waste sites or industrial waste
dumps.
In addition to the commercial applications discussed above,
various efforts are under way to investigate other application
areas where airborne laser altimetry may offer significant
advantages.
22 Commercial Instruments
The current generation of commercial airborne laser altimetry
instruments use a combination of three mature technologies;
rugged compact laser rangefinders (LIDAR), highly accurate
inertial reference systems (INS) and the global positioning
satellite system (GPS). By integrating these subsystems in to a
single instrument, it is possible to rapidly produce accurate
digital topographic maps of the terrain beneath the flight path of
the aircraft. Similar to aerial cameras, the instruments can be
installed in small single or twin-engine planes or helicopters.
For commercial surveys, the absolute accuracy of the laser-
derived elevation data is generally quoted as 15 cm; relative
accuracy less than 5 cm. Absolute accuracy of the planimetric
data is dependent on operating parameters such as flight
altitude but is usually quoted at decimeter to meter levels.
Accuracy tends to degrade with terrain slope, roughness and
vegetation cover resulting in generally lower accuracy than
quoted assuming a smooth, flat surface. To date there have
been limited independent studies published that verify the
accuracy claims of commercial operators (Huising and Gomes
Pereira, 1998; Kraus and Pfeifer, 1998). However, there is a
growing body of work by independent agencies such as the
USGS, FEMA and similar agencies in Europe that indicates
these levels of absolute accuracy are achievable, but only if
commercial operators are rigorous in their attention to
calibration of their instruments and implement appropriate
QA/QC procedures on the laser data.
With current commercial instruments, elevation data is
generated at 1000s of points per second, resulting in elevation
point densities far greater than traditional ground survey
methods. One hour of data collection can result in over
10,000,000 individually geo-referenced elevation points. With
these high sampling rates, it is possible to rapidly complete a
large topographic survey and still generate DTMs with a grid
spacing of 1 m or less. With current commercial systems it is
possible to survey one thousand square kilometers in less than
12 hours and have the geo-referenced DTM data available
within 24 hours of the flight. A 500-kilometer linear corridor,
such as a section of coastline or a transmission line corridor can
be surveyed in the course of a morning, with results available
the next day. Airborne laser mapping instruments are active
sensor systems, as opposed to passive imagery such as cameras.
Consequently, they offer advantages and unique commercial
