Environmental Engineering Reference
In-Depth Information
the Shuttle Radar TopographyMission (SRTM) on
board Space Shuttle Endeavour in February 2000.
The SRTMwas equipped with two radar antennae
separated by 60m, and collected data over about
80%of the Earth's land surface, between latitudes
60
N and 54
S. The vertical accuracy is about
16m, with a spatial resolution of 30m in the
USA and 90m in all other areas (Smith and
Sandwell 2003).
An InSAR DSM of the UK was produced using
repeat pass InSAR techniques applied to Earth
Resources Satellite-2 (ERS-2) satellite data in the
LandMap project (Muller 2000). This has a height
standard deviation of
11m and a spatial resolu-
tion of 25m.
The main airborne InSAR is the InterMap
STAR-3i. This is a single-pass across-track X-band
SAR interferometer on board a Learjet 36, with the
two antennae separated by a baseline of 1m. In
the NextMap Britain project in 2002-03, an accu-
rate high-resolution DSM of the whole of Britain
was built up containing over 8 billion elevation
points. Thismeant that for the first time therewas
a national height database with height accuracies
better than
1m and spatial resolutions of 5m
(10m) in urban(rural) areas (www.intermap.com).
Using in-house software, Intermap is able to filter
the DSM to strip away features such as trees and
buildings to generate a bare-earth DTM.
Fig. 11.1
Typical LIDAR (Light Detection and Ranging)
system and its main components. GPS, global position-
ing system. After Smith et al. (2006).
scan angle and GPS base station, the 3-D position
of the ground feature can be calculated in the GPS
coordinate system (WGS84) and then transformed
to the local map projection. A high vertical accu-
racy of
5-25 cmcan be achieved. At typical flight
speeds, platform altitudes and laser characteris-
tics, terrain elevations can be collected at a density
of at least one point every 0.25-5m. The laser
pulse may reflect from more than one part of
a ground feature; for example, in vegetated areas
the pulse may reflect from the top of the foliage
and also from the ground below. Many LIDAR
systems can collect both the first return (from
the foliage) and the last return (from the ground),
and in some systems it is possible to collect the
complete reflected waveform. The intensity of the
reflected pulse can also provide useful information
about the surface feature being imaged.
High-resolution LIDAR data suitable for
flood modelling are available for a number of
selected floodplain and coastal areas of the UK.
Light Detection and Ranging (LIDAR)
Light Detection and Ranging (LIDAR) is an air-
borne laser mapping technique that produces
highly accurate and dense elevation data suitable
for flood modelling (Wehr and Lohr 1999;
Flood 2001). A LIDAR system uses a laser scanner
mounted on an aircraft or helicopter platform
(Fig. 11.1). Pulses from the laser are directed to-
wards the Earth's surface, where they reflect off
features back towards the platform. Knowing the
round-trip time of the pulse and the velocity of
light, the distance between the laser and the
ground feature can be calculated. The instanta-
neous position and orientation of the laser are
known using the GPS and INS systems on board
the platform. Using additional information on the
