INTEGRATION OF LIDAR AND IFSAR FOR MAPPING
Ian Dowman
University College London, Gower Street, London, WCIE 6BT, UK
idowman(@ge.ucl.ac.uk
Invited paper Commission II, WGII/2
KEYWORDS:
ABSTRACT
LIDAR, Interferometric SAR, Integration, Mapping, DEM
LiDAR and IfSAR data is now widely used for a number of applications, particularly those needing a digital elevation model. The
data is often complementary to other data such as aerial imagery and high resolution satellite data. This paper will review the current
data sources and the products and then look at the ways in which the data can be integrated for particular applications. The main
platforms for LiDAR are either helicopter or fixed wing aircraft, often operating at low altitudes, a digital camera is frequently
included on the platform, there is an interest in using other sensors such as 3 line cameras of hyperspectral scanners. IfSAR is used
from satellite platforms, or from aircraft, the latter are more compatible with LiDAR for integration. The paper will examine the
advantages and disadvantages of LiDAR and IfSAR for DEM generation and discuss the issues which still need to be dealt with.
Examples of applications will be given and particularly those involving the integration of different types of data. Examples will be
given from various sources and future trends examined.
INTRODUCTION
Geospatial databases are becoming increasingly important in
many areas. There is an increasing demand for National
Mapping Agencies to provide geospatial data — to be used by
utility companies, environmental agencies, transport agencies
and industry such as telecoms. At the same time mapping
organisations are looking to use new technology to satisfy these
requirements. Two of these important new sources are LiDAR
and IfSAR, acquired from airborne and spaceborne platforms.
Data from these sensors has been applied to a number of novel
applications such as mapping flood plains, powerlines and
transport infrastructure. This paper sets out to define the role of
photogrammetry and remote sensing in this, and. in particular,
the role of IfSAR and LIDAR.
The paper will first set out the characteristics of the sensors and
the data, and the products being generated. It will then deal
with airborne data collection also look at the data producers
and discuss some of the open questions relating to the use of
LiDAR and IfSAR. Some characteristics and aspects of
spaceborne IfSAR will be considered. Finally the paper will
look at how the technology and applications are progressing.
2. THE CHARACTERISTICS OF LiDAR AND IfSAR
2.1 LiDAR
The principles of LIDAR are well known. These have been
described by Baltsavias (1999b). To summarise: range is
measured from a platform with a position and attitude
determined from GPS/INS using a scanning device which
determines the distance from the sensor to the ground of a series
of points roughly perpendicular to the direction of flight. Figure
1 shows schematically a laser scanner and its main components.
As a result, the raw airborne LiDAR data is collected in the
GPS reference system WGS 84.
The wavelength in which most lasers operate is in the range of
1040-1060 nm. (Baltsavias, 1999a) Airborne laser scanners can
record up to 5 different returns (multiple returns). If a laser
pulse or a part of the pulse is reflected from a roof top or the top
of a tree, the sensor will record the first return. However, a part
90
of the pulse might partly penetrate the tree canopy and/or travel
through and reach the ground as it can be seen in figure 1. In
that case, the sensor will also record intermediate returns when
the pulse hits various parts of the canopy and the last return, the
return from the ground.
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Not all laser scanners collect multiple returns, in many cases
only single returns (first or last pulse) are recorded. In addition,
most systems record the reflected intensity image.
Lasers also operate as continuous wave sensors which can
depict the interaction between the laser energy and the elements
of the vegetation canopy.
There are currently many LiDAR systems available and these
operate from fixed wing and helicopter airborne platforms at
altitudes from 50 — 3500m. The latest systems operate at
100Hz and can produce point densities from helicopters of 30
points per m^. There are now many companies operating LiDAR
systems, most of which work commercially to provide data to
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