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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
orientation accuracy. Constellations of small satellites are
planned which will extend the availability and flexibility of
IfSAR data.
GeoSAR is a dual-frequency, dual-polarimetric, interferometric
airborne radar mapping system that generates DEMs and
orthorectified radar reflectance maps near the tops of trees as
well as beneath foliage,
(http://southport.jpl.nasa.gov/html/projects/geosar/geosar.html).
The GeoSAR system collects radar data in two frequencies. The
X-band maps the first surface, near the top of trees and the P-
band maps beneath the foliage and assists in the production of a
bare-earth terrain model and the detection of structures beneath
trees. Mercer (2003b) reports on the use of Polarimetric P band
data for generation of DEMs of forest areas, and compares this
with X band InSAR.
We are beginning to see the economy of airborne IfSAR being
used for wide area DEMs to complement the global data from
SRTM. These can be created from a single source, hence
providing a homogeneous data set, generated over a short period
of time. The use of permanent scatterers to monitor subsidence
with IfSAR is also being developed (Ferretti et al, 1999)
A better control infrastructure is becoming established to allow
woder and easier use of GPS, INS systems. National mapping
agencies are establishing permanent continuous recording GPS
stations, but operators prefer to set up their own base stations.
The introduction of Galileo will further extend the use of
positioning systems.
The importance of validation and improved quality assurance is
being recognised and the introduction of internationally
accepted standards is being discussed.
As the data becomes more widely used, new image processing
systems are becoming available. TerraSolid is widely used now
for processing LiDAR data, and more tools are becoming
available. Packages such as eCognition are particularly suited
to use with SAR data and DEMs. Intelligent systems such a
ALFIE, (Automated Linear Feature Information Extraction), a
new system for generating simulations for military use being
developed in the UK (Wallace et al, 2004). The system is based
on existing algorithms integrated into a toolkit within a
processing environment which can automatically select which
tools to use with particular data for specified applications, and
which can also make use of context in extracting features.
ALFIE is also linked to an object oriented data base and works
with a developed feature extraction environment.
16. CONCLUSIONS
It has been shown in this paper that LIDAR and IfSAR are now
widely used and that this type of data is opening up new
markets and new opportunities in areas such as powerline
surveys, flood risk mapping and large area mapping. The two
types of data are complementary with each other and each can
be used with other data sources to generate new value added
products.
That having been said, we have also shown that there are still
problems with using the data and more development needed
before the technology is fully mature. The calibration of
LiDAR data is not well developed, and neither are
specifications or quality assurance techniques. The generation
of bare earth models (DTMs) are still liable to error and manual
editing is still needed. The main areas for further research are
*
99
to develop threoretical models for sensors and data fusions, to
improve bare earth filtering and to improve feature extraction.
User need to be educated more and to aid the greater use of the
data, standards need to be defined for products and for data
exchange.
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