Charles Toth 
  
COMPLEMENTARITY OF LIDAR AND STEREO IMAGERY 
FOR ENHANCED SURFACE EXTRACTION 
Charles K. TOTH', Dorota A. GREJNER-BRZEZINSKA™ 
The Ohio State University, USA 
"Center for Mapping 
toth ? cfm.ohio-state.edu 
"Department of Civil and Environmental Engineering and Geodetic Science 
dorota €? cfm.ohio-state.edu 
Working Group III/2 
KEY WORDS: Sensor Integration, LIDAR, Digital Imaging Sensors, GPS/INS, DEM, Airborne Mapping. 
ABSTRACT 
Modern, integrated GPS/INS-based direct orientation systems, combined with multi-sensor imaging hardware such as 
digital cameras and laser ranging devices, allow the simultaneous collection of independent observations, offering a 
diversity of spatial/spectral information. This forms the basis for an optimal geo-spatial data fusion since different 
properties of objects are recorded, based on different physical principles of the sensors, bringing together 
complementary and often redundant information. 
Light Detection and Ranging (LIDAR) sensors have shown remarkable developments over recent years, reaching at the 
same time cost-effectiveness and reliability, and currently represent a new and independent technology for a highly 
automated generation of digital elevation (DEM) and surface models (DSM). However, there are a few inherent 
shortcomings of the LIDAR technology such as the lack of correspondence to objects, no redundancy in the 
measurements, strong dependency on material features, missing visual coverage, etc. Recently, rapid digital camera 
developments have reached the performance level whereby such systems can be integrated into airborne LIDAR 
systems. The introduction of direct digital imagery into the LIDAR system has two primary benefits: 1) it can improve 
the surface extraction process, and 2) it provides the necessary visual coverage of the area. Both processes can be 
sufficiently automated, promising an almost near real-time mapping performance. This paper deals with some aspects 
of the sensor fusion problem of LIDAR with digital imagery for airborne surveying applications. 
1 INTRODUCTION 
1.1 Airborne Laser Systems 
Airborne laser ranging (ALR) is not a new technology. What is new is that these systems have become affordable 
recently and ALR is about to enter mainstream mapping production. The earliest experimental applications of LIDAR 
date back to the 1970s and 1980s, but the technology was introduced to the mapping community only about a decade 
ago. Recently, the technology's maturity and also rapid developments of the GPS/INS direct orientation systems 
supporting ALR have increased the economical potential of laser-based systems. Three main periods can be identified 
with respect to applications. At the beginning, ALR was almost exclusively used for scientific explorations, mostly 
under NASA supervision. With improving technology and falling prices, LIDAR entered the commercial market 
roughly a decade ago. New companies were founded to offer data services for special applications such as transmission 
line surveying. Operating from helicopter or fixed-wing aircraft, these LIDAR systems typically had limited capabilities 
— the low flying height allowed only for corridor mapping, albeit the spot density was rather good. Finally, the third era 
of the LIDAR applications arrived by the late nineties. Further advancing technology as well as the affordability of 
LIDAR allowed traditional airborne surveying companies to acquire LIDAR systems and to integrate them into 
production under normal conditions. Most importantly, the flying altitude has been substantially extended; DeLoach 
and Leonard (2000) have reported about a LIDAR project with a 20,000-ft flying height. 
Interest toward LIDAR systems in both academia and industry had increased dramatically by the mid- and late nineties. 
Most recently, the ISPRS Journal of Photogrammetry and Remote Sensing devoted a special issue to this topic (see 
54(2-3), 1999). An excellent primer for the basic principles of LIDAR systems is provided by Baltsavias (1999), while 
Ackermann (1999) offers a good review of the current status and future trends. Comparison between photogrammetry 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 897