6A-4-3 
required ground resolution. Line CCD sensors can 
overcome the limited coverage problem, but at the 
price of more complex modeling of the sensor 
geometry, which has further implications on the 
surface extraction performance. To compensate for 
both the small coverage of the frame sensors and the 
need of complex modeling with line CCDs, the use of 
GPS/INS-based orientation with these imagers is 
mandatory (Toth 1997). A new feature of CCD sensors 
is a much higher gray-scale intensity range, easily 
extending up to 12 or 14 bits. 
Road/Building Extraction. Currently one of the most 
popular research areas in digital photogrammetry is 
definitely algorithmic research on extracting man 
made objects, such as roads and buildings, from aerial 
imagery (Fritsch and Ameri 1998; Haala et. al. 1998; 
Wang 1998). Identifying and modeling these objects 
can help resolve ambiguities in the matching process 
and can increase the robustness of surface extraction 
methods far beyond simply reconstructing a “draped” 
surface. 
Laser Scanning. Scanning laser-ranging (LIDAR) 
sensors have substantially improved over recent years 
and are about to enter map production. In fact, they are 
rapidly becoming a de facto first choice for fast digital 
surface data acquisition. Operational systems can 
easily provide a large number of elevation spots with 
excellent vertical accuracy, which depends primarily 
only on the positioning performance of the GPS/INS 
module. An unmatched feature of the laser scanning 
sensors is the capability to process multiple returns, 
thus being able to separate vegetation from terrain 
surface and other objects (Pfeifer et. al. 1998). A 
weakness of the technique is the strong signal 
dependence on the surface slope. 
Hyperspectral Imagery/SAR. These new sensor 
techniques offer an additional dimension to the surface 
extraction and interpretation tasks by providing 
material-specific signatures, which can further enhance 
the performance of the matching process (Tonjes and 
Growe 1998). Interferometric SAR can itself provide 
range data, and it is viewed as the future tool for fast 
and large area terrain data acquisition. 
3. TEST FLIGHT WITH LIDAR AND 4K BY 4K 
DIGITAL CAMERA 
To support our surface extraction research on integrating 
LIDAR data with stereo imagery, a recent test flight was 
organized to simultaneously collect laser data and direct 
digital monochrome frame images over a well-surveyed 
area at Hagerstown, MD in cooperation with EarthData 
Technologies. A similar test flight was conducted in the 
Northern Florida region a year earlier. However, the 
Florida flight did not allow for the concurrent operation of 
the two imaging sensors, and the project area did not have 
acceptable surface data necessary for ground truth 
comparisons. The surface extraction experiences using 
only the 4K by 4K direct oriented imagery are reported 
elsewhere (Toth and Grejner-Brzezinska 1998). 
For the Hagerstown test flight, EarthData Technologies 
provided the LIDAR system and all necessary flight 
support, while the complete AIMS™ prototype, including 
the 4K by 4K digital camera and the GPS/INS system, 
came from OSU. In several missions, LIDAR and direct 
digital image data were collected at different flying 
heights over a one square kilometer area. A representative 
image taken at 850 m AGL is shown in Figure 1. The 
Hagerstown test site has been routinely used for 
calibration and system performance evaluation tests and 
has excellent and accurate photogrammetrically derived 
ground-truth data, including a topographic surface and 
man-made objects (mostly residential buildings). 
Figure 1. Typical 4K by 4K image taken at 850 m AGL 
over Hagerstown, MD. 
Traditional aerial-triangulation was performed on images 
collected at the lower flying height (the GSD for higher 
altitude flights was around 1 m, preventing any control 
point identification). The aerial-triangulation served two 
purposes: to determine the best orientation of the block 
and consequently, through those results, to provide the 
boresight misalignment for the GPS/INS to deliver the 
exterior orientation data for the remaining blocks. The 50 
mm lens equipped 4K by 4K camera was laboratory- 
calibrated prior to the test Eights (Seedahmed et. al. 
1998). The difficulty of measuring control points as 
illustrated in Figure 2 comes from two sources. First, the 
limited angular resolving power provides only a very 
coarse pixel resolution on the ground. Second, the very 
asymmetrical target pattern is troublesome for computer- 
assisted point extraction, which is typically tailored 
toward symmetrical objects.