3-2-2 
Georeferenced imagery that matched with DEM accurately is essential for a multitude of 
remote sensing purpose, such as geometric and radiometric rectification of images, additional 
information sources for multispectral and hyperspectral classification, modeling and simulation in 
Geographic Information system (GIS). Georeferenced multispectral imagery and DEM be matched 
accurately when they are captured. This is reached by using Laser-Ranging & Multispectral- 
Imaging Coupled Scanner (LRMICS) that developed by our team in IRSA. This paper aims at the 
problem of positioning principles and accuracy of ALIMS. 
2. Operating Principles 
ALIMS is based on the principles of laser ranging and detection that used by Topeye that 
produced by SAAB Dynamics and ALTMS by Op tech Inc.. The different aspect of the ALIMS to 
Topeye and ALTMS is the former can capture DEM (as the latter) and spectral information 
simultaneously. The accuracy of DEM and georeferenced image depends on the positioning accuracy 
of Laser-Range-Finder (LFR) footprints. This is because the DEM’s quality is determined by the 
accuracy of LFR’s footprints directly and georeferenced imagery generated from multispectral 
information and DEM of the earth surface. 
(a) (b) 
Fig.l Principle of Airborne Laser-Ranging & Multispectral Imaging Mapping System 
The flight direction taken as the X-axis of the object space coordinate system. The Z-axis 
coincide with the zenith directions at the origin of the coordinate system. The X and Y-axis form a 
horizontal plane. In this coordinate system, the orientation parameters (X s ,Y s ,Z s ,(p,CO,K) 
measured by GPS and INS. The distance from aircraft to earth surface S is measured by laser- 
Range-Finder (LRF). The multispectral scanner that coupled with LFR is used to capture the 
spectral information of the earth surface. The angle between the direction of laser pulse and nadir 
determined by encoder. For whiskbroom and conic scanner, the coordinates of a specific LFR’s 
footprint can computed take the way similar to photogrammetry (Wang Z. 1990) and expressed as 
the follows: