DATA SIMULATION OF LADAR SENSOR: FOCUSING ON GEOMETRIC MODELING 
Seonghong Min a , Seongjoon Kim a , Impyeong Lee a * 
a Dept, of Geoinfomatics, The University of Seoul, 90 Jeonnong-dong Dongdaemun-gu Seoul, Korea 
(minssy0306, sinus7953, iplee)@ uos.ac.kr 
Commission I, WG 1/2 
KEY WORDS: Simulation, LADAR, Multi-Sensor System, Sensor Model, Geometric Model, Sensor Equation 
ABSTRACT: 
LADAR (LAser Detection And Ranging or Laser Radar) can rapidly generate 3D points by sampling the surfaces of targets using 
laser pulses, which can be efficiently utilized to reconstruct 3D models of the targets automatically. To make wide use of LADAR, it 
is necessary to assess the data quality and to develop data processing algorithms. However, the accuracy verification of LADAR 
system is difficult, because we cannot know the accurate reflected positions of the returned signals at target's surface. Under the 
consideration of this difficulty, the verification based on LADAR simulation can be a more feasible alternative solution. The purpose 
of this study is to derive the geometric models of such LADAR sensors and to generate simulated data based on these models. Here, 
we derived the sensor equation by modeling not only the geometric relationships between the LADAR sub-modules, such as GPS, 
INS, Laser Scanner but also the systematic errors associated with them. This is an important step to establish mutual geometric and 
time correspondence among the individual sensors on a multi-sensor system. The geometric correspondence means that each sensor 
is defined with its position and attitude in a common coordinate system. And the time correspondence means that individual sensor 
time is synchronized. Based on this equation (the geometric model), we developed a program that generates simulated data with the 
system parameters of a LADAR sensor, a terrain model, and its trajectories over this model given. The results of this study will be 
useful for the system design of a LADAR sensor and the algorithmic development for LADAR applications. 
1. INTRODUCTION 
A LADAR (LAser Detection And Ranging or Laser Radar) 
sensor can generate 3D points by sampling the surfaces of 
targets using laser pulses, which can be efficiently utilized to 
reconstruct 3D models of the targets automatically. This sensor 
has the advantage of observing a large area for a short time, 
supporting higher resolution and accuracy on measurements of 
range, velocity, and angular position than other sensors (for 
examples, microwave radar, etc.). Since it can measure each 
sub-area of target's surface with high resolution, it can permit 
more robust identification and recognition of the targets 
(Kamerman, 1993). Therefore, LADARs have been 
increasingly applied to the fields of Defense and Security, for 
examples, being employed to intelligently guided missiles and 
manned/unmanned reconnaissance planes. It has been also 
applied to the fields of Remote Sensing such as precise 
construction of three-dimensional spatial models of the targets, 
the creation of DTM (Digital Terrain Model) for the forest area 
or the rapid change detection of city regions. 
Computer simulation has taken important roles in modelling 
diverse physical systems. Generally it can be effectively applied 
to the design, performance estimation and analysis of hardware. 
It is useful for the design of a new system and the improvement 
of an existing system. 
To utilize LADAR sensors effectively in various applications, it 
should be necessary to assess more accurately their data and to 
develop data processing algorithms dedicated to specific 
applications (Lee, 2003). However, the accuracy assessment of 
LADAR system is relatively difficult because we cannot 
accurately determine the true position on a target surface at 
which the returned laser signal is reflected. The verification 
based on LADAR simulation can be thus a more feasible 
alternative solution. 
The purpose of this study is to derive the geometric models of 
such LADAR systems and to generate simulated data based on 
these models. Here, we derived the sensor equation by 
modeling not only the geometric relationships between the 
individual sensors of a LADAR system, such as GPS, INS, 
Laser Scanner but also the systematic errors associated with 
them. Using the sensor equation based on the geometric model, 
we developed a program that generates simulated data with the 
system parameters of a LADAR system, a terrain model, and its 
trajectories over this model given. 
The simulation will be effectively used to validate the accuracy 
about a variety of sensors and to assess the performance of the 
data processing algorithms in more economical ways. 
Furthermore, it will be also used to determine the optimal 
parameters for a LADAR system being developed. 
2. METHODOLOGY 
2.1 Geometric Modelling 
To simulate LADAR data, we need to derive the sensor model 
and its corresponding sensor equation. This equation indicates 
the mathematical representation of the three dimensional 
coordinates of the position on a target surface where the 
returned laser signal is reflected. In a multi-sensor system like a 
Corresponding author.