ISPRS Commission III, Vol.34, Part 3A ,,Photogrammetric Computer Vision“, Graz, 2002 
  
OSIRIS: A SIMULATOR OF OUTDOOR SCENES IN THERMAL INFRARED RANGE 
T. Poglio ®° *, E, Savaria?, L. Wald? 
* Alcatel Space Industries, System Architecture Division, 06156 Cannes, France — 
(thierry.poglio, eric.savaria)@space.alcatel.fr 
e Groupe Télédétection & Modélisation, Ecole des Mines de Paris, 06904 Sophia Antipolis, France — 
(thierry.poglio, lucien.wald)@ensmp.fr 
KEY WORDS: Imagery, Landscape, Modelling, Remote Sensing, Temperature, Three-Dimensional 
ABSTRACT: 
This paper deals with the simulation of very high spatial resolution images in the thermal infrared range, from 3 to 14 um. It recalls 
the physical processes occurring in this spectral range. The complexity of the simulation of such processes is explained. The 
specifications of the simulator and a methodology for the simulation of infrared imagery are proposed. This methodology enables a 
very accurate simulation of the signal coming from each object constituting the landscape. The interactions between the radiations 
and objects and the convective and conductive interactions between objects themselves are considered. Their variations in time, and 
the recent past of the temperature and the humidity for each object, are taken into account. To reproduce these physical phenomena, 
the computation is performed on elements, which are defined as homogeneous entities with respect to the physical processes. The 
architecture of the simulator OSIRIS using the elements is presented. Finally, examples are shown, showing the efficiency of the 
simulator and the methodology used. 
1. INTRODUCTION 
There is a growing concern of very high spatial resolution 
imagery in the infrared range from 3 to 14 um. Simulators of 
landscapes in thermal infrared range need to be developed. One 
of the major points in the simulation is the accurate knowledge 
of the input parameters, and particularly the accurate knowledge 
of the scene to be observed. Synthesis approaches to outdoor 
scenes offer the possibilities to simulate changing 
meteorological conditions, different places, different 
landscapes, different times and different spectral bands. 
As physical processes play an essential part in the signal coming 
from the scene, there is a need for research on spatial, spectral 
and temporal properties of natural and human-formed objects, 
their image signatures and their modelling. The synthesis of 
outdoor scenes in the infrared range is at the crossings of 
computer vision, physics and remote sensing. 
In thermal infrared, the flux coming from an object is partly 
emitted by the object because of its own temperature, and partly 
due to the reflection of incident rays on the surface of this 
object. Depending on the surface material and the spectral band, 
emission or reflection process dominates the signal. For each 
object in the scene, the landscape simulator predicts the heat 
exchanges between objects, the temporal evolution of heat 
balance, the surface temperature, the spectral emission and the 
spectral reflection of all incident fluxes. Such a simulator takes 
into account 3-D landscape description, environmental 
conditions, thermal and optical characteristics of the objects, 
and the spectral band of the sensor. 
Jaloustre-Audouin (1998) and Jaloustre-Audouin ef al. (1997) 
have developed a simulator of any type of landscape in 2-D in 
the infrared band. Image simulators taking into account a 3-D 
representation of the landscape as input exist, but they are for 
  
* Corresponding author. 
visible range or dedicated to specific applications. For example, 
Thirion (1991) has developed a simulator of high spatial 
resolution image in the visible range. Johnson et al. (1998) have 
developed a simulator in the infrared range to simulate the 
behaviour of vehicles. Guillevic (1999) was interested in 
radiative budget modelling for vegetation canopy studies. 
Barillot (2001) has developed MISTRAL, which can simulate 
an image taking into account a 3-D description of the landscape. 
A simulator of landscape adapted to remote sensing applications 
does not exist and has to be developed. It should take into 
account a 3-D description of the scene with high spatial 
resolution. 
Physical processes occurring in the signal coming from the 
scene are described in the following section. Next, the 
specifications of the simulator are given. The main difficulties, 
related to these specifications and the infrared range are 
explained. A new methodology is proposed for the simulation 
of very high-resolution 3-D scenes and the consequences on the 
landscape modelling are explained. Section 4 details the 
architecture of the simulator using this modelling; each subpart 
of the simulator is presented, and its operation is explained. 
Finally, section 5 presents examples of synthesised scenes. 
2. PHYSICAL PROCESSES OCCURRING IN THE 
INFRARED RANGE 
2.1 The radiance balance equation 
In the general case, the energy equilibrium for a set of radiating 
objects is expressed, independently on the wavelength A, by the 
following equation: 
A - 240