In: Stilla U, Rottensteiner F, Paparoditis N (Eds) CMRT09. IAPRS, Vol. XXXVIII, Part 3/W4 — Paris, France, 3-4 September, 2009 
A PROOF OF CONCEPT OF ITERATIVE DSM IMPROVEMENT THROUGH SAR 
SCENE SIMULATION 
D. Derauw 
Signal and Image Centre - Royal Military Academy, Renaissance Av., 1000 Brussels, Belgium - dderauw@elec.rma.ac.be 
Centre Spatial de Liège - Université de Liège, Avenue du Pré Aily, 4031 Angleur, Belgium - dderauw@ulg.ac.be 
KEY WORDS: SAR, Scene, Simulation, DEM, reconstruction 
ABSTRACT: 
In Very High Resolution (VHR) Synthesis Aperture Radar (SAR) context, very fine and accurate georeferencing and geoprojection 
processes are required. Both operations are only applicable if accurate local heights are known. 3D information may be derived from 
SAR interferometry (InSAR), But in VHR context, InSAR reveals to be inaccurate mostly due to phase unwrapping problems and to 
phase/height noise. Generated InSAR Digital Surface Models (DSM) can only be considered as a first good approximation of the 
observed surface. Therefore, we proposed to start from the InSAR DSM, to project it on ground range on a given datum, to model the 
observed scene using this projected DSM, then to simulate in slant range the intensity image issued from this structure model. 
Comparison between simulated and observed intensity image can then be used as a criterion to modify and improve the considered 
underlying DSM. 
In this paper, we present the different steps of the proposed approach and results obtained so far, showing that the proposed process 
can be run iteratively to modify the DSM and reach a stable solution. 
1. INTRODUCTION 
A cooperation programme named ORFEO (Optic and Radar 
Federated Earth Observation) was set up between France and 
Italy to develop an Earth observation dual system, optic and 
radar, with metric resolution. Italy is in charge of the radar 
component (COSMO-Skymed), and France of the optic 
component (PLEIADES). 
Beside ORFEO, an accompanying programme was set-up to 
prepare the use and joint exploitation of images that will be 
provided from this satellites constellation. In the frame of this 
accompanying programme, the Belgian Science Policy 
(BelSPo) is financing the EMSOR project aiming at performing 
man-made object detection for urban map updating using VHR 
SAR and optical data. 
While such objective is well addressed in the optical imagery, 
this topic stays highly challenging in SAR imagery due to 
inherent peculiarities of SAR acquisition and imaging mode. 
Main obstacles are geometrical on one side and linked to SAR 
signal content on the other side. Geometrical deformation 
specific to SAR systems, i.e. layover, foreshortening, 
shadowing, make man-made structures appearing very 
differently in shape with respect to their appearance in optical 
imagery (Balz T. 2003). 
Specificities of SAR signal, mainly speckle, radar cross section 
dependence with incidence angle and multiple reflection 
processes make identical objects appear sufficiently differently 
to compromise, or make inoperative, classical detection 
techniques applicable in optical imagery. Man-made structures 
detection in SAR images based on speckle filtering followed by 
image segmentation is not applicable as such. Classification is 
often considered as a first processing step that, combined with 
other information layers, is used in higher level processing for 
fine Digital Surface Model (DSM) extraction and man-made 
structure detection (Tison et al. 2007, Thiele et al. 2007). SAR 
scene simulation was also proposed to help in fine 
georeferencing process (Blaz T. 2006) or to iteratively steer 
building structures detection and identification (Soerger et al., 
2003). 
Similarly, in this paper, we propose an iterative way to improve 
a seed DSM that is obtained through classical Interferometric 
processing of single pass VHR SAR data. We developed a basic 
SAR intensity image simulator adapted to very high resolution. 
This one is then used to improve our seed DSM, comparing the 
simulated image in intensity with the detected one and using 
this comparison to perform blind DSM corrections without any 
a priori knowledge of the underlying urban structure. 
The proposed approach is justified by the fact that classical 
interferometric SAR (InSAR) is showing its limits in the VHR 
context. Therefore, on-ground projected InSAR DSM can be 
considered as a first approximation of the 3D observed surface 
and be used as a seed DSM to be improved. 
The main aim being man-made structure detection, 
improvement means here reaching a DSM representation 
allowing better detection and localisation of searched structures. 
This paper describes first results obtained and choices that have 
been made up to now to assess the validity of the proposed 
iterative process. Our first aim was to perform a proof of 
concept of the proposed approach, i.e. DSM improvement based 
on iterative comparison between a simulated and detected SAR 
intensity image. 
2. TEST SITE AND SEED DSM 
2.1 Data set description 
To generate our seed DSM, we are using a VHR InSAR pair 
acquired in February 2006 above Toulouse (France) by the 
RAMSES X-band sensor (Dupuis et al. 2000). Resolution cell 
dimensions are 0.55m in azimuth by 0.35m in slant range. We