698 
Optical-Radar Data Fusion for Land Use Classification 
Michele Crosetto (*) , Marek Mróz (**) 
(*) DIIAR - Sez. Rilevamento - Politecnico di Milano, Italy 
(**) Chair of Photogrammetry and Remote Sensing - Olsztyn University, Poland 
Abstract 
This paper is focused on the fusion between optical and radar data for DEM (Digital Elevation Model) generation 
and Land Use Classification. The first part of the paper is concerned with the DEM generation and the analysis of the 
DEM quality. The DEMs are an input of the land use classification procedure based on SPOT and interferometric 
SAR data described in the second part of the paper. The first results obtained with this procedure are presented. 
Keywords: DEM generation, SAR Interferometry, SPOT Stereoscopy, Data Fusion, Land Use Classification. 
1. Introduction 
Recovering information about the topography and the 
physical characteristics of the earth's surface is a 
requisite of many disciplines (e.g. forestry, land use 
management, hydrology and telecommunication). 
The spaceborne sensors allow gathering data about 
wide areas with low production costs. However, often 
the quality of the information derived from this kind 
of data is affected by the intrinsic limitation of the 
remote sensing systems. For instance, optical images 
can be corrupted if fog or clouds cover the imaged 
scenes; SAR images are affected by strong geometric 
distortions in rugged areas. 
These limitations in the original data can influence 
both the accuracy and the completeness of the recov- 
ered information. 
Nowadays, the large number of remote sensing sys- 
tems makes worldwide available a huge amount of 
data characterised by different spectral, spatial and 
temporal resolutions. 
The use of data coming from many remote sensing 
sources and their integration (data fusion) can offer a 
solution to overcome the above-mentioned limita- 
tions. 
The effectiveness of the integration lies in the proper 
selection of the complementary data and in the correct 
methodology employed to fuse them. 
This paper is focused on the fusion between optical 
and radar data for DEM (Digital Elevation Model) 
generation and Land Use Classification. In particular, 
the synergetic use of panchromatic SPOT (stereo 
image pair) and complex SAR (interferometric image 
pair) is addressed. 
The following paragraph is concerned with the de-' 
scription of the DEM generation based on SPOT and 
SAR data. DEMs represent a valuable product used in 
many disciplines (e.g. mapping, GIS, telecommuni- 
cation). They are also an important input for the Land 
Use Classification procedure described in the last part 
of the paper. 
2. Data Fusion for DEM Generation 
The description of the terrain surface is a requisite of 
many engineering activities. Since the advent of the 
first spaceborne sensors, DEM generation has been 
based mainly on electro-optical data and photogram- 
metric techniques. Beside this kind of data, SAR 
images are recently gaining increasing importance 
thanks both to the development of different promising 
techniques to exploit them and to the world-wide 
availability of spaceborne SAR data. The DEM gen- 
eration based on SAR images can be accomplished 
basically by means of three kinds of techniques: inter- 
ferometry, stereoscopy (radargrammetry) and shape 
from shading. 
This paper is concerned with two different techniques 
for DEM generation. The first one is based on radar 
data (InSAR, Interferometric SAR). The second one 
is based on optical data (stereoscopy with SPOT 
images). Beside a brief description of the two tech- 
niques, in next paragraphs the characteristics of the 
InSAR and SPOT generated DEMs are analysed. 
Aiming at data fusion, the analysis is mainly focused 
on the complementarity of the height data coming 
from the two different techniques. Finally, the data 
fusion procedure implemented by the authors and its 
results are presented. 
2.1 SAR Interferometry 
The traditional use of SAR imagery in remote sensing 
is based on the amplitude of the radar signal. The 
complex SAR images contain both the amplitude and 
the phase of the signal. Processing a pair of SAR 
complex images acquired from slightly different 
points of view (interferometry), the phase brings a 
valued information useful to generate the DEMs. 
Although the investigations about the generation of 
DEMs by means of SAR interferometry started more 
than a decade ago, up to day a fully automatic and 
reliable InSAR procedure is not available. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998