Michele Crosetto
QUALITY ASSESSMENT OF INTERFEROMETRIC SAR DEMs
Michele CROSETTO*, Bruno CRIPPA**
* Joint Research Centre, Italy
Global Vegetation Monitoring Unit, Space Applications Institute
michele.crosetto@ jrc.it
** Università degli Studi di Messina, Italy
bruno@ipmtf4.topo.polimi.it
KEY WORDS: Interferometric Procedure, DEM Generation, Image Coherence, Atmospheric Effects.
ABSTRACT
A new interferometric SAR (InSAR) procedure for DEM generation was employed to generate different DEMs from
ERS SAR image pairs. The procedure was validated comparing the InSAR DEMs with a suited reference DEM. In the
first part of the paper the principal features of the procedure are briefly summarised. The second part is focused on the
quality assessment of the INSAR DEMs. They cover the same test area and come from one ascending SAR image pair,
one descending pair and from the fusion of data coming from ascending and descending images. The analysis includes
the influence of the SAR image coherence, the degradation of the DEM quality related to the terrain topography and the
artefacts due to atmospheric effects.
1 INTRODUCTION
Interferometric SAR is a technique which allows to extract information on the terrain topography from the phase of the
SAR signal. InSAR is based on the processing of complex SAR images acquired from slightly different points of view.
A general review of the technique is given in (Gens and Van Genderen, 1996). It was applied for the first time at JPL
(Jet Propulsion Laboratories) in 1986 using airborne data (Zebker and Goldstein, 1986). Today, a large number of
research groups are working on DEM generation with InSAR data coming from different airborne and spaceborne
systems. The importance of InSAR is related to its high spatial resolution, the good potential precision and the highly
automated DEM generation capabilities.
About three years ago, five research groups (University of Thessaloniki, ICC - Cartographic Institute of Catalonia, ETH
Zurich, Technical University of Graz and Polytechnic of Milan) joined in the frame of an European Union Concerted
Action called ORFEAS (Optical-Radar sensor Fusion for Environmental ApplicationS). The purpose of the project was
to assess the benefits of the integration (fusion) of data coming from different sources in orthoimage and DEM
generation and land cover classification. A comprehensive data set, covering South Catalonia (Spain), was made
available to ORFEAS participants by ICC. An important part of the ORFEAS project was devoted to the generation of
DEMs using optical and SAR data. In this frame, the authors’ activity at Polytechnic of Milan was focused on
implementing a complete InSAR procedure for DEM generation, assessing the InSAR DEM quality and evaluating the
pros and cons of the interferometric technique (validation).
In the following section, the main characteristics of our InSAR procedure are briefly described. For a comprehensive
description of the procedure refer to (Crosetto, 2000). The second part of the paper is concerned with the analysis of the
generated InSAR DEMs.
1.1 Interferometric SAR Procedure
The complete INSAR procedure we employ to generate DEMs, processing spaceborne (repeat-pass) data, consists of the
following stages (Crosetto, 2000):
- image registration
- interferogram generation
- interferogram filtering
- coherence calculation
- phase unwrapping
- geometry calibration
46 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.
