It is well-known that SAR Interferometry (InSAR) presents a completely new approach for topographic mapping. Differential InSAR (D-InSAR), an extension of the standard InSAR method, allows for the detection of subtle deformation of land surface at millimeter accuracy. With the emergence of InSAR, remote sensing data has played an increasingly important role in recent years in geotechnical application but has not become an operational technique due to its inconsistent performance regarding the quality of interferograms this method produces. Currently, InSAR is a much sought-after tool that is rapidly evolving in various fields such as the construction of Digital Elevation Models (DEMs) of the Earth’s surface, the monitoring of earthquakes, volcanoes, land subsidence and glacier dynamics, the classification of different land types and other thematic mapping applications.

In order to bring together investigators to demonstrate the innovative methodology of InSAR/D-InSAR and explore differing approaches to the operational technique, the Joint Laboratory for Geoinformation Science (JLGIS) launched the “Advanced Workshop on InSAR for Measuring Topography and Deformation of the Earth Surface,” held in December, 2002, at the Chinese University of Hong Kong. Many active Scholars from Asia, Europe and North America gathered at the forum to present their on-going research and discuss product development for future projects. One of the most important products of this Workshop should be wide collaboration between individual research groups. All workshop participants agreed to the establishment of a regional network to promote research in the fields of InSAR technical development, and more importantly, technical diffuse as well as operational applications in China and the Asia-Pacific region.

This special issue contains a collection of papers presented in that workshop. Each submission was considered within the standard reviewing procedures for PE&RS. The foremost eight papers were selected. The papers encompass three main themes: InSAR methodologies and techniques for DEM generation, application of D-InSAR in deformation detection and InSAR extension application in thematic mapping.

The first theme involves three papers. Two of these focus on interferogram, the key point in InSAR data processing. The paper from Zilin Li et al. proposes a more robust quantitative measure for InSAR interferogram, which is based on phase differences. The simulation experiments show that the new measurement reflects the quality of interferograms very well. The subsequent paper produced by Mingsheng Liao et al. presents the automatic method for SLC image registration using a multi-step matching strategy that completes the registration procedure from coarse to fine precision. Only intensity images are used in all the steps including the coherence estimation. The authors attempt to attain a good compromise between accuracy, reliability and computation cost. Another paper from Dongchen E et al. describes a case study of DEM generation with InSAR technique in the Antarctic. The experimental InSAR DEM in the core area is compared with the DEM derived with field surveying data. It is expected that InSAR is a very promising technique to be utilized in Antarctica and can complement the field surveying and photogrammetric approach.

The second theme involves four papers on D-InSAR application in different fields. Ground settlement has long been a problem in Hong Kong, which has special land-cover characteristics. The paper by Xiaoli Ding assesses the performance of InSAR in the environment of Hong Kong, especially the temporal decorrelations of SAR images and the potential atmospheric effects on InSAR measurements. Ground settlements measured over the airport at Chek Lap Kok and a residential area are presented. The paper from Chao Wang et al. introduces the application of D-InSAR in China through two case studies: the 1998 Zhangbei-Shangyi earthquake in Northern China and urban subsidence in the city of Suzhou from 1993 to 2000. In their paper, Ye Xia and his colleagues investigate the capability of the D-InSAR technique for monitoring surface displacement related to by landslides, rock-falls and subsidence on a very small-scale area. They propose the utilization of an approach based on artificial corner reflectors, which can be identified from long temporal series of interferometric SAR images, including those with large baselines, and therefore decrease the risk of image decorrelation. The Three Gorges area has been selected as the experimental site, with its difficult environment for DInSAR technique, due to its variable atmospheric effect and heavy vegetation-cover.

Further discussions within the InSAR community center on methods of improving the assimilation of InSAR products with conventional ground-based observations (GPS, levelling, tacheometry, etc.) and other spatial products. Systematic studies on data fusion are necessary to account for the differences in the nature of InSAR and other data in terms of temporal and spatial scale. The paper from Linlin Ge et al. describes their work using GPS and GIS to assist InSAR data analysis. An application of the integrated InSAR-GPS-GIS technique in monitoring subsidence due to underground mining southwest of Sydney has been demonstrated.

The third theme received only one paper, from Jianguo Liu et al. Their paper shows that Interferometric coherence has been proven a useful tool for thematic mapping and environmental monitoring and will extend to new application fields of InSAR technique. This paper proposes the methodology for the use of multi-temporal coherence imagery as a tool for land-cover change detection. The paper demonstrates that Interferometric coherence enables effective detection and assessment of rapid erosion across a wide area, without the need for a detailed physical model.

We would like to thank all the authors and reviewers who have contributed to this collection. We hope this special issue will enhance the exchange and cooperation between the research groups in China and colleagues from all over the world.

Editors
Professor Hui Lin
Professor and Director
Joint Laboratory for Geoinformation Science
Chinese Academy of Sciences and the Chinese University
of Hong Kong

Professor Mingsheng Liao
State Key Laboratory for Information Engineering in Surveying, Mapping & Remote Sensing
Wuhan University