Gamma Remote Sensing: more details on typical applications

GAMMA at “ERS ENVISAT Symposium” in Gothenburg last October:
GAMMA at “ERS ENVISAT Symposium” in Gothenburg last October

Gamma Remote Sensing (Swiss SME) is often carrying out Earth Observation Research and Development (EO R&D) with other European research institutions and in close collaboration with ESA.

According to Mr. Urs Wegmüller, Director of GAMMA, EO R&D in the area of processing and adding value to remote sensing data will always remain a key activity of the company in order to continuously exploit new potential areas for EO data.

In many R&D contracts with ESA, GAMMA has elaborated and matured the utilisation of the enormous quantity of Earth observation data being produced daily by both ESA and non-ESA satellites. Although it is a small European company, GAMMA has succeeded in being recognised for its scientific competence and often presents its finding to the international research community at major meetings, the last occasion being the ESA ERS-ENVISAT Symposium, held in Gothenburg, Sweden in October 2000. Here GAMMA presented three papers on the use of EO data from ERS SAR and JERS SAR.

GAMMA's declared goal is to maintain the highest level of technical and scientific expertise. This is an essential prerequisite for the development of new applications, consulting activities, and improving and maintaining commercial EO data software tools. To achieve this ambitious goal GAMMA is involved in research project with ESA, the European Union and national entities and co-operates with partners from universities, public institutes and the private sector. When searching for opportunities in new fields of applications, GAMMA often prefers to join consortia in order to assemble the best scientific know-how in all relevant domains.

Commercialisation of Earth observation products

Mr. Urs Wegmüller emphasises that the R&D activity with ESA and other research institutions has paved the way for GAMMA's entering into the commercial use of EO-data. It has managed based upon its experience with ESA to establish a high level of competence for advanced SAR data processing and the use of EO data.

Subsidence map of Bologna from ERS differential interferometry
Subsidence map of Bologna from ERS differential interferometry

GAMMA has high capabilities for advanced SAR processing. SAR processing, precision image registration, geocoding, absolute radiometric calibration and interferometric processing are fully operational steps in GAMMA's supply chain and are offered to customers with attractive conditions. Advanced data processing can also be offered, as well as consultancy. This comprises support in data selection, elaboration of processing strategies, value adding and interpretation of results.

Surface Deformation Maps measuring millimetre to decimetre surface displacement can be retrieved with differential SAR interferometry. GAMMA does not only offer to conduct the necessary data processing, but also provides assistance and consultancy to better meet the operational needs of the customer. Thanks to the immense and continuous ERS archives being built since 1991 the possibility that well-suited historic data exists over a given site is high.

With a project called 'Geophysical Surface Deformation Mapping Service using ERS INSAR' GAMMA have recently won a contract in the new Earth Observation Market Development (EOMD) initiative of ESA. This activity will allow GAMMA to bring their geo-information service closer to the commercial market through specific activities such as: service assessment in an operational context, engineering testing in cooperation with major oil and gas companies with interest in monitoring mining subsidence, refining the end-to-end service concept, formulating the business case, and, finally, promoting the offer and expanding their customer base.

Based upon the participation in EO activities and research with ESA, GAMMA has also managed to create a series of common software packages and tools supporting the entire processing from SAR raw data to products such as digital elevation models, deformation, and landuse maps. This proven software has been available commercially on the market place on a world wide basis since 1995, and is continuously upgraded to include new evolving techniques.

GAMMA demonstrates new successful areas
for the SAR Earth observation data at the scientific data processing forefront both for commercial use and for the general public good

In order to expand the customer base for operational geo-information products based on ERS Tandem interferometry the company Spot Image, France, and GAMMA developed the Coherence Product, which was put on the market as a commercial product in late 1999.

Mosaic of JERS L-band backscattering coefficient for Siberia
Mosaic of JERS L-band backscattering coefficient for Siberia

The Coherence Product consists of data layers generated using ERS Tandem data, i.e. ERS acquisitions with a time difference of 24 hours, which comprise calibrated SAR backscattering coefficients, interferometric correlation or coherence between the two acquisition of the tandem pair, and the corresponding temporal backscatter change. Image data and auxiliary information are provided in the DIMAP format based on XML and GEOTIFF, the future format for geo-information using data from the SPOT satellites.

An impressive example of the usefulness of the Coherence Product was the Storm Forest Damage Mapping conducted in early 2000 for Switzerland. Damage to forests could be mapped with high accuracy and over large surface areas following a change detection approach by combining two Coherence Products using Tandem pairs acquired before and after the storm. GAMMA has been involved in similar projects in France - such as that with the French company SERTIT - and with end users such as Civil Protection Authorities concerned with managing fire risks related to the damage caused by the December 1999 storms.

RGB composite of JERS interferometric signatures
RGB composite of JERS interferometric signatures for a 40 km x 34 km section of Siberia

A much larger forest map was generated as part of the SIBERIA Project, again conducted in the context of the EC Environment and Climate Programme by partners from eight European countries. GAMMA's main contributions were in the methodological development and the operational processing of JERS SAR data. In the frame of this project GAMMA conducted processing of more than 600 JERS SAR scenes at full resolution. The processing included absolute radiometric calibration and geocoding. The large Siberia JERS mosaic is shown on the left.

Interferometric processing of acquisitions from consecutive repeat-orbits was conducted where available. The JERS SAR L-band interferometric signatures contain valuable landuse information for forestry as shown on the right as an RGB composite generated using a pair of acquisitions with a 44 day time difference. The composite display coherence is red, the average backscattering coefficient is green and the temporal change of backscattering coefficient for this pair is blue.

Mexico City: ERS SAR interferometric subsidence map
Mexico City: ERS SAR interferometric subsidence map

During the last few years GAMMA was strongly involved in the development of differential SAR interferometry for land surface deformation mapping. Impressive results include maps of the ground-water extraction related subsidence of Mexico City (left) and Bologna as well as of the complex temporal and spatial deformations observed for an active coal mining area. In the case of slow deformations millimetre accuracy was achieved by the combination ("stacking") of multiple interferograms.

In the meantime deformation mapping has evolved into a relatively mature application with a strong potential for commercial exploitation within the mining industry.

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