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SIGMA0 has two independent modules:

1. A remote-sensing module to detect changes with RADARSAT imagery;
2. A geomatics module to relate the detected changes to a collection of contextual data.

The remote-sensing module includes a series of algorithms for analyzing the RADARSAT image and automatically detecting changes. Interestingly enough, change is not detected by comparing images taken on different dates. In actuality, it involves only those sectors declared vacant based on the last land-use map available. This map serves as a guide in determining areas of change on a single recent radar image.

The second module uses the position of the areas of change detected as the automatic access key to a database of the territory using a user interface designed with MapObjects and Visual Basic. This interface provides the means for displaying and manipulating vector data (National Topographic Data Bases, assessment roll, cadastral data) and images (orthophotos). The user can use the data sources as often as he wants in order to establish, if possible, the nature of the changes and to produce change reports. Once the changes have been characterized, the map can be updated with the user's geographic tools (geometry and attributes) and new maps can be produced as work progresses.

Conclusive Results
Tests carried out to date with SIGMA0 on the entire territory of the Montreal Urban Community (close to 4 000 km2) speak eloquently in its favor. The system detects nearly all new buildings on the vacant lots on the previous land-use plan or existing land-use map. The percentage of error does not exceed 1%.

Indeed, combining the information extracted from RADARSAT images with existing digital mapping data significantly accelerates the process for updating land-use maps. And what's the end result? SIGMA0 enhances the existing legacy map data held by various organizations and substantially lowers the costs associated with map updating.


a) Vacant lots (MUC map)

b) Changes detected in the RADARSAT image Ó Canadian Space Agency (1999)

c) The user checks the municipal assessment roll against the corresponding orthophotos on his computer.

d) A photo of the site proves that there is a new building at the location indicated by RADARSAT.
References

• Cavayas, F., Y. Baudouin, and C. Gosselin, "SIGMA0: Better Monitoring of Urban Change", GéoInfo Newletter of the Plan géomatique du gouvernement du Québec, January-February 2003, http://www.pggq.gouv.qc.ca/geoinfo/num_e/fev03_e/fev03_5_e.htm
• Cavayas, F., Y. Baudouin, R. Fiset, and M. Lapointe, "Systèmes prototypes pour le suivi des changements de l'occupation du sol par fusion de l'imagerie RADARSAT et d'autres données d'observation de la terre", 12 pages, Géomatique 2000, Montreal.

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