## 2 System Overview  
SIMONS has been programmed with independent modules according to the task to develop. Figure 1 presents a summary of the main blocks gathered in three basic stages, namely:  
* **Data acquisition**. This stage regards data input ingestion, both from SAR satellite images and transponder polls (mainly AIS). Data acquisition is automatically done via dedicated FTP links each time new datasets are available. Three types of streams are adopted, namely:
* SAR images from different sensors with meta-data extraction. Accepted formats are ENVISAT.N1, and ERS.JP2 and.E2. New formats, such as TerraSAR-X and ALOS-PALSAR, will be included in a near future.
* Satellite AIS streams obtained via communication satellite links.
* Coastal AIS streams acquired via coastal on-ground stations.
* **Data Processing**. Three main tasks are defined, namely:
* Pre-processing that erases undesired image aberrations that can affect the final performance of the system. Main efforts are focused to compensate the slant-range dependent reflectivity pattern and to calibrate the images, if not done so.
* SAR processing that isolates all the information needed from SAR images. This task uses the three CD, SD and SC modules. The first module (CD) isolates the coastline with an algorithm that evaluates the gradient variances of the reflectivity information. It is supported by external shape files when necessary. The second module (SD) detects the ships with a multi-scale approach involving wavelets. This allows the enhancement of those spots having a specific reflectivity and morphological pattern. To avoid confusion with ship-like features and reduce false alarms, a confidence parameter is defined from the wavelet processing parameters. Finally, the third module (SC) analyzes the distribution of the reflectivity values along the SAR ship signature to make ship categorization via fuzzy logic.
* AIS' processing that correlates ship detection reports with AIS polls. The slant-range projection and the azimuth shifts caused by targets in motion are taken into account.
* **Result Dissemination**. This stage delivers final products to users via an advanced and user-friendly web interface. It works on a common Geographic Information System (GIS) platform with OpenSource standards that are compliant with OGC. Different layers of information can be managed, such as GeoTIFF reflectivity images, detected coastline, ships data (location, bearing, category and dimensions) and the confidence of each ship report. SIMONS has been designed to be modular, flexible, reliable and unsupervised. The processing chain is fully-automatic and needs less than 10 min to deliver final products to users (compliant with NRT). In some cases, however, delivery time has been penalized by unexpected delays on data reception. As shown in Figure 2, delays of two and a half hours have been registered due to problems on the provider side. This limitation is expected to be resolved as otherwise, it could affect the performance of future applications such as route tracking. System capabilities have been checked by
Spanish police authorities (Guardia Civil) and naval forces. Currently, they are using SIMONS for operational purposes and they have found it very useful for supporting decision making. Their feedback has allowed the development of some added-value tools that support data analysis. For instance, alarm generation that filters useless information according to user profile and enhances the requested layers.