# Smart Environmental Data Infrastructures: Bridging the Gap between Earth Sciences and Citizens
## 2 System Architecture  
A software architecture organized in three layers (three-tier architecture) is a classic design pattern that is still of common use in current systems [20]. At the bottom of the architecture, a data layer is responsible for all the required data management tasks, which include data and metadata storage, data access, query processing, and transaction management. In the middle of the architecture, an application layer, also called business logic layer, implements all the processes that define the application functionality. The architecture is completed with a presentation layer at the top, which enables the friendly interaction with the users. The adoption of the above architectural design pattern in the area of GIS is also widespread. Thus, for example, the generic architecture for GIS proposed in [21] describes the main structure and functionality that the above three layers should have in GIS data browsing applications. Another example is the OpenGIS Service Architecture [22] proposed by the OGC, which has also been adopted by ISO (ISO 19119:2016). The above standard classifies geographic services into six categories, namely, human interaction, model/information management, workflow/task, processing, communication, and system management. The standard shows also how the above types of services fit the different layers of a multi-tiered architecture. Thus, the data layer is composed of model/information management services, the application layer includes processing and workflow/task services, the presentation layer has human interaction services, the communication services enable the interaction between the layers and system management services are transversal to the architecture. To enable the interoperable interchange of geospatial data and metadata in Europe, the INSPIRE directive [23] proposes the use of network services. The most important ones are those related to the data layer, and they include the following. Discovery services that enable the searching of metadata to find both datasets and services. View services that enable the displaying and navigation of geospatial datasets. Download services that enable obtaining parts of geospatial datasets in standard formats. A specific software architecture for an environmental observatory information system has been proposed in [24]. General components are proposed for observation and communication, i.e., sensor data acquisition, data and metadata storage, data quality and provenance, publication and interoperability and discovery and presentation. The functionality of the above components is mainly related to that of a data Layer, except the discovery and presentation component that deals with human interaction at an application layer. Based on the context described above, the SEDIs considered in this paper fit completely inside the data layer of a three-tier geospatial software architecture. As it is shown in Figure 2, the architecture is composed of three main components that enable data acquisition from different sources of earth observation and modeling, data storage and data searching and browsing. **Data acquisition and integration (Section 4). ** Nowadays, real-time data of what is happening on the Earth's surface may be obtained by infrastructures that are based on machines and/or people. Since long ago, different types of sensing and computing infrastructures have been used to perform environmental observation and modeling. Models are available in many scientific domains such as hydrology, meteorology, oceanography, ecology, etc. They generate large amounts of numerical estimations of many variables related to the past, present and future of different physical systems. Many Earth observation infrastructures are currently deployed along the surface of our planet, including many networks of in-situ stations with different types of sensors and many remote sensing complex systems and campaigns.