# Sensor Observation Service API for Providing Gridded Climate Data to Agricultural Applications
## 2 Basic Concepts and Related Information
### Sensor Observation Service  
SOS is a standard protocol and application program interface (APIs), which was adopted as an OGC standard in the SWE framework for accessing measured sensor observations and sensor metadata registered. Official OGC implementation specification Version 2.0 is available [10]. Clients can obtain point weather data through the SOS API in the same format and mechanism even though data are from different data sources or structures. Once users experience SOS API, they can retrieve data from any source with SOS support. The same program can be reused without modification. SOS API assures the interoperability of point-based weather data in time series format.  
The main objectives of SOS are accessing observed data in a standard way and being a mediator of data exchange and the sensor system while hiding the heterogeneous structure of sensor data formats and protocols. Three core operations required for SOS are:  
1. getCapabilities: This operation allows clients to access metadata and a list of available operations on the SOS server. The request and response format is defined in [11].  
2. describeSensor: This is the operation for retrieving the metadata of physical sensors. Sensor Model Language (SensorML) is used for encoding sensor metadata [12].  
3. getObservation: This operation is for accessing observed data by allowing spatial, temporal and thematic filtering. The data are returned in O&M document encoding approved as an OGC standard, which is XML format [11]. O&M is used for encoding data observed by sensors. The observation comprises timestamp, value, observed property and the feature of interest.  
There are several examples of applications and services, which manage weather data and metadata, using SOS API, such as the agriculture service application [13] and the crop simulation application [14]. These applications have been providing information to farmers in Japan. They retrieve weather data from various kinds of sensors from various sources through the same program. The National Oceanic and Atmospheric Administration (NOAA) has been utilizing SOS API for providing weather data, such as in [15].  
SOS API is suitable as an intermediate layer for providing weather data to applications. A system can request metadata and data without knowing how the data are stored in the database, but just following the API specification. Applications do not need to prepare data accessing routines for each data source, which reduces the time and cost of programming [16] demonstrated the efficiency of SOS in an agricultural application that accesses several different sensor systems.  
The Ministry of Internal Affairs and Communications in Japan accepts SOS as one of the standard APIs for managing agro-environmental sensor data in agriculture [17].  
In this regard, we utilize AmGSD as the data source for providing point weather data to agriculture applications through SOS API. To seamlessly provide pointed climate data from the grid data source, several mechanisms are developed as described in the Methodology Section.