ISO 19156 ‘Observations and measurements’ provides a conceptual schema for observations and the features involved in sampling when making observations, and specifically designed to support the exchange of information describing both the observing event and the results of the observation between different scientific and technical communities.<br /></p><p><br /></p><p>Whilst the name of the model invokes a particular concept to meteorologists (e.g. ‘observation’, the measurement of physical phenomena with an instrument or sensor – disjoint from the concept of ‘forecast’) it is important to consider the semantics of the model. The class OM_Observation is defined as ‘an estimate of the value of some property of some Thing using some specified Process’. The process may be an instrument/sensor (directly) measuring some physical parameter or a numerical simulation predicting future values. Thus the ‘Observations and measurements’ conceptual model may be used to represent both observations and forecasts.<br /></p><p><br /></p><p>Meteorological observations or forecasts clearly relate to the real world. For example, we may observe the weather for Exeter or provide a weather forecast for the ‘North Atlantic European’ area. However, there is a level of abstraction to resolve:<br /></p><p>- An observation of the weather for the city of Exeter happens at some representative location within the city or some representative locale nearby; or<br /></p><p>- The forecast domain for ‘North Atlantic European’ is specified so that it covers the areas for which a forecast is required<br /></p><p><br /></p><p>In each case, the ‘observation’ event relates to some sampling regime that is a proxy for the real entity of interest (e.g. the site of the weather station, or the extent of the forecast domain). The observation or forecast is not directly related to real-world entities.<br /></p><p><br /></p><p>ISO 19156 ‘Observations and measurements’ provides a conceptual model for describing this layer of indirection: Sampling Features. Further specialisations of Sampling Feature are provided based on spatial topology (SF_SpatialSamplingFeature and sub-types thereof).<br /></p><p><br /></p><p>In all cases identified thus far in meteorology, it appears useful to describe an observation, measurement or forecast with respect to the sampling regime (e.g. the Sampling Feature) and indirectly refer to the real-world entity for which the Sampling Feature is a proxy.<br /></p><p><br /></p><p>Spatial Sampling Features are considered an essential part of METCE: all observations, measurements and forecasts of meteorological phenomena shall define the ‘featureOfInterest’ as a concrete sub-type of SF_SpatialSamplingFeature.<br /></p><p><br /></p><p>Class 'OM_Process' (related to OM_Observation via the 'Procedure' Association) is used to define the process(es) involved in generating an observation. In order to ensure a consistent implementation of the abstract OM_Process class, *ALL* Application Schema based on METCE shall use the Process class defined therein (or sub-class thereof) to describe the observation procedure.<br /></p><p><br /></p><p>METCE provides three specialised types of OM_Observation; each of which enforce the constraints that 'featureOfInterest' shall refer to an entity of type SF_SpatialSamplingFeature (from ISO 19156), or subclass thereof, and 'procedure' shall refer to an entity of type Process (from METCE), or subclass thereof.<br /></p><p>- SamplingObservation: subclass of OM_Observation providing a general purpose observation type;<br /></p><p>- ComplexSamplingMeasurement: subclass of OM_ComplexObservation for use where the observation event is concerned with the evaluation of multiple measurands at a specified location and time instant or duration - the result of this observation type shall refer to an entity of type Record (from ISO 19103), or subclass thereof; and<br /></p><p>- SamplingCoverageMeasurement: subclass of OM_DiscreteCoverageObservation for use where the observation is concerned with the evaluation of measurands that vary with respect to space and/or time - the result of this observation type shall refer to an entity of type CV_DiscreteCoverage (from ISO 19123).<br /></p>