E.2.4 Temporal Accuracy For a gridded coverage the temporal reference time for the data at all grid points is the same. Temporal accuracy is not defined. ANNEX F. SURFACE CURRENT DATA This Annex describes the sources of data, methods of organizing surface current data (the time series and the grid), how the data product format is derived. In the last section we discuss additional features of current data. F.1 Data Sources For the purposes of this Product Specification, surface current data categorized as one of three types, depending on the source of production. These are: Historical and real-time observation, Astronomical prediction, and Model-based forecast or prediction. An historical observation consists of a time series of values at a specific location or area, often at a specific elevation above the bottom or below the surface. Observations can be for a fixed point (current meter), a moving point (e.g., a Lagrangian drifter), along a vertical or horizontal line (Doppler profiler), or an area (coastal radar). A real-time (or near-real-time) observation is actually a historical observation but for the very recent past. The astronomical tidal current prediction is often a time series computed by a mathematical formula using harmonic constants. This prediction applies to a specific location and depth, and is often produced many months ahead of time. The astronomical predictions for multiple stations are often combined into a digital tidal atlas, and the individual predicted currents are usually keyed to the time and amplitude of tidal water levels at a nearby station. Finally, model-based forecasts or predictions are usually produced by a two- or numerical hydrodynamic model, and include astronomical tide, meteorological forcing, river inflow, spatially varying water density, and open ocean boundary inputs. A hindcast, including an analysis, is based on historically-observed conditions. A forecast is usually produced to predict conditions a few hours or days ahead into the future. F.2 Data Organization Data are usually organized by the HO producer into either (a) a time series of values, such as for historical and real-time observations at a single point, or (b) a gridded set of values, such as from a model-based forecast or sea-surface analysis.
E.2.4 Temporal Accuracy For a gridded coverage the temporal reference time for the data at all grid points is the same. Temporal accuracy is not defined. ANNEX F. SURFACE CURRENT DATA This Annex describes the sources of data, methods of organizing surface current data (the time series and the grid), how the data product format is derived. In the last section we discuss additional features of current data. F.1 Data Sources For the purposes of this Product Specification, surface current data categorized as one of three types, depending on the source of production. These are: Historical and real-time observation, Astronomical prediction, and Model-based forecast or prediction. An historical observation consists of a time series of values at a specific location or area, often at a specific elevation above the bottom or below the surface. Observations can be for a fixed point (current meter), a moving point (e.g., a Lagrangian drifter), along a vertical or horizontal line (Doppler profiler), or an area (coastal radar). A real-time (or near-real-time) observation is actually a historical observation but for the very recent past. The astronomical tidal current prediction is often a time series computed by a mathematical formula using harmonic constants. This prediction applies to a specific location and depth, and is often produced many months ahead of time. The astronomical predictions for multiple stations are often combined into a digital tidal atlas, and the individual predicted currents are usually keyed to the time and amplitude of tidal water levels at a nearby station. Finally, model-based forecasts or predictions are usually produced by a two- or numerical hydrodynamic model, and include astronomical tide, meteorological forcing, river inflow, spatially varying water density, and open ocean boundary inputs. A hindcast, including an analysis, is based on historically-observed conditions. A forecast is usually produced to predict conditions a few hours or days ahead into the future. F.2 Data Organization Data are usually organized by the HO producer into either (a) a time series of values, such as for historical and real-time observations at a single point, or (b) a gridded set of values, such as from a model-based forecast or sea-surface analysis.
Surface%20Current%20Draft%20Product%20Specification_Version_0.1.12-(Clean).docx