The SCOUT rainfall processing system is based on the combined use of weather radar measurements and rain gauge measurements. If available, data issued from a numerical weather prediction model can be merged with the radar information.
- Spatially detailed rainfall measurements
- Radar supported rainfall forecasts for lead times of up to two hours
- Reliability estimations for the forecasted values
The results can be presented in various forms, as catchment or pixel specific time series, radar images of intensities or cumulated rainfall amounts, and specialised information screens.
Radar image (radar Hamburg, DWD) as global overview (left) and as defined section (right)
(click on images for large scale)
Short historical background
The history of SCOUT started in 1983 when it was first designed as a pure pattern matching and forecasting tool until 1991. For subsequent projects, radar adjustment methods based on rain gauge data and any reflectivity - intensity relationship (Z-R-relationship) was added as well as a radar data viewer and an interface for catchment specific data supply in a time series format.
SCOUT Spatial Rainfall Estimation
Rainfall over an area can only be estimated, not measured: the rain gauge measures at a point which has limited validity for a catchment, radar data do not measure rainfall directly but its reflectivity. However, it has been shown in the past that these estimations are able to provide sufficiently reliable values for rainfall runoff simulations, if the data are handled with the required experience and caution.
SCOUT combines rainfall measurement as seen by radar and rain gauges applying a reflectivity to intensity transformation and, additionally, an adjustment procedure which modifies radar data as function of the rain gauge values. The procedure is based on the different probability density functions of radar and rain gauge data. The SCOUT rainfall processing system computes a spatially detailed rainfall information as image and as time series for selected locations or subcatchments.
SCOUT Rainfall Forecasting
A rainfall forecast is an estimation of the rainfall for some time in the future, based on the best use of the presently available information. A rainfall forecast can never predict the exact behaviour of the rainfall, but it can give information on the observed trends and thus give a plausible estimation of the future behaviour of rainfall. Such a plausible estimation can considerably improve the accuracy of subsequent applications, e.g. flood forecasting, traffic control or basin control.
The extremely high density of measurement points in a radar measurement allows the viewing of radar data as "images" and a sequence of images as animation. The human viewer recognizes the apparent movement of the rainfield as well as its development in the near future. This feature has been used for the development of the pattern recognition techniques that form the core of the SCOUT radar rainfall forecasting module. This approach tries to recognize individual "radar echoes" and therefore is particularly appropriate to meet hydrological concerns regarding the "most threatening rainfall areas".
Rainfall Forecasting Quality Estimation
Information gets less accurate with larger lead times, therefore a performance index for the forecast is estimated. This index uses the growth and decay tendency of important clouds and cloud systems on their way to the catchment area. This increases the confidence in the results of applications based on the forecasted rainfall, because data quality is made more transparent.
Use of Numerical Weather Prediction data
Where the lead time of the radar forecast is not sufficient, use of results from numerical weather prediction models (NWP models) can be made, if such information is available. The forecasted values by NWP will be added at the end of the radar forecast lead time to the catchment specific time series until the desired lead time is reached. By this method, the detailed spatial and temporal information from the radar data will be used for up to two hours ahead, and the NWP data will provide the required information for the remaining time interval.
Applications of SCOUT
SCOUT was applied in all radar projects of hydro & meteo in an online or offline mode. Details can be read on the project overview of radar projects.
The currently actual version of SCOUT is version 3.34. If you are interested in the SCOUT rainfall processing system or if you want more information, please contact us.