Definition Areal Series Weights
With 'Definition Areal Series Weights' the user can make areal relations by selecting Series Codes for the Areal Series and for the Point Series. The function gives the possibility to enter equal weights or specified station weights.
Equal Station Weights
The weight given to a station is inversely proportional to the number of point rainfall stations: if the number of stations is N then the weight is 1/N. The weight is adjusted if at one or more point rainfall stations a value is missing; say at M stations an observation for a particular time step is missing, then the weights for the remaining stations for that time step becomes 1/(N-M). Only if M=N a missing value will be entered for the areal rainfall.
The combination of point rainfall stations to compute the areal rainfall can be stored in a file to be used at a later stage for different time periods.
User Specified Station Weights
If point rainfall station weights are not wished to be computed by one of the options offered, then combinations of station codes and weights can respectively be selected from and entered via the screen. Let c~k~ ,(k=1,N) be the weight factors then the areal rainfall follows from:
P~c,t~ = c~1~ P~1,t~ + c~2~ P~2,t~ + ... + c~k~ P~k,t~ + ... + a~N~ P~N,t~
with:
P~k,t~ = point precipitation value at time t of series k,
P~c,t~ = catchment precipitation value at time t.
Note that the sum of weights not necessarily adds up to 1, in order to allow orographical adjustments. If for a time step at one or more of the point rainfall stations an observation is missing then automatically a missing value will be entered for the areal rainfall.
The combination of point rainfall stations codes and weights to compute the areal rainfall can be stored in the data base to be used at a later stage for different time periods.
Series Ccodes
Area Series can be selected by selecting a series in the series list box and pressing the Select button. Point Series are selected by selecting a series in the series list box and pressing the '>>' button. To deselect a point series, select the series in the spreadsheet and press '<<'. By selecting more point series at a time, multiple series can be added to the point series spreadsheet, therefore use the <Shift> or <CTRL> key together with your left mouse button.
Relation Validity Period
By default the start and end-time of the validity period are taken from the specified working time period. These start and end time can be changed by double-clicking the time-label.
Save Relation
When pressing <Save> the relation is saved in the database. For the Areal Weights function the first two characters of the saved relation are 'AW'. For Thiessen these are 'TH'.
