3. Drop Size Distribution (Full Screen)

 

 

 

The full screen representation of the diagram "Drop Size Distribution" can be selected from the Main Screen by moving the mouse cursor on top of the according diagram icon and doubleclick the left mouse button.

 

3.1 Determination of DSD graph

In order to obtain the drop size distribution from the distrometer measured raindrop data, drops have to be classified into drop size classes. The equivolumetric diameter of each drop is used as a classification parameter. Since the drop size distribution is the number of drops per unit volume and per unit size, for unit size class the following quotient has to be summed up:

 

 

where:

A ...     effective measuring area of drop

Dt ...    time integration interval

v ...      velocity of drop

 

Therefore the number of drops per unit volume and per unit size for a particular size class is computed as:

 

 

          

 

 

 

where:

 

Dt ...    integration time interval (sec)

DD ... width of size class (mm)

Aj ...    effective measuring area of drop j (mē)

vj ...     velocity of drop j (m/s)

i ...       denotes drop size class

j ...       denotes single drop

Mi ...    number of drops in class i measured during Dt

Di ...    diameter of class i

 

3.2 Menu Buttons

 

button: RUN

Pushing this button starts calculation of the drop size distribution using the present setting of the integration interval. The integration interval can be a time interval, a rainfall quantity, or a number of drops. Every time the RUN button is pushed, a new Drop Size Distribution diagram is drawn. The mouse cursor changes its appearance to an hourglass cursor during calculations, and the RUN button toggles to be the STOP button.

 

button: MAIN

Pushing this button returns control to the Main Screen.

 

button: HELP

Pushing this button displays a help window.

 

button: Delta -

This button decreases the drop size class width.

Possible values: 0.05, 0.10, 0.15, 0.20, 0.25 mm.

 

button: Delta +

This button increases the drop size class width.

Possible values: 0.05, 0.10, 0.15, 0.20, 0.25 mm.

 

button: INTEGR.

Pushing this button allows to select an integration interval mode (time, rainfall quantity, or number of drops, full time range) for the computation of the drop size distribution. In addition to the integration mode the interval size can be entered. The current integration interval mode is highlighted in the diagram header.

 

 

 

button: COMP

If this button is pushed, the measured DSD is compared with a Marshall - Palmer - DSD of the same rainrate.

 

button: DEFAULT

This button restores the default integration criterias.

 

button: RESET TIME

This button causes the file-pointer set to the beginning of the time interval.

 

 

3.3 Diagram Header

 

The diagram header contains information on filter settings and also includes the following fields.