Rainfall rate tests

To test Oww's measurement of rainfall rate (which uses the time-between-increments technique) I ran water into the gauge from a coffee filter funnel, at various rates. Results were collected with TherMon. OK, I should really have done nicer plots from a log file, but I didn't yet get around to adding the rainfall rate to the log output.

A common feature is the tailing off by 1/t. This is down to the nature of the calculation. But the real rate also tailed off, as the water ran out of the funnel. On the late shoulder of each ‘pulse’ the two match nicely, such that when the later bucket tips come there is no ‘join’ in the plot.

An important feature, in my opinion, is that the rate value responds fully by the second bucket tip.

y scale is rainfall rate (inches / hour) – green line gauge reading (inches) – blue line

10 minutes. Filter filled, re-filled, allowed to empty, and then refilled.

10 minutes. Filter filled almost to top, then topped up to around 50%, then left to drain.

10-reading averages - 38 minutes. Starts with data from the above plot. Then 3 more cycles.

Gauge readings to go with the above plot. 0 – 1.5 inches

Dr. Simon J. Melhuish. 6th December, 2000.

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