Is there further information available on exactly how the rain rate is calculated?
From AN28:
'RAINFALL RATE
Parameters Used: Rain Total (actually, rain rate is a measured variable in the sense that it is
measured by the ISS and transmitted to the display console, whereas all other calculated
variables are determined by the console from data received from the ISS.)
Formula:
Under normal conditions, rain rate data is sent with a nominal interval of 10 to 12 seconds.
Every time a rain tip or click occurs, a new rain rate value is computed (from the timer values)
and the rate timers are reset to zero.
Rain rate is calculated based on the time between successive tips of the rain collector. The rain
rate value is the highest rate since the last transmitted rain rate data packet. (Under most
conditions, however, a rain tip will not occur every 10 to 12 seconds.)
If there have been no rain tips since the last rain rate data transmission, then the rain rate based
on the time since that last tip is indicated. This results in slowly decaying rate values as a rain
storm ends, instead of showing a rain rate which abruptly drops to zero. This results in a more
realistic representation of the actual rain event.
If this time exceeds roughly 15 minutes, than the rain rate value is reset to zero. This period of
time was chosen because 15 minutes is defined by the U.S. National Weather Service as
intervening time upon which one rain "event" is considered separate from another rain "event".
This is also the shortest period of time that the Umbrella will be seen on the display console
after the onset of rain.
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Not sure that provides much extra illumination, but it's all there is.