There is a H2O peak in the IR band not far from the CO2 peak.  An =
optical band pass filter at this nm range would detect the moisture from =
the rain.  It is a good humidity detector as well as a rain detector.  I =
have built such devices years ago.  It is easy to look up the IR =
spectrum for the H2O Peaks and choose the best one.  The detector =
sensitivity is also important. =20

Richard

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