Re: [TASS] photometric vs. non-photometric

[Peter Mount <peter@retep.org.uk>]

On Thu, 02 Sep 1999, Tom Droege wrote:
> There is a scheme to detect sky conditions.  I have allowed a channel for
> this and possibly can include it later.  One takes a thermal electric
> cooler and glues it between two plates.  One side is allowed to look at the
> ground, or anything of constant temperature.  One could water cool one
> side.  The other side looks at the sky.  One can use optics, or just a
> plate exposed to the sky.  Sky without clouds looks "colder".  So one uses
> the TEC to measure a wide area of the sky for its ability to absorb radiation.

I have here a collection of old BAA Journals (some older than I am), and
there's 3 or 4 different clear sky detectors. Most of them are based on two
thermistors (remember it's a 60's design), 1 metre apart, with the lower one
just above the ground. When the temperature gradient between them exceeds a
certain amount, it indicates a clear sky.

Peter

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