Calculate ET using fineoffset WH1080 and manual rain recording

[Glen Napthali]

Hi,

I have been running weewx on a RPi with a fineoffset WH1080 for a year or two. Recently I have thought it would be nice to calculate the daily ET to help inform me about irrigation needs for my farm. The WH1080 doesn't have a radiation monitor can an approximation be made using the sun's azimuth angle and sunrise/sunset times? If possible how can it be done?

My second question is the rain guage tipping bucket is quite prone to interference from the wind and its windy at my place. So I have a manual (plastic cylinder) rain gauge that I check after it rains. Is it possible to capture and display this data in weewx? Is it better to capture it in a separate database and display in weewx? anyone got a pointer on how to do this?

Thanks

Glen

[Greg from Oz]

I have the same weather station and the wind affects the rain gauge so I moved the rain gauge further down the pole I have it on and it has been good ever since.
The pipe was wobbling in the wind and was moving the tipper.
Don't know if yours it set up the same.

[Glen Napthali]

Previously I had the  PWS mounted on a star picket and the whole thing was shaking around quite a lot. In August I made a bracket from some gal C-section, and screwed it to a fence H-brace cross rail with the tipping bucket screwed to the gal. A few drain holes in the gal and it seems much better. I don't get pseudo-rain anymore unless it is really windy (70km/h) and in a specific direction.

The tipping bucket seems to under report by at least 50%, I added a StdCalibrate function over the weekend to help correct the error. I probably need to do a spider check to see if that is part of the trouble. The manual guage is good confirmation.

[Greg from Oz]

Oh yeah I forgot to mention the spiders as well....It was raining and nothing was being recorded because the spiders had made their web and the tipper wouldn't move.

[Xant]

"Radiation approximation using the sun's azimuth angle and sunrise/sunset" to calculate ET doesn't make sense.

Solar Radiation is a crucial data to calculate ET, and radiation varies tremendously through the day depending on cloud cover and shades. WeeWX is actually capable of calculate the Theoretical Maximum Solar Radiation (maxSolarRad), but by using this data for ET calculation would be irrational.

An approximation to convert Illuminance to Radiation - or vice-versa - by a multiple of ~120 is acceptable. So, the image underneath can be seen as a radiance example to compare measured vs theoretical. That is, the measured data rarely touches the theoretical.

If ET of importance, then consider a PWS system that is capable of measuring radiance (there are some inexpensive systems available nowadays).

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