ET WDL and Meteohub

[gibsonmb]

Hi all, I have a question: when I populate WDL using an ftp from WD, ET populates fine. When I use the same WDL template with Meteohub, ET does not populate with data. Why is this@? I'd quite like to have the ET ( think it stands for evapotranspiration), which a number of farmers where I live use. Something to do with the amount of watering reqired and the rate of evaporation of water into the atomosphere.

Currently using Meteohub to provide the data to WDL at the follwing url

http://www.bromsash.com

Any thoughts greatly received.

Mike

[admin]

I am not sure if Meteohub supports that value. I can't find it in the clientraw definition. You might have a look here to point me to the entry# that holds this number.

http://www.tnetweather.com/nb-0100.php

[gibsonmb]

532 or 533 in the clientrawextra.txt file

[gibsonmb]

One of the calculation methods for ET can be found here http://weather.nmsu.edu/pmcomp.htm

[admin]

I will try to add this for Vantage stations in the next release.

[gibsonmb]

Many thanks, it is measure that is being used more a more by farmers for watering schedules and predicting various agronomy disease scenarios

[gibsonmb]

I installed 4.3D yesterday, current Daily ET on the Vantage Pro console is 0.3mm (about 10:30am) but I've just parsed the clientrawextra file and bytes 532 and 533 are still reading zero. This does not appear to be working yet. Is there something else I can provide to help? Mike

[admin]

Do you have a variable named "actual_sol0_evotranspiration_mm" when browsing "http.//my-meteohub-ip/meteograph.cgi?text=all"?

What value does it show.

You also have to press "save" on "wdlive" page to propagate the changes made with 4.3d on clientraw templates.

[gibsonmb]

I do have the variable below present, it is reading 53. Currently the Davis Console is calulating 1.3mm and WD is calculating 4.3 mm. No idea why they are different.

I've just pressed save on the WD Live page but I already had the solar sensor in place for a few months

[gibsonmb]

Having pressed save etc. neither byte 533 or 532 are populated. I would image it would 532 that you would populate with data as that is the one that WD pupolates and hence the one that WDL woudl use I guess.

On page 28-15 is an explanatiion of how Davis calculate ET.

http://www.davisnet.com/product_documen ... ote_28.pdf

[gibsonmb]

Reading now as follows for ET:

actual_sol0_evotranspiration_mm 118.0
Vantage Pro 2 Console 2.8mm
Weather Display 5.6mm

The difference between WD and VP2 could be that WD is based on a reference of "well watered alphalfa" and VP2 is based on "well watered grass" but how is the measure calculated for Meteohub and what reference is it based on? All three are using the same raw sensor data over the same time period.

Below is a really interesting papaer on the calculation methods using well watered grass as a reference http://www.fao.org/docrep/x0490E/x0490e04.htm

[admin]

Meteohub reports the daily ET value as it comes from Vantage. Units are 1/100 inch, so "mm" is misleading. Next update will report in "inch" and "mm". However, converting values you posted here to mm still don't seem to match Vantage display values, or do they?

[sevenless]

I see a similar inconsistency on my system -- my console right now reads 0.02 inches ET for the day (which should be approximately 0.51 mm), but actual_sol0_evatranspiration_mm reads 26.0!

Perhaps the Vantage output is meant to be divided by 1000?

[gibsonmb]

So, about 22:30pm local time, reading as follows


actual_sol0_evotranspiration_mm 140.0
WD 4.6mm
VP2 Console 3.6mm

THink this area needs more investigation as to the reference methods do all use the same constants and references in the first place?

[sevenless]

Well, remembering what Boris said about that figure actually being hundredths of an inch, 140.0 means 0.140 inches, which is equal to 3.556 mm, and since the Console can only display one decimal point that gets rounded to 3.6mm.

There seem to be two fairly simple problems here -- one is what Boris mentioned about actual_sol0_evotranspiration_mm actually being in inches (to be fixed next update), and then something trivial seems to be going wrong with the math that converts that figure to millimeters for the WD figure you cite above. Is that your own conversion, or processed by Meteohub itself?

Beyond that we can discuss the method different vendors use to define ET, but it's all fairly academic since few of us are probably growing freshly watered alfalfa :)