Author Topic: Delta T Synthetic Channel  (Read 3040 times)

mikegf

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Delta T Synthetic Channel
« on: December 10, 2014, 11:15:25 pm »
Hi Guys,

After recently being caught (again) with poor spraying conditions in the Aussie summer, I thought I'd attempt to generate a Delta T synthetic channel to monitor/graph (I do have a Kestral 3500DT but it only provides the instantaneous value).  With assistance from Edouard's scripts (which were a great help to fast track my understanding of Applescript) I have what appears to be a working channel based on the wet bulb estimate (originally in JavaScript) from the NOAA site, some functions from Deivy's Matematica scripts and some code from Edouard's ET channel.  The code appears to be accurate (based on a limited set of comparisons with the 3500) but I have not tested the Imperial bit (we are metric here), nor on anything else except with WeatherCat 2.0.1 running on Yosemite (10.10.1)

I assume that there is at least one farmer out there in the Weathercat world that may find some benefit from this, so I have attached the script (I am new here so hopefully I have not broken any rules - being without 'proper' (wired) internet here means I don't have website access to load and post a link to).

Cheers

Mike

Blicj11

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Re: Delta T Synthetic Channel
« Reply #1 on: December 10, 2014, 11:23:55 pm »
Mike:

Thanks for sharing mate. Nice piece of work. And welcome to the WeatherCat forum!
Blick


elagache

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Thanks Mike - how is it used? (Re: Delta T Synthetic Channel)
« Reply #2 on: December 11, 2014, 09:46:31 pm »
Dear Mike, Blick, and WeatherCat tinkerers,

Thank you very much for your contribution!   I have added information on your posting to the page on the WeatherCat Wiki on integration:

http://wiki.trixology.com/index.php/Integration

Could you tell us a little more about the Delta T is used in your application?  I'll add the information to the Wiki!

Cheers, Edouard

mikegf

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Re: Delta T Synthetic Channel
« Reply #3 on: December 12, 2014, 11:12:44 pm »
Delta T is the difference between wet bulb and dry bulb, and it is indicative of evaporation rate.  The higher the Delta T the higher the evap rate. When spraying pesticides/herbicides, if the Delta T is too high the evaporation rate will also be too high, reducing the droplet life and therefore reducing the effectiveness of the spray.  The preferred conditions for spraying are with a Delta T between 2 and 8 - if it is higher then for the same effectiveness you may need to increase application rates - with the resultant cost as well as potential environmental side effects.  A short intro on weather effects for spraying is at http://www.bom.gov.au/info/leaflets/Pesticide-Spraying.pdf.

In the "old days" DT was easy to measure by comparing the two std thermometers.  These days with instruments reading dry bulb and RH, you need to reverse engineer an estimate of wet bulb to calculate DT.  The NOAA algorithm uses an iterative process to estimate wet bulb based on dry bulb, RH and atm pressure (the latter parameter needed, I think, due to vapour pressure changing with pressure)

DT becomes critical here as often the times suitable for spraying to prepare for next years crop also coincide with the onset of warmer temps etc.  For example the other day, once I cleared the paddock it was around 1200 and the Delta T was  around 12 (temp about 30C and RH around 40 from memory) - making it too hot/dry to spray.  Of course since then the weather turned (DT is currently around 4 and has been sitting around 2 for the last couple of days) but the wind also has picked up too much and there has been intermittent showers!  On the bright side,  the weather here has, in general, has been better here than in CA by all accounts!!!

Regards

Mike

elagache

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Thanks, explanation added. (Re: Delta T Synthetic Channel)
« Reply #4 on: December 13, 2014, 10:17:26 pm »
Dear Mike and WeatherCat tinkerers,

Delta T is the difference between wet bulb and dry bulb, and it is indicative of evaporation rate. 

. . . . .

Thanks for the explanation.  I have adjusted the prose slightly to look more like Wikipedia and added it to the WeatherCat Wiki.

On the bright side,  the weather here has, in general, has been better here than in CA by all accounts!!!

Well, we have been in a terrible drought so we really cannot afford to be too choosy about the rain we get.  Thanks to this storm we are at last ahead of normal rainfall for the first time this wet season.  We really need a significantly above normal rainy season to avoid rationing next year.  Nothing at our house had any problems, so let it rain!!  [WCSmall]

Cheers, Edouard  [cheers1]

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Re: Delta T Synthetic Channel
« Reply #5 on: December 14, 2014, 06:29:42 pm »
Nice  [tup]