Topic: Let the new rain calibrations begin... Tropo gauge installed

[kheller2]

I finally got around to installing my new Tropo rain gauge next to the Stratus.  Here is to the 2.5% correction I will now do to all my Ecowitt gear. 


BTW, a Cocorahs page on this has a funny statement -- which was very apropos today given the differences I can visually see between these two after a rain storm.

As a final thought, consider this old adage (Segal's law), reinterpreted for precipitation measurements:

"A person with a rain gauge knows how much rain fell. A person with two rain gauges is never sure."

 [ You are not allowed to view attachments ]

[Wooks61]

BTW, a Cocorahs page on this has a funny statement -- which was very apropos today given the differences I can visually see between these two after a rain storm.

As a final thought, consider this old adage (Segal's law), reinterpreted for precipitation measurements:

"A person with a rain gauge knows how much rain fell. A person with two rain gauges is never sure."

 [ You are not allowed to view attachments ]

 

The same can be said about barometers and pressure 

[Gyvate]

the German expression used in the "technical measuring" community is:
"Wer viel misst misst Mist" 
in English:
who measures a lot measures crap
the beauty of the German expression lies in the rhyming:
"misst" (3rd person singular of "messen" - to measure)
and "Mist" (literally: [horse/cow] dung)
are homophones - i.e. are pronounced the same way and cannot be distinguished by pronounciation

[davidmc36]

Hee Hee Cheeky little phrase.

Maybe that dual install will prove to the unbelievers why their neighbour's gauge down the block is no parallel to theirs. 

[Billyram]

I believe you could have 2 identical rain gauges a foot apart and they would not read the same all the time.

[Rover1822]

This is correct. Although started as an experiment, my arrangement pictured below , does, for me demonstrate that the 2 units are very close on their readings, within a few percentage points, with neither being dominant. I may get a slightly higher reading from one than the other, then next time, the other way around. So in reality , for me, I could get away with one of the units.

However, there was another unexpected benefit. If the variance between the 2  is larger than usual, it essentially lets me know that one may have a blockage or issue, and I go check, whereas if I didn't have the other one, I may not know. So from that regard, I like my arrangement.

 [ You are not allowed to view attachments ]

[kheller2]

Shouldn't the funnels be all straight line parallel for more accurate readings?  Angular rain to the stratus is blocked by the WH40s.  Could just be the picture.  Mine look way off in the picture but are level with each other.

[Rover1822]

Yes, and they use to be on the same plane, but I added the extensions and changed the funnels on the WH40s. So yes, I need to push up the Stratus.

There is no angle variation, it's a height thing you are seeing

I'll be honest though, they are so close, with the stratus , hasn't been on my list of important things to do. In fact, I rarely check my stratus any more. But yes , they should all be at the same height.

[karss]

I have a Stratus rain gauge and a personal weather station (PWS) sited 15 feet apart. The PWS was calibrated using data from the manual rain gauge, and for successive rainfall measurements, the deviation between them remains within ±2%. A manual rain gauge definitely helps validate automated weather station (AWS) data.

However, using two manual gauges from different vendors introduces complexity, as measurement accuracy largely depends on the calibration of the inner tubes. To verify whether the gauges are functioning properly, the best method is to remove the inner tubes from both and measure the collected rainfall using a scale. Unfortunately, this kind of calibration requires a sufficiently substantial rainfall event to yield meaningful results.

[Rover1822]

I have a Stratus rain gauge and a personal weather station (PWS) sited 15 feet apart. The PWS was calibrated using data from the manual rain gauge, and for successive rainfall measurements, the deviation between them remains within ±2%. A manual rain gauge definitely helps validate automated weather station (AWS) data.

However, using two manual gauges from different vendors introduces complexity, as measurement accuracy largely depends on the calibration of the inner tubes. To verify whether the gauges are functioning properly, the best method is to remove the inner tubes from both and measure the collected rainfall using a scale. Unfortunately, this kind of calibration requires a sufficiently substantial rainfall event to yield meaningful results.

Also means one is really concerned about deviation of 2% , which , actually is within percent error of the units WH40s. I can live with a 2 percent error.  But  yes, one can always improve, I'm simply not that bored.

[kheller2]

I have a Stratus rain gauge and a personal weather station (PWS) sited 15 feet apart. The PWS was calibrated using data from the manual rain gauge, and for successive rainfall measurements, the deviation between them remains within ±2%. A manual rain gauge definitely helps validate automated weather station (AWS) data.

However, using two manual gauges from different vendors introduces complexity, as measurement accuracy largely depends on the calibration of the inner tubes. To verify whether the gauges are functioning properly, the best method is to remove the inner tubes from both and measure the collected rainfall using a scale. Unfortunately, this kind of calibration requires a sufficiently substantial rainfall event to yield meaningful results.

That's why I picked up the Tropo when on sale a few months back.  There are a few scientific comparisons between the two that show just how off the Stratus CAN be, even though it's still within tolerance of the official 8" weather devices vs 4" consumer.   Generally, the Stratus over reads by 2.5%.  (This is a generalization!)  But when I see readings of .68" vs .70" you can really start to physically see the difference.  The Stratus is a very good device (I also like its plastic material better).  But the Tropo is a more accurate device.

The sucky part is having to recalibrate all my Ecowitt buckets

Here is marketing but interesting scientific comparison https://www.youtube.com/watch?v=XWge9wWPzKk  if you can get past the creepy horror music.

[Gyvate]

Generally, the Stratus over reads by 2.5%. 

Just wondering - how can such a gauge over-read (unless the scale, the markers for the amounts,  is/are not precisely set) ?
Who will systematically over- or under-read is the user by not being exactly level to water surface - and possibly also due to surface tension effects...

[Rover1822]

Generally, the Stratus over reads by 2.5%. 

Just wondering - how can such a gauge over-read (unless the scale, the markers for the amounts,  is/are not precisely set) ?
Who will systematically over- or under-read is the user by not being exactly level to water surface - and possibly also due to surface tension effects...

Just to reiterate on how to read the cylinder. You read at the bottom of the meniscus (bottom of the concave curve), this is true for all graduated cylinders , and this is a graduated cylinder.  As far as the markers on a Stratus not being precisely set, they are molded in, so that is unlikely to cause an error. 

I assume everyone know that, this was just in case some did not.

[kheller2]

I don’t think any explanation has been given as to why it’s off, you can just show that it is by various percentages as the inner tube fills up.  I think the normal example is .98 Stratus is 1.00 Tropo. So when measured by volume and weight, 1” of real rain will overflow the Status. 

[Rover1822]

I don’t think any explanation has been given as to why it’s off, you can just show that it is by various percentages as the inner tube fills up.  I think the normal example is .98 Stratus is 1.00 Tropo. So when measured by volume and weight, 1” of real rain will overflow the Status.

True, and the Tropo also overflows at some point, but it matters how you remove the top and measure the other liquid in the cylinder.

Regardless, I'm not going to sweat over 2%. And as much as I would like to , I am not going to buy a Tropo (for like $70 US) , to discover that you are correct. .It really doesn't matter that much to me. I mean you can chase down accuracy until it makes you blind and readings asymptotes with averages , sorry ... I'm OK , lol .  Did that with the WS90s ... LOL

[Prestonsden]

This is correct. Although started as an experiment, my arrangement pictured below , does, for me demonstrate that the 2 units are very close on their readings, within a few percentage points, with neither being dominant. I may get a slightly higher reading from one than the other, then next time, the other way around. So in reality , for me, I could get away with one of the units.

However, there was another unexpected benefit. If the variance between the 2  is larger than usual, it essentially lets me know that one may have a blockage or issue, and I go check, whereas if I didn't have the other one, I may not know. So from that regard, I like my arrangement.

 [ You are not allowed to view attachments ]

Do you use any gain on your WH40’s with the new extension or have your studies concluded it is accurate without any adjustments.

[Rover1822]

This is correct. Although started as an experiment, my arrangement pictured below , does, for me demonstrate that the 2 units are very close on their readings, within a few percentage points, with neither being dominant. I may get a slightly higher reading from one than the other, then next time, the other way around. So in reality , for me, I could get away with one of the units.

However, there was another unexpected benefit. If the variance between the 2  is larger than usual, it essentially lets me know that one may have a blockage or issue, and I go check, whereas if I didn't have the other one, I may not know. So from that regard, I like my arrangement.



 [ You are not allowed to view attachments ]

Do you use any gain on your WH40’s with the new extension or have your studies concluded it is accurate without any adjustments.

I do , but I base it on my other manual rain gauge. Also, note the values from the WH40 drift over the years, my experience. Others may have a different experience. Cleaning the WH40 is key though.

[Gyvate]

Do you use any gain on your WH40’s with the new extension or have your studies concluded it is accurate without any adjustments.

No - the WH40 was always pretty accurate. It had only losses due to wind over-blow and splash loss, which cannot be compensated by a gain adjustment - it's too unpredictable. As the surface of the funnel is still the same, no adjustment is needed.

The only gain factor proposed for those working with the metric system is 1.02 to compensate for rounding errors during the conversation from inches to mm.

[Dador]

I have been using TROPO for almost half a year. I bought it mainly because of the metric division and the clear scale every 0.2 mm (actually, you can read every 0.1 mm). My observations over that time show that the WH40 with an edge-raising extension usually presents the closest results. Davis with a single spoon often outperforms Tropo and WH40 by up to +10%.

Edit:
Recent rainfall confirms what I wrote above.

3 days with light to moderate rain. No sun, meaning minimal evaporation.

Davis VP2 (single spoon) - 19,4 mm
WH40 - 18,1 mm
TROPO - 18,0 mm

[kheller2]

There are entire threads about the comparison of the two:
https://www.wxforum.net/index.php?topic=45404.msg463152#msg463152