Another rain calibration experience

[aaardvaark]

I have a poorly sited set of 1091 sensors attached to the edge of my second floor unit but still wanted to get the rain reading as accurate as I could. I installed a conventional rain gauge (plastic wedge type) next to the 1091. Both will be subject to excessive wind but about the same amount.

Anyway the calibration after several days of fantastic rain seems consistent around 1.2 (1.17 is current best guess). This was for rain with low and medium winds (0 for long periods to gusts 15kph). The finesoft gauge is as supplied, no additional collector or spider proofing.

So from me 1.17 calibration factor. Are there any others with unmodified gauges who have done some kind of calibration?

Julian

[scientistuk]

hi there , just like to add I have wh1080 model . and modded with a funnel and bucket with a 4x surface area than the original guage.. my calibration is set at 0.35, which i assume equals to 1.40 without the mod.
I found yesterday with 2.9 ml of light/moderate rainfall, against my manual rain catcher to calibrate it was spot on..
I also found that rain droplets were collecting on the side which I used some vaseline on the inside of the funnel, just a light coating mind. Vaseline does have other uses

[aaardvaark]

So yours is 1.4 in light rain with a modified gauge. It'll be interesting to see the difference in heavier rain.

There's a few others reported round the place, below are the one's I can find. I'm not rabid about accuracy, there's such a huge difference between locations it's not worth worrying about too much. I'm aiming for 10% compared with 'conventional' gauge in the same location. I'll modify my calibration as more rain happens.

Summary of calibrations found on Fine Offset forum...

Unmodified gauges
Repairman Oct09: 1.21
Dionaea Nov09: 1.11
Dc1500 Nov09: 1.3
Jrsubs (me): 1.2, 1.17



Modified gauges
Scientistuk Feb10: 1.4
Repairman Dec09: all over the place
Hills: 0.9

[scientistuk]

ye looking forward to see the difference with heavy rainfall , I will definately post my findings. Hopefully we will get some nice convectional showers that are curling in to the south east from france and the channel ..
Rainfall tends to be alot lighter and much less.. I think the driest part of the country is St Osyth, Essex, which aint too far from here

[scientistuk]

oh ye I just found this 'In terms of annual average rainfall, St Osyth is the driest recorded place in the UK, with an average of just 513 mm per year. This is only slightly wetter than a "semi-arid Steppe" climate (250mm-500mm)' lol

[Gina]

We get plenty of rain in the south west I'm planning on getting something to measure the rain manually as a check.

[aaardvaark]

I can only say WOW I had no idea anywhere in the UK had rainfall lower than Canberra and similar places! Ours is around 600mm and in my opinion not nearly enough. It's been considerably less on average for the last 5 years. Looking forward to seeing your and Gina's results. Gina is your gauge modified? I think it is but I've lost track.

[bruce45]

if you really want rain try the west cost of scotland (BBC Scotland " Between the showers it will pour down")

when its not raining you cant find a better place.

[aaardvaark]

if you really want rain try the west cost of scotland (BBC Scotland " Between the showers it will pour down")

ah I know - I was fortunate to spend 6 weeks in west Scotland including a week sailing on a fine ketch (at least, I wasn't sailing, just doing what I was told) out of Tobermory, and I do remember the storms and rain. And wind. At one point we were leaning out over a sea cliff on Canna, honestly 30 degrees or more from vertical so we could see directly below to the bottom of the cliffs. This angle was possible because the wind was so strong and so steady. I'd like to have had my toy weatherstation in one hand then to record wind velocity.

Last week I watched a BBC doco about the sea eagles on Mull and noted in passing that it seemed to be wet a lot of the time.

From where we stand, rain is all good, but sure I could change my mind if stuck in lots of it for too long.

when its not raining you cant find a better place.

I know, I agree, I want to live in Scotland. Even Iona where we picked potatoes and ... er ... looked at the monastery (what else can you do?) was wonderful. You're very fortunate to live where you do.

[Gina]

Gina is your gauge modified? I think it is but I've lost track.

Yes, I have a large funnel giving four times the catchment area of the original.

[6719jason]

ye looking forward to see the difference with heavy rainfall , I will definately post my findings. Hopefully we will get some nice convectional showers that are curling in to the south east from france and the channel ..
Rainfall tends to be alot lighter and much less.. I think the driest part of the country is St Osyth, Essex, which aint too far from here

Well if you want to check on totals for a village just a few miles from my location....

Please visit my Weather Station...... http://www.weeleyweatherstation.info

Some Areas of Essex are far drier than others

[scientistuk]

yet another essex weather station .. well we had some heavy burts today and so far a total of 2.1ml has fallen, seems still to be accurate comparing with the manual guage.. really need a day of 10 ml + to compare as the margins of error will be greater. Im a little bit of a calibration freak.

so ye for me looks like 1.40 is a good calibration factor, Im assuming the way these fineoffsets are made everyones is different.

just have to figure out this Ftp thing so i can get my Cumulus data online...

[scientistuk]

We get plenty of rain in the south west I'm planning on getting something to measure the rain manually as a check.

99p shop do some in the gardening section for ermm 99p lol. made in germany with metric calibration.

[Gina]

Sounds good But don't know of one round here . Thanks for the info

[aaardvaark]

so ye for me looks like 1.40 is a good calibration factor, Im assuming the way these fineoffsets are made everyones is different.

I reckon that by the nature of the way they are made (the tipping bucket) as long as you don't change the collection funnel thing they all will perform more or less the same, which is why I was interested in other people's calibrations. I believe that if you put two side by side they'd be almost identical in calibration. The big differences are in how they are used, where located, how high located, the rainfall rate, and wind at the time. And any modifications, which will change calibration because different funnels and protection mesh etc must affect the dynamics of raindrop collection and accumulation.

Locating it near the ground or up high apparently has a significant effect on recorded rain due to wind changes so I'm only comparing mine to a co-located gauge.

I think in reality the 'correct' calibration factor would be different for light rain compared to heavy, and for light wind and strong, but that this is getting to the point of diminishing returns when you realise how different rain is from one spot to another anyway.

just have to figure out this Ftp thing so i can get my Cumulus data online...

The on-line stuff is still beyond me and apart from rain I don't particularly feel the need to report my weather to the outside world. I can't imagine why people would be interested in anything other than rain but would definitely like to have a whole host of weather stations around Canberra all reporting rain, because there is real interest in knowing how much fell on the other side of the city or in the catchment areas. So I will have to work out how to broadcast the rain at least.

Hope you get some more rain soon, and a gauge -- as you say 10 or 20mm would help. You do need to compare it to a manual gauge right next to your station. Those cheap ones sound good, I wish I'd been able to find one for that price!