Rain Bucket Modification - Fine Offset WH1081

[Palmyweather]

It has possibly been well documented that the Fine Offset WH1081 and similar have a very shallow rain bucket. Around this time last year I modified the cover of my station to have larger sides using an ice cream plastic container. This worked well however the harsh New Zealand summer sun has taken its toll and is no longer useful.

However my work has started selling this type of weather station. After having a couple of returns I have made an almost perfect modification by using two rain covers.

Using a cutting tool, I took the centre out of one, flipped it upside down and used silicon glue with UV resist to attach it to complete one (unmodified). I also sanded down any rough edges to make a clean transition from one to the other.

Results look much more professional and will probably provide a longer lasting result to fix the shallow bucket problem.

I realise that not everyone has access to such resources, however maybe if you pop into a store selling this model, they too may have returns that you can use to achieve this. We usually give away any parts as replacement.

Undertaking this also helped pass a rather slow day at work.

This adaptation can also be seen on my live webcam http://palmyweather.co.nz/webcams.php

[robynfali]

I would have thought not, but any calibration needed on that?

[Palmyweather]

I don't think any calibration would need to be conducted as it is the same catchment area surface, however it is just deeper, preventing any splash out. The only issue I may have is with snow, however it only ever snows here once every 80 years.

What do other people think, would it need any other calibration? Is this option potentially more or less accurate?

[MickinMoulden]

This will fix the problem and make it more accurate. No calibration required. Although I would suggest setting up a manual unit to compare as even though the modification makes a difference, it still won't make it perfect. Whether you have made the modification or not, it's best to calibrate your unit and have good placement and fitting of your rain gauge.

[Stephenwx82]

I did something similar with my gauge but I made a cut about 2/3 of the way up my old 1081 gauge (I upgraded to the 3081) cleaned the edges up and just sleeved it over my existing gauge as a shroud though mine is more aimed at preventing splashing out in wind as opposed to just conventional splash out itself.

I sanded the inside of the shroud with very fine wet and dry paper so it was all rather smooth too.

[MickinMoulden]

It doesn't look sealed. I would check by pouring in water and making sure it doesn't come out the sides. If it isn't sealed I suggest you do, as all water that enters through the top should be going through the tipper to be measured. Spare parts can definately be handy. I had to make my own with triple layered laminated sheets.

[Stephenwx82]

its not sealed yet before I do so I'm cross checking the readings with the manual gauge as said its more a wind shroud as opposed to a sealed funnel design like your's also I'm in the process as I speak of building a DIY Stevenson screen for it based on the thread on here

[MickinMoulden]

I'd seal it first, as the harder the rain fall's the higher the error rate will be.
I'm in the design process of my own version of screen, it'll be a tube design, self ventilating to draw ambient temp air through during the day (no need for fans). Good luck with yours, post some pics!

[Stephenwx82]

shall look at sealing it then very valid point

good luck with your design too, pics to come of this build, just about to bolt it all together and mount it

[faa440]

My problem is leaves. The shallow bucket gives the wind a chance to blow the leaves off the dish. How about a screen mesh that would allow the rain to fall through but would significantly reduce splash out?

[hungerdunger]

I've finally got round to trying this modification myself, as I have a spare rain gauge. Before I set it up permanently, can I clarify something?

The top and bottom of the cover don't have the same catchment area. According to my calculations (which ignore the fact that the corners are rounded) the catchment area is approx 18% larger at the bottom than at the top. So if you flip it over as the OP appears to have done I think you would need to make an adjustment.

However he has achieved a much neater joint than if you keep the cover the right way up. I haven't fixed mine yet, but it looks as if it will need some mastic to make the joint waterproof, as the bottom of the top cover is larger than the top of the bottom coverand it won't fit neatly. (see photo)

Gauge[1].jpg

Before I make my final decision, does anyone have further thoughts on this? And if I do fix it upside down with an area 18% bigger than the original, what adjustment should I make in Cumulus? I think it should be 0.85 as this is 18% less than 1.00, but maths has never been my strong point!

[steve]

And if I do fix it upside down with an area 18% bigger than the original, what adjustment should I make in Cumulus? I think it should be 0.85

Yes, that's right.

[yv1hx]

My problem is leaves. The shallow bucket gives the wind a chance to blow the leaves off the dish. How about a screen mesh that would allow the rain to fall through but would significantly reduce splash out?

I would recommend you use some rain bucket shield like this http://www.met.tamu.edu/class/metr451/C ... sld014.htm

This manual http://www.comptus.com/PDF/CWOP_Guide.pdf have some examples too. (page 45 onwards)

Good luck!

[denlong]

I have just calibrated my WH1081 rain gauge. The inner dimensions of the top of the collector is close to 11cm x 5cm = 55 cm^2.
The bucket needs 1.5 ml water to tip it (result of 3 tests using a syringe and counting the number of tips to take 7.5 ml = 5, 7.5/5 = 1.5).
1.5 ml divided by 55 cm^2 gives 0.0273 cm or 0.273 mm of rainfall per tip of the bucket not 0.3 mm as used in all the rainfall calculations. This means that if all our collectors are the same size then we are exaggerating our rainfall by 9.9%. To correct this without the need for recalibrating the software I am planning to decrease the inside collecting dimension of my rain gauge to 10 cm x 5 cm to give a collection area of 50 cm^2, this gives (1.5/50) x 10 = 0.3 mm per tip of the bucket. I will also raise the height by 5 to 10 cm in order to stop splashing from giving low readings during heavy rain fall or high winds.

Here in the UK I am trying to work out the conditions needed in our village to forecast a flood event similar to the events of 24/11/2012. I am working as part of a village committee to try and help people to take precautions in the event of a predicted flood.

Our work is being co-ordinated with 16 other at risk villages in Devon by the local UK Environment Agency, and we hope that we can become well informed and accurate in our predictions, hence the need for me to get my rain gauge accurate. If I succeed in this, it could be useful to the whole country.

Next job is to find a way of getting automatic warning of the combination of humidity, rainfall, wind direction and atmospheric pressure, which I think could be the parameters needed to make a forecast.

I will be interested in any comments members care to make.

[steve]

Just a couple of points. I don't think 7.5 ml is sufficient. You should really be using a much larger amount, 250 ml or more, and this needs to drip through very slowly - over a period of an hour or so. That's not to say that you won't get the same result.

You don't say whether you are using Cumulus to gather your data, but if you are, an alternative to changing the area of the gauge would be to set a calibration factor in Cumulus.