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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#11
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"Nick Gardner" wrote in message
news ![]() "Bernard Burton" I don't think that the KZ rcorder uses the same method as the R&D, Nick. The latter uses a shadow post to generate a difference in output from a ring of photo-diodes. The KZ uses '3 photo-diodes with specially designed diffusers the determine when a threshold of 120 W per sq m is exceeded' See also: measuringtheweather.com/wp-content/uploads/2012/06/An-overview-of-sunshine-recorders-July-2012.pdf by Stephen Burt. Bernard Burton Bernard, I've just read the link to Stephen B's article and he says that the KZ works by having at least one of the three photodiodes in the shade giving a voltage differential. This is a similar principle to the R&D. Stephen also writes in the book version of Measuring the Weather that the KZ and the R&D are likely to give close results as they use similar principles to determine whether the sun is shining or not. The BL uses a simple solar irradiation measurement coupled with a quite clever software code to determine a sunshine/no sunshine output. -- Otter Valley, Devon 20 m AMSL http://www.ottervalleyweather.me.uk I was quoting from the KZ litrature Nick, unless thay have changed the design since that was written, I would accept what they say. -- Bernard Burton Satellite images and weather data for Wokingham at: www.woksat.info/wwp.html --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
#12
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On 23/04/2018 12:43, Keith Harris wrote:
So it is true what Ole said, and the algarithm seems correct based on the WMO definition of 120W/m2, which is very old... I'm not sure that the age of the definition has much to do with it (is it very old anyway?). Isn't the reality that sunshine hours is not actually a well-defined parameter and can't be because what you're trying to measure, ie the boundary between bright sun conditions and not, is subjective. It's a different kind of parameter to eg temperature or rainfall. So different measurement techniques inevitably give different answers and probably always will. The WMO definition is one approach and an appealing one because it defines a threshold which can be accurately measured with the right kit. But how well it parallels human feelings about what is bright sun, especially in hazy or dawn/dusk conditions, is endlessly debatable. I suppose an alternative definition could be built around just how sharp a shadow might be, given modern sensors and image analysis software. But even so, someone will still need to make the call about precisely where the cutoff is to be made. |
#13
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On 22/04/2018 20:28, Graham Easterling wrote:
OK, there are a few assumptions, but all this suggests that the BLake Larsen is under-recording slightly (compared to Camborne) by perhaps 5%, but certainly a fair bit less than the 15% that Nick is experiencing. Graham, Ole has just contacted me and has recalibrated the threshold as it was set too high. That probably explains the rather large discrepancy. Also, I have noted that the sensor is catching a shadow caused by the apex of the dormer before sunset. The sensor is a little below the R&D recorder which itself gets a clear view of the western horizon. My mistake so I'll plan to get 'up there' and sort it at some point in the near future. Interesting that today the BL recorded 1.2 hours and the R&D recorded 1.1 hours. That's the first time the BL has recorded more so the calibration seems to have worked! -- Nick Gardner Otter Valley, Devon 20 m amsl http://www.ottervalleyweather.me.uk |
#14
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On Monday, April 23, 2018 at 7:25:32 PM UTC+1, Nick Gardner wrote:
On 22/04/2018 20:28, Graham Easterling wrote: OK, there are a few assumptions, but all this suggests that the BLake Larsen is under-recording slightly (compared to Camborne) by perhaps 5%, but certainly a fair bit less than the 15% that Nick is experiencing. Graham, Ole has just contacted me and has recalibrated the threshold as it was set too high. That probably explains the rather large discrepancy. Also, I have noted that the sensor is catching a shadow caused by the apex of the dormer before sunset. The sensor is a little below the R&D recorder which itself gets a clear view of the western horizon. My mistake so I'll plan to get 'up there' and sort it at some point in the near future. Interesting that today the BL recorded 1.2 hours and the R&D recorded 1.1 hours. That's the first time the BL has recorded more so the calibration seems to have worked! -- Nick Gardner Otter Valley, Devon 20 m amsl http://www.ottervalleyweather.me.uk Glad you've found the probable issues Nick. I've obviously had no experience of using the Blake Larsen, but everything I'd read, and been told, suggested that over a month or 2 there was very little difference between it and the other recorders. Alan had also told me about successful parallel trials.. I thought there had to be a reason(s) why yours was 15% low. I know that a firm has now taken over development of the Sun Recorder, so hopefully there will be some progress on the data logging front. Graham Penzance |
#15
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On Monday, 23 April 2018 19:25:32 UTC+1, Nick Gardner wrote:
On 22/04/2018 20:28, Graham Easterling wrote: OK, there are a few assumptions, but all this suggests that the BLake Larsen is under-recording slightly (compared to Camborne) by perhaps 5%, but certainly a fair bit less than the 15% that Nick is experiencing. Graham, Ole has just contacted me and has recalibrated the threshold as it was set too high. That probably explains the rather large discrepancy. Also, I have noted that the sensor is catching a shadow caused by the apex of the dormer before sunset. The sensor is a little below the R&D recorder which itself gets a clear view of the western horizon. My mistake so I'll plan to get 'up there' and sort it at some point in the near future. Interesting that today the BL recorded 1.2 hours and the R&D recorded 1.1 hours. That's the first time the BL has recorded more so the calibration seems to have worked! -- Nick Gardner Otter Valley, Devon 20 m amsl http://www.ottervalleyweather.me.uk I generally find the R&D records more on clear days, mainly because the BL doesn't treat a hazy sunrise / sunset as full sun. However, with a very clear start today the BL started recording within 15 minutes of sunrise. But to my surprise the BL recorded 7.73 hours and the R&D only 4.77 hours, 3 hours less. So far the months totals are BL 117.06 hours, R&D 113.56 hours. Keith (Southend) |
#16
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On Sunday, 22 April 2018 19:32:02 UTC+1, Nick Gardner wrote:
On 22/04/2018 18:30, Keith Harris wrote: I've come to the conclusion you can't compare the two systems like for like. However, I do feel the BL is more accurate, Hmmmm, at the moment I am far from convinced that the BL recorder is 'more' accurate. I find it hard to believe that when the sun is shining brightly and you can feel its heat, with its disk clearly visible and there is a distinct, sharp edged shadow on the ground - that the sun is NOT shining. The BL recorder can say that. Also, and Ole agrees with me that the BL recorder can be fooled by indirect light, i.e., lots of small cumulus clouds giving plenty of reflected light can raise (as it does with my solar irradiation and UV measurements) the level somewhat above the threshold and record sunlight even though the sun itself is partly obscured and not casting a shadow. I have noticed this on occasions and I contacted Ole to report it. The Met Office might take some convincing as to the 'accuracy' of the BL as I believe the KZ recorder uses the same method as the R&D, i.e., the difference between sunlight and shadow. I prefer to keep it simple, if there's a sharp-edged, distinct shadow then then the sun is shining. -- Nick Gardner Otter Valley, Devon 20 m amsl http://www.ottervalleyweather.me.uk I've not noticed the indirect sunlight recording, however, today my R&D recorded 0.02 hours, whereas the BL 2.00 hours, it did brighten up, but I don't remember much blue sky. It's a shame I wasn't at home as I would like to have monitored what was going on. Keith (Southend) |
#17
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On Wednesday, April 25, 2018 at 6:39:48 AM UTC+12, Keith Harris wrote:
On Sunday, 22 April 2018 19:32:02 UTC+1, Nick Gardner wrote: On 22/04/2018 18:30, Keith Harris wrote: I've come to the conclusion you can't compare the two systems like for like. However, I do feel the BL is more accurate, Hmmmm, at the moment I am far from convinced that the BL recorder is 'more' accurate. I find it hard to believe that when the sun is shining brightly and you can feel its heat, with its disk clearly visible and there is a distinct, sharp edged shadow on the ground - that the sun is NOT shining. The BL recorder can say that. Also, and Ole agrees with me that the BL recorder can be fooled by indirect light, i.e., lots of small cumulus clouds giving plenty of reflected light can raise (as it does with my solar irradiation and UV measurements) the level somewhat above the threshold and record sunlight even though the sun itself is partly obscured and not casting a shadow. I have noticed this on occasions and I contacted Ole to report it. The Met Office might take some convincing as to the 'accuracy' of the BL as I believe the KZ recorder uses the same method as the R&D, i.e., the difference between sunlight and shadow. I prefer to keep it simple, if there's a sharp-edged, distinct shadow then then the sun is shining. -- Nick Gardner Otter Valley, Devon 20 m amsl http://www.ottervalleyweather.me.uk I've not noticed the indirect sunlight recording, however, today my R&D recorded 0.02 hours, whereas the BL 2.00 hours, it did brighten up, but I don't remember much blue sky. It's a shame I wasn't at home as I would like to have monitored what was going on. Keith (Southend) My issue with any single fixed threshold is that it doesn't allow for seasonality - in higher latitudes at least, I don't regard winter's bright sunshine as being equivalent to summer's bright sunshine. But I agree with the notion that when compared with rainfall and temperature measurement, sunhisne measurement will always be more subjective. |
#19
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I always wanted one of the charred paper crystal ball sun recorders. Here's one for sale https://www.metcheck.co.uk/collectio...recorder-25-60 and don't forget the cards https://www.metcheck.co.uk/collectio...recorder-cards I notice one went for £750 on ebay this year. |
#20
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On 25/04/2018 11:55, Metman2012 wrote:
. I always wanted one of the charred paper crystal ball sun recorders. Here's one for sale https://www.metcheck.co.uk/collectio...recorder-25-60 and don't forget the cards https://www.metcheck.co.uk/collectio...recorder-cards I notice one went for £750 on ebay this year. Ouch! That is expensive. I was planning on a DIY version using a 4" glass ball I ordered up from China on eBay when I get a roundtuit. Another slightly weather related demo I have always wanted to do is start a fire from sunlight using a lens made out of clear water ice. My attempt this winter failed as the hemispherical mould leaked. -- Regards, Martin Brown |
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