Data loggers for grass min

For discussion of any observing equipment, from Stevenson Screens and manual instruments to electronic weather stations

Data loggers for grass min

Postby Tom Blagden » 2012 Feb 18, 19:54

I have been using some of the latest miniature data loggers for the purposes of grass minima recording. The loggers look just like CR type lithium batteries as one might find in calculators, watches etc. The diameter is 17mm with a thickness of 6mm. I have housed the device in a silicone waterproof cover to protect it from the elements without hampering the responsiveness. The device has a quoted accuracy of +/- 0.5C, I have found it to be well within these limits when tested against thermometers in the screen. The logger can then be attached to a suitable mounting (tent peg works well!) so that it will pierce the turf nicely and stand open to the sky. The main advantage here is that you only have to visit and download it once a week (if you set the appropriate recording interval) - useful if you often forget (like me) to put the thing out. In comparisons with a BS692 sheathed pattern minimum thermometer, the results were very close. The attractive thing about these systems is the price, with the cheapest logger kits priced less than a glass minimum thermometer.
Exminster Hilltop, Devon, SW England
55m AMSL, records from July 2003
Tom Blagden
Posts: 6
Joined: 2012 Jan 27, 19:16

Re: Data loggers for grass min

Postby Stephen Burt » 2012 Feb 19, 09:50

Tom - perhaps you can share details of the equipment you use, with supplier details, prices etc? I'm sure others on this Forum would be interested in knowing more.

You've said you have compared the device against thermometers in the screen. Have you tried side-by-side comparisons with a calibrated grass minimum thermometer or sensor out in the open? The reason I ask is that differences in sensor long-wave emissivity can result in significant variations in observed temperature under clear skies at night, whereas sensor emissivity variations would be negligible within a screen. The difference in response times between a small, metallic sensor and a relatively large, glass and spirit thermometer may also influence the minimum temperatures recorded - such response time variations would be largely masked within the longer response time of a screen.

It would be interesting to know whether you have noticed any discrepancies between measurements out in the open - although minor differences between any two sensors, and any two pieces of grass surface for that matter, are to be expected of course. To my knowledge, very little work has been undertaken to look into such sensor-related effects on grass minumum temperatures.

Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook:
Stephen Burt
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

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