18 Weather Monitoring Spotlight
Environment Agency Builds New Technology into Rain Monitoring Network
During recent trials conducted by the Environment Agency (EA) and the Scottish Environment Protection Agency (SEPA), in cooperation with the UK Met Office, OTT Hydrometry’s Pluvio2 raingauge exceeded the target performance requirements of the assessment and over 100 units have now been purchased by the EA. As a result, the quality of monitoring data will be improved and the cost of running the more remote sites will be significantly reduced because site visits are only necessary once or twice per year, instead of approximately quarterly, which is the typical frequency undertaken for tipping bucket raingauges by the EA.
Initial results look promising; the Pluvio2
is
proving to be very reliable, so we have been able to reduce the frequency with which we have to make site visits. This is particularly advantageous with remote sites where we are making considerable savings in time and travel; payback periods vary from almost immediate, up to several years.
Background In the 17th
century Sir Christopher Wren, a designer, astronomer,
geometer, and one of the greatest English architects of his time, was best known for the design of 53 London churches, including St Paul's Cathedral. However, one of his lesser known achievements was the creation in 1662, of a raingauge that did not require daily visits - the world's first tipping bucket raingauge (TBR). The real advantage of this technique was that it enabled a clockwork chart to record rainfall so that Sir Christopher did not need to read and record every single day's data. Since that time the same principle has formed the basis of almost all national rainfall monitoring networks around the world. However, a TBR requires regular maintenance to ensure that its funnel and filter are not blocked, and the ‘buckets’ require regular cleaning and calibration to ensure that all of the collected water ‘tips’ and does not adhere to accumulated dirt and that the raingauge operates within specification.
Latest Precipitation Monitoring Technology In contrast with traditional techniques, the Pluvio2
The Pluvio was first launched in 1994 and there are now more than 5000 units in operation all over the world, this has been followed by the development and implementation of a successor; the 'OTT Pluvio2
Author Details: Simon Wills,
Managing Director OTT Hydrometry UK Unit 2 Magnet Business Park 14 High Hazels Road Barlborough
Chesterfield S43 4UZ Tel: 01246 573480 Fax: 01246 813873
Email:
sales@ott-hydrometry.co.uk Web:
www.ott-hydrometry.co.uk
measures rainfall by
collecting precipitation and weighing the collected liquid with a highly accurate load cell.
Pluvio2
for reasons of power consumption. In contrast, the unheated version of the OTT Pluvio2
operates on very low power – typically 12 mA at 12V. ', which provides even better precipitation measurement and at
a proven lower cost of ownership, which makes it accessible to a wide range of applications.
The key feature of the Pluvio2 is that it can measure precipitation
accurately and reliably in all weather conditions, while requiring minimal maintenance.
The instrument's accuracy is not diminished by the intensity of precipitation - the measurement range extends from 0.1 to 30 mm/min. This technology is also well suited to freezing conditions because the EA uses a physical frost protector to preserve the gauge during freezing conditions - the measurement range extends from - 40 to +60 °C. An optional heating ring is available to prevent snow capping.
TBRs occasionally include thermostatically controlled internal heaters to address the problem of snow/ice accumulation, but this can incur a delay in the measurement and may be impractical in remote locations
A sophisticated software filter eliminates the potential effects of wind and each OTT Pluvio2
is individually temperature calibrated.
weighing measuring principle is based upon an edge compensated and sealed single load cell, with inbuilt overload protection, direct mounting on the weighing platform and highly sophisticated electronics and algorithm features as standard. The individual temperature characteristics of the load cell are memorised in the electronics and corrected by in-situ temperature compensation. This achieves precise weight measurements with incremental accuracy of 2 grams equal to 0.10 mm and provides resolution of 0,01 mm of precipitation. The load cell is also insensitive to eccentric load that may occur for example, as a result of unsymmetrical distribution of snow in the buckets.
The OTT Pluvio2 Standard Methods
The committee which recently updated the British Standard on the acquisition and management of meteorological precipitation data
IET September / October 2013
www.envirotech-online.com
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