FSTWP 9/9/2002 1

10s Rainrate Statistics for the UK

Kevin Paulson

Rutherford Appleton Laboratory, Chilton Didcot, Oxfordshire, OX11 0QX

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Current Situation

Currently, ITU recommendations and RA license/power calculations are based on 1 minute rain rate statistics.

Historically, one-minute raingauges were fast-response, links were long – introducing large spatial averaging.

Now 10s raingauges commercially available and short links of increasing importance.

Higher frequencies also mean that detecting mist mixed with heavy rain is more important.

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Temporal Spatial Averaging

Temporal averaging point rain-rate over one-minute is roughly equivalent to spatial averaging over 1 Km.

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Problems with 1-minute statistics

One-minute rain-rates will underestimate the incidence of high attenuation on short links (<1 Km)

One-minute rain-rates smooth over short-term high attenuation events on longer links.

One-minute sampling as restrictive as one-minute averaging

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First Order Statistics

Measure 10s rainrate distributions at various sites

• More information on short outages

• Better characterisation of short link (<1km) performance

• Check and develop transformations between statistics measured at longer integration times

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Second Order Statistics

Measure 10 s rainrate time series at various sites

• Synthetic Storm method allows terrestrial or satellite link time series to be synthesised

• Develop/test fade duration/slope models

• Develop/test fade mitigation techniques

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RAL Rapid Response Gauge

Collector: standard UK Meteorological Office Mk IV

Water formed into equi-volume drops which are counted optically

Range 5->200 mm/hr in 1.4mm/hr steps

Accuracy: ±10%

Cost: £3000

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ORG 815

Optical Scientific inc.

ORG-815

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ORG 815 Specification

Rain rate dynamic range: 0.1 – 500 mm/hr

Rain rate accuracy: about 5%

Integration time: 10 s

Precipitation type: rain/snow/mixed

NOT effected by wind

NO moving parts, very low maintenance

Self-monintoring, self correcting

Cost about £2000

Users: FAA, NASA, NOAA, US military, BAS, BMO ...

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Vaisala FD12P

Detects 11 precipitation types

Range 0-999 mm/hr with 30% accuracy

One-minute integration time reporting every 15 s

Cost: £7000

Used by UK Met. Off.

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Biral VPF-730

Made in UK.

Rainrates: 0.015 - 250 mm/hr

Errors: rainrate 10%, snowrate 20%

Also measures visibility and precipitation type.

Cost £7000

Typically 10-13 years operation without ANY maintenance!

Used by Swedish Airports, FAA, USAF. ...

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Parsivel M300

Laser disdrometer designed by Voss

Yields 10 s rainrate and WMO precipitation code, visibility, and particle size-velocity distribution.

Rainrate derived from drop size-velocity distributions. Reported accuracy only for one-hour rainrates of 10%.

Drops: 0.25 - 25 mm diameters

Speed 0.1 - 20 m/s

Cost: £16000 and up

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Proposal

• Install and operate a selection of optical gauges and RAL rapid response gauges at several sites around the UK for several years.

• This will yield 10s rainrate time series at each site and information on the performance, reliability and maintenance effort for each type of gauge.

• Based on this experience, the experiment could be extended in both duration and number of sites to yield UK wide 10 s rain rate statistics.