10s Rainrate Statistics for the UK

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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 (lt1
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 (lt1km)
  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-gt200 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 ...
10
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.