Rain Masking

(Gauge Response Times)

John Goddard

and thanks to Elizabeth Slack for help with data

Chilbolton Facility for Atmospheric and Radio Research

Chilbolton Facility for Atmospheric and Radio Research

Equipment mounted on portakabin roof.

Optical Rain Gauge

Ground located gauges

500 metre Range at Chilbolton

Cluster of gauges

Chilbolton Facility for Atmospheric and Radio Research

Device Manufacturer Technique Collector Area Range/ Calibration

RAL RRDC[1] Gauge (on roof)

RCRU (MKIV) Volumetric Drop 150cm² 5-200mm/hr,0.004mm/drop

Optical Rain Gauge Sci Tech Inc. (ORG700)

Optical Extinction 300cm² 0.1-3000mm/hr

Impact Distrometer Distromet Ltd (RD-69)

Impact Momentum

50cm² 0.3mm-5mm (drop diameter)

Rain Sensor R&D Instrumet (SN-R)

Volumetric Drop 50cm² 0.01mm/drop

Tipping Bucket Gauge RWMunro (R100) Bucket Volume 324cm² (8"diam) 0.2mm/bucket

Self-Syphoning Capacitance Gauge

RMYoung (50202) Water Level ~ Capacitance

100cm² 50mm/Syphon

RAL RRDC Gauge (on ground)

RCRU (MKIV) Volumetric Drop 150cm² 5-200mm/hr, 0.004mm/drop

RAL RRDC Gauge (on ground)

RCRU (MKIV) Volumetric Drop 324cm² (8"diam) 3-100mm/hr,0.002mm/drop

Rain Sensors deployed at Chilbolton

Chilbolton Facility for Atmospheric and Radio Research

Drop CountingGauge

Optical Gauge Tipping Bucket Gauge

Distrometer

Rain Sensor

Syphon Gauge

Chilbolton Facility for Atmospheric and Radio Research

2 July 2002

16.38 Spurious (?) drop on DC816.41 Impact distrometer16.41 Optical gauge records rain16.49 DC6 records first drop16.57 Rain Sensor17.00 Tipping bucket (1020 mins.)

Chilbolton Facility for Atmospheric and Radio Research

2 July 2002

08.10 Optical gauge and distrometer only08.30 Start of event recorded by most instruments

Chilbolton Facility for Atmospheric and Radio Research

4 July 2002 22.35 Small event on optical gaugeand impact distrometer

22.45 Optical gauge and impact distrometer record stronger rain22.55 DC8 records first drop23.01 DC6 records first drop23.20 Tipping bucket (~1400 mins.)

Chilbolton Facility for Atmospheric and Radio Research

8 July 2002 (1)

06.25 Spurious count on Rain Sensor

06.44 Optical gauge records rain

06.48 DC6 and DC8 record first drops

07.47 Tipping bucket (~468 mins.)

Chilbolton Facility for Atmospheric and Radio Research

8 July 2002 (2)

13.15 Optical gauge records rain (795 min.)13.18 DC6 and DC8 record first drops13.19 Rain Sensor records drop13.19 Tipping bucket (~799 mins.)

Chilbolton Facility for Atmospheric and Radio Research

15.40 Optical gauge records rain (940 min.)15.54 DC8 record first drops15.55 DC 6 records first drops15.57 Rain Sensor records drop15.58 Tipping bucket (~958 mins.)

8 July 2002 (3)

Chilbolton Facility for Atmospheric and Radio Research

Conclusions

Distrometer and Optical gauge - both good indicators of precipitation onset

Drop counting gauges lag these by 2-5 minutes(maybe depending on how wet the collector has remained since the last event)

Tipping bucket gauge - not useful for this purpose - lags of tens of minutes in weak precipitation- 2 factors, collector wetting and bucket capacity