OTT Parsivel® - Enhanced precipitation identifier and new generation of present weather sensor by OTT Messtechnik, Germany

Author: Kurt Nemeth Co-Author: Jens-Michael Hahn

OTT PARSIVEL®: Laser-based optical Disdrometer for simultaneous measure- ment of PARticle SIze and VELocity of all liquid and solid precipitation

Background and design requirements: The design requirements for the instru- ment lead to a universal Commercial Off- The-Shelf (COTS) equipment which meets substantially the meteorological and hydrological requirements of the sensor specification according to WMO and NWS regulation as an enhanced pre- cipitation identifier and present weather sensor. The patented extinction method for simultaneous measurements of particle size and velocity of all liquid and solid precipitation performs the direct physical measuring principle and classification of hydrometeors. ® The instrument provides a full picture of OTT Parsivel - Enhanced Precipitation Identification Sensor the precipitation event in all weather phe- nomena and provides accurate reporting Parsivel® can be integrated into an Auto- of precipitation types and intensities with- mated Surface/Weather Observing Sys- out degradation of performance in severe ® tem (ASOS/AWOS) as part of the sensor outdoor environments. Parsivel operates suite. The derived data can be processed in any climate weather regime and the and included into the transmitted weather incorporated heating device minimizes observation report and messages (WMO, the negative effect of freezing and frozen SYNOP, METAR and NWS codes). precipitation accreting critical surfaces on The new generation of Parsivel® the instrument. disdrometer provides the latest state of This piece of equipment detects and the art laser optical technology. The data identifies 8 different precipitation types as performance has been tested drizzle, mixed drizzle/rain, rain, mixed successfully in comparison with a rain/snow, snow, snow grains, freezing meteorological observer with a distinction rain and hail. rate better than 97%. The output data - consisting of raw data, Due to modern and high speed DSP classification related to size and velocity technology the wide spectrum of of particles, rain accumulation and precipitation from drizzle to tropical rain intensity, present weather reports and with extreme intensities up to 20 mm/min housekeeping data - make the instrument can be acquired and processed without suitable to any kind of meteorological and limitation regarding influence of wind and hydrological application.

1 effecting catching orifice problems – Low power and heating operation by concerning conventional rain gauges. software commands The instrument supports meteorological – Identification of all precipitation types, observer missions in general and weather including mixed precipitation in the service missions for improving severe melting layer winter weather warnings for snow and ice – Comprehensive precipitation analysis conditions, flood forecast and warnings, using 2-dimensional distribution of size support to aviation and road traffic, and and velocity severe thunderstorm forecast and warn- – Special measuring head prevents ings. secondary spectra caused by drops The derived radar reflectivity coefficient splashing on the sensor head together with ground based precipitation – Transmitter and receiver head in perfect data improves essentially the design with no obstacles for precipitation performance of the spatial weather radar catching information, improves the regional weather forecasts and high water early Extinction measuring principle warning system by combination and The new generation of enhanced correlation of precise and overall precipitation identifier measures directly precipitation network data. each single hydrometeor and performs a revolutionary change compared to for- Parsivel® feature unique performance ward scattered laser optical systems – Patented extinction measurement pro- which needs additional sensors onboard cedure and is based on experimental and – Unattended and reliable operation, proofed algorithm to determine the rain using maintenance-free laser technology rate and identification of precipitation – Operable in all environmental and types. weather conditions (lightning protection and self-regulated heating)

U

Ui

∆Ui

D

∆t t A) B) C) v

A) The sensor's transmitter B) This signal changes when- C) The degree of dimming is a unit generates a flat, horizontal ever a hydrometeor falls measure of the hydrometer’s beam of light, which the re- through the beam anywhere size, and together with ceiver unit converts into an within the measurement area duration of the signal, the fall electric signal. velocity can be derived.

2 Multipurpose instrument featuring en- suitable for the use in various hanced precipitation measurements: meteorological and hydrological The full data output of precipitation is applications featuring five single accomplished with additional algorithm instruments in one unique unit: and the derived data make the instrument

Present Weather Visibility in Sensor Precipitation ww - Code Extinction- Parsivel® Coefficient

Rain Gauge Energy of Precipitation Rain Rate Soil Erosion

Z/R-Correlation Adjustment of weather Radars Flood waters warning

The different Features of the Parsivel®

Precipitation hydrometeor and the atmospheric Measurements designed for determining visibility – in every kind of weather! the distribution and amount of Monitoring of disposal sites precipitation can be carried out The functions of precipitation kinetic maintenance-free with Parsivel®, regard- energy distribution and precipitation less of the intensity, duration or type of measurement are utilised by Parsivel® to precipitation. Additionally, its composition record the effect of rain on the condition – i. e. the distribution of particles with re- of the disposal sites in conjunction with spect to their type – is obtained directly other sensors, e. g. ground-condition from the measured sizes and velocities of probes. each single particle and is recorded statistically. Monitoring road conditions Local intense precipitation can lead to Present Weather Sensor (PWS) aquaplaning or packed snow on roads. The present weather and the types of Therefore, rapid traffic warning and con- precipitation (rain, drizzle, snow, hail and trol systems are necessary in order to sleet) are classified in accordance with a prevent accidents. Precipitation weather code established by the WMO. measurement, hydrometeor composition Unmanned weather stations require and atmospheric visibility are of automatic detection, reliably and considerable importance in such systems. unambiguously. Parsivel® can ascertain Parsivel® is an integrated instrument that the type, quantity and composition of the

3 measures all required parameters in energy and firmware related information accurate quality and performance. are displayed as digital information.

Flood early warning To assure a timely warning of impending high water it is necessary to measure the amount and spatial distribution of pre- cipitation rapidly and accurately. This goal can be achieved by combining weather radar measurements (spatial information with reduced accuracy) and ground based disdrometer measurements: Parsivel® provides drop size distributions on the ground and a function to derive a local Z/R relation – ready to be used to adjust the radar data. In combination with water level sensors and drainage Screenshot ASDO- 3D Mode modelling, a high-performance regional flood early warning system can be The precipitation spectrum can be erected. evaluated as graphical displays and spectrum distribution in 2 and 3 Expert Software ASDO dimensional mode. The corresponding Software ASDO All data are stored in a powerful data monitors the outdoor precipitation event base and can be retrieved by browser to comfortable indoor evaluation with with related date and time and displayed windows performance. in equal form as online display. All configuration tasks like time interval from 10 sec to 120 minutes, baud rate and size of telegram and others can be selected and stored as configured variables.

Screenshot ASDO – Tabular view and 2D Mode

The sensor transmits all data to a PC and supports the observer with full information of present weather and precipitation and provides a history of precipitation falls stored in a data base. Present weather icon, all derived precipitation data and weather codes as well as housekeeping data like supply, voltage laser output

4 Parsivel® references includes e.g.: Parsivel® History • USA 1995 -1998 o NASA First ideas, prototypes and tests of a o University of Iowa laser based optical disdrometer by o University of Washington Dr. Löffler-Mang (University Karlsruhe) • Europe 1999 o Deutsche Wetterdienst DWD Foundation of PMTech motivated by Hamburg Germany the intention of the DWD to provide it’s o Germatronik Neuss Germany planned “Messnetz 2000” (OTT o BAST Munich Germany delivers the Pluvio) with fully automatic ® o University of Hannover weather stations. The Parsivel Germany development, characteristics, and o University of Freiburg Germany practical evaluations were done in o University of Grenoble France close cooperation with DWD, o Met Office UK Hamburg. • Asia/Pacific 2000 - 2003 o Meteorological Service Turkey Enhancements on the electronic o National Space Development components and the algorithms were Japan done. During that time intensive tests o CSIRO Australia at customer’s sites were performed. PMTech concentrate on development, Scientific Essays manufacture and repair, distribution Löffler-Mang, M., and J. Joss, 2000: An agreement with Scintec AG, Tübingen. optical disdrometer for measuring size Parsivel M300 operational in different and velocity of hydrometeors. J. Atmos. applications Ocean. Tech., 17, 130-139. 2004 Löffler-Mang, M., and U. Blahak, 2001: OTT took over all rights and the ® Estimation of the equivalent radar production know-how of the Parsivel reflectivity factor from measured snow technology size spectra. J. Appl. Meteor., 40, 843- 849. Jitze P. van der Meulen, 2003: Exploratory actions on automatic Present Weather observations; Final Report with recommendations EUMETNET Yuter, S. E., D. Kingsmill, L. B. Nance, and M. Löffler-Mang, 2005: Observations of precipitation characteristics near and within the melting layer. J. Atmos. Sci., revised.

OTT MESSTECHNIK GmbH & Co. KG Postfach 2140 D - 87411 Kempten Ludwigstraße 16 D - 87437 Kempten GERMANY Tel. 0831/5617-0 Fax 0831/5617-209 E-Mail: [email protected] www.ott-hydrometry.com

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