International audienceThe Dual Beam spectropluviometer (DBS) measures the equivalent diameter, the fall velocity and the time of arrival of raindrop

Akrour, Nawal

Barthès, Laurent

Chazottes, Aymeric

Delahaye, Jean-Yves

Golé, Peter

Lavergnat, Jacques

Vinson, Jean-Paul

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The dual beam spectropluviometer

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The dual beam spectropluviometerNawal Akrour, Laurent Barthe`s, Aymeric Chazottes, Jean-Yves Delahaye,Peter Gole´, Jacques Lavergnat, Jean-Paul VinsonTo cite this version:Nawal Akrour, Laurent Barthe`s, Aymeric Chazottes, Jean-Yves Delahaye, Peter Gole´, et al..The dual beam spectropluviometer. Journe´e Scientifique SIRTA 2014, Jun 2014, Palaiseau,France. 2014. <hal-01108783>HAL Id: hal-01108783https://hal.archives-ouvertes.fr/hal-01108783Submitted on 23 Jan 2015HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.Discrete view of rain :Various studies allowed the modeling and the simulation of rainfall as a raindrop point process.Lavergnat and Golé, 1998 et 2006.The DBS also allowed some investigations on the DSD. Mallet and Barthès, 2009. Barthès and Mallet, 2013.Continuous view of rain :At the Latmos, various studies on the multifractal properties of rain are basedon measurements of the DBS. De Montera at al., 2009 & 2010Verrier et al., 2011 & 2013.TECHNICAL CHOICESMEASUREMENT  GOALS METHODS USEDDIAMETERDown to 0.1 mm• 2 thin (2 mm) and closely spaced (2 mm)flat beams (L x l = 250 x 40 mm) at λ=0.8µm.• 16-bit digitization oversampled at 40 kHzand averaged to 10 kHz for noise reduction.• Software :- slope detection- baseline = averages before and afterslope change- correction for drops larger than beamthickness- likelihood test by comparing 2 channels• Quality flag for small diameters.FALL VELOCITYOptimized• Averaging of ∆t1 and ∆t2 (see diagramabove).• Interpolation for high velocities.TIME STAMPING OF DROPS1 millisecond• Clocking: sensor’s sampling frequencyused between PC times inserted atbeginning and end of files.ERROR REDUCTION• Sunlight• Water on internal glass windows• Dripping water drops• Wind sensitivity• External splash on sensor body• Internal splash• Condensation• Sunlight rejection filter.• Air circulation pump.• Water draining slots above windows.• Very rigid cast iron support ring.• Anti-splash circular ribs and scouring rolls.• Internal vanes.• Heated electronics and Moisture absorbers.ERROR DETECTION• Self-test for monitoringbaselines, synchronization, andwindow cleanness• Reciprocating 0.4 mm diameter rod withinbeam triggered daily or manually and motordriven. Induced signal variations recorded toself-test file.A rain drop falls through both, upper and lower, beams disrupting the optical signal. The processing algorithm allows the simultaneous detection of the drop diameter andfall velocity at precisely defined arrival time. Outdoor measurement signals with a   small isolated drop: 0.2mm and 0.89 m/stimeRain dropReceiver  photodiodesLight sourceDual slotUpper beam signalLower  beam signalUpper beamLower  beamFresnel’s  biprism∆ t1 ∆ t210 ms/divPRINCIPLE50m cableProcessing & recording softwareSelf-test motor16 bits A/D ConverterSeries/parralel interface16 bits A/D ConverterSeries/parralel interfaceSelf-testClockSync.BLOC DIAGRAMSuccessfully compared with other optical disdrometers.Krajewski et al., DEVEX-disdrometer evaluation experiments : Basic results and implications for hydrologic studies, 2005, Advances in Water Resources.FIELD EVALUATION : (DEVEX experiment)2D homogeneity of beams and noiseTECHNICAL CHARACTERISTICS2 mm Up Low2 mm Up Low2 mm Up Low2 mm Up LowAAAAAAAAAAEmitter Receiver250 mmSlotsØ 69 Ø 69A B C DMeasurement areaRibsTHE DUAL BEAM SPECTROPLUVIOMETERN. Akrour, L. Barthès, A. Chazottes, J.Y. Delahaye,, P. Golé, J. Lavergnat and J.P. VinsonLATMOS/IPSL/UVSQ/UPMC/CNRSThe Dual Beam spectropluviometer (DBS) measures the equivalent diameter, the fall velocity and the time of arrival of raindrops. Its main advantage over previous optical disdrometers is its ability to capture the whole measurement range of atmospheric precipitating particles (down to 0.1mm raindrops).Delahaye et al., A dual beam spectropluviometer concept, Journal of Hydrology , 2006.Room for improvement and rejuvenating:A 2014 IPSL funding is asked for in order to modernize the DBS (both hardware and software components).The processing algorithm as well as the calibration process are under study to improve the quality of the measurements (and among others to reduce the noise for the small drops).Intercomparisons with other instruments at Sirta is in progress.RELATED WORKSPower spectra of the time series collected from july 2008 to july2009 at the Sirta. This picture display the various scaling of the rain measurements

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The dual beam spectropluviometer

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