Lukas Pfitzenmaier

Mar 212017
 

Retrieving fall streaks within cloud systems using Doppler Radar

 

Abstract: Interaction of the ice crystals with super-cooled liquid droplets in mixed-phase clouds leads to an enhanced growth of the ice particles. However, such processes are still not clearly understood although they are important processes for precipitation formation in mid-latitudes. To better understand how ice particles grow within such clouds, changes of microphysical parameters of a particle population falling through the cloud have to be analyzed. The Transportable Atmospheric Radar (TARA) can retrieve the full 3-D Doppler velocity vector based on a unique three-beam configuration. Using the derived wind information, a new fall streak retrieval technique is proposed so that microphysical changes along those streaks can be studied. The method is based on Doppler measurements only. The shown examples measured during the ACCEPT campaign (Analysis of the Composition of Clouds with Extended Polarization Techniques) demonstrate that the retrieval is able to capture the fall streaks within different cloud systems. These fall streaks can be used to study changes in a single particle population from its generation (at cloud top) till its disintegration. In this study fall streaks are analyzed using radar moments or Doppler spectra. Synergetic measurements with other instruments during ACCEPT allow the detection of liquid layers within the clouds. The estimated microphysical information is used here to get a better understanding of the influence of super-cooled liquid layers on ice crystal growth. This technique offers a new perspective for cloud microphysical studies.

The full text of the paper from L. Pfitzenamier et. al., 2017, can be found in the here on the J-Tech web page

 

Sep 232016
 

Assessment of the rain drop inertia effect for radar-based turbulence intensity retrievals

A new model is proposed on how to account for the inertia of scatterers in radar-based turbulence intensity retrieval techniques. Rain drop inertial parameters are derived from fundamental physical laws, which are gravity, the buoyancy force, and the drag force. The inertial distance is introduced, which is a typical distance at which a particle obtains the same wind velocity as its surroundings throughout its trajectory. For the measurement of turbulence intensity, either the Doppler spectral width or the variance of Doppler mean velocities is used. The relative scales of the inertial distance and the radar resolution volume determine whether the variance of velocities is increased or decreased for the same turbulence intensity. A decrease can be attributed to the effect that inertial particles are less responsive to the variations of wind velocities. An increase can be attributed to inertial particles that have wind velocities corresponding to an average of wind velocities over their backward trajectories, which extend outside the radar resolution volume. Simulations are done for the calculation of measured radar velocity variance, given a 3-D homogeneous isotropic turbulence field, which provides valuable insight in the correct tuning of parameters for the new model.

The full paper from A. Oude Nijhuis et. al. can be found here

Nov 182015
 

Members of the ATMOSpheric remote sensing groupe contrubuted to the AMS conference, 14-18 September 2015, Norman OK, USA

Ricardo Reinoso Rondinel contributed presenting a poster:

Title: “High resolution estimation of specific differential phase and backscatter differential phase for polarimetric X-band weather radars

  • An advanced method to estimate the specific differential phase (Kdp) and backscatter differential phase (dhv) from rain at X-band frequencies is proposed. The method aims to obtain high spatial resolution of Kdp and dhv estimators while controlling their inherent bias-variance dilemma. In addition, the variance of Kdp was mathematically formulated for quality control.
  • Poster and abstract link here
  • This poster was awarded as the 3rd best student poster presentation.

Albert Oude Nijhuis  presented a poster, too:

Title: “Turbulence intensity retrieval in precipitation via optimal estimation using polarimetric radar

Summary and a pdf version of his paster can be found here

The talks of Lukas Pfitzenmaier

Title: “Correcting radar Doppler spectra for atmospheric dynamics to study microphysics within mixed phase clouds” (here)

and Yunlong Li

Title: “A Novel Radar-Based Visibility Estimator

are also avilable online (here)

Aug 242015
 

londonreading

During the last 4 weeks I was for a secondment at the University of Reading. Main goal was to learn more about microphysical retrievals of cloud properties. But also exchanging knowledge and ideas was on the agenda. So I was very glad that I got the chance to work with Chris Westbrook and his colleagues.

houseSince the very successful ACCEPT campaign I have plenty of data to look into and develop ideas. One of them was to retrieve mean ice particle size using the wavelength ration of the operated radars  (3 GHz and 35 GHz). The group in Reading was really helpful in answering questions and discuss first preliminary results. They already had experience with such retrievals.

Discussion with other PhDs and Scientists brought also some very fruitful and promising input. I exchange some of the ACCEPT and hope that the collaboration will go on in the future. An improvement of my retrieval for retrieving fall-streaks within radar data was tested on a different data set. This improved the understanding of my own retrieval and helped to validate it.

So all in all a successful exchange for both sides. I thank once again the colleagues from Reading for the collaboration and all the rest. And I hope that the collaboration will go on in the future

Jul 082015
 
High-Resolution Raindrop Size Distribution Retrieval Based on the Doppler Spectrum in the Case of Slant Profiling Radar

Doppler spectra from vertically profiling radars are usually considered to retrieve the raindrop size distribution (DSD). However, to exploit both fall velocity spectrum and polarimetric measurements, Doppler spectra acquired in slant profiling mode should be explored. Rain DSD samples are obtained from simultaneously measured vertical and slant profile Doppler spectra and evaluated. In particular, the effect of the horizontal wind and the averaging time are investigated.

The Doppler spectrum provides a way to retrieve the DSD, theradial wind,and a spectralbroadening factor by means of a nonlinear optimization technique. For slant profiling of light rain when the horizontal wind is strong, the DSD results can be affected. Such an effect is demonstrated on a study case of stratiform light rain. Adding a wind profiler mode to the radar simultaneously supplies the horizontal wind and Doppler spectra. Before the retrieval procedure, the Doppler spectra are shifted in velocity to remove the mean horizontal wind contribution. The DSD results are considerably improved.

Generally, averaged Doppler spectra are input into this type of algorithm. Instead, high-resolution, low-averaged Doppler spectra are chosen in order to take into account the small-scale variability of the rainfall. Investigating the linear relations at fixed median volume diameter, measured reflectivity-retrieved rainfall rate, for a slant beam, the consistency of the integrated parameters is established for two averaging periods. Nevertheless, the corresponding DSD parameter distributions reveal differences attributed to the averaging of the Doppler spectra.

The new aspects are to obtain the same retrieval quality as vertically profiling and highly average spectra in an automated way.

Link to C. Unals paper can be found here

Jun 222015
 
In view of preparing the future European operational satellite missions  dedicated to the atmosphere sounding, the European Space Agency (ESA) organised the ATMOS 2015 conference in at the university of Crete (Greece – Heraklion). This workshop allowed to exchange about retrieval techniques and harmonization of dataset  derived from past and present space-borne atmospheric missions (e.g. GOME, SCIAMACHY, MIPAS, GOMOS, OMI, IASI etc…) and application projects (e.g. Climate Change Initiative, Copernicus). Different sessions were organised about specific topics (greenhouse gases, reactive trace gases and air quality, limb missions). A strong focus was given on the crucial steps to be led by ESA for the successful  preparations of the Sentinel-4 and Sentinel-5 missions (scheduled between 2020 and 2021), the next TROPOMI mission on Sentinel-5 Precursor (before Summer 2016) and the competition between CarbonSat and FLEX missions with a final decision to be taken in September 2015. Around 200 researchers involved in the measurements of atmospheric trace gases, aerosols and clouds from passive satellite sensors were present.
Julien Chimot, PhD in the Atmosphere research team of the GRS department, had the opportunity to present his poster about the impact of aerosol particles on the quantification of  NO2 concentrations in the troposphere from the OMI measurements. This poster relies on a paper recently submitted to the AMT journal (Atmospheric Measurement Technique).
more information can be found on the following websites:
– ATMOS 2015: http://seom.esa.int/atmos2015/
– Competition between CarbonSat and FLEX: http://www.esa.int/Our_Activities/Observing_the_Earth/Save_the_date_selection_of_ESA_s_eighth_Earth_Explorer
– the TROPOMI project: http://www.tropomi.eu/

Julien Chimot
Jun 122015
 

RainGain is a project within the Framework of the COP21 Preparation and stands for

“RESEARCHERS & WATER MANAGERS PREPARING CITIES FOR A CHANGING CLIMATE”

Raingain_converence

The EU INTERREG NWE IVB RainGain project has focused on recent remote sensing technologies to achieve a finer urban water management and to build up resilience to weather extremes and climate change. The RainGain conference will address all the issues related to high-resolution rainfall measurement, nowcasting and hydrological modelling, as well as their advanced applications to urban water management and stakeholder’s capacity building.

More info can be found here:

http://www.raingain.eu/en/raingain-final-conference-regitration-open

The poster that was presented was titled: ” Dual-Polarimetric X-Band Weather Radar: Accurate Rainfall Estimation and Storm Observations ” and can be found here.

More RainGain news:

International RainGain Workshop on March 24th 2015 in Rotterdam.

Topics:

  • Extreme rainfall in Jakarta
  • Amsterdam Rainproof
  • Coping with extreme rainfall
  • Added value X-band radar

More info can be found in: http://www.raingain.eu/en/node/4619

http://www.raingain.eu/en/raingain-international-workshop-rotterdam-0

Ricardo_small herman_small

by Ricardo Reinoso Rondinel

Apr 202015
 

Last week Stephanie Prianto Rusli and Lukas Pfitzenmaier presented posters at the European Geoscience Union in Vienna. This conference gave a grate opportunity to meet a brought range of scientists from all kinds of Geoscience and come into discussion. It also gave the opportunity to go into interdisciplinary sessions and generate new ideas.

EGU_2015_2EGU_2015_3EGU_2015_1

Stephanies poster was in the the session: Remote Sensing of Clouds and Aerosols: Techniques and Applications and its title: Multi-sensor approach to retrieving water cloud physical properties and drizzle fraction  (poster here)

Lukas poster could be find in the new session about Observing and modeling processes in moderately supercooled clouds and was dealing with Effect of cloud microphysics on particle growth under mixed phase conditions  (poster here). Discussions and comments within the supercooled cloud community where very fruitful and caused quite some attention. So the changes are high to have a second one in the next EGU 2016.

 

Nov 272014
 

In the last ITaRS Summer School on “Clouds and Precipitation: Observation and Processes”, which was held in the Jülich Research Center (Germany), the group working on the topic “When does a cloud form?” was selected as the one that made the best work in such a short period of time. The name of the group was “The Transformers” and the integrants were Elisa Adirosi (CNR-ISAC, Rome, Italy), Pilar Gumà-Claramunt (CNR-IMAA, Potenza, Italy), Lukas Pfitzenmaier (TU Delft, The Netherlands), Stefanos Samaras (University of Potsdam, Germany) and Veronika Wolf (DWD, Lindenberg, Germany)

IMG_3940-700

The Transformers were awarded with the possibility to attend the meeting of TOPROF, the acronym of a COST Action standing for “Towards operational ground based profiling with ceilometers, doppler lidars and microwave radiometers for improving weather forecasts”, which was held in the DTU Risø Campus in Roskilde, Denmark. There, the students presented to the participants of the meeting the ITaRS project, the work they did during the Summer School, the Atmospheric Emitted Radiance Interferometer (AERI) instrument and their individual research projects. Furthermore, they attended many interesting talks, participated in the working groups meetings (ceilometers [WG1], Doppler lidars [WG2], Microwave radiometers [WG3] and/or Data assimilation [WG4]) and had the opportunity to discuss with experts in Remote Sensing of the atmosphere.

Finally, the three ITaRS students stayed one day after the meeting to visit Copenhagen

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We would like to thank ITaRS and TOPROF for the opportunity of attending this interesting experience.

Oct 312014
 

Today we went to Cabauw to fix some  radar issues that we have. The weather forecast of today was good for lidar measurements too we started the Raman-lidar CAELI as well. As you can see as all the measurement quick-looks for the lidar systems (Polly and CAELI) we had some nice cirrus layer over Cabauw. So we expected also that our colleagues from Munich would have a good change to observe some HALOs within the cirrus clouds. But the conditions where that good, that we could also observe this HALOs over Cabauw.

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Halos are optical reflections produced by hexagonal oriented ice crystals within ice clouds. This reflections produce a ring around the sun and also some bright dots next to the sun. Observations of such HALOs make it possible to get information about the ice crystal shape and their orientation. Lidar measurements could also give such information. Combining the measurements of the lidar systems and the HALO-camera in de Bilt will hopefully produce some nice results.

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