Untersuchungen zur Ableitung von Windböen aus Doppler-Lidar-Messungen

<p>Mit Hilfe von Doppler-Lidar-Systemen, lassen sich die Profile von Windgeschwindigkeit und -richtung in der Atmosphärischen Grenzschicht (AGS) auf der Basis klassischer Messstrategien wie einem VAD-24 Scan (Velocity Azimuth Display mit 24 Strahlrichtungen) zuverlässig bestimmen (Päschke et al., 2015). Für praktische Anwendungen von großem Interesse sind jedoch neben dem mittleren Windprofil auch kurzzeitige Fluktuationen des Windes, wie sie zum Beispiel in Verbindung mit Windböen auftreten. Untersuchungen zu Windböen waren ein wesentlicher Aspekt der Messkampagne FESSTVaL (Field Experiment on Sub-Mesoscale Spatio-Temporal Variability in Lindenberg, www.fesstval.de).</p><p>Eine Studie von Suomi et al. (2017) hat gezeigt, dass eine Ableitung von Windböen aus Doppler Lidar Messungen prinzipiell möglich ist. Allerdings wird mit üblichen Messstrategien die hierfür erforderliche hohe zeitliche Auflösung in der Ermittlung des Windvektors nicht erreicht, so dass mit Skalierungsansätzen unter Verwendung von in-situ Windmessungen eine Korrektur der aus den Lidar-Daten abgeleiteten Böenwerte erfolgen muss.</p><p>Im Rahmen der vorliegenden Arbeit wurde eine alternative Messstrategie für Doppler-Lidar-Systeme vom Typ „Streamline“ (Halo Photonics) entwickelt und über mehrere Monate in den Jahren 2020/21 auf dem Grenzschichtmessfeld Falkenberg des DWD erprobt. Die Böenableitung basiert auf einem sog. Continous Scan Mode (CSM); dabei werden die während einer vollständigen Rotation des Lidar-Scan-Kopfes kontinuierlich durchgeführten Messungen 10-11 Strahlrichtungen zugeordnet und die Radialwindgeschwindigkeiten wiederum mit dem VAD-Verfahren ermittelt. Die Dauer eines Scans beträgt etwa 3.4s, damit kann eine Zeitauflösung erreicht werden, die der heute weit verbreiteten Definition einer Windbö entspricht (3s gleitendes Mittel; WMO (2018)).</p><p>Diese neue Konfiguration bringt Herausforderungen an die Datenverarbeitung mit sich. Im CSM muss mit vergleichsweise wenigen Lidar-Pulsen pro Messstrahl gearbeitet werden, so dass klassische Ansätze der Datenfilterung (Signal-to-Noise Schwellwert, Consensus Filterung) nicht verwendet werden können. Es wird ein alternatives Verfahren für die Prozessierung der Lidar-Rohdaten vorgeschlagen. Die Ergebnisse der Ableitung sowohl des mittleren Windvektors als auch der jeweiligen maximalen Windbö in einem 10-Minuten-Mittelungsintervall werden mit Sonic-Messungen in 90m Höhe verglichen. </p><p>Im Rahmen des FESSTVaL Experimentes wurde diese neue Messkonfiguration an drei Standorten, die ein annähernd gleichseitiges Dreieck mit einer Kantenlänge von etwa 5 km bildeten, genutzt. Es werden Fallbeispiele aus der FESSTVaL Kampagne für die Variabilität im Auftreten von Windböen gezeigt.</p><p><strong>Referenzen</strong></p><p>Päschke, E., Leinweber, R., and Lehmann, V. (2015): An assessment of the performance of a 1.5 μm Doppler lidar for operational vertical wind profiling based on a 1-year trial, Atmos. Meas. Tech., 8, 2251–2266, https://doi.org/10.5194/amt-8-2251-2015</p><p>Suomi, I., Gryning, S.‐E., O'Connor, E.J. and Vihma, T. (2017): Methodology for obtaining wind gusts using Doppler lidar. Q.J.R. Meteorol. Soc., 143: 2061-2072. https://doi.org/10.1002/qj.3059</p><p>World Meteorological Organization (WMO) (2018): Measurement of surface wind. In Guide to Meteorological Instruments and Methods of Observation, Volume I -Measurement of Meteorological Variables, No.8: 196–213, URL: https://library.wmo.int/doc_num.php?explnum_id=10616 (accessed November 2021)</p>

Separating Cloud and Drizzle Signals in Radar Doppler Spectra Using a Parametric Time Domain Method

The ability to separate cloud and drizzle returns in active remote sensing observations is important for understanding the microphysics of clouds and precipitation. Yet, robust separations remain challenging in radar remote sensing. Prior methods for cloud and drizzle separation for radar observations use the properties of the Doppler spectra such as skewness. However, these methods have challenges when the drizzle becomes dominant in the observation volume. This paper presents a parametric time domain method (PTDM) that separates cloud and drizzle using the Doppler spectra measurements without assuming any prior properties of cloud and drizzle. The advantage of PTDM is that it can estimate the signal properties in the time domain and can obtain the cloud and drizzle estimates simultaneously. Based on our radar signal simulations, the uncertainty in estimated power and velocity from PTDM are within 2 dB and 0.02 m s−1, respectively. We have also evaluated the PTDM algorithm using observations from the Atmospheric Radiation Measurement (ARM) Program W-band cloud radar in the Clouds, Aerosols, and Precipitation in the Marine Boundary Layer (CAP-MBL) campaign at the Azores in 2009–10. Two cases corresponding to light and moderate drizzling conditions are considered for the study. The statistics of the estimates obtained show that the PTDM method performs well in separating the cloud and drizzle returns. Finally, the estimated cloud and drizzle reflectivity from PTDM were used to retrieve their corresponding microphysical properties, showing that the retrieved liquid water path agrees to 25 g m−2 with the benchmark microwave method.

3D super-resolved imaging in live cells using sub-diffractive plasmonic localization of hybrid nanopillar arrays

Analysing dynamics of a single biomolecule using high-resolution imaging techniques has been had significant attentions to understand complex biological system. Among the many approaches, vertical nanopillar arrays in contact with the inside of cells have been reported as a one of useful imaging applications since an observation volume can be confined down to few-tens nanometre theoretically. However, the nanopillars experimentally are not able to obtain super-resolution imaging because their evanescent waves generate a high optical loss and a low signal-to-noise ratio. Also, conventional nanopillars have a limitation to yield 3D information because they do not concern field localization in z-axis. Here, we developed novel hybrid nanopillar arrays (HNPs) that consist of SiO2 nanopillars terminated with gold nanodisks, allowing extreme light localization. The electromagnetic field profiles of HNPs are obtained through simulations and imaging resolution of cell membrane and biomolecules in living cells are tested using one-photon and 3D multiphoton fluorescence microscopy, respectively. Consequently, HNPs present approximately 25 times enhanced intensity compared to controls and obtained an axial and lateral resolution of 110 and 210 nm of the intensities of fluorophores conjugated with biomolecules transported in living cells. These structures can be a great platform to analyse complex intracellular environment.

Background reduction in STED-FCS using coherent-hybrid STED

Fluorescence correlation spectroscopy (FCS) is a valuable tool to study the molecular dynamics of living cells. When used together with a super-resolution stimulated emission depletion (STED) microscope, STED-FCS can measure diffusion processes at the nanoscale in living cells. In twodimensional (2D) systems like the cellular plasma membrane, a ring-shaped depletion focus is most commonly used to increase the lateral resolution, leading to more than 25-fold decrease in the observation volumee, reaching the relevant scale of supramolecular arrangements. However, STED-FCS faces severe limitations when measuring diffusion in three dimensions (3D), largely due to the spurious background contributions from undepleted areas of the excitation focus that reduce the signal quality and ultimately limit the resolution. In this paper, we investigate how different STED confinement modes can mitigate this issue. By simulations as well as experiments with fluorescent probes in solution and in cells, we demonstrate that the coherent-hybrid (CH) depletion pattern reduces background most efficiently and thus provides superior signal quality under comparable reduction of the observation volume. Featuring also the highest robustness to common optical aberrations, CH-STED can be considered the method of choice for reliable STED-FCS based investigations of 3D diffusion on the sub-diffraction scale.

peakTree: a framework for structure-preserving radar Doppler spectra analysis

Clouds are frequently composed of more than one particle population even at the smallest scales. Cloud radar observations frequently contain information on multiple particle species in the observation volume when there are distinct peaks in the Doppler spectrum. Multi-peaked situations are not taken into account by established algorithms, which only use moments of the Doppler spectrum. In this study, we propose a new algorithm that recursively represents the subpeaks as nodes in a binary tree. Using this tree data structure to represent the peaks of a Doppler spectrum, it is possible to drop all a priori assumptions on the number and arrangement of subpeaks. The approach is rigid, unambiguous and can provide a basis for advanced analysis methods. The applicability is briefly demonstrated in two case studies, in which the tree structure was used to investigate particle populations in Arctic multilayered mixed-phase clouds, which were observed during the research vessel Polarstern expedition PS106 and the Atmospheric Radiation Measurement Program BAECC campaign.

Nanoaperture fabrication via colloidal lithography for single molecule fluorescence imaging

In single molecule fluorescence studies, background emission from labeled substrates often restricts their concentrations to non-physiological nanomolar values. One approach to address this challenge is the use of zero-mode waveguides (ZMWs), nanoscale holes in a thin metal film that physically and optically confine the observation volume allowing much higher concentrations of fluorescent substrates. Standard fabrication of ZMWs utilizes slow and costly E-beam nano-lithography. Herein, ZMWs are made using a self-assembled mask of polystyrene microspheres, enabling fabrication of thousands of ZMWs in parallel without sophisticated equipment. Polystyrene 1 μm dia. microbeads self-assemble on a glass slide into a hexagonal array, forming a mask for the deposition of metallic posts in the inter-bead interstices. The width of those interstices (and subsequent posts) is adjusted within 100-300 nm by partially fusing the beads at the polystyrene glass transition temperature. The beads are dissolved in toluene, aluminum or gold cladding is deposited around the posts, and those are dissolved, leaving behind an array ZMWs. Parameter optimization and the performance of the ZMWs are presented. By using colloidal self-assembly, typical laboratories can make use of sub-wavelength ZMW technology avoiding the availability and expense of sophisticated clean-room environments and equipment.

Measuring mobility in chromatin by intensity sorted FCS

The architectural organization of chromatin can play an important role in genome regulation by affecting the mobility of molecules within its surroundings via binding interactions and molecular crowding. The diffusion of molecules at specific locations in the nucleus can be studied by Fluorescence Correlation Spectroscopy (FCS), a well-established technique based on the analysis of fluorescence intensity fluctuations detected in a confocal observation volume. However, detecting subtle variations of mobility between different chromatin regions remains challenging with currently-available FCS methods.Here we introduce a method that samples multiple positions by slowly scanning the FCS observation volume across the nucleus. Analyzing the data in short time segments, we preserve the high temporal resolution of single-point FCS while probing different nuclear regions in the same cell. Using the intensity level of the probe (or a DNA marker) as a reference, we efficiently sort the FCS segments into different populations and obtain average correlation functions that are associated to different chromatin regions. This sorting and averaging strategy renders the method statistically robust while preserving the observation of intranuclear variations of mobility.Using this approach, we quantified diffusion of monomeric GFP in high versus low chromatin density regions. We found that GFP mobility was reduced in heterochromatin, especially within perinucleolar heterochromatin. Moreover, we found that modulation of chromatin compaction by ATP depletion, or treatment with solution of different osmolarity, differentially-affected the ratio of diffusion in both regions. Then, we used the approach to probe the mobility of estrogen receptor-α (ER) in the vicinity of an integrated multicopy prolactin gene array. Finally, we discussed the coupling of this method with stimulated emission depletion (STED)-FCS, for performing FCS at sub-diffraction spatial scales.

Can a bottom-moored echo sounder array provide a survey-comparable index of abundance?

A small number of stationary echo sounders have the potential to produce abundance indices where fish repeatedly occupy localized areas (e.g., spawning grounds). To investigate this possibility, we deployed three trawl-resistant moorings with a newly designed autonomous echo sounder for ∼85 days during the walleye pollock (Gadus chalcogrammus) spawning season in Shelikof Strait, Alaska. Backscatter observed from the moorings was highly correlated with ship-based acoustic surveys, suggesting that the mooring observations reflect abundance over much larger areas than the observation volume of the acoustic beam. A retrospective analysis of a 19-year time series of prespawning walleye pollock surveys was used to select mooring locations and determine that three to five moorings can produce an index of walleye pollock backscatter comparable to that produced by a ship-based survey covering ∼18 000 km2 (mean prediction error of <11% for five moorings). The three moorings deployed in Shelikof Strait yielded a backscatter estimate that was within ∼15%–20% of that observed during the survey. Thus, it appears feasible to design a relatively sparse mooring array to provide abundance information and other aspects of fish behavior in this environment.