3-D observations of absolute humidity from the land surface to the lower troposphere with scanning differential absorption lidar

The water vapor (WV) distribution in the atmospheric boundary layer (ABL) is spatially and temporally highly variable. To investigate this behavior, the Institute of Physics and Meteorology at the University of Hohenheim (UHOH) developed a unique scanning differential absorption lidar (DIAL). This instrument allows for water vapor measurements with high temporal and spatial resolutions of the orders of seconds and tens of meters in the range of several kilometers from the surface up to the lower troposphere. Additionally, the UHOH DIAL system can perform scanning measurements which allows for observations down to the surface as well as for observations of the horizontal moisture variability. Within this thesis, three aspects regarding high-resolution observations of moisture in the ABL with scanning DIAL are demonstrated: 1) the development of a new seeder system for the laser transmitter, 2) the presentation of three scan modes, and 3) applications of 2-D to 3-D WV DIAL data. The newly developed seeder system is based on distributed feedback (DFB) laser diodes as seed lasers and an electro-optical deflector as optical switch. The setup and its specifications are presented. Scanning measurements were performed to capture the spatial WV structures. For this purpose, three scan modes with measurement examples are presented: 1) Range-height indicator (RHI) scans provide vertical cross-section images of the atmospheric humidity distribution. The presented series of four measurements show several humidity layers with different WV content and their evolution. Clouds appear in the last scan. 2) A volume scan captures the whole three-dimensional WV structure made out of several conical scans of different elevation angles. The horizontal variation of the layer heights can be related to the terrain profile with a small hill near the DIAL site. 3) Low elevation scans observe the WV distribution directly above the surface. Thus, relationships of the ground characteristics and vegetation with the humidity content above can be investigated. It is shown that there was more moisture above a maize field and above a forest than above grassland. For the analysis of scanning measurements, new analysis and visualization routines as well as new methods for the error estimation were developed. More scientific applications of high-resolution WV data from DIAL measurements are presented in three publications. A evaluation study compared humidity profiles from model simulations with different land-surface schemes with horizontal mean profiles of scanning DIAL measurements. High-resolution humidity fluctuations from vertical measurements were used to determine higher-order moments up to the fourth-order as well as skewness and kurtosis. Furthermore, such WV profiles were combined with profiles of temperature and vertical wind velocities and used for the development of new turbulence parameterizations and for model validation.Die Wasserdampfverteilung in der atmosphärischen Grenzschicht ist räumlich und zeitlich sehr variabel. Zur Untersuchung dieses Verhaltens entwickelte das Institut für Physik und Meteorologie an der Universität Hohenheim (UHOH) ein einzigartiges scannendes differentielles Absorptionslidar (DIAL). Dieses ermöglicht Wasserdampfmessungen mit einer zeitlichen und räumlichen Auflösung von wenigen Sekunden und einigen zehn Metern in einem Bereich von mehreren Kilometeren vom Boden bis zur unteren Troposphäre. Das UHOH DIAL-System erlaubt zudem scannende Messungen, die zum einen Messungen bis an den Boden und zum anderen Messungen der horizontalen Variabilität der Feuchtigkeit ermöglichen. Diese Arbeit behandelt drei Aspekte bezüglich hochaufgelöster Feuchtemessung in der atmosphärischen Grenzschicht mit scannendem DIAL: 1) Die Entwicklung eines neuen Seedersystems für den Lasertransmitter, 2) die Vorstellung verschiedener Scan-Modi und 3) Anwendungen von mit dem DIAL gemessenen 2-D bis 3-D Wasserdampfdaten. Das neu entwickelte Seedersystem basiert auf Distributed Feedback (DFB) Laserdioden als Seedlaser und einem elektro-optischen Strahlablenker als optischen Schalter. Der Aufbau und die Spezifikationen werden vorgestellt. Zur Erfassung der räumlichen Wasserdampfstruktur werden scannende Messungen durchgeführt. Dazu werden folgende 3 Scanverfahren mit Messbeispielen vorgestellt: 1) Range-height indicator (RHI) Scans liefern vertikale Schnittbilder der atmosphärischen Feuchteverteilung. Die vorgestellte Serie aus vier Messungen zeigt verschiedene Feuchteschichten mit unterschiedlichem Wasserdampfgehalt und deren Entwicklung. Im Messbeispiel treten im letzten durchgeführten Scan Wolken an der Oberkante der konvektiven Grenzschicht auf. 2) Der Volumenscan erfasst die gesamte 3-dimensionale Wasserdampfstruktur mittels mehrerer konischer Scans mit unterschiedlichen Elevationswinkeln. Die horizontalen Unterschiede der Schichtenhöhen können anhand des Geländeprofiles mit einem kleinen Hügel in der Nähe des DIAL-Standorts erklärt werden. 3) Bodennahe Scans geben die Wasserdampfverteilung direkt über dem Erdboden wieder. Damit können Beziehungen zwischen der Bodenbeschaffenheit und dem -bewuchs mit der darüber liegenden Atmosphäre untersucht werden. So zeigten sich über einem Maisfeld und über Wald höhere Wasserdampfwerte als über einer Grasfläche. Für die Analyse der scannenden Messungen wurden neue Auswerte- und Darstellungsroutinen, sowie neue Methoden zur Fehlerabschätzung entwickelt. Die wissenschaftliche Anwendung von hochaufgelösten Wasserdampfdaten aus DIAL Messungen werden anhand von drei Veröffentlichungen vorgestellt. Eine Evaluierungsstudie zu Modellsimulationen mit unterschiedlichen Land-Atmosphären-Austauschmodellen verglich Feuchtigkeitsprofile aus den Modellen mit horizontal gemittelten Wasserdampfdaten aus scannenden DIAL-Messungen. Hochaufgelöste Feuchtefluktuationen aus Vertikalmessungen wurden verwendet, um höhere Momente bis zur vierten Ordnung sowie Skewness und Kurtosis zu bestimmen. Weiter wurden solche Feuchteprofile mit Profilen von Temperatur und Vertikalwind kombiniert und genutzt, um neue Turbulenzparametrisierungen zu entwickeln und zu testen

Determination of the diameter of simulated human capillaries using shifted position‐diffuse reflectance imaging

Abstract Multiple diseases are associated with a wide spectrum of microvascular dysfunctions, microangiopathies and microcirculation disorders. Monitoring the microcirculation could thus be useful to diagnose many local and systemic circulatory disorders and to supervise critically ill patients. Many of the scores currently available to help identify the condition of a microcirculation disorder are invasive or leave scope for interpretation. Thus, the present study aims to investigate with Monte‐Carlo simulations (as numerical solutions of the radiative transfer equation) whether shifted position‐diffuse reflectance imaging (SP‐DRI), a non‐invasive diagnostic technique, reveals information on the capillary diameter to assess the state of the microcirculation. To quantify the SP‐DRI signal, the modulation parameter K is introduced. It proves to correlate almost perfectly with the capillary diameter (R¯2≈1), making it a valid parameter for reliably assessing microcirculation. SP‐DRI is emerging as an important milestone on the way to early and conveniently diagnosing microcirculation associated diseases

Observation of sensible and latent heat flux profiles with lidar

We present the first measurement of the sensible heat flux (H) profile in the convective boundary layer (CBL) derived from the covariance of collocated vertical-pointing temperature rotational Raman lidar and Doppler wind lidar measurements. The uncertainties of the H measurements due to instrumental noise and limited sampling are also derived and discussed. Simultaneous measurements of the latent heat flux profile (L) and other turbulent variables were obtained with the combination of water-vapor differential absorption lidar (WVDIAL) and Doppler lidar. The case study uses a measurement example from the HOPE (HD(CP)$^{2}$ Observational Prototype Experiment) campaign, which took place in western Germany in 2013 and presents a cloud-free well-developed quasi-stationary CBL. The mean boundary layer height z$_{i}$ was at 1230 m above ground level. The results show – as expected – positive values of H in the middle of the CBL. A maximum of (182±32) W m$^{-2}$, with the second number for the noise uncertainty, is found at 0.5 z$_{i}$. At about 0.7 z$_{i}$, H changes sign to negative values above. The entrainment flux was (−62±27) W m$^{-2}$. The mean sensible heat flux divergence in the observed part of the CBL above 0.3 z$_{i}$ was −0.28 W m$^{-3}$, which corresponds to a warming of 0.83 K h$^{-1}$. The L profile shows a slight positive mean flux divergence of 0.12 W m$^{-3}$ and an entrainment flux of (214±36) W m$^{-2}$. The combination of H and L profiles in combination with variance and other turbulent parameters is very valuable for the evaluation of large-eddy simulation (LES) results and the further improvement and validation of turbulence parameterization schemes

Towards shifted position-diffuse reflectance imaging of anatomically correctly scaled human microvasculature

Due to significant advantages, the trend in the field of medical technology is moving towards minimally or even non-invasive examination methods. In this respect, optical methods offer inherent benefits, as does diffuse reflectance imaging (DRI). The present study attempts to prove the suitability of DRI—when implemented alongside a suitable setup and data evaluation algorithm—to derive information from anatomically correctly scaled human capillaries (diameter: 10μm, length: 45μm) by conducting extensive Monte–Carlo simulations and by verifying the findings through laboratory experiments. As a result, the method of shifted position-diffuse reflectance imaging (SP-DRI) is established by which average signal modulations of up to 5% could be generated with an illumination wavelength of λ=424nm and a core diameter of the illumination fiber of 50μm. No reference image is needed for this technique. The present study reveals that the diffuse reflectance data in combination with the SP-DRI normalization are suitable to localize human capillaries within turbid media

Threshold behavior and tunability of a diffusive random laser

© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement: https://doi.org/10.1364/OA_License_v2#VOR-OAIn this study, it is shown that the dynamics of the lasing threshold and the intensity saturation of a diffusive random laser can be visualized by one spectral feature: the peak wavelength shift (tunability). The varied ink concentration and pump energy were utilized to experimentally induce the peak shift and the lasing threshold dynamics. It was found that the peak wavelength progressively turns from blueshift to redshift upon crossing the lasing threshold. A unique random laser threshold regime instead of a threshold point is revealed. This threshold regime was also compared with those deduced from the replica symmetry breaking and the Lévy statistics, both are the state-of-the-art methods to predict the behavior of a complex system. All three results show the high agreement in terms of unveiling the lasing nature of the random lasers.</jats:p

Development and evaluation of a scoring system for assessing incisions in laser surgery

The idea of laser surgery is nearly as old as the laser itself. From the first trials to modern laser surgery systems, it was and is the aim to selectively cut the tissue in the focus spot without causing harm to surrounding structures. This is only possible when the correct parameters for the surgical laser are chosen. Usually, this is done by parameter studies. However, the concrete evaluation scheme often differs between groups and more precise approaches require staining and microscopic evaluation. To overcome these issues, a macroscopic scoring system is presented and evaluated. It can be shown that the scoring system works well and, thus, a laser cut can be evaluated within a few seconds. At the same time, the whole cutting front is taken into account. The presented scoring system is evaluated by the intra class correlation (ICC). The final agreement between different raters is more than 0.7. Therefore, the scoring system can be used to optimize and evaluate the cutting process and it should be suitable for comparing the results between different groups. Definitely, it can be applied for scoring within a group to enable e.g., a profound statistical analysis for a parameter study

The influence of the optical properties on the determination of capillary diameters

Various clinically applicable scores and indices are available to help identify the state of a microcirculatory disorder in a patient. Several of these methods, however, leave room for interpretation and only provide clues for diagnosis. Thus, a measurement method that allows a reliable detection of impending or manifest circulatory malfunctions would be of great value. In this context, the optical and non-invasive method of shifted position-diffuse reflectance imaging (SP-DRI) was developed. It allows to determine the capillary diameter and thus to assess the state of the microcirculation. The aim of the present study is to investigate how the quantification of capillary diameters by SP-DRI behaves in different individuals, i.e. for a wide range of optical properties. For this, within Monte-Carlo simulations all optical properties (seven skin layers, hemoglobin) were randomly varied following a Gaussian distribution. An important finding from the present investigation is that SP-DRI works when the optical properties are chosen randomly. Furthermore, it is shown that appropriate data analysis allows calibration-free absolute quantification of the capillary diameter across individuals using SP-DRI. This underpins the potential of SP-DRI to serve as an early alert system for the onset of microcirculatory associated diseases

Proof of Principle for Direct Reconstruction of Qualitative Depth Information from Turbid Media by a Single Hyper Spectral Image

In medical applications, hyper-spectral imaging is becoming more and more common. It has been shown to be more effective for classification and segmentation than normal RGB imaging because narrower wavelength bands are used, providing a higher contrast. However, until now, the fact that hyper-spectral images also contain information about the three-dimensional structure of turbid media has been neglected. In this study, it is shown that it is possible to derive information about the depth of inclusions in turbid phantoms from a single hyper-spectral image. Here, the depth information is encoded by a combination of scattering and absorption within the phantom. Although scatter-dominated regions increase the backscattering for deep vessels, absorption has the opposite effect. With this argumentation, it makes sense to assume that, under certain conditions, a wavelength is not influenced by the depth of the inclusion and acts as an iso-point. This iso-point could be used to easily derive information about the depth of an inclusion. In this study, it is shown that the iso-point exists in some cases. Moreover, it is shown that the iso-point can be used to obtain precise depth information

Profiling the molecular destruction rates of temperature and humidity as well as the turbulent kinetic energy dissipation in the convective boundary layer

A simultaneous deployment of Doppler, temperature, and water-vapor lidars is able to provide pro- files of molecular destruction rates and turbulent kinetic energy (TKE) dissipation in the convective boundary layer (CBL). Horizontal wind profiles and profiles of vertical wind, temperature, and moisture fluctuations are combined, and transversal temporal autocovariance functions (ACFs) are determined for deriving the dissipation and molecular de- struction rates. These are fundamental loss terms in the TKE as well as the potential temperature and mixing ratio variance equations. These ACFs are fitted to their theoretical shapes and coefficients in the inertial subrange. Error bars are estimated by a propagation of noise errors. Sophisticated analyses of the ACFs are performed in order to choose the correct range of lags of the fits for fitting their theoretical shapes in the inertial subrange as well as for minimizing systematic errors due to temporal and spatial averaging and micro- and mesoscale circulations. We demonstrate that we achieve very consistent results of the derived profiles of turbulent variables regardless of whether 1 or 10 s time resolutions are used

Analysis of diffuse reflectance spectroscopy by means of Bayesian inference and separation of the parameters for scattering strength and spectral dependence of the scattering

Abstract For many applications in tissue optics, knowledge of the scattering coefficient or at least the reduced scattering coefficient is essential. In addition, its spectral dependence is also an important feature, as this provides information about scatterer sizes. While the characterization of the spectral dependence should be a simple fit, experimental results show strong fluctuations even for the same tissue type. For in‐vivo measurements, this problem is even greater. Therefore, it is the aim of this study to analyze the instabilities of the scattering characterizations and find a solution for it by means of Bayesian inference. In this study, this behavior is investigated using the example of diffuse reflectance spectroscopy. It can be shown that the currently used fitting functions are unstable for the fitting as both parameters for characterizing the reduced scattering coefficient describe the spectral dependence as well as the scattering strength. However, by a simple coordinate transform, a stable mathematical description of the scattering is derived. By the fact that a posteriori probability of the reduced scattering coefficient narrows down significantly with the Bayesian inference, the new fitting function is verified