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Topics for master thesis projects at MIM and the DLR Remote sensing group

Synthetic satellite images for improved aerosol forecasts

Some of today’s most important environmental concerns are related to the presence of aerosols in the atmosphere. Dust, sand, smoke and volcanic aerosols affect the safe operation of transport systems and the availability of power from solar generation and influence the formation of clouds and rainfall. Moreover, not only the increasing concentration of greenhouse gases but also changes in the aerosols affect climate change and the extent of the aerosol impact is still uncertain. Numerical weather prediction models have made significant progress in accurately predicting the transport of aerosols, changes in their composition, and their effects on the dynamics of the atmosphere. However, large uncertainties exist in the initial and boundary conditions. Often neither the initial aerosol distribution nor the strength of aerosol sources is well known. These problems can be addressed by assimilating more and better aerosol observations. Aerosol information with high spatial and temporal resolution and excellent coverage is contained in solar channel geostationary satellite images.

Only recently radiative transfer (RT) methods for the visible spectrum have been developed by our group that are sufficiently fast to use solar channels in operational data assimilation systems. So far, information about water and ice clouds has been be assimilated. An important challenge in extending these methods to include aerosols is that considerably more parameters are required to describe them, compared to clouds. To make a look-up table based RT method feasible for aerosols, the number of parameters has to be reduced. The aim of this master thesis is therefore to compute synthetic satellite images from model data including aerosols and to investigate the following questions:

These investigations will be an important step towards improved aerosol forecasts and a better understanding of the influence of aerosols on weather and climate.

Responsible Leonhard Scheck, Bernhard Mayer

Analysis of a Temporal / Spectral Integration Scheme for Radiative Transfer Calculations in Numerical Weather Prediction Models

Due to the computational complexity of radiative transfer computations, atmospheric models usually try to minimize the computational effort for this important boundary condition, the only energy source in the physical system. They sub-step the radiation module, i.e. call the radiation routines only every n-th timestep. A too coarse temporal sampling strategy, may however have implications for the evolution of clouds and the model dynamics in general. Preliminary results for a parameterization of the temporal sampling have shown promising results. The parameterization uses a simple regression model, fitting the error growth in heating rates and radiative fluxes to estimate the next point in time where radiative transfer has to be computed.

The thesis involves the testing and further development of this adaptive integration scheme and the assessment of its applicability and limitations for various model types, ranging from high-resolution LES to Global Circulation Models.

Responsible Fabian Jakub, Bernhard Mayer

Determine the Influence of Radiatively Induced Surface Inhomogeneities using High-Resolution Satellite Imagery

Current research efforts (Jakub and Mayer 2017) suggest that 3D effects of radiative heating may lead to convective organization resulting in the formation of cloud streets. The above mentioned study examines the cloud-radiative-surface feedback in an idealized enviroment without complex wind fields and surface heterogeneities.

A subsequent step is to investigate if this kind of organization can be found in the complex environment of earths' atmosphere. To this end, this master thesis aimes at a determination of a possible observable correlation between radiative heating and the organization of shallow and deep convection in the real world.

The thesis likely encompasses the tasks of

Responsible Fabian Jakub, Bernhard Mayer

Extracting Atmospheric Parameters from Spectrometer Measurements and Comparison with Established Methods

A major challenge for remote sensing of the Earth surface is the influence of the atmosphere on the airborne and satellite data. For dark surfaces like open water, more than 90 % of the signal can be caused by the atmosphere. To correct the contribution of the atmosphere, its variable components (aerosol concentration, aerosol type, water vapour, ozone) must be measured. The determination of these parameters often requires in-situ measurements, because of their high spatial variability. These measurements are usually performed with dedicated sunphotometers, such as Microtops or CIMEL. The main goal of this thesis is to develop a measurement concept and evaluation method for extracting atmosphere components from measurements with any spectrometer which has a suitable spectral range and resolution. Furthermore this method should be validated in respect to established measurement protocols and hardware (in particular AERONET/CIMEL).

This thesis will be conducted in cooperation with the German Aerospace Center (DLR). Place of work and supervision will primarily be at the DLR site at Oberpfaffenhofen near Munich.

A background in meteorology, physics, or a related subject is required. Programming skills in an object oriented programming language, basic understanding of the operation principles of a spectrometer and willingness to take part in measurement campaigns at different sites in Germany are desired.

Responsible Tobias Kölling, Sebastian Riedel (DLR), Peter Gege (DLR)

Optische Eigenschaften von dünnen Eiswolken aus Halo-Beobachtungen und spektraler Fernerkundung

Die optischen Eigenschaften dünner Eiswolken sind von hohem Interesse für die Klimaforschung, da diese Eiswolken große Teile der Erde bedecken. Dünne Eiswolken haben generell einen starken erwärmenden Einfluss auf die Bodentemperaturen, da sie wenig solares Licht reflektieren aber die thermische Abstrahlung der Erde stark reduzieren. Im sich verändernden Klima durch den Anstieg der Treibhausgase stellen die Veränderungen der optischen Eigenschaften dieser Wolken eine starke Rückkopplungsmöglichkeit dar. Die Beobachtung solcher Eigenschaften wie der optischen Dicke und der Partikelgrößen und Partikelformen sowie ihrer Veränderungen spielt daher eine wichtige Rolle. Wir beschäftigen uns als eine der ersten Gruppen mit der Weiterentwicklung der Beobachtungsmethoden unter Berücksichtigung der Kristallformen.

Für die Ableitung der optischen Dicke und Effektivradius von Zirren aus passiven Fernerkundungs-Methoden, ist es notwendig Form und Orientierung der Eispartikel in den Zirren zu berücksichtigen. Ein Verfahren zur Ableitung von Eispartikelform und -orientierung basierend auf Halo-Beobachtungen existiert bereits und wird im Rahmen einer Doktorarbeit weiter entwickelt. Für dieses Retrieval wird der Zusammenhang zwischen Halo-Erscheinungen und Eiskristallformen bzw. -orientierung genutzt. Ziel dieser Arbeit ist es bereits ebenfalls am MIM vorhandene spektrale Ableitungsverfahren durch Verwendung dieser zusätzlichen Information zu verbessern und zu vergleichen.

In dieser Arbeit sollen die Daten einer Messkampagne am MIM aus dem April 2014 verwendet werden, um die beiden bodengebundenen Verfahren zu vergleichen, die bestmögliche Kombination der beiden zu finden und diese mit zeitgleich gemessenen Flugzeug und Satellitendaten zu vergleichen.

Responsible Linda Forster, Tobias Zinner

Hat Strahlung einen Einfluss auf konvektive Bewoelkung?

Die Antwort darauf ist eine klares „ja“: Konvention wird durch Absorption solarer Strahlung am Erdboden ausgeloest. Die Frage ist, welche Relevanz die einzelnen Prozesse (Absorption und Emission solarer und thermischer Strahlung am Boden und in der Atmosphaere) haben. Und diese Frage versuchen wir, in verschiedenen Projekten im Verbund mit externen Partnern zu beantworten, um mittelfristig die Vorhersage von Wetter und Klima zu verbessern. In dieser Arbeit sollen dazu Simulationen konvektiver Bewoelkung mit dem an der Uni installierten ICON-LES durchgefuehrt werden. ICON wird in Zukunft zur Basis der DWD Wettermodellierung. Dazu muessen die im Rahmen von zwei Doktorarbeiten (Klinger, Jakub) neu konzipierten Strahlungsroutinen auf das Dreiecksgitter des ICON-LES angepasst und getestet werden. Dies ist eine anspruchsvolle und sehr interessante Aufgabe, die unter anderem die Entwicklung eines statistischen Monte-Carlo-Modells auf einem Dreiecksgitter sowie einer einfachen deterministischen Loesung des thermischen Strahlungstransports umfasst. Die zugrunde liegenden Methoden sind bei uns etabliert, aber eben „nur“ auf einem Rechtecksgitter. Die Arbeit ist zentrales Thema des Lehrstuhls fuer Experimentelle Meteorologie und wuerde die Arbeitsgruppe massgeblich voranbringen.

Responsible Bernhard Mayer, Carolin Klinger, Fabian Jakub

Aerosol-cloud interactions: the search for the smoking gun in the Amazon

Understanding the interactions between aerosol and clouds is instrumental for our ability not only to predict the further development of, especially convective, clouds but also whole regional weather systems and climate feedbacks. For this reason, the research aircraft HALO has been sent to the Amazon region within the framework of the ACRIDICON measurement campaign. In-situ measurements of clouds were taken, and our hyperspectral imager specMACS was on board as well. In this thesis we would like to investigate which clouds were influenced by biomass burning, and what the effect on cloud microphysical parameters was. Using a numerical (Lagrangian trajectory) model we recently calculate the history of airmasses probed by HALO during ACRIDICON. A major question was if and when those trajectories encountered a convective event. Such events are „parameterized“ in weather prediction models like the one used to create the meteorological input the trajectory calculations were based upon. That means while their frequency of occurence and location is statistically correct, it is not necessarily true that single thunderstorm cells are represented correctly in timing and location. With the aid of geostationary satellites and the trajectory calculations we would like to determine whether a trajectory encountered a convective event. In case of an encounter we would conduct new trajectory simulations starting at the inflow region of the thunderstorm. Using satellite observations as well as specMACS we will determine fire activity and match with the calculated trajectories. This allows us to create a statistical analysis of the influence of biomass burning emissions on clouds probed by HALO during ACRIDICON.

Responsible Christoph Knote, Tobias Zinner

Solar energy forecasting: Derivation of cloud optical thickness and solar irradiance at ground from spectral all-sky data

During a recent master's thesis, a short-term forecasting technique for cloud cover based on all-sky camera images was developed. This so called nowcasting algorithm is based on the use of consecutive cloud images, detection of cloud cover, and an extrapolation cloud cover in time. Results are to be used in solar energy generation in the context of grid integration and power plant control. This algorithm allows for the successful forecast of cloud cover, i.e. cloud/ no cloud. This information is sufficient for concentrating solar energy production which uses direct sunlight. However photovoltaics can generate energy also during shadowed episodes and need more quantitative information.

The algorithm should be extended with a retrieval of cloud optical thickness, in order to amend the cloud/ no cloud decision with quantitative information. To this end, a technique proposed by Marshak et al. a few years ago, called RED-vs-NIR, should be adapted for the use with all-sky measurements. This method uses the contrast of RED (below 0.7 micrometer wavelength) and NIR cloud transmittance (near-infra-red, above 0.7) which is caused by the sharp vegetation albedo change in this region to derive optical thickness.

Based on this idea, a retrieval will be developed applying our radiative transfer model libRadtran. All-sky data from our cloud spectrometer will be used to test and demonstrate the possibilities. In real application more simple off-the-shelf fish-eye camera systems will be equipped with spectral filters to proved the neccessary data.

The work is supervised jointly by LUM Tobias Zinner and Dexa Solar (www.dexasolar.com).

Radiative transfer in next-generation weather models

The next-generation German weather model ICON is planned to be run on 100m-resolution. On this scale 3D-radiative transfer influences cloud formation. Current weather models (e.g., COSMO) do not account for these effects as they simulate radiation only in very simplified 1D way. In the framework of HDCP2, the High Definition Clouds and Precipitation for Climate Prediction Project, we are currently developing a 3D Radiative Transfer code that is fast enough to drive dynamical processes. The basic concept is to use a combination of linear algebra with pre-calculated transfer coefficients.

At the moment. these transfer coefficients are calculated with a simple Monte Carlo ray-tracing model and stored in a look-up table. Due to the complexity of radiative transfer and the many influencing variables this table is big and its use is computationally expensive. Earlier approaches using neural-networks and adaptive high order polynomial regression have shown promising results but need further thought. Your part is to develop a fast yet flexible parameterization for the generation of the transfer coefficients replacing the mentioned approach.

This work is a crucial step to enable high resolution model runs with realistic radiative forcing. The goal is to further our understanding of cloud-radiation interactions which will advance short term weather prediction as well as reduce uncertainties in climate projections. We hope for a candidate with appreciation for radiative transfer, applied mathematics and programming.

Responsible Fabian Jakub, Bernhard Mayer

Cloud remote sensing using polarized multi-angle observations

A new mission to measure cloud and aerosol properties is currently prepared by NASA-JPL. The satellite instrument will measure polarized radiances from a large number of viewing directions at several wavelengths from the UV to the NIR spectral region. Data from the airborne demonstrator of this instrument (AirMSPI, http://airbornescience.jpl.nasa.gov/instruments/airmspi) is already available. The aim of this thesis is develop an algorithm to retrieve parameters of the cloud droplet size distribution from these measurements. The algorithm shall be validated by simulating the observations using the 3D radiative transfer model MYSTIC. The retrieval algorithm may then be applied to the synthetic data, and the retrieved results may be compared to the real input. In particular the impact of 3D effects shall be investigated using this method. Part of the work can be performed at NASA-JPL in Pasadena, USA, if the student is interested to go abroad.

Responsible: — Claudia Emde

Ground-based remote sensing: Cloud and aerosol properties from simple polarized observations

Aim of the thesis is to use an existing off-the-shelf camera system to determine the degree of polarization of sky and clouds and to study how much information about cloud cover, optical thickness, cloud phase, droplet size, width of the size distribution, etc. can be obtained from such observations. At MIM we have a digital camera equipped with a polarizer. This work is meant as a pre-study for the cloud spectrometer which could be equipped with polarization capabilities in the future. Raw data of the camera system has to be used to determine the degree of polarization. Advantage of this quantity - which is a ratio of several images - is that there is no need for absolute calibration of the camera pictures. Questions to be answered: How accurate is the derived degree of polarization? Can we detect the thermodynamic phase of clouds from polarization images of their flanks or bottoms? Can we derive aerosol optical thickness or aerosol type from the clear sky?

Claudia Emde, Tobias Zinner

Sun photometer: Microphysical inversion

Data sets of our SSARA-radiometer (multi-spectral radiances: direct sun, diffuse sky) are available from the almucatar viewing geometry. Adapt the Nakajima inversion code (SKYRAD) for SSARA measurements and determine microphysical properties, e.g., size distribution. Perform sensitivity studies and determine uncertainties. Compare the results with well established inversion schemes (e.g., AERONET) for selected days.

This work would constitute a big progress in the exploitation of not only the SSARA data, but also for the SSARA-Z at the Schneefernerhaus. Currently, we only determine the aerosol optical depth; so the extension towards microphysical properties would be of longterm benefit.

Responsible: Matthias Wiegner

Ceilometer: Spatial and temporal variability of aerosol and cloud parameters

Backscatter signals of ceilometers of the „Ceilonet“ of the German Weather Service can be provided for several stations and years. They shall be used to determine boundary layer heights, cloud base heights and sort of a cloud cover (in contrast to the conventional cloud cover that considers the whole hemisphere every few hours, a ceilometer measures continuously in zenith direction). Determine and compare local climatologies of different cloud- and aerosol parameters at different sites, and with independent data sets, e.g. satellite based climatologies (literature) or numerical models.

Responsible: Matthias Wiegner

Application of a new gridding method on OMI satellite data

Recently Prof. Wenig’s group developed a new gridding method that can map satellite data on a grid to produce concentration maps with a significantly more realistic distribution of the shown trace gas. Currently most gridding methods plot the concentrations measured by the satellite instrument as constant values within the boundary of the ground pixel, so called tiles. This approach produces unrealistic edges and jumps and makes it very difficult to analyze high resolution details in the maps.

The new method uses piecewise polynomial splines under the constraint that it can reproduce measurement values when integrated over the satellite’s ground pixel. This approach is called histopolation and allows the generation of grids with a higher resolution than sampled by the satellite.

The goal of this thesis is to use this approach to generate high resolution concentration maps from OMI (Ozone Monitoring Instrument) measurements in order to analyze spatial patterns of cities. Because of the large number of measurements available (the instrument was launched into orbit in 2004) the data can be filtered for different meteorological conditions (weather, cloud cover, viewing geometry, etc.). If the data is sorted for the days of the week for example, emission patterns can be made visible.

This thesis is part of a collaboration with Prof. Cohen, University of California, Berkeley, with the aim to develop a new satellite data product using OMI data in combination with high resolution ancillary data e.g. high resolution ground albedo and the histopolation gridding method as the final step.

This thesis involves a short stay at Prof. Cohen’s group at Berkeley.

The project includes the following steps:

  1. Familiarization with the OMI instrument and the retrieval algorithm, as well as the new gridding method
  2. Application of the gridding method on 11 years of OMI NO2 data and determining optimal tuning parameters of the algorithm in terms of spatial and temporal resolution
  3. Visualization and analysis of the weekly NO2 cycles for source type determination

contact: Mark Wenig

Imaging DOAS

This project is about the interpretation of differential optical absorption spectroscopy (DOAS) measurements in an imaging setup in order to determine the horizontal and vertical distribution of NO2 concentrations in cities. DOAS uses differential absorption structures of different trace gases like ozone or NO2 to derive their concentrations from spectral measurements. The DOAS method can be applied in different setups, both in an active and a passive mode, depending on whether an artificial light source or the sun light which had been scattered and partly absorbed in the earth’s atmosphere is used. In this setup the telescope of the instrument can be pointed in different directions and can generate an image of so called slant column densities when scanning in two dimensions (called imaging DOAS). Slant column densities represent concentrations integrated along all possible light paths. Those light paths have to be simulated using a radiative transfer model in order to interpret the slant column densities derived for a given scene correctly. Since the measurement setup aims at measuring NO2 concentrations in cities, the 3D radiative transfer model has to be able to include the geometry of buildings and other objects within the field of view, so the model to be used, MYSTIC, has to be extended accordingly.

The project includes the following steps:

  1. Familiarization with the 3D radiative transfer model MYSTIC
  2. Extending the model to include vertical surfaces with a defined albedo
  3. Modeling the building forming the observed scene (e.g. the Hong Kong skyline) to include in the MYSTIC simulation
  4. Learn the basics of DOAS
  5. Retrieval of slant column densities of already existing DOAS measurements using standard DOAS software
  6. Combining the DOAS results with the model output to form a consistent image of concentrations.

Responsible: Mark Wenig and Claudia Emde

Estimation of visibility from image sequences

In this project image sequences have to be analyzed in order to derive visibility range information. Different landmarks at different distances from the camera, e.g. high-rise building or church spires, can be used to derive optical parameters that depend on the visibility. Those parameters could be the local variability or the difference of the intensity of the object compared to the view in the sky close to the object, and can be compared to aerosol optical depths that have been measured at the same time.

The project includes the following steps:

  1. Automatic adjustment of the images from the sequence in case the camera shifted
  2. Chose useful objects in the field of view
  3. Determine intensity differences between objects and the sky
  4. Derive local structure parameters, e.g. local variability
  5. Explore further optical parameters using digital image processing operators
  6. Analysis of the dependency of the derived parameters on aerosol optical depths measured independently
  7. Simulation of the optical parameters using a radiative transfer model and comparison with parameters derived from the image sequence
  8. Installation of more cameras and implementation of a real-time evaluation

Responsible: Mark Wenig and Matthias Wiegner

Development of a dust resuspension module in a chemistry-transport-model

Fine particulate matter („Feinstaub“) is a major air quality hazard, especially in urban settings like Munich. Numerical models have been developed to understand the sources and transformation of particles in the atmosphere, and to develop efficient mitigation strategies. These regional or global scale models are based on numerical weather prediction models (like WRF or COSMO) and were extended by a description of particulate matter and trace gases. Particulate matter, its size distribution and chemical composition, is a prognostic quantity in such models they hence describe its complete lifecycle from emission (think Diesel exhaust) to deposition on surfaces (the dirt on your window sill). Currently those models do not consider that the dust deposited might be resuspended (e.g. through traffic). In this work you would develop a module to consider the resuspension of dust depending on factors like wind speed, relative humidity, precipitation and location which could then be implemented in chemistry-transport-models like WRF-Chem. Depending on your interests you could evaluate your developments on the regional to continental scalem but also on the local scale to estimate the effect of this paramterization on curbside measurements of particulate matter concentrations.

Responsible: Christoph Knote

Satellite remote sensing: Simulation of cloudbow and glory for MSG/SEVIRI

Particular optical phenomena like the cloudbow and the glory can be exploited for the investigation of cloud properties that are usually not accessible using passive optical measurements. However, they probably require constant cloud optical properties over large areas or high spatial resolution measurements. The SEVIRI radiometer aboard the geostationary Meteosat Second Generation (MSG) satellite has a sampling distance of 3 km at the subsatellite point and has therefore a rather coarse spatial resolution.

Aim of this thesis is the realistic simulation of SEVIRI radiances for these special sun-satellite geometries in order to check whether cloud properties derived from SEVIRI are sensitive to these phenomena.

Responsible: Luca Bugliaro

Satellite remote sensing: Retrieval of cirrus cloud properties from MODIS using a variational approach

Cirrus clouds play an important role for climate since they can have both a positive and a negative radiative forcing. Nevertheless, the understanding of the physical processes that govern their formation and evolution is still poorly understood, as is their representation in climate models. To this end, satellite instruments provide an irreplaceable way to study their properties at the global scale. The Moderate Resolution Imaging Spectroradiometer MODIS aboard the NASA polar orbiting satellites Aqua and Terra, with its 36 spectral channels and its high spatial resolution of 250 m, 500 m and 1 km, enables the determination of macrophysical, optical and microphysical cirrus cloud parameters in great detail. In particular, from solar measurements it is possible to derive cirrus cloud optical thickness and effective particle size information.

Goal of this thesis is the adaption of a physically based variational algorithm originally developed for the remote sensing of greenhouse gases and aerosols to cirrus clouds. The method derives the desired optical properties by minimising the differences between the observations and a radiative transfer model, used to simulate MODIS solar radiances, by means of an inversion procedure, the Philips–Tikhonov regularisation scheme. This approach has the advantage of producing detailed uncertainty measures and can be easily extended to consider additional quantities and/or additional input parameters.

The thesis will be conducted at DLR Oberpfaffenhofen near Munich.

Responsible: Luca Bugliaro and Andre Butz


Alte Themen, usw.


Juni 2016