1,722,612 research outputs found
Introduction to airborne measurements of the Earth atmosphere and surface
No full textThe article describes in general terms concepts of airborne measurements of the Earth atmosphere and surface. This includes: application types, range of operations, examples of research aircraft, design of instrumentation, sampling techniques, accommodation to environmental conditions, operation in turbulence, navigation, safety, campaign planning, data processing, intercomparison flight
Five-day backwards trajectories at one minute resolution along the flight tracks of the Polar 6 research aircraft during BACSAM II
No full textThe BACSAM II Arctic airborne campaign took place in spring 2024. It involved the Polar 6 research aircraft stationed in Longyearbyen on Svalbard. Polar 6 was equipped with a wide range of in-situ instruments to measure meteorological and aerosol properties in the Arctic atmosphere around Svalbard and the Fram Strait. In order to understand the origin of air masses sampled by Polar 6, this dataset here was created as follows. For all research flights, every one minute along the flight track and at the coordinates and pressure altitude of Polar 6, one air mass was initialized using the the trajectory calculation tool Lagranto in conjunction with wind fields from the ERA5 reanalysis. Latter has an output resolution of around 30 km and one hour. The hourly data was bi-linearly interpolated to one minute resolution. Trajectories were then calculated five days backwards in one minute steps. Several parameters were traced along the trajectories, based on ERA5 output: Surface pressure, geopotential altitude, atmospheric boundary-layer height, air temperature, specific humidity, sea-ice concentration, and cloud liquid/ice/rain/snow water contents. Thus, it is possible to investigate the origin of the sampled air masses, as well as to estimate the relevant air-mass transformations and cloud processes they underwent during transport towards Polar 6
Five-day backwards trajectories at one minute resolution along the flight tracks of the Polar 6 research aircraft during BACSAM I
No full textThe BACSAM I Arctic airborne campaign took place in autumn 2022. It involved the Polar 6 research aircraft stationed in Longyearbyen on Svalbard. Polar 6 was equipped with a wide range of in-situ instruments to measure meteorological and aerosol properties in the Arctic atmosphere around Svalbard and the Fram Strait. In order to understand the origin of air masses sampled by Polar 6, this dataset here was created as follows. For all research flights, every one minute along the flight track and at the coordinates and pressure altitude of Polar 6, one air mass was initialized using the the trajectory calculation tool Lagranto in conjunction with wind fields from the ERA5 reanalysis. Latter has an output resolution of around 30 km and one hour. The hourly data was bi-linearly interpolated to one minute resolution. Trajectories were then calculated five days backwards in one minute steps. Several parameters were traced along the trajectories, based on ERA5 output: Surface pressure, geopotential altitude, atmospheric boundary-layer height, air temperature, specific humidity, sea-ice concentration, and cloud liquid/ice/rain/snow water contents. Thus, it is possible to investigate the origin of the sampled air masses, as well as to estimate the relevant air-mass transformations and cloud processes they underwent during transport towards Polar 6
Radiative energy budget, cloud radiative forcing, LWP, and cloud-free albedo derived from airborne broadband irradiance observations during AFLUX flight on 11 April 2019 (subset)
No full textLongwave and shortwave radiative energy budget components derived from broadband irradiance observations during the Airborne measurements of radiative and turbulent FLUXes of energy and momentum in the Arctic boundary layer (AFLUX) campaign north of Svalbard in March / April 2019. This dataset contains a subset of the entire AFLUX dataset (which will be made available later) and represents a section during the 11 April 2019 flight. This dataset contains different parameters relevant for the included estimates of cloud radiative forcing, like a cloud equivalent liquid water path equivalent derived from the shortwave transmissivity, or a cloud-free albedo estimate during cloudy observations. Details are provided in the header and doi:10.5194/acp-20-9895-202
Radiative Effect of Mixed Mineral Dust and Biomass Burning Aerosol in the Thermal Infrared
Full text linkThis thesis treats the optical properties of mixed mineral dust and biomass burning aerosol in the thermal infrared (TIR) based on Fourier Transform infrared spectrometer (FTIR) measurements and radiative transfer simulations. The measurements were part of the Saharan Mineral Dust Experiment 2 (SAMUM-2) conducted from January to February 2008 at Praia, Cape Verde. The large amount of different instruments co-located at the main field site during the campaign resulted in a unique dataset comprising in-situ information and remote sensing data perfectly suited for column closure studies. The ultimate goal of this work is to investigate the consistency of microphysical and TIR remote sensing data. This is achieved by reproducing the measured radiances at top and bottom of the atmosphere (TOA, BOA) with a radiative transfer model, which assimilates the microphysical aerosol information gathered during SAMUM-2.
The first part of the thesis describes several experimental efforts, including a novel calibration method and a drift correction algorithm for the ground-based FTIR instrument operated within the scope of SAMUM-2 by the author. The second part introduces the concurrent radiative transfer library PIRATES, which has been developed in the framework of this thesis for the analysis of TIR aerosol optical properties. The third and final part of the treatise compares measured and simulated spectra for various typical scenarios encountered during SAMUM-2.
It is demonstrated in three case studies, that measured radiances in the TIR atmospheric window region (8-12 µm) can be reproduced at BOA and TOA by radiative transfer simulations assuming spheroidal model particles. Moreover,
spherical particles are shown to be an inadequate model for mineral dust aerosol
in this spectral region unless the aerosol optical depth is small
A study of Arctic sea-ice surface albedo and its uncertainty: impact of varying insolation and instrument characteristics
No full textThe Arctic sea-ice surface albedo is observed by ground-based, airborne, and satellite instruments. However, the observed albedo is influenced by varying insolation, instrument characteristics, and associated retrieval processes. This thesis quantifies these influences, develops and improves corrective schemes, and gives recommendations to increase the accuracy of the surface broadband albedo products. The analysis is based on simulations with the radiative transfer model SCIATRAN. A single-scattering property database of nine ice crystal habits is implemented into SCIATRAN to enable a realistic snow surface reflection. The associated far-field assumption of snow grains is justified. A comparison of simulated and measured reflectance factors and albedo spectra reveals discrepancies of usually less than 0.05, legitimating the utilized SCIATRAN set-up. The atmosphere decreases the black-sky surface broadband albedo by a RMSD of less than 0.04. An optically thin (thick) cloud additionally influences the albedo of up to a RMSD of 0.02 (0.06). The albedo from irradiance measuring devices suffers from the instrument’s cosine error (RMSD<0.15) and has to be corrected for by calibration factors (RMSD<0.03). The total uncertainty of the satellite broadband albedo (RMSD<0.26) is mainly controlled by the anisotropic correction (RMSD<0.25) and the narrow-to-broadband conversion (NTBC) (RMSD<0.09). New, most accurate NTBCs are developed (RMSD≤0.02). Applying those and the RossThick-LiSparseReciprocal or the modified Walthall model as angular correction almost halve the total satellite albedo uncertainty. The new NTBC improves the MERIS derived sea-ice surface broadband albedo by up to one third. Surface inhomogeneities also significantly affect the observed surface albedo. A seasonal comparison of the Arctic sea-ice surface broadband albedo from MERIS, CLARA-A2, and ERA5 reanalysis reveals RMSDs exceeding 0.10 which is partly due to the above-mentioned uncertainties
Der Einfluss von Wolken auf den Strahlungsantrieb der Erde
Full text linkThe aim of this study is to estimate radiative budgets and radiative effects by clouds onto the radiation balance of the earth. The estimation was performed at the surface, the top of the atmosphere and for the atmospheric column. In addition, the surface radiative fluxes have been simulated by the single column model ECHAM5.
The robust data base of the radiative measurements was set up along five cruises of the icebreaker POLARSTERN and the corresponding satellite remote sensing by MSG. A full sky imager for a rough offshore application was developed to derive the total cloud amount and the cloud type. Utilizing a microwave radiometer, the atmospheric temperature and humidity profiles as well as the liquid water path were measured continuously. The surface net budget is dominated by the solar radiative component with a mean value of 144W/m2, whereas the solar impact is high for cirrus and low for stratus. At the top of the atmosphere the solar fluxes are predominantly within the daily net budgets at tropical latitudes.
This results in a radiative forcing of 37W/m2. The atmospheric column shows a strong thermal emittance and a slight solar absorption. Its net heat loss amounts to a total of −100W/m2. The strongest surface cloud longwave effectswere determined in the presence of low level clouds. Clouds with a high optical density induce strong negative solar effects when the solar altitude is high. The mean surface net effect is −34W/m2. For the purpose of calculating the mean surface net effect, a new parametrization was created, considering the total cloud amount and the solar zenith angle. At the top of the atmosphere the clear sky radiative fluxes are approached inaccurately. The average atmospheric cloud effect is −3W/m2. Cirrus clouds have little atmospheric solar effects and strong longwave effects, thus cirrus is the only cloud type causing a heating of the climate. The atmospheric longwave effects are highly negative for optical thick low level clouds. Mean atmospheric solar effects are positive for each cloud type. The atmospheric net effect is −4W/m2.
Based on ECHAM5 simulations, the surface solar effects are about 20W/m2 higher than the measured effects. Surface longwave effects are simulated well. Under existence of cirrus and stratus the model physics with its single cloud layer works exactly. The surface solar effects of convective clouds, especially stratocumulus, show a large overestimation of up to 120W/m2
Radiance fields of clouds and the Arctic surface measured by a digital camera during HALO-(AC)3
No full textDuring the HALO-(AC)3 campaign performed in March/April 2022 a downward-looking commercial digital camera equipped with a 180° - fisheye lens was installed on the aircraft Polar 5. Images of the Arctic surface and clouds were taken every 4 - 6 seconds. The data set provides rectified fields of calibrated radiances along the flight track for the three spectral bands (red, green, and blue)
Solare Monte Carlo Strahlungstransportsimulationen in Saharastaubwolken
Full text linkRadiative fields of three-dimensional inhomogeneous Saharan dust clouds have been calculated at solar wavelengths by means of a Monte Carlo radiative transfer model.
Scattering properties are taken from measurements in the SAMUM campaigns, from light scattering calculations for spheroids based on the MISCHKA code, from Mie Theory for spheres and from the Geometric Optics Method assuming irregular shaped particles.
Optical properties of particles with different projected area equivalent shapes are compared.
Large differences in optical properties are found especially in the phase functions.
Modelled scattering properties are compared to laboratory measurements with good agreement.
Results of radiative transfer calculations based on the Monte Carlo Method are shown exemplarily for one dust cloud simulated by the cloud resolving atmospheric circulation model COSMO-MUSCAT.
Shape induced differences in the radiation fluxes are pronounced, for example, the domain averaged normalized radiance is about 20% lower in the case of a dust plume consisting of spheroids or irregular particles compared to spheres.
Further the modelled radiative fields are compared to simulated fields from COSMO-MUSCAT and to satellite measurements with the SEVIRI instrument onbord the MSG satellite.
In some cases the patterns of the radiative fields agree quiet well, especially with the simulated fields from COSMO-MUSCAT.
But because by uncertainties in particular in the input data, the modelled radiative fields do not agree very well with most of the satellite measured fields.
The satellite measurements are also used to compare with the measured radiances from an aircraft.
There good agreements are found.
In the Monte Carlo radiative transfer calculations the horizontal photon transport can be switched of, which was used for investigations on its effect (3D-effect) on the reflected radiance fields.
The 3D-effect is only notable at the largest gradients in optical thickness.
For example, the reflectance at low sun position differs locally about 25% when horizontal photon transport is accounted for. 'Sharp edges' due to 1D calculations are smoothed out in the 3D case.Die solaren Strahlungsfelder einer dreidimensionalen Saharastaubwolke wurden mit einem Monte Carlo Strahlungstransportmodellberechnet.
Die benötigten Streueigenschaften wurden aus Messungen in den SAMUM Kampangen ermittelt und durch Lichtstreuberechnungen, für Spheroide basierend auf dem MISCHKA Code, für Kugeln mithilfe von Mie Theorie und mit der Methode der geometrischen Optik für irregulär geformte Teilchen ergänzt.
Die optischen Eigenschaften von Partikeln mit unterschiedlichen Formen aber gleichen Projektionsflächen wurden verglichen und es wurden besonders in den Streufunktionen deutliche Unterschiede fest gestellt.
Modellierte Streueigenschaften wurden mit Labormessungen verglichen und gute Übereinstimmungen konnten festgestellt werden.
Die Ergebnisse der Strahlungstransportrechnungen mit der Monte Carlo Methode wurden exemplarisch für eine Staubwolke gezeigt, die vom Wolken auflösenden athmosphärischen Zirkulationsmodell COSMO-MUSCAT simuliert wurde.
Ausgeprägte forminduzierte Unterschiede in den Strahlungsflüssen sind beispielsweise in den normierten Strahldichten, die über das Modellgebiet gemittelt wurden, vorhanden.
Bei einer Staubwolke aus elliptischen oder unregelmäßigen Teilchen sind diese ungefähr 20% kleiner als bei Staubwolken, die aus kugelförmigen Teilchen bestehen.
Weiterhin werden die modellierten Strahlungsfelder mit simulierten Feldern aus COSMO-MUSCAT und Satelliten-Messungen des MSG-Satelliten verglichen.
Vor allen mit den den simulierten Strahlungsfeldern aus COSMO-MUSCAT stimmen die Monte Carlo modellierten Felder gut überein.
Durch Unsicherheiten, insbesondere in den Eingabedaten, stimmen die modellierten Strahlungsfelder jedoch nicht sehr gut mit den vom Satelliten gemessenen Feldern überein.
Die Satelliten-Messungen werden auch verwendet, um sie mit den Radianzen aus Flugzeugmessungen zu vergleichen, wobei sich gute Übereinstimmungen ergaben.
In den Monte Carlo Strahlungstransportrechnungen kann der horizontale Photonentransport aus geschaltet werden. Dies wurde für Untersuchungen seines Einflusses (3D-Effekt) auf die reflektierten Strahldichtefelder eingesetzt.
Der 3D-Effekt ist nur an den größten Gradienten der optischen Dicke relevant.
Zum Beispiel unterscheidet sich das Reflexionsvermögen bei niedrigen Sonnenstand lokal um etwa 25%, wenn der horizontale Photonentransport berücksichtigt wird. "Scharfe Kanten" aufgrund der 1D Berechnungen werden in der 3D-Variante geglättet
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