A Solar Radiation Parameterization for Atmospheric Studies

The solar radiation parameterization (CLIRAD-SW) developed at the Goddard Climate and Radiation Branch for application to atmospheric models are described. It includes the absorption by water vapor, O3, O2, CO2, clouds, and aerosols and the scattering by clouds, aerosols, and gases. Depending upon the nature of absorption, different approaches are applied to different absorbers. In the ultraviolet and visible regions, the spectrum is divided into 8 bands, and single O3 absorption coefficient and Rayleigh scattering coefficient are used for each band. In the infrared, the spectrum is divided into 3 bands, and the k-distribution method is applied for water vapor absorption. The flux reduction due to O2 is derived from a simple function, while the flux reduction due to CO2 is derived from precomputed tables. Cloud single-scattering properties are parameterized, separately for liquid drops and ice, as functions of water amount and effective particle size. A maximum-random approximation is adopted for the overlapping of clouds at different heights. Fluxes are computed using the Delta-Eddington approximation

Use of airs and modis thermal infrared channels to retrieve ice cloud properties

In this study, we use thermal infrared channels to retrieve the optical thickness and effective particle radius of ice clouds. A physical model is used in conjunction with Atmospheric Infrared Sounder (AIRS) temperature and water vapor profiles to simulate the top-of-atmosphere (TOA) brightness temperatures (BTs) observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) for channels located at 8.5, 11.0, and 12.0 õm (1176, 909, and 833 cm-1). The model is initially validated by comparing simulated clear-sky BTs to MODIS-observed clear-sky BTs. We also investigate the effect of introducing a +3 K bias in the temperature profile, a +3 K bias in the surface temperature, and a +20% bias in the water vapor profile in order to test the sensitivity of the model to these inputs. For clear-sky cases, the simulated TOA BTs agree with MODIS to within 2-3 K. The model is then extended to simulate thermal infrared BTs for cloudy skies, and we infer the optical thickness and effective radius of ice clouds by matching MODIS-observed BTs to calculations. The optical thickness retrieval is reasonably consistent with the MODIS Collection 5 operational retrieval for optically thin clouds but tends to retrieve smaller particle sizes than MODIS

A Fast Vector Radiative Transfer Model for Polarimetric Remote Sensing

Polarimetric remote sensing technologies have been demonstrated to be irreplaceable and effective for inferring cloud, aerosol, and ocean properties. To infer atmospheric and oceanic constituent properties from observational data, an efficient and accurate retrieval algorithm is needed. The accuracy and efficiency of the retrieval algorithm depends on the radiative transfer model (RTM) used in the forward calculations involved in implementing the retrieval algorithm. If a radiative transfer calculation is implemented in-line as part of a retrieval algorithm, rather than simply generating and interpolating from a look-up table, the atmospheric profiles and surface properties can be directly incorporated into the retrieval system to improve accuracy. Some interpolation errors can also be avoided. However, an in-line radiative transfer calculation usually does not satisfy computational efficiency requirements for an operational remote sensing application. To fully exploit the capability of satellite polarimetric instruments, it is imperative to develop an accurate and fast vector RTM. The reported research develops a fast vector RTM in support of atmospheric and oceanic polarimetric remote sensing. This model is capable of simulating the Stokes vector observed at the top of the atmosphere and at the terrestrial surface by considering absorption, scattering, and emission in the atmosphere and ocean. Gas absorption is parameterized in terms of gas concentration, temperature, and pressure. The parameterization scheme uses a regression method and can be easily applied to an inhomogeneous atmospheric path. An efficient two-component approach combining the small-angle approximation and the adding-doubling method is utilized to solve the vector radiative transfer equation (RTE). The thermal emission source is approximated as a linear function of optical thickness in homogeneous layers. Based on this approximation, the thermal emission component of the RTE solution can be obtained by an efficient doubling process. The air-sea interface is treated as a wind-ruffled rough surface in the model to mimic a realistic ocean surface. Several bio-optical models are introduced to model ocean inherent optical properties. It is shown that the developed RTM can be used in a retrieval algorithm by comparing the simulation results with observations by POLDER and MODIS satellite instruments

Satellite-based Cloud Remote Sensing: Fast Radiative Transfer Modeling and Inter-Comparison of Single-/Multi-Layer Cloud Retrievals with VIIRS

This dissertation consists of three parts, each of them, progressively, contributing to the problem of great importance that satellite-based remote sensing of clouds. In the first section, we develop a fast radiative transfer model specialized for Visible Infrared Imaging Radiometer Suite (VIIRS), based on the band-average technique. VIIRS, is a passive sensor flying aboard the NOAA’s Suomi National Polar-orbiting Partnership (NPP) spacecraft. This model successfully simulates VIIRS solar and infrared bands, in both moderate (M-bands) and imagery (I-bands) spatial resolutions. Besides, the model is two orders of magnitude faster than Line-by-line & discrete ordinate transfer (DISORT) method with a great accuracy. The second and third parts are going to investigate the retrieval of single-/multi- layer cloud optical properties, especially, cloud optical thickness (τ) and cloud effective particle size (De) with different methods. By presenting the comparison between results derived from VIIRS measurements and benchmark products, potential applications of Bayesian and OE retrieval methods for cloud property retrieval are discussed. It has proved that Bayesian method is more suitable for single-layer scenarios with fewer variables with fast speed, while Optimal Estimation method is superior to Bayesian method for more complicated multi-layer scenarios

Anwendungen zur Abschätzung des Strahlungseinflusses von Aerosolen

The aim of this PhD research is to contribute to a better estimation of the radiation budget of the Earth and the atmosphere by delving into the further understanding of physical phenomena of the atmosphere. The studied phenomena are the atmospheric radiative transfer and aerosols. The radiative transfer code MOMO (Matrix Operator Model) has been extended from shortwave [0.2 – 4 μm] to the full spectral range [0.2 – 100 μm] in order to obtain a versatile radiative transfer code that can be used for different radiative transfer studies (e.g. inversion of remote sensing measurements, optimization and calibration of measurement instruments and methods, estimation of radiative transfer fluxes, estimation of radiative forcings and heating rates), with different exigencies of precision and rapidity and over the full spectral range. The extension of MOMO to the full range consisted of the integration of the emission of thermal infrared radiation by gases, aerosols and clouds into the matrix operator algorithm of the code. The extension of MOMO also required the development of a spectroscopy module for the modeling of the water vapor continuum of absorption in the thermal infrared. In MOMO, the gas transmission for spectral bands is modeled by means of a k-distribution method. This k-distribution algorithm has also been extended to the thermal infrared and now includes the gas emission of radiation. In a second step, MOMO has been applied in a study on the contribution of aerosols to the radiation budget. This application has been carried out in 3 steps: 1) The characterization of the aerosols by means of observations on a regional scale (measurement campaign or spaceborne measurements). 2) The development of a radiative transfer scheme with radiative transfer code MOMO in its full range version. 3) The estimation of the radiative fluxes and of instant aerosol radiative forcings and heating-rates. The results of this work demonstrate the importance of the instrumental synergy of in-situ measurements and lidar remote sensing for the characterization of aerosol microscopic properties (refractive index and size distribution). The latter method was applied to aerosols in the Mediterranean basin within the measurement campaign TRAQA. The results have revealed the differences between pollution aerosols and desert dust aerosols regarding their microscopic and radiative properties. Further case studies have shown that the presence of clouds below the aerosols has a decisive influence on the sign and on the order of magnitude of aerosol direct radiative forcing.Das Ziel dieser Doktorarbeit ist das Verständnis von physikalischen atmosphärischen Phänomenen zu vertiefen, um eine bessere Abschätzung der Strahlungsbilanz zu erhalten. Die Phänomene, die untersucht wurden sind der Strahlungstransport in der Atmosphäre und die Aerosole. Das Strahlungstransportprogramm MOMO (Matrix-Operator Method) wurde vom kurzwelligen Spektralbereich [0.2 – 4 μm] zum gesamten Spektralbereich [0.2 – 100 μm] erweitert. Dadurch erhielten wir ein Programm, das für Strahlungstransportsimulierungen unterschiedlicher Art und ohne spektrale Einschränkung verwendet werden kann. Die Erweiterung des Spektralbereiches MOMOs besteht in der Implementierung der Strahlungsemission von Gasen, Aerosolen und Wolken in den Matrix-Operator Algorithmus des Programms. Für die Erweiterung des Programms zum langwelligen Spektralbereich wurde auch ein spektroskopisches Modul entwickelt, um das Absorptionskontinuum von Wasserdampf im thermischen infraroten Spektralbereich zu modellieren. Innerhalb von MOMO wird die Transmission von Gasen für breite Spektralbände anhand einer sogenannten „k-Verteilung Methode“ modelliert. Des Weiteren wurde der k-Verteilungsalgorithmus MOMOs zum thermischen Infrarot erweitert, um die Strahlungsemission von Gasen zu berücksichtigen. In dieser Arbeit wurde MOMO verwendet, um den Beitrag der Aerosole zur Strahlungsbilanz abzuschätzen. Die Studie wurde in 3 Schritten durchgeführt: 1) Die Charakterisierung der Aerosole anhand von Beobachtungen auf der regionalen Skala (aus Messkampagnen oder Satellitendaten). 2) Die Entwicklung eines Schemas zur Strahlungssimulation mit der neuen Version MOMOs als Kern. 3) Die Abschätzung der Strahlungsflüsse und des Strahlungsantriebes und der Heizrate der Aerosole. Die Ergebnisse dieser Studie zeigen wie effizient die Synergie von in-situ Messungen und LIDAR-Messungen für die Charakterisierung der mikroskopischen Eigenschaften der Aerosole ist. Diese Methode wurde innerhalb der Messkampagne TRAQA (Aerosole in der Region des Mittelmeeres) zur Datenauswertung verwendet. Die Ergebnisse zeigen große Unterschiede zwischen Verschmutzungsaerosolen und Wüstenaerosolen bezüglich ihrer mikroskopischen Eigenschaften und Strahlungseigenschaften. Weitere Fallstudien in dieser Arbeit haben gezeigt, dass Wolken unter Aerosolschichten einen entscheidenden Einfluss auf sowohl das Vorzeichen als auch den Betrag des Strahlungsantriebes der Aerosole haben

Modeling and Simulation in Engineering

This book provides an open platform to establish and share knowledge developed by scholars, scientists, and engineers from all over the world, about various applications of the modeling and simulation in the design process of products, in various engineering fields. The book consists of 12 chapters arranged in two sections (3D Modeling and Virtual Prototyping), reflecting the multidimensionality of applications related to modeling and simulation. Some of the most recent modeling and simulation techniques, as well as some of the most accurate and sophisticated software in treating complex systems, are applied. All the original contributions in this book are jointed by the basic principle of a successful modeling and simulation process: as complex as necessary, and as simple as possible. The idea is to manipulate the simplifying assumptions in a way that reduces the complexity of the model (in order to make a real-time simulation), but without altering the precision of the results

Rigorous Testing of the Rapid Radiative Transfer Model Across the Infrared Spectrum

Global circulation models (GCMs) and climate simulations often use radiative fluxes and heating rates from radiative transfer models. However, the calculations that are used are those where scattering of a cloudy atmosphere is neglected. In this study, computed fluxes and heating rates are compared when absorption is the only process, and when scattering is included. Computations for the absorption only process were performed using the Rapid Radiative Transfer Model (RRTM), and the Discrete Ordinates Radiative Transfer Model (DISORT) is used when scattering is included. Over 8,000 model runs were conducted across various cloud layers, cloud water paths, cloud particle sizes, cloud particle shapes, and atmospheric profiles to deduce the effects of scattering in the infrared (IR) portion of the electromagnetic spectrum due to clouds. On average, the difference in upward flux at the top of the atmosphere (TOA) was roughly 4-12 W/m^2 and difference in downward flux at the surface (SFC) was roughly 1- 4 W/m^2. These differences were found mainly in the middle portion of the IR spectrum, although some instances were found to be close to the far IR portion of the spectrum as well. As mentioned in other similar studies, these numbers are significant when compared to average longwave radiation budget values. Neglecting them could lead to inaccurate calculations in GCMs and climate simulations. Similar tests were also computed when carbon dioxide was doubled in the atmosphere. Results show that the differences in fluxes compared to an atmosphere with current carbon dioxide values was less than 0.5 W/m^2

Modeling Atmosphere-Ocean Radiative Transfer: A PACE Mission Perspective

The research frontiers of radiative transfer (RT) in coupled atmosphere-ocean systems are explored to enable new science and specifically to support the upcoming Plankton, Aerosol, Cloud ocean Ecosystem (PACE) satellite mission. Given (i) the multitude of atmospheric and oceanic constituents at any given moment that each exhibits a large variety of physical and chemical properties and (ii) the diversity of light-matter interactions (scattering, absorption, and emission), tackling all outstanding RT aspects related to interpreting and/or simulating light reflected by atmosphere-ocean systems becomes impossible. Instead, we focus on both theoretical and experimental studies of RT topics important to the science threshold and goal questions of the PACE mission and the measurement capabilities of its instruments. We differentiate between (a) forward (FWD) RT studies that focus mainly on sensitivity to influencing variables and/or simulating data sets, and (b) inverse (INV) RT studies that also involve the retrieval of atmosphere and ocean parameters. Our topics cover (1) the ocean (i.e., water body): absorption and elastic/inelastic scattering by pure water (FWD RT) and models for scattering and absorption by particulates (FWD RT and INV RT); (2) the air-water interface: variations in ocean surface refractive index (INV RT) and in whitecap reflectance (INV RT); (3) the atmosphere: polarimetric and/or hyperspectral remote sensing of aerosols (INV RT) and of gases (FWD RT); and (4) atmosphere-ocean systems: benchmark comparisons, impact of the Earth's sphericity and adjacency effects on space-borne observations, and scattering in the ultraviolet regime (FWD RT). We provide for each topic a summary of past relevant (heritage) work, followed by a discussion (for unresolved questions) and RT updates

The FORUM end-to-end simulator project: architecture and results

FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) will fly as the ninth ESA's Earth Explorer mission, and an end-to-end simulator (E2ES) has been developed as a support tool for the mission selection process and the subsequent development phases. The current status of the FORUM E2ES project is presented together with the characterization of the capabilities of a full physics retrieval code applied to FORUM data. We show how the instrument characteristics and the observed scene conditions impact on the spectrum measured by the instrument, accounting for the main sources of error related to the entire acquisition process, and the consequences on the retrieval algorithm. Both homogeneous and heterogeneous case studies are simulated in clear and cloudy conditions, validating the E2ES against appropriate well-established correlative codes. The performed tests show that the performance of the retrieval algorithm is compliant with the project requirements both in clear and cloudy conditions. The far-infrared (FIR) part of the FORUM spectrum is shown to be sensitive to surface emissivity, in dry atmospheric conditions, and to cirrus clouds, resulting in improved performance of the retrieval algorithm in these conditions. The retrieval errors increase with increasing the scene heterogeneity, both in terms of surface characteristics and in terms of fractional cloud cover of the scene

Modeling Atmosphere-Ocean Radiative Transfer: A PACE Mission Perspective

The research frontiers of radiative transfer (RT) in coupled atmosphere-ocean systems are explored to enable new science and specifically to support the upcoming Plankton, Aerosol, Cloud ocean Ecosystem (PACE) satellite mission. Given (i) the multitude of atmospheric and oceanic constituents at any given moment that each exhibits a large variety of physical and chemical properties and (ii) the diversity of light-matter interactions (scattering, absorption, and emission), tackling all outstanding RT aspects related to interpreting and/or simulating light reflected by atmosphere-ocean systems becomes impossible. Instead, we focus on both theoretical and experimental studies of RT topics important to the science threshold and goal questions of the PACE mission and the measurement capabilities of its instruments. We differentiate between (a) forward (FWD) RT studies that focus mainly on sensitivity to influencing variables and/or simulating data sets, and (b) inverse (INV) RT studies that also involve the retrieval of atmosphere and ocean parameters. Our topics cover (1) the ocean (i.e., water body): absorption and elastic/inelastic scattering by pure water (FWD RT) and models for scattering and absorption by particulates (FWD RT and INV RT); (2) the air-water interface: variations in ocean surface refractive index (INV RT) and in whitecap reflectance (INV RT); (3) the atmosphere: polarimetric and/or hyperspectral remote sensing of aerosols (INV RT) and of gases (FWD RT); and (4) atmosphere-ocean systems: benchmark comparisons, impact of the Earth’s sphericity and adjacency effects on space-borne observations, and scattering in the ultraviolet regime (FWD RT). We provide for each topic a summary of past relevant (heritage) work, followed by a discussion (for unresolved questions) and RT updates