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Earth observing instruments, such as those embarked on the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth's Radiant Energy System (CERES), have been used to monitor the arriving solar and the upwelling solar reflected and longwave emitted radiation from low Earth orbit for the past three decades. These instruments have played a crucial role in studying the Earth's radiation budget and developing a decadal climate data record. Prior to launch, these instruments go through several robust design phases followed by rigorous ground calibration campaigns to establish their baseline characterization spectrally, spatially, temporally, and radiometrically. The knowledge gained from building and calibrating these instruments has aided in technology advancements as the need for developing more accurate instruments has increased. In order to understand the prelaunch performance of these instruments, NASA's Langley Research Center (LaRC) has partnered with the Thermal Radiation Group at Virginia Tech to develop first-principle, dynamic electrothermal, numerical models of scanning radiometers that can be used to enhance the understanding of such instruments. The body of research presented here documents the construction of these models by highlighting their development and results and possible applications to the next generation of Earth radiation budget instrument. Much of the effort reported here is based on the author's contribution to NASA's now-deselected Radiation Budget Instrument (RBI) project. / Doctor of Philosophy / Earth Radiation Budget (ERB) sensors, such as the Earth Radiation Budget Experiment (ERBE) and the Clouds and the Earth's Radiant Energy System (CERES) have been a crucial part of studying the Earth's radiation budget for the past three decades. The Earth's radiation budget is the natural balance that exists between the energy received from the Sun and the energy radiated back into space. These instruments, which measure the radiative energy arriving and leaving at the top of the Earth's atmosphere, enhance understanding of the roles played by clouds and aerosols in reflecting and absorbing energy, thereby cooling or heating the planet. In order to enable the design for the next-generation Earth radiation budget sensors, NASA Langley has partnered with the Thermal Radiation Group at Virginia Tech to develop a capability for high-fidelity computer modeling that permits the complete characterization of an Earth radiation budget instrument. The resulting simulation consists of computer models for optical components, calibration targets, detecting elements and a source that includes information on anisotropy of a given Earth scene-type (clear vs. cloudy scene, ocean, desert, etc.). The modeling tool permits simulation of the entire science data stream as photons entering the instrument are converted to digital counts leaving the instrument, and provides the flexibility to observe various scene-types whether they be calibration targets or Earth scenes. This dissertation highlights the construction of this modeling tool and its capabilities as it is applied to NASA's now-deselected Radiation Budget Instrument.

Researchers at the NASA Langley Research Center (LaRC) are developing a next-generation instrument for monitoring the Earth radiation budget (ERB) from low Earth orbit. This instrument is called the DEMonstrating the Emerging Technology for measuring the Earth's Radiation (DEMETER) instrument. DEMETER is a candidate to replace the Clouds and Earth's Radiant Energy System (CERES) instruments which currently monitor the ERB. LaRC has partnered with the Thermal Radiation Group at Virginia Tech to model and evaluate the thermal and optical design of the DEMETER instrument. The effort reported here deals with the numerical modeling of the optical and thermal radiative performance the DEMETER instrument. The numerical model is based on the Monte Carlo Ray-Trace (MCRT) method. The major optical components of the instrument are incorporated into the ray-trace model using 3-D surface equations. A CAD model of the instrument baffle is imported directly into the ray-trace environment using an STL triangular mesh. The instrument uses a single freeform mirror to focus radiation on the detector. A method for incorporating freeform surfaces into a ray-trace model is described. The development and capabilities of the model are reported. The model is used to run several ray-traces to compare two different quasi-black surface coatings for the DEMETER telescope baffle. Included is a list of future tests the Thermal Radiation Group will use the model to accomplish. / Master of Science / For decades NASA has used satellite-mounted scientific instruments to monitor the Earth radiation budget (ERB). The ERB is the energy balance of the planet Earth with its surroundings. Radiation from the sun is absorbed and reflected by the Earth. The Earth also emits radiation. The balance between these heat transfer components drives the planetary climate. Researchers at the NASA Langley Research Center (LaRC) are developing a new instrument for monitoring the ERB from low Earth orbit. This Earth observing instrument is called the DEMonstrating the Emerging Technology for measuring the Earth's Radiation (DEMETER) instrument. NASA has partnered with the Thermal Radiation Group at Virginia Tech to model and evaluate the thermal and optical design of the DEMETER instrument. The effort reported here deals with the numerical modeling of radiation heat transfer in the DEMETER instrument. The numerical model uses the Monte Carlo Ray-Trace (MCRT) method to evaluate the thermal and optical behavior of the DEMETER instrument. The development and capabilities of the model are reported. The model is used to run a series of simulations to compare the performance of two different quasi-black surface coatings for the DEMETER telescope baffle. Included is a list of future tasks the Thermal Radiation Group will accomplish using the model.

The Thermal Radiation Group, a laboratory in the department of Mechanical Engineering at Virginia Polytechnic Institute and State University, is currently working towards the development of a new technology for cavity-based radiometers. The radiometer consists of a 256-element linear-array thermopile detector mounted on the wall of a mirrored wedge-shaped cavity. The objective of this research is to provide analytical and experimental characterization of the proposed radiometer. A dynamic end-to-end opto-electrothermal model is developed to simulate the performance of the radiometer. Experimental results for prototype thermopile detectors are included. Also presented is the concept of the discrete Green's function to characterize the optical scattering of radiant energy in the cavity, along with a data-processing algorithm to correct for the scattering. Finally, a parametric study of the sensitivity of the discrete Green's function to uncertainties in the surface properties of the cavity is presented. / Master of Science

Durch die Verbrennung von Biomasse werden Partikel freigesetzt, die u.a. schwarzen Kohlenstoff enthalten. Dieser ist wesentlich für die Absorption der solaren Strahlung in der Atmosphäre verantwortlich. Um den Effekt der emmitierten Partikel auf den Strahlungshaushalt quantifizieren zu können, ist die Kenntnis der physikalischen und chemischen Eigenschaften dieser Partikel nötig. Diese sind aber nur zum Teil bekannt. Dieser Bericht beschreibt eine Methode, die optischen Eigenschaften solcher Partikel unter Verwendung bestimmter Annahmen zu berechnen. Auÿerdem wird ein erster Vergleich zwischen berechneten Größen und Messungen aus Laborfeuern durchgeführt. / Biomass burning is an important source for particles containing black carbon, which is known as a strong light absorbing substance. To quantify the effect of such emitted particles on the radiation budget, the knowledge of their physical and chemical properties is necessary. Until now these properties are only partly known. In the following we describe a possibility of calculating the optical properties of such particles using certain simplifications. Also a first comparison between the calculated values and measurements from lab experiments is shown.

Le suivi journalier du bilan radiatif solaire est indispensable à l’étude des processus à l'interface sol-atmosphère, en particulier en climatologie et en hydrologie. Dans le cadre du projet CEOP-Aegis visant à étudier l'hydrologie du plateau du Tibet, cette thèse se concentre sur le développement d'une méthode permettant d’en estimer le bilan radiatif solaire de surface de façon quotidienne. Une série temporelle de flux radiatifs produite à partir de produits satellitaires existants met en évidence la nécessité d’intégrer la variabilité sous-pixel du terrain et des nuages pour les zones aussi hétérogènes que le Tibet. L’analyse de l’impact de la variabilité spatiale et temporelle des nuages sur le rayonnement solaire illustre le bénéfice lié à l’utilisation de la répartition des nuages plutôt que la fraction de nébulosité et l’importance d’une résolution temporelle élevée. Une méthode novatrice proposée pour la correction topographique sous-pixel montre que l’utilisation d’un modèle numérique de terrain à haute résolution spatiale améliore significativement l'estimation de l’éclairement ainsi que de l'albédo. Deux approches sont proposées pour améliorer l’estimation du bilan radiatif intégrant de manière adéquate l’hétérogénéité sous-pixel. / Monitoring the solar radiation budget on a daily basis is a prerequisite to study land surface processes, especially in climatology and hydrology. As part of the CEOP-Aegis project studying the hydrology of the Tibetan Plateau, this thesis focuses on developing a method to adequately estimate at-surface daily solar radiation budget over this particular area. A radiation budget time series produced based on existing satellite data products highlights the necessity to consider terrain and clouds sub-pixel variability when working over heterogeneous areas such as the Tibetan Plateau. The analysis of the impact of spatial and temporal variability of clouds on solar radiation demonstrates that the surface irradiance estimation would benefit from using cloud distribution instead of cloud fraction and the significance of high temporal resolution. A new sub-pixel topographic correction method is proposed and shows that using high resolution digital elevation model improves the irradiance as well as the albedo retrieval. Two approaches are proposed to improve solar radiation budget estimates taking into account adequately the sub-pixel heterogeneity.

Durch die Verbrennung von Biomasse werden Partikel freigesetzt, die u.a. schwarzen Kohlenstoff enthalten. Dieser ist wesentlich für die Absorption der solaren Strahlung in der Atmosphäre verantwortlich. Um den Effekt der emmitierten Partikel auf den Strahlungshaushalt quantifizieren zu können, ist die Kenntnis der physikalischen und chemischen Eigenschaften dieser Partikel nötig. Diese sind aber nur zum Teil bekannt. Dieser Bericht beschreibt eine Methode, die optischen Eigenschaften solcher Partikel unter Verwendung bestimmter Annahmen zu berechnen. Auÿerdem wird ein erster Vergleich zwischen berechneten Größen und Messungen aus Laborfeuern durchgeführt. / Biomass burning is an important source for particles containing black carbon, which is known as a strong light absorbing substance. To quantify the effect of such emitted particles on the radiation budget, the knowledge of their physical and chemical properties is necessary. Until now these properties are only partly known. In the following we describe a possibility of calculating the optical properties of such particles using certain simplifications. Also a first comparison between the calculated values and measurements from lab experiments is shown.

In this thesis, the radiative effect of Arctic clouds during early summer is investigated based on observations collected aboard the research vessel Polarstern during the expedition PS106 conducted in 2017 in combination with passive satellite observations. The interactions of clouds with radiation, and the relevance of several macro- and microphysical properties of clouds and surface conditions are analyzed. An investigation of the small-scale variability of solar radiation on an ice floe based on a network of autonomous pyranometers covering an area of 0.83 km x 1.59 km, and the period from 4-16 June 2017 is given. Five distinct sky conditions are identified, and the mean and variance of atmospheric transmittance of global radiation are determined. Using a wavelet-based multi-resolution analysis, a comparison of individual station records and spatially averaged observations indicates that the absolute magnitude and scale-dependence of variability contain characteristic features for different sky conditions. For overcast conditions, distinctive patterns are identified in the diurnal variability and spatial distribution of the network observations, presumably caused by multiple reflection radiation between surface and cloud base in combination with the inhomogeneous surface conditions. A sensitivity analysis of radiative fluxes is performed for clear-sky and cloudy conditions using a 1-dimensional radiative transfer model, and is used as a basis to investigate how well state-of-the-art shipborne and passive satellite remote sensing observations can constrain the radiative effect of clouds and can serve to quantify the Arctic radiation budget. Cloud properties derived from the shipborne remote sensing observations with the Cloudnet algorithm are used as input for radiative transfer simulations. Simulated fluxes are compared to shipborne observations of the downward-terrestrial and solar fluxes as well as satellite products from CERES (Clouds and the Earth's Radiant Energy System, SYN1deg Ed. 4.1) to test closure of simulated and observed radiative fluxes, and to analyse the cloud radiative effect. Closure is achieved for clear-sky conditions. Based on selected case studies and an analysis for the entire PS106 period, the largest discrepancies are identified for low-level stratus, precipitation and ice clouds. Moreover, the cloud radiative effect inferred along the cruise track is compared to the entire Arctic to expand the regional context, making use of the wide spatial coverage of the CERES products. The results indicate a strong contribution of the solar flux to the radiation budget for the study period. Due to the reduction of solar radiation by clouds, a cooling effect of -8.8 W/m² and -9.3 W/m² is found at the surface for the PS106 cruise and the central Arctic, respectively. The similarity of local and regional CRE suggests that the PS106 cloud observations can be considered as representative of Arctic cloud conditions during the early summer of 2017.:Contents 1 Introduction 1.1 Motivation 1.2 Characteristics of Arctic Clouds 1.3 Effect of Arctic Clouds on the Radiation Budget 1.4 Link Between Arctic Clouds and Surface Conditions 1.5 Objectives of (AC)3 and this Thesis 1.6 Outline 2 Theoretical Background 2.1 Radiative Quantities 2.2 Radiative Interactions 2.2.1 Absorption 2.2.2 Scattering and Extinction 2.3 Radiative Transfer Equation 2.4 Radiative Transfer in the Arctic 2.4.1 Surface Reflection and Transmission 2.4.2 Clear-sky Conditions 2.4.3 Optical Properties of Clouds 2.5 Radiative Transfer Modelling 2.5.1 Two-stream Approximation 2.5.2 Correlated k -distribution 2.5.3 RRTMG 2.6 Energy Budget and Cloud Radiative Effect 3 PS106 Expedition, Instrumentation, Data sets, and Methods 3.1 Instrumentation 3.1.1 Pyranometer Network 3.1.2 Ship-borne Instrumentation 3.2 Data sets 3.2.1 Cloudnet 3.2.2 CERES data set 3.2.3 Ancillary data set 3.3 General Conditions During PS106 3.3.1 Synoptic and Surface Conditions 3.3.2 Atmospheric Temperature and Humidity Conditions 3.3.3 Statistical Analysis of Cloud Properties 3.4 Radiative Transfer Simulation Setup 4 Sensitivity Analysis of Arctic Fluxes 4.1 Clear-sky Perturbations 4.1.1 Atmosphere 4.1.2 Surface 4.2 Clear-sky Radiative Flux Uncertainty 4.3 Cloud Perturbations 4.3.1 Cloud Water Path 4.3.2 Cloud Particle Effective Radius 4.3.3 Liquid Fraction and Surface Albedo 4.3.4 Cloud Base Height 4.3.5 Cloud Geometrical Thickness 4.4 Synopsis 5 Cloud Induced Spatiotemporal Variability of Solar Radiation 5.1 Data Analysis 5.1.1 Data Processing 5.1.2 Sky Classification 5.2 Case Studies 5.2.1 Clear-sky Case 5.2.2 Overcast Case 5.2.3 Thin Cloud Case 5.2.4 Multilayer Case 5.2.5 Broken Cloud Case 5.3 Wavelet-based Multiresolution Analysis 5.4 Synopsis and Discussion 6 Radiation Closure 6.1 Radiative Flux Comparison Between CERES and T-CARS 6.2 Radiative Closure for Clear-sky Atmosphere 6.3 Radiative Closure for Cloudy Atmosphere 6.4 Synopsis and Discussion 7 Case Studies 7.1 Clear-sky Case 7.2 Single and Multilayer Ice Cloud Case 7.3 Mixed Phase Cloud Case 7.4 Synopsis 8 Radiation Budget and Cloud Radiative Effects 8.1 Cloud Radiative Effect (CRE) Analysis 8.2 Radiation Budget 8.3 Synopsis 9 Summary, Conclusions and Outlook 9.1 Summary and Conclusions 9.2 Outlook Appendix A Cloud Microphysical Properties During PS106 B CRE of Sensitivity Analysis C CERES Aerosol Products D Additional Observations Literature List of Abbreviations List of Symbols List of Figures List of Tables Acknowledgements

Earth radiation budget instruments are devices designed to study global climate change. These instruments use telescopes embarked on low-earth-orbit satellites to measure Earth emitted and reflected solar radiation. Radiation is sensed as temperature changes caused by radiation absorbed during scans of the earth on a delicate gold-black coated detector. This work is part of a larger effort to develop an end-to-end dynamic electro-thermal model, based on first-principles, for the next generation of earth radiation budget instruments, the Radiation Budget Instrument (RBI). A primary objective of this effort is to develop a numerical model of the detector to be used on RBI. Specifically, the sensor model converts radiation arriving at the detector, collimated and focused through telescopes, into sensible heat; thereby producing a voltage. A mathematical model characterizing this sensor is developed. Using a MATLAB algorithm, an implicit finite-volume scheme is implemented to determine the model solution. Model parameters are tuned to replicate experimental data using a robust parameter estimation scheme. With these model parameters defined, the electro-thermal sensor model can be used, in conjunction with the remaining components of the end-to-end model, to provide insight for future interpretation of data produced by the RBI. / Master of Science

Two aspects of the study of the Earth radiation budget and the effects of clouds on our climate system are considered in this dissertation : instrumentation and data interpretation. Numerical models have been developed to characterize the optical/thermal-radiative behavior, the dynamic electrothermal response and the structural thermal transients of radiometric channels. These models, applied to a satellite-borne scanning radiometer, are used to determine the instrument point spread function and the potential for optical and thermal-radiative contamination of the signal due to out-of-field radiation and emission from the radiometer structure. The capabilities of the model are demonstrated by scanning realistic Earth scenes. In addition, the optical/thermal-radiative model is used for the development of an infrared field radiometer to interpret results from the experimental characterization of the instrument. The model allowed the sensitivity of the instrument response to assembly uncertainties to be determined. Data processing consists of converting radiometric data into estimates of the flux at the top of the atmosphere. Primary error sources are associated with the procedures used to compensate for unsampled data. The time interpolation algorithm applied to a limited number of observations can produce significantly biased estimates of monthly mean fluxes. A diurnal interpolation protocol using correlative ISCCP cloudiness data is developed to compensate for sparse temporal sampling of Earth radiation budget data. The bias is shown to be significantly reduced in regions where the variability of the cloud cover is well accounted for by ISCCP data. / Ph. D.