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.

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.

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

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.