Thesis (Ph. D.)--Brigham Young University. Dept of Electrical and Computer Engineering, 2006. / Includes bibliographical references (p. 115-121).

Thesis (Ph. D.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2004. / Includes bibliographical references (p. 161-167).

Thesis (Ph.D.)--University of Central Florida, 2009. / Adviser: W. Linwood Jones. Includes bibliographical references (p. 129-132).

Microwave radiometers are used to measure blackbody microwave emissions emitted by natural targets. Radiative transfer theory provides a well founded physical relationship between the atmosphere and surface geophysical parameters and the brightness temperature measured by these radiometers. The atmospheric brightness temperature is proportional to the integral of the microwave absorption of water vapor, oxygen, and liquid water between the top of the atmosphere and the surface. Inverse radiative transfer models use to retrieve the water vapor, cloud liquid and oxygen content in the atmosphere are very well known; however, the retrieval of rain rate in the atmosphere is still a challenge. This project presents a theoretical basis for the rain rate retrieval algorithm, which will be implemented in the Aquarius/SAC-D Microwave Radiometer (MWR). This algorithm was developed based on the radiative transfer model theory for a single layer atmosphere using four WindSat channels. Transmissivity due to liquid water (rain and cloud liquid water) is retrieved from the four channel brightness temperatures, and a statistical regression is performed to relate the rain rate, rain physical temperature and rain height to the liquid water transmissivities at 24 GHz and 37 GHz. Empirical validation results are presented using the WindSat radiometer observations.

The Microwave Radiometer (MWR) on the Aquarius/SAC-D mission measures microwave radiation from earth and intervening atmosphere in terms of brightness temperature (Tb). It takes measurements in a push-broom fashion at K (23.8GHz) and Ka (36.5 GHz) band frequencies using two separate antenna systems, each producing eight antenna beams. Pre-launch knowledge of the alignment of these beams with respect to the space-craft is used to geolocate the antenna footprints on ground. As a part of MWR’s on-orbit engineering check-out, the verification of MWR’s pointing accuracy is discussed here. The technique used to assess MWR’s pointing involved comparing the radiometer image of land with high-resolution maps. When the beam’s instantaneous field of view (IFOV) passes over a land water boundary, the brightness temperature changes from a radiometrically hot land scene to a radiometrically cold ocean scene. This "step-function" change in brightness temperature provides a very sensitive way to characterize the mispointing error of the MWR sensor antenna footprints. This thesis describes the algorithm used for the MWR geolocation calibration. MWR sensor observed boundaries are determined by the absolute maximum Tb slope location. A system of linear equations is produced for each sensor observed land/water crossing to determine the true intersection of the MWR track with the coastline. The observed and expected boundary locations are compared by means of an error distance. Results, presented for all eight beams of the three MWR channels, show that the mispointing error (standard deviations) are overall less than 15 km from the true coastline.

<p> A micrometeorological investigation was conducted over and within a crop of corn (Zea mays, var. Seneca Chief). The purpose of the experiment was to observe net radiation profiles within the canopy and to determine their behavior with respect to crop density. Discussion of the construction and evaluation of linear net radiometers for use in this study is included. The net radiation profiles are examined and compared with existing theoretical models. The form of the profiles is studied and a new model of net global radiation profiles based on micrometeorological data and crop parameters is discussed. </p> / Thesis / Master of Science (MSc)

The Earth Radiation Budget Experiment (ERBE) and the Clouds and Earth's Radiant Energy System (CERES) are systems that measure the earth's radiation budget, or the difference between earth-emitted radiation and radiation absorbed from the sun. Both these systems use three scanning radiometers based on a Cassegrain telescope design. Each of the three radiometers is sensitive in one of three wavelength intervals: shortwave, longwave, and total. A numerical model has been developed to investigate the radiative and optical characteristics of these instruments. The Monte-Carlo ray-trace method has been applied to the ERBE and CERES scanning radiometer instruments to calculate radiation exchange. In a radiative analysis, the surfaces of both instruments are found to emit a significant amount of radiation to the detector. In an optics analysis, both the ERBE and CERES instrument are found to have excellent directional selectivity. The field-of-view limits in the design of both instruments are verified using results from the optical analysis. / Master of Science

Virginia Tech has recently developed and constructed seven ground terminals for use in a propagation experiment employing the Advanced Communications Technology Satellite. This satellite was deployed by NASA in September of 1993. The ground terminals are used in the study of propagation effects caused by the atmosphere for 20 and 30 GHz signals. Each of these terminals contains one total power radiometer for each frequency. These radiometers are used to set clear sky attenuation reference levels for satellite beacon calibration. This thesis describes the design, implementation and testing of the radiometers built at Virginia Tech. In addition, a mathematical algorithm used for the prediction of clear sky attenuation along satellite paths is tested for correlation with radiometer predicted clear sky attenuation. Test data is compared to determine if the algorithm might serve as a radiometer replacement in future propagation experiments or other applications. / Master of Science

This paper discusses the total power radiometers in the propagation experiment at Virginia Tech using the OLYMPUS communications satellite. The experiment is set up to measure the received signal strength of beacons at 12.502, 19.770 and 29.656 GHz on board the OL YMPUS satellite in order to gather space-earth propagation statistics for a period of one year. The radiometers are used to set the clear sky reference levels for the beacon receivers. The paper begins with an overview of radio signal attenuation mechanisms, and a general discussion of radiometry. A description of the OLYMPUS radiometers follows, with sections on calibration techniques and the methods required to convert radiometer data into derived path attenuation for use in setting the clear air reference levels for the beacon receivers. Several novel techniques were used in the Virginia Tech radiometers including the use of voltage to frequency converters for integration purposes, and reference load calibration using a waveguide switch to swap the radiometer input from the antenna to a waveguide load of known and stable temperature. The penultimate chapter contains data recorded in the course of the experiment which was selected at random from the month of January 1991. The data is compared to corresponding free space beacon attenuation data and shows conclusively that the total power radiometer can produce highly accurate and stable attenuation measurements for extended periods of time. / Master of Science

In 1984, the Earth Radiation Budget Experiment (ERBE) was started by the National Aeronautics and Space Administration (NASA) to provide data to the meteorological community to predict long-term weather and climate trends. Three satellites employing nonscanning active cavity and scanning thermistor bolometer radiometers are orbiting the Earth to monitor its radiative emission. A numerical model has been formulated to better understand the performance of the ERBE scanning radiometer and to aid future radiometric design and calibration procedures. The Monte Carlo method is applied to the ERBE scanning radiometer to spectrally characterize its optical and radiative performance. The optical analysis reveals that the ERBE scanning radiometer design successfully limits the amount of energy that reaches the active sensor to the designated instrument field of view. Distribution factors between the diffuse-specular surfaces of the scanning radiometer are calculated using the Monte Carlo method and are then used to perform the radiative analysis. This analysis shows that less than three percent of the radiation emitted from the passive surfaces of the radiometer reaches the active sensor, an acceptable level for radiometric instrumentation used in space. / Master of Science