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Universiẗat, Diss., 2002--Bremen.

The Remote Sensing Group (RSG) at the University of Arizona performs the vicarious calibration of airborne and spaceborne sensors using ground-based measurements. Vicarious calibration is important because it is independent of the sensor and any onboard calibration system, but it requires that RSG personnel be present at a test site during the aircraft or satellite overpass. The ground-based data collection can be limited by poor weather, and also by the large travel distances from RSG's laboratory to the test sites.This dissertation presents an automated methodology that is used in support of vicarious calibration. The most important parameter measured during a vicarious calibration field campaign is the surface reflectance, and this work describes the method and instrumentation to obtain surface reflectance in the absence of RSG personnel. The instrumentation required to measure the surface and atmospheric parameters is discussed. The design and laboratory characterization of a nadir-viewing, multispectral radiometer is presented. Finally, results using this methodology are compared to those obtained using vicarious calibration, and also with the top-of-atmosphere radiance for one Terra MODIS, and two Aqua MODIS overpasses.

University, Diss., 2002--Bremen.

University, Diss., 2003--Bremen.

Radiometers measures background radiation noise power of a target. The dominant quality factor of the radiometer is determined by how sensitive it is, so the lower the noise figure and the higher the gain, the more sensitive it is. It must also calibrate out any interfering noise such as sky background and system noise. Any change in gain of the radiometer receiver must also be taken into account. A Dicke radiometer compensates system gain and noise variation by switching between the target and a known noise source. To accomplish this, a single pole, double throw (SPDT) switch, switches between the receiving antenna and the noise source. The common terminal of the switch goes to the input of the low noise amplifier (LNA). This switch has a noise figure approximately equivalent to its loss and its noise is amplified by the LNA. To eliminate the loss of the switch, this paper studies a new approach of combining the switch and the LNA to become a “switchable” LNA by designing a two-stage gain block with the first stage capable of switching between the two inputs. Because the first stage is amplifying, there is no signal loss. This thesis investigates the new switching LNA and the design approach used in choosing the technology, the transistor size, biasing, extractions and matching. Two variations of the design were built using IBM’s SiGe 8HP 120nm process. The expected and measured results are compared. Results show a measured gain of 10dB and noise figure of 5dB at 19GHz. These results fall short of expectations for reasons explained in the thesis. The overall performance of this switching LNA is compared to the traditional methods. Performance criteria include gain, noise figure, isolation, matching and linearity vs. frequency and their stability vs. power and temperature variation. Power consumption, physical size and cost are also considered. The degree to which the two inputs track one another is discussed.

This thesis describes the construction of a sea surface temperature (SST) dataset from Along-Track Scanning Radiometer (ATSR) observations suitable for climate applications. The algorithms presented here are now used at ESA for reprocessing of historical ATSR data and will be the basis of the retrieval used on the forthcoming SLSTR instrument on ESA’s Sentinel-3 satellite. In order to ensure independence of ATSR SSTs from in situ measurements, the retrieval uses physics-based methods through the use of radiative transfer (RT) simulations. The RT simulations are based on the Reference ForwardModel line-by-line model linked to a new sea surface emissivity model which accounts for surface temperature, wind speed, viewing angle and salinity, and to a discrete ordinates scattering (DISORT) model to account for aerosol. An atmospheric profile dataset, based on full resolution ERA-40 numerical weather prediction (NWP) data, is defined and used as input to the RTmodel. Five atmospheric trace gases (N2O, CH4, HNO3, and CFC-11 and CFC-12) are identified as having temporal and geographical variability which have a significant (∼0.1K) impact on RT simulations. Several additional trace gases neglected in previous studies are included using fixed profiles contributing ∼0.04K to RT simulations. Comparison against ATSR-2 and AATSR observations indicates that RT model biases are reduced from 0.2–0.5K for previous studies to ∼0.1K. A new coefficient-based SST retrieval scheme is developed from the RT simulations. Coefficients are banded by total column water vapour (TCWV) from NWP analyses reducing simulated regional biases to <0.1K compared to ∼0.2K for global coefficients. An improved treatment of the instrument viewing geometry decreases simulated view-angle related biases from ∼0.1K to <0.005K for the day-time dual-view retrieval. To eliminate inter-algorithmbiases due to remaining RT model biases and uncertainty in the characterisation of the ATSR instruments the offset coefficient for each TCWV band is adjusted to match the results from a reference channel combination. As infrared radiometers are sensitive to the skin SST while in situ buoys measure SST at some depth below the surface an adjustment for the skin effect and diurnal stratification is included. The samemodel allows adjustment for the differing time of observation between ATSR-2 and AATSR to prevent the diurnal cycle being aliased into the final record. The RT simulations are harmonised between sensors using a double-difference technique eliminating discontinuities in the final SST record. Comparison against in situ drifting and tropical moored buoys shows the new SST dataset is of high quality. Systematic differences between ATSR retrieved SST and in situ drifters show zonal, regional, TCWV, and wind speed biases are less than 0.1K except for themost extreme cases (TCWV <5 kgm−2). The precision of ATSR retrieved SSTs is ∼0.15 K, lower than the precision ofmeasurement of the global ensemble of in situ drifting buoys. From 1995 onwards the ARC SSTs are stable with instability of less than 5mK year−1 to 95% confidence (demonstrated for tropical regions).

The objective of the proposed research is to create new reconfigurable RF and millimeter-wave circuit topologies that enable significant systems benefits. The market of RF systems has long evolved under a paradigm where once a system is built, performance cannot be changed. Companies have recognized that building flexibility into RF systems and providing mechanisms to reconfigure the RF performance can enable significant benefits, including: the ability support multiple modulation schemes and standards, the reduction of product size and overdesign, the ability to adapt to environmental conditions, the improvement in spectrum utilization, and the ability to calibrate, characterize, and monitor system performance. This work demonstrates X-band LNA designs with the ability to change the frequency of operation, improve linearity, and digitally control the tradeoff between performance and power dissipation. At W-band frequencies, a novel device configuration is developed, which significantly improves state-of-the-art silicon-based switch performance. The excellent switch performance is leveraged to address major issues in current millimeter-wave systems. A front-end built-in-self-test switch topology is developed to facilitate the characterization of millimeter-wave transceivers without expensive millimeter-wave equipment. A highly integrated Dicke radiometer is also created to enable sensitive measurements of thermal noise.

The SMAPVEX12 (Soil Moisture Active/Passive Validation Experiment 2012) was carried out over the summer of 2012 in Manitoba, Canada. The goal of the project was to improve the accuracy of satellite-based remote sensing of soil moisture. Data were gathered during a 42-day field campaign with surface measurements on 55 different agricultural fields in south-central Manitoba. The extended duration of the campaign, contrast in soil textures, and variety of crop types over the study region provided an excellent range of soil moisture and vegetation conditions. The study fields ranged from bare to fully vegetated, with volumetric soil moisture levels spanning a range of almost 50%. Remotely sensed data were collected on 17 days by aircraft at 1.4 Ghz with a microwave radiometer at two different resolutions. Observed brightness temperatures from the radiometer showed a typical inverse relationship to the near simultaneous soil moisture measurements from the field. Field-by-field relationships using all sampling dates with both soil and emissivity data were all shown to be significant with the exception of two of the pasture fields and a soybean field. Linear regressions across multiple fields and by flight lines also had statistically significant slopes. The significance of all these relationships improved with the removal of pasture fields from the analysis. On most fields, the sensitivity (slope) of the relationship and correlation coefficient (R2) between emissivity and observed soil moisture increased when vegetation and roughness effects were taken into account. The b parameter that relates vegetation water content to optical depth in the tau-omega model was optimized using the collective slope and R2 values of the individual fields. A b parameter value of 0.06 for horizontal polarization and 0.13 for vertical polarization were found to be optimal across the range of all fields in this analysis. / May 2016

The accuracy of ozone measurements in the middle atmosphere is of great importance when determining its diurnal variation. A high time resolution of the measured data is desirable and depends on the sensitivity of the receiver used to detect the ozone. This thesis aims to improve the sensitivity of a groundbased 142 GHz microwave radiometer used for measuring atmospheric ozone data. This is done by replacing the previous receiver components with a series of new components and arranging them in different setups for comparison purposes. Mechanics and wiring were changed in order to install the setups along with changes in the optics. Each test setup could be implemented as a first step towards improving the sensitivity of the radiometer. The result show that the optics contribute with an unexpected addition of noise to the measurements and hence the overall performance and improvement of the radiometer could not be determined. Suggestions are made for further work which include improving the optics and performing cryo-measurements.