Radiative transfer theory for active and passive remote sensing of sea ice

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (p. 147-153).by Hong Tat Ewe.M.S

Remote sensing backscattering model for sea ice: Theoretical modelling and analysis

Remote sensing has been used in Antarctic studies as an earth observation technique to study the polar region. A remote sensing forward model is an important tool in polar research to study and understand scattering mechanisms and sensitivity of physical parameters of snow and sea ice. In this paper, a reliable theoretical model to study sea ice is developed. The theoretical model in a prior work was improved by including multiple-surface scattering, based on an existing integral equation model and additional second-order surface-volume scattering. This model is applied to a desalinated ice layer above thick saline ice and analyzed using different frequencies, bottom surface roughness and sea-ice layer thickness. Improvement in calculation of the backscattering coefficient of the sea-ice layer is investigated for both co-polarized and cross-polarized returns. The effect on each scattering mechanism is also investigated, to understand in more detail the effect of surface multiple scattering and second-order surface-volume scattering. Comparisons are also made with field measurement results, to validate the theoretical model. Results show improvement in the total backscattering coefficient for cross-polarized return in the studied range, suggesting that multiple-surface scattering and surface-volume scattering up to second order are important scattering mechanisms in the sea-ice layer and should not be ignored in polar research

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3, reports on three research projects and a list of publications.California Institute of Technology/Jet Propulsion Laboratory Contract 959548National Aeronautics and Space Administration Grant NAGW-1617National Aeronautics and Space Administration Grant Contract 958461U.S. Navy - Office of Naval Research Grant N00014-92-J-1616U.S. Navy - Office of Naval Research Grant N00014-92-J-4098Digital Equipment Corporation AGMT DTD 11/16/93Joint Services Electronics Program Contract DAAL03-92-C-0001Joint Services Electronics Program Grant DAAH04-95-1-0038MIT Lincoln Laboratory P.O. No. BX-5424U.S. Navy - Office of Naval Research Grant N00014-90-J-1002U.S. Navy - Office of Naval Research Grant N00014-89-J-1019DEMACO Agreement 11/15/93Federal Aviation Administration Grant 94-G-007U.S. Army Cold Regions Research and Engineering Laboratory Contract DACA89-93-K-000

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3, reports on four research projects and a list of publications.National Aeronautics and Space Administration Grant NAGW-1617National Aeronautics and Space Administration Agreement 958461National Aeronautics and Space Administration Grant NAGW-1272U.S. Army Corp of Engineers Contract DACA39-87-K-0022U.S. Navy - Office of Naval Research Grant N00014-89-J-1107U.S. Navy - Office of Naval Research Grant N00014-92-J-1616Digital Equipment CorporationJoint Services Electronics Program Contract DAAL03-92-C-0001U.S. Navy - Office of Naval Research Grant N00014-90-J-1002U.S. Navy - Office of Naval Research Grant N00014-89-J-1019U.S. Department of Transportation Agreement DTRS-57-88-C-00078TTD13U.S. Department of Transportation Agreement DTRS-57-88-C-00078TTD30U.S. Department of Transportation Agreement DTRS-57-92-C-00054TTD1DARPA/Consortium for Superconducting Electronics Contract MDA972-90-C-0021National Science Foundation Fellowship MIP 88-5876

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3 and reports on four research projects.California Institute of Technology/Jet Propulsion Laboratory Agreement 959548National Aeronautics and Space Administration Grant NAGW-1617National Aeronautics and Space Administration Agreement 958461U.S. Navy - Office of Naval Research Grant N00014-89-J-1107U.S. Navy - Office of Naval Research Grant N00014-92-J-1616U.S. Navy - Office of Naval Research Grant N00014-92-J-4098Digital Equipment CorporationJoint Services Electronics Program Contract DAAL03-92-C-0001U.S. Navy - Office of Naval Research Agreement N00014-90-J-1002U.S. Navy - Office of Naval Research Agreement N00014-89-J-1019DEMACOU.S. Army Cold Regions Research and Engineering Laboratory Contract DACA89-93-K-0009U.S. Department of Transportation Agreement DTRS-57-92-C-00054TTD1Advanced Research Projects Agency/Consortium for Superconducting Electronics Contract MDA972-90-C-0021National Science Foundation Fellowship MIP 88-58764National Science Foundatio

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

A Microwave Scattering Model For An Electrically Dense Discrete Random Medium

This thesis contains a theoretical study of the microwave scattering problems in electrically dense discrete random media and the development of the microwave scattering models with applications to these dense media. A medium is considered electrically dense when the average distance between the scatterers is smaller than the wavelength. In this case, the conventional assumption of independent scattering from the scatterers is no longer valid and the coherence effect from the scatterers should be taken into account. This effect can be included by incorporating the array phase correction factor to the scattering matrix of the scatterers. The array phase correction factor is developed based on the antenna array concept where the overall phase contributions from the correlated scatterers are considered. In this study, the array phase correction factor for spherical scatterers developed by Chuah et.al. ( 1996) is generalized to non -spherical scatteres with either prescribed or random orientation. Theoretical analysis of the array factor for various frequencies, valume fractions and scattering angles is also carried out. In addition to the coherence effect, the near field interaction between the scatterers should also be incorporated in the scattering theory for a dense medium. For spherical scatterers, this near field interaction effect is considered through the amplitude correction where the range dependent terms in the exact expression of the scattered field of Mie scatterers are included. For disks, needles and cylinders, since the overall scattered field of a scatterer is approximated by integrating the scattered fields from each volume element of the scatterer, the near field interaction effect is considered by including not only the near field amplitude term of the scattered fields ( as the amplitude correction ) but also the higher order terms in the phase of the scattered fields ( as the Fresnel phase correction ). For the application of the theoretical model in a dense medium embedded with spherical scatterers such as now, a scattering problem from a single layer of Mie scatterers bounded both on top and bottom by rough interfaces characterized by the IEM model is considered. Theoretical analysis of the model with the amplitude and the array phase corrections is carried out with comparison to the predictions of the dense medium matrix doubling model. In addition, the model predictions are also compared with laboratory and snow field measurement data. Encouraging results are obtained where good agreement with the snow measurement data for co-polarization returns is observed. For cross-polarization returns, more high order terms are found to be necessary for better model predictions. For the study of scattering mechanisms in a vegetation medium, the single layer model is extended to a multilayer model. The leaves, branches and trunks are modelled by simple geometrical shapes such as disks, needles and cylinders. The IEM model is again used to characterize the ground surface. Theoretical studies of the effects of the array phase, the amplitude and the Fresnel phase corrections on the phase matrices of disks, needles and cylinders are presented and good agreement is obtained between the theoretical results and the backscattering cross section measurement of rods, disks, birch stick and aspen leaf. The phase matrices are then applied in the backscatter model and theoretical analysis of the backscattering returns from both the single layer and the multilayer models is carried out. Three types of forests are chosen for the theoretical study of the multilayer model: temperate coniferous forest, tropical deciduous forest and tropical evergreen forest. Various dominat scattering contributions from the vegetation are identified and siscussed. Good agreement is obtained between model predictions and multi-frequency, multi-angle and multi-polarization measurement data for Japanese Cypress, soybean and wheat canopies, boreal forest, walnut orchard and Sugi coniferous trees. In conclusion, it is generally found that the arry phase correction is necessary for an electrically dense medium. In addition, near field interactions such as the amplitude correction and the Fresnel phase correction are also vital in the dense medium models. Good agreement of the model predictions with the available measurement results validates the applicability of the models in this study

A model for secure knowledge sharing

Improvements made in digital data processing resulted in the ability to store knowledge objects in sharing systems in the form of documents, images, audio and even video streams. However, with the increasing reliance on online knowledge sharing technologies, there is also an increasing danger that knowledge objects stored in digital forms are subjected to concerted malicious and possible criminal attacks. Digital knowledge objects can become easy prey to tampering and modifications which may defeat the original intent for knowledge sharing as well as causing loss of confidence among users. The preservation of the integrity of digital knowledge objects becomes increasingly important now than ever and the need has come for technologies to safeguard the authenticity and integrity of such objects. This paper proposes a model to incorporate automated detection and recovery mechanisms for tampered knowledge objects to make sure that knowledge-processing resources continue to perform correct processing operations at all times

Backscattering analysis for snow remote sensing model with higher order of surface-volume scattering

The study of earth terrain in Antarctica is important as this region has a direct impact on global environment and weather condition. There have been many research works in developing remote sensing technologies, as it can be used as an earth observation technique to monitor the polar region (Giles et al., 2009; Park et al., 2012). In previous studies, remote sensing forward model has been developed to study and understand scattering mechanisms and sensitivity of physical parameters of snow and sea ice. This paper is an extended work from previous studies (Syahali et al., 2011; Syahali, 2012; Syahali and Ewe, 2012, 2013), where an improved theoretical model to study polar region was developed. Multiple-surface scattering, based on an existing integral equation model (IEM) that calculates surface scattering and additional second-order surface-volume scattering, were added in the model from prior research works (Ewe et al., 1998) for improvement in the backscattering calculation. We present herein the application of this model on a snow layer above ground which is modeled as a volume of ice particles that are closely packed and bounded by irregular boundaries above a homogenous half space. The effect of including multiple surface scattering and additional surface-volume scattering up to second order in the backscattering coefficient calculation of snow layer is studied for co-polarized and cross-polarized returns. Comparisons with satellite data are also done for validation. Results show improvement in the total backscattering coefficient for cross-polarized return in the studied range, suggesting that multiple-surface scattering and surface-volume scattering up to second order are important scattering mechanisms in the snow layer and should not be ignored in polar research