Specular null polarization theory: applications to radar meteorology

Includes bibliographical references.Specular null polarization theory (SNPT) has been recently introduced for the case of coherent scattering where a 2 x 2 scattering matrix is sufficient to describe the scattering process. In this paper, SNPT is extended to the case of incoherent scattering. Optimum polarization states are derived and the results are discussed in relation to the classic radar optimum polarizations. In traditional radar polarimetry, modeling of the radar receive/transmit network is included in the radar voltage equation and consequently this affects the optimum polarizations and polarization responses of scatterers. SNPT eliminates this effect and therefore allows for a more direct analysis of scatterers. Modeling of ensembles of precipitation particles is used to illustrate the results of the analysis.This work was supported by the National Science Foundation under Grants ATM-8915141 and ATM-9214864

Fundamental remote sensing science research program. Part 1: Scene radiation and atmospheric effects characterization project

Brief articles summarizing the status of research in the scene radiation and atmospheric effect characterization (SRAEC) project are presented. Research conducted within the SRAEC program is focused on the development of empirical characterizations and mathematical process models which relate the electromagnetic energy reflected or emitted from a scene to the biophysical parameters of interest

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3 and reports on seven research projects.Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Contract ECS 86-20029Schlumberger- Doll ResearchU.S. Army Research Office Contract DAAL03 88-K-0057National Aeronautics and Space Administration Contract NAGW-1617U.S. Navy - Office of Naval Research Contract N00014-89-J-1107National Aeronautics and Space Administration Contract NAGW-1272National Aeronautics and Space Administration Contract 958461Simulation Technologies Contract DAAH01-87-C-0679U.S. Army Corp of Engineers Contract DACA39-87-K-0022WaveTracer, Inc.U.S. Navy - Office of Naval Research Contract N00014-89-J-1019U.S. Air Force Systems - Electronic Systems Division Contract F19628-88-K-0013Digital Equipment CorporationInternational Business Machines CorporationU.S. Department of Transportation Contract DTRS-57-88-C-0007

Polarization studies in electromagnetic scattering by small Solar-system particles

In remote-sensing studies, particles that are comparable to the wavelength exhibit characteristic features in electromagnetic scattering, especially in the degree of linear polarization. These features vary with the physical properties of the particles, such as shape, size, refractive index, and orientation. In the thesis, the direct problem of computing the unknown scattered quantities using the known properties of the particles and the incident radiation is solved at both optical and radar spectral regions in a unique way. The internal electromagnetic fields of wavelength-scale particles are analyzed by using both novel and established methods to show how the internal fields are related to the scattered fields in the far zone. This is achieved by using the tools and methods that were developed specifically to reveal the internal field structure of particles and to study the mechanisms that relate the structure to the scattering characteristics of those particles. It is shown that, for spherical particles, the internal field is a combination of a forward propagating wave with the apparent wavelength determined by the refractive index of the particle, and a standing wave pattern with the apparent wavelength the same as for the incident wave. Due to the surface curvature and dielectric nature of the particle, the incident wave front undergoes a phase shift, and the resulting internal wave is focused mostly at the forward part of the particle similar to an optical lens. This focusing is also seen for irregular particles. It is concluded that, for both spherical and nonspherical particles, the interference at the far field between the partial waves that originate from these concentrated areas in the particle interior, is responsible for the specific polarization features that are common for wavelength-scale particles, such as negative values and local extrema in the degree of linear polarization, asymmetry of the phase function, and enhancement of intensity near the backscattering direction. The papers presented in this thesis solve the direct problem for particles with both simple and irregular shapes to demonstrate that these interference mechanisms are common for all dielectric wavelength-scale particles. Furthermore, it is shown that these mechanisms can be applied to both regolith particles in the optical wavelengths and hydrometeors at microwave frequencies. An advantage from this kind of study is that it does not matter whether the observation is active (e.g., polarimetric radar) or passive (e.g., optical telescope). In both cases, the internal field is computed for two mutually perpendicular incident polarizations, so that the polarization characteristics can then be analyzed according to the relation between these fields and the scattered far field.Kaukokartoitustutkimuksissa aallonpituusluokkaa olevat hiukkaset aiheuttavat niille luonteenomaisia piirteitä sähkömagnettisessa säteilyssä, varsinkin lineaarisen polarisaation asteessa. Nämä piirteet vaihtelevat hiukkasen fyysisten ominaisuuksien, kuten muodon, koon, taitekertoimen ja orientaation myötä. Tässä väitöskirjassa ratkaistaan sähkömagneettisen sironnan suora ongelma uudella tavalla, samalla kun hiukkasten ominaisuudet oletetaan tunnetuiksi. Aallonpituusluokkaa olevien hiukkasten sisäisiä sähkökenttiä analysoidaan sekä uusilla että vakiintuneilla menetelmillä, jotta voidaan osoittaa, mikä on sisäisten kenttien suhde sironneisiin kenttiin kauko-alueessa. Tämä on saavutettu käyttämällä työkaluja ja menetelmiä, jotka on kehitetty paljastamaan sirottajien sisäisen kentän rakenne ja joilla voidaan tutkia mekanismeja, jotka liittävät näiden sirottajien rakenteen niiden sirontaominaisuuksiin. Tutkimuksessa näytetään, että pallomaisten hiukkasten sisäinen kenttä on yhdistelmä eteenpäin etenevää aaltoa, jonka allonpituus määräytyy hiukkasen taitekertoimen mukaan, ja seisovaa aaltoa, jonka aallonpituus on sama kuin tulevan aallon. Koska hiukkanen on eriste ja sen pinta on kaareva, tuleva aaltorintama kokee vaihesiirron ja tuloksena oleva sisäinen aalto fokusoituu pääasiassa hiukkasen etupuolelle optisen linssin tavoin. Tämä fokusointi havaitaan myös epäsäännöllisillä hiukkasilla. Johtopäätöksenä on, sekä pallomaisille että ei-pallomaisille hiukkasille, että kaukokentässä tapahtuva interferenssi osittaisten aaltojen välillä, jotka ovat peräisin näistä fokusoituneista alueista hiukkasen sisällä, on vastuussa tietyistä, aallonpituusluokkaa oleville hiukkasille ominaisista piirteistä lineaarisessa polarisaatiossa, kuten negatiiviset arvot ja paikalliset maksimit, vaihefunktion asymmetria, ja intensiteetin kasvaminen lähellä takaisinsirontasuuntaa. Tässä väitöskirjassa esitellyt paperit ratkaisevat suoran ongelman, sekä yksinkertaisille, että epäsäännöllisille hiukkasille osoittaakseen, että nämä interferenssimekanismit ovat yhteisiä kaikille aallonpituusluokkaa oleville, eristäville sirottajille. Lisäksi näytetään, että näitä mekanismeja voidaan soveltaa sekä regoliittihiukkasille näkyvän valon alueella että hydrometeoriiteille mikroaaltoalueessa. Yksi tällaisen tutkimuksen eduista on, että ei ole merkitystä, onko havaitsija aktiivinen (esim. polarisaatiotutka) vai passiivinen (esim. optinen teleskooppi). Molemmissa tapauksissa sisäinen kenttä lasketaan kahdelle keskenään kohtisuorasti polarisoituneelle tulevalle kentälle, jotta polarisaatiossa havaitut piirteet voidaan analysoida näiden kenttien ja sironneen kentän suhteen avulla

Joint Scattering Environment Sensing and Channel Estimation Based on Non-stationary Markov Random Field

This paper considers an integrated sensing and communication system, where some radar targets also serve as communication scatterers. A location domain channel modeling method is proposed based on the position of targets and scatterers in the scattering environment, and the resulting radar and communication channels exhibit a two-dimensional (2-D) joint burst sparsity. We propose a joint scattering environment sensing and channel estimation scheme to enhance the target/scatterer localization and channel estimation performance simultaneously, where a spatially non-stationary Markov random field (MRF) model is proposed to capture the 2-D joint burst sparsity. An expectation maximization (EM) based method is designed to solve the joint estimation problem, where the E-step obtains the Bayesian estimation of the radar and communication channels and the M-step automatically learns the dynamic position grid and prior parameters in the MRF. However, the existing sparse Bayesian inference methods used in the E-step involve a high-complexity matrix inverse per iteration. Moreover, due to the complicated non-stationary MRF prior, the complexity of M-step is exponentially large. To address these difficulties, we propose an inverse-free variational Bayesian inference algorithm for the E-step and a low-complexity method based on pseudo-likelihood approximation for the M-step. In the simulations, the proposed scheme can achieve a better performance than the state-of-the-art method while reducing the computational overhead significantly.Comment: 15 pages, 13 figures, submitted to IEEE Transactions on Wireless Communication

Broadband and statistical characterization of echoes from random scatterers : application to acoustic scattering by marine organisms

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013The interpretation of echoes collected by active remote-sensing systems, such as sonar and radar, is often ambiguous due to the complexities in the scattering processes involving the scatterers, the environment, and the sensing system. This thesis addresses this challenge using a combination of laboratory and fi eld experiments, theoretical modeling, and numerical simulations in the context of acoustic scattering by marine organisms. The unifying themes of the thesis are 1) quantitative characterization of the spectral, temporal, and statistical features derived from echoes collected using both broadband and narrowband signals, and 2) the interpretation of echoes by establishing explicit links between echo features and the sources of scattering through physics principles. This physics-based approach is distinct from the subjective descriptions and empirical methods employed in most conventional fisheries acoustic studies. The fi rst part focuses on understanding the dominant backscattering mechanisms of live squid as a function of orientation. The study provides the first broadband backscattering laboratory data set from live squid at all angles of orientation, and conclusively con firms the fluidlike, weakly-scattering material properties of squid through a series of detailed comparisons between data and predictions given by models derived based on the distorted-wave Born approximation. In the second part, an exact analytical narrowband model and a numerical broadband model are developed based on physics principles to describe the probability density function of the amplitudes of echo envelopes (echo pdf) of arbitrary aggregations of scatterers. The narrowband echo pdf model signi cantly outperforms the conventional mixture models in analyzing simulated mixed assemblages. When applied to analyze fish echoes collected in the ocean, the numerical density of sh estimated using the broadband echo pdf model is comparable to the density estimated using echo integration methods. These results demonstrate the power of the physics-based approach and give a rst-order assessment of the performance of echo statistics methods in echo interpretation. The new data, models, and approaches provided here are important for advancing the eld of active acoustic observation of the ocean.Taiwan Merit Scholarship (NSC-095-SAF-I-564-021-TMS), Office of Naval Research (ONR; grants N00014-10-1-0127, N00014-08-1-1162, N00014-07-1-1034), National Science Foundation (NSF; grant OCE-0928801), Naval Oceanographic Offi ce (grant N62306007-D9002), WHOI Ocean Life Institute, and the WHOI Academic Programs O ffice funds