A comparison of SAR image speckle filters

High quality images of Earth produced by synthetic aperture radar (SAR) systems have become increasingly available, however, SAR images are difficult to interpret. Speckle reduction remains one of the major issues in SAR imaging process, although speckle has been extensively studied for decades. Many reconstruction filters have been proposed and they can be classified into two categories: multilook and/or minimum mean-square error (MMSE) despeckling using the speckle model; and maximum a posteriori (MAP) or maximum likihood (ML) despeckling using the product model. The most well known Lee, Kuan, and Frost filters belong to first category. These filters are based on conventional techniques that were originally derived for stationary signals, such as MMSE. In the second category, filters are based on the product model, such as the MAP Gaussian filter and the Gamma filter, and require knowledge of the a priori probability density function. These filters force speckle to have nonstationary Gaussian or gamma distributed intensity mean. The speckle filtering is mainly Bayesian model fitting that optimizes the MAP criteria. Scene reconstruction is performed using an inversion of the ascending chain. An objective measure is required to compare the technical merits of these filters, and Shi et al. presented a comparison 15 years ago. In this paper, a brief introduction of speckle, product, and filter models is summarized. A review of some most widely used SAR image speckle filters is given. And stationary speckle filters, like Lee, Kuan, and Frost filters, and nonstationary speckle filters like Gamma MAP filter are studied. Despeckling results on stationary and nonstationary SAR image of these speckle filters are presented. © 2009 Copyright SPIE - The International Society for Optical Engineering.published_or_final_versio

A Study of Parton Energy Loss in Au+Au Collisions at RHIC using Transport Theory

Parton energy loss in Au+Au collisions at RHIC energies is studied by numerically solving the relativistic Boltzmann equation for the partons including $2 \leftrightarrow 2$ and $2 \to 2 + final state radiation$ collision processes. Final particle spectra are obtained using two hadronization models; the Lund string fragmentation and independent fragmentation models. Recent, preliminary $\pi^0$ transverse momentum distributions from central Au+Au collisions at RHIC are reproduced using gluon-gluon scattering cross sections of 5-12 mb, depending upon the hadronization model. Comparisons with the HIJING jet quenching algorithm are made.Comment: 6 pages, 6 figures, attached files are replaced (wrong files were uploaded in version 1

利用滲透試驗探討雙層土壤之滲流沖蝕行為及其數值模擬

Seepage erosion occurs when finer particles are dragged out from other soil particles by water. This type of erosion causes progressive failure inward into the slopes and slope instabilities. Therefore, it is necessary to explore the behavior of seepage erosion in order to prevent such failure in slopes. According to results of field investigations, we do seepage erosion experiments in a laboratory to understand the erosion behavior. After that, we utilize FEM soft-ware – FLAC5.0 in order to determine the feasibility of numerical analysis in simulating seepage erosion behavior.滲流沖蝕係指土壤中的細顆粒因地下水流驅動通過較大顆粒間之孔隙，被帶離坡面後，會由坡面向坡體內部發展出漸進式破壞，進而引發邊坡問題，故對邊坡滲流沖蝕行為的瞭解有其必要性。因此，本研究根據現地調查結果，於室內利用滲透試驗儀器進行滲流沖蝕試驗，以了解不同情形下各試體之沖蝕行為。而後，為了解數值軟體用於模擬滲流沖蝕行為之可行性，故嘗試採用有限差分法軟體－FLAC5.0 進行模擬，以期能作為未來用於滲流沖蝕模擬之參考

Vertical Heating Structures Associated with the MJO as Characterized by TRMM Estimates, ECMWF Reanalyses, and Forecasts: A Case Study during 1998/99 Winter

The Madden–Julian oscillation (MJO) is a fundamental mode of the tropical atmosphere variability that exerts significant influence on global climate and weather systems. Current global circulation models, unfortunately, are incapable of robustly representing this form of variability. Meanwhile, a well-accepted and comprehensive theory for the MJO is still elusive. To help address this challenge, recent emphasis has been placed on characterizing the vertical structures of the MJO. In this study, the authors analyze vertical heating structures by utilizing recently updated heating estimates based on the Tropical Rainfall Measuring Mission (TRMM) from two different latent heating estimates and one radiative heating estimate. Heating structures from two different versions of the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses/forecasts are also examined. Because of the limited period of available datasets at the time of this study, the authors focus on the winter season from October 1998 to March 1999. The results suggest that diabatic heating associated with the MJO convection in the ECMWF outputs exhibits much stronger amplitude and deeper structures than that in the TRMM estimates over the equatorial eastern Indian Ocean and western Pacific. Further analysis illustrates that this difference might be due to stronger convective and weaker stratiform components in the ECMWF estimates relative to the TRMM estimates, with the latter suggesting a comparable contribution by the stratiform and convective counterparts in contributing to the total rain rate. Based on the TRMM estimates, it is also illustrated that the stratiform fraction of total rain rate varies with the evolution of the MJO. Stratiform rain ratio over the Indian Ocean is found to be 5% above (below) average for the disturbed (suppressed) phase of the MJO. The results are discussed with respect to whether these heating estimates provide enough convergent information to have implications on theories of the MJO and whether they can help validate global weather and climate models