A High-Order Imaging Algorithm for High-Resolution Space-Borne SAR Based on a Modified Equivalent Squint Range Model

Two challenges have been faced in signal processing of ultrahigh-resolution spaceborne synthetic aperture radar (SAR). The first challenge is constructing a precise range model, and the second one is to develop an efficient imaging algorithm since traditional algorithms fail to process ultrahigh-resolution spaceborne SAR data effectively. In this paper, a novel high-order imaging algorithm for high-resolution spaceborne SAR is presented. First, a modified equivalent squint range model (MESRM) is developed by introducing equivalent radar acceleration into the equivalent squint range model, and it is more suitable for high-resolution spaceborne SAR. The signal model based on the MESRM is also presented. Second, a novel high-order imaging algorithm is derived. The insufficient pulse-repetition frequency problem is solved by an improved subaperture method, and accurate focusing is achieved through an extended hybrid correlation algorithm. Simulations are performed to validate the presented algorithm

Correction: "Epidemiology and aetiology of influenza-like illness among households in metropolitan Vientiane, Lao PDR": A prospective, community-based cohort study.

[This corrects the article DOI: 10.1371/journal.pone.0214207.]

"Epidemiology and aetiology of influenza-like illness among households in metropolitan Vientiane, Lao PDR": A prospective, community-based cohort study.

Respiratory diseases are a major contributor to morbidity and mortality in many tropical countries, including Lao PDR. However, little has been published regarding viral or bacterial pathogens that can contribute to influenza-like illness (ILI) in a community setting. We report on the results of a community-based surveillance that prospectively monitored the incidence of ILI and its causative pathogens in Vientiane capital in Lao PDR. A cohort of 995 households, including 4885 study participants, were followed-up between May 2015 and May 2016. Nasopharyngeal swabs, throat swabs, and sputum specimens were collected from ILI cases identified through active case-finding. Real-Time PCR was used to test nasopharyngeal swabs for 21 respiratory pathogens, while throat and sputum samples were subjected to bacterial culture. Generalized linear mixed models were used to assess potential risk factors for associations with ILI. In total, 548 episodes of ILI were reported among 476 (9.7%) of the study participants and 330 (33.2%) of the study households. The adjusted estimated incidence of ILI within the study area was 10.7 (95%CI: 9.4-11.9) episodes per 100 person-years. ILI was significantly associated with age group (p<0.001), sex (p<0.001), and number of bedrooms (p = 0.04) in multivariate analysis. In 548 nasopharyngeal swabs, the most commonly detected potential pathogens were Streptococcus pneumoniae (17.0%), Staphylococcus aureus (11.3%), influenza A (11.1%; mostly subtype H3N2), rhinovirus (7.5%), and influenza B (8.0%). Streptococci were isolated from 42 (8.6%) of 536 throat swabs, most (27) of which were Lancefield Group G. Co-infections were observed in 132 (24.1%) of the 548 ILI episodes. Our study generated valuable data on respiratory disease burden and patterns of etiologies associated with community-acquired acute respiratory illness Laos. Establishment of a surveillance strategy in Laos to monitor trends in the epidemiology and burden of acute respiratory infections is required to minimize their impact on human health

Kinematic interpretation of the Centaurus A absorption line

The location of the gas responsible for the absorption line system towards the nucleus of Centaurus A is a puzzle. It is generally accepted that the line features close to the systemic velocity originate in the disk. Especially the redshifted line features, however, are usually thought to be due to gas close to the nucleus or even falling towards it. We present new &quot;1&quot;2CO(1-0), HCO&quot;+(1-0) and the HCN(1-0) absorption line measurements as well as an alternative interpretation of the line system. Previous papers have demonstrated that the distribution of line emission of the inner molecular and outer atomic hydrogen disk can be accounted for by a system of tilted rings with varying inclination. Using the same model but assuming that co-rotating absorbing gas is located at high altitudes above the disk one can account for all major features of the absorption line system. In this model the absorption takes place in high altitude clouds which are up to about 160 pc above the molecular disk of Centaurus A at radii between 1.7 to 1.9 kpc, accounting for the two strongest central line features. In our model the redshifted line features are due to gas associated with disk material up to about 300 pc above the disk at radii of 0.4 kpc to 0.6 kpc orbiting in the non-spherically symmetric potential of the Centaurus A galaxy. In this model the systemic velocity is at 546 km/s which is the velocity of the sharp spectral feature about 6 km/s to the blue of the deepest absorption line. Our new model provides a natural explanation for the general structure of the complex absorption line system based on a tilted ring model that already explains the disk line emission. In this model no significant absorbing gas component closer than 200 pc to the nonthermal radio continuum nucleus is required and the peculiar velocity structure of the absorption line system is due to the kinematics of the molecular gas disk. (orig.)SIGLEAvailable from TIB Hannover: RN 9303(457) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman