Возможности исследования возрастных характеристик льда Карского моря на основе спутниковых данных СryoSat-2 и SMOS

Sea ice age is a proxy for thickness, which can be obtained through the use of satellite data. The paper presents the results of comparison of CryoSat-2, SMOS and CryoSat-2 & SMOS fusion data with detailed ice charts (October–April, 2010–2018). The AARI ice charts were chosen as references for comparison because they integrate knowledge and data from various sources, including expert analysis of operational satellite information, in-situ measurements at coastal stations, data on ice conditions from ships of the Northern Sea Route (NSR). The division of satellite data elements into classes (stages of development) was performed according to the maximum likelihood classifier. The recognition result for each stage of development was evaluated by means of three criteria, in accordance with the class value of Mode, Median and Mean. The effectiveness of satellite data in determining the Kara Sea ice thickness varies depending on the sea ice stage of development and winter season time. Four stages of development (old ice, thick first-year ice, medium first-year ice, nilas) showed the best recognition results. Although the CryoSat-2 mission was designed primarily to detect climate-dependent variations of the thickness of floating ice, in terms of statistical recognition of the Kara Sea ice stages of development, CryoSat-2 data can also be used to retrieve the thickness of thick first-year ice (January–April) and the thickness of medium first-year ice (January–February). For the remaining stages within the study area, the altimetry method shows a significant uncertainty, which can be resolved for nilas, thin first-year ice and medium first-year ice (March) by using SMOS data and CryoSat-2 & SMOS fusion data. In general, altimetric data, radiometric data and combination thereof can be applied in the complex analysis of all available information to ensure hydrometeorological and navigation support. Also, it is proposed to use the data of the ICESat-2 laser altimeter and to make a general comparison with in-situ measurements.Получение информации о пространственно-временной изменчивости распределения толщины льда — ключевой вопрос для прогноза состояния арктического морского льда. Несмотря на очевидные успехи применения данных CryoSat-2 и SMOS, соответствующие оценки толщин морского льда нуждаются в валидации. В качестве эталонов для сравнения на основе метода максимального правдоподобия были выбраны детализированные ледовые карты ААНИИ (октябрь–апрель 2010–2018 гг.). В статье приводятся результаты распознавания различных возрастных стадий льда Карского моря, наилучшие результаты по- казали многолетний, однолетний толстый, средний лед и нилас. Использование данных Cryosat-2, SMOS и их комбинации Cryosat-2 & SMOS может помочь в комплексном анализе всей доступной информации для гидрометеорологического и навигационного обеспечения

Progress in development of high-power FELs with two-dimensional Bragg resonators

Theoretical and experimental studies of novel free-electron laser (FEL) schemes with 2-D Bragg resonators of planar and coaxial geometry are discussed. The highly selective properties of 2-D Bragg resonators are described including comparison with results of "cold" microwave measurements. First results of experimental studies of a planar W-band FEL based on the accelerator ELMI (INP RAS) are presented. Progress in a coaxial Ka-band FEL experiment under construction at the University of Strathclyde is described. A new project at the Budker Institute investigating a multibeam FEL where 2-D distributed feedback is used to synchronise several FEL units of planar geometry is also discussed

Theory and design of a free-electron maser with two-dimensional feedback driven by a sheet electron beam

The use of two-dimensional Bragg resonators of planar geometry, realizing two-dimensional (2D) distributed feedback, is considered as a method of producing spatially coherent radiation from a large sheet electron beam. The spectrum of eigenmodes is found for a 2D Bragg resonator when the sides of the resonator are open and also when they are closed. The higher selectivity of the open resonator in comparison with the closed one is shown. A time-domain analysis of the excitation of an open 2D Bragg resonator by a sheet electron beam demonstrates that a single-mode steady-state oscillation regime may be obtained for a sheet electron beam of width 100-1000 wavelengths. Nevertheless, for a free-electron maser (FEM) with a closed 2D Bragg resonator, a steady-state regime can also be realized if the beam width does not exceed 50-100 wavelengths. The parameters for a FEM with a 2D planar Bragg resonator driven by a sheet electron beam based on the U-2 accelerator (INP RAS, Novosibirsk) are estimated and the project is described. [S1063-651X(99)04207-5]