C-band SAR observations of marginal ice zone rheology in theLabrador Sea

Synthetic-aperture radar (SAR) imagery collected during the LIMEX'87 field program in the Labrador Sea is used to qualitatively interpret the deformation modes in play throughout the experiment. The ice cover exhibited two distinct rheologies separated by a clear line of shear: a nonlinear viscous outer regime, and a quasi-brittle inner regime. A single constitutive relation capable of effectively modeling both is unlikely within a plastic rate-independent formulation. Rate-dependent effects are discussed in relation to favoring brittle fraction in an otherwise ductile material     

Classification of Baltic Sea ice types by airborne multifrequencymicrowave radiometer

An airborne multifrequency radiometer (24, 34, 48, and 94 GHz, vertical polarization) was used to investigate the behavior of the brightness temperature of different sea ice types in the Gulf of Bothnia (Baltic Sea). The measurements and the main results of the analysis are presented. The measurements were made in dry and wet conditions (air temperature above and below 0°C). The angle of incidence was 45° in all measurements. The following topics are evaluated: a) frequency dependency of the brightness temperature of different ice types, b) the capability of the multifrequency radiometer to classify ice types for winter navigation purposes, and c) the optimum measurement frequencies for mapping sea ice. The weather conditions had a significant impact on the radiometric signatures of some ice types (snow-covered compact pack ice and frost-covered new ice); the impact was the highest at 94 GHz. In all cases the overall classification accuracy was around 90% (the kappa coefficient was from 0.86 to 0.96) when the optimum channel combination (24/34 GHz and 94 GHz) was used     

Baltic Sea ice SAR segmentation and classification using modified pulse-coupled neural networks

A method for segmentation and classification of Baltic Sea ice synthetic aperture radar (SAR) images, based on pulse-coupled neural networks (PCNNs), is presented. Also, automated training, which is based on decomposing the total pixel value distribution into a mixture of class distributions, is presented and discussed. The algorithms have been trained and tested using logarithmic scale Radarsat-1 ScanSAR Wide mode images over the Baltic Sea ice. Before the decomposition into mixture of class distributions, an incidence angle correction, specifically designed for these Baltic Sea ice SAR images, is applied. Because the data distributions in the uniform areas of these images are very close to Gaussian distributions, the data are decomposed into a mixture of Gaussian distributions, using the Expectation-Maximazation algorithm. Only uniform image areas are used in the decomposition phase. The mixture of distributions is compared to the distributions of the Baltic Sea ice classes, based on earlier scatterometer measurements and visual video interpretations of the sea ice classes. The parameter values for the PCNN segmentation are defined based on this mixture of distributions. The PCNN segmentation results are also compared to the operational sea ice information of digitized ice charts and to visual interpretation of the sea ice class.     

Doppler signatures of radar backscattering from objects with micro-motions

Radar backscattering from objects with micro-motions is subject to Doppler modulations that help determine dynamic properties of objects and provide useful information about the objects. Doppler modulations represented by joint time-frequency analysis provide useful time-varying Doppler characteristics and, thus, add additional time-dimension information to exploit motion characteristics. The author discusses how to simulate radar backscattering from objects with rigid body motions and objects with non-rigid body motions, and how to analyse, interpret and characterise Doppler signatures of objects that undergo these micro-motions. Precession heavy top and human locomotion are used as examples of rigid and non-rigid body motions, respectively. Radar micro-Doppler signatures derived from these motions illustrate the potential of the joint time-frequency analysis for exploiting kinetic and dynamic properties of objects.     

Comparison of temperature dependence in C-band and L-band EDFAs

Temperature-dependent gain and noise characteristics of conventional band and long wavelength band erbium-doped fiber amplifiers are compared. Gain variations and noise figure penalties are shown for 980- and 1480-nm pump wavelength bands at different average inversion levels when the erbium coil temperature is cycled from -10°C to 80°C. Experimental results demonstrate that the L-band exhibits greater temperature-dependent gain and noise figure excursions compared to the C-band. Furthermore, it is shown that the impact of erbium coil temperature in the L-band is comparatively less dependent upon pump wavelength     

Field observations and model calculations of dielectric propertiesof Arctic sea ice in the microwave C-band

The complex dielectric constant of first-year and multiyear sea ice was measured during the Seasonal Ice Monitoring and Modeling (SIMMS) field experiments, conducted in the Arctic in the spring of 1992, 1993, and 1995. The dielectric constant was also computed based on an established dielectric mixing model by using different assumptions about inclusion shape. Computations were based on detailed measurements and observations of ice physical properties and crystalline structure. Comparison between measurements and model results was conducted to identify working models for first-year and multiyear ice. For first-year ice, models that employ the assumption of vertically oriented brine pockets are applicable to columnar ice and those with the assumption of randomly oriented brine pockets are applicable to frazil ice. The validity of the models are established only for ice temperatures less than -8°C. For multiyear ice, there is no need to account for air bubble shape. The coexistence of brine and air inclusions in multiyear pond ice makes it characteristically different from hummock ice. Best results for pond ice were obtained from a simple model that accounts only for volume fractions of inclusions, rather than their shape. Physical parameters that can be retrieved directly from the dielectric constant are salinity of first-year ice at temperatures below -15°C and density of multiyear hummock ice. Detailed measurements of permittivity and loss of first-year and multiyear ice are presented along with some insight into interactions between the dielectric constant and physical parameters     

The effect of inhomogeneous roughness on radar backscattering fromslightly deformed sea ice

This paper focuses on the spatially varying backscattering signature of an area of refrozen brash ice observed by a ship based scatterometer. The measurements were carried out as part of the Baltic Experiment for ERS-1 in 1994. The scatterometer was operated at 5.4 GHz at different incidence angles and polarizations. By analysing the scatterometer data over azimuth scans, it was found that the backscattering variabilities are not only due to fading but also contain a textural component. Surface height profiles were measured using a laser. The observed ice surface roughness was nonstationary over the measurement area. The ice surface can be approximated by adjacent patches of stationary roughness with patch dimensions of about 4.5 m. From the roughness spectra of different stationary patches, two roughness classes can be distinguished. The implications of estimating the roughness parameters from relatively short profile lengths is discussed and the effect on theoretical predictions of the backscattering coefficient is investigated. The texture variance is evaluated theoretically on the basis of the simulated backscattering coefficients of the two observed roughness classes and is found to compare with the scatterometer data     

Statistical properties of Rayleigh backscattering in single-modefibers

An analytical model that takes into account the influence of the laser linewidth on Rayleigh backscattering is given. For an unmodulated source the power spectral density is found to be identical to the delayed self-homodyne spectrum of the laser. The backscattered signal was measured for different laser linewidths, and the results are compared with the theory. The effects of Rayleigh backscattering noise on fiber gyroscopes and bidirectional optical systems are discussed     

Polarization properties of Rayleigh backscattering in single-modefibers

The state and degree of polarization (SOP, DOP) of Rayleigh backscattered light in low birefringent optical fibers was calculated using Stokes calculus. It was found that the SOP of Rayleigh backscattered light in low birefringent fiber is constant, viz. the same as the SOP of the incoming light. The DOP of Rayleigh backscattered light is one-third of the DOP of the incoming light, and not just anywhere between 0 and 100% as often mentioned in the literature. The experimental results agree with the calculations     

环形腔中背向散射特性的理论研究

研究了连续激光注入时无源环形腔的背向散射特性。首先,分析了注入光与无源腔频率完全匹配时,正向光和背散光振幅的稳态解,以及充光和快速关断过程中正向光和背散光振幅随时间的演化。其次,推导了无源腔中正向光和背向散射光的峰值半宽。最后,讨论了正向光和背散光随注入光频率扫描速度的变化。发现在环形腔中,总背向散射光强要比单圈背向散射光强大,背向散射光的峰值半宽为正向光的0.64倍。这些发现对背向散射精密测量、扫频法测腔损具有一定的参考作用。     

Wavelength and power dependence of injected C-band laser on pumpconversion efficiency of L-band EDFA

The effect of wavelength and power of an injected C-band laser on the pump conversion efficiency of a L-band erbium-doped fiber amplifier was studied via numerical simulation and experiment. In the studied C-band wavelength range of 1530-1560 nm, for higher injected power with longer wavelength, the backward output amplified spontaneous emission power is compressed more; but the residual laser power is greater due to the smaller emission coefficient at longer wavelength. Thus there is a best choice for injection wavelength and power. With an injection of -2 dBm at 1550 nm, 4.3 and 2.5 dB of gain enhancement for -12 and -2.6 dBm input at 1586 nm were achieved, respectively     

Azimuthal modulation of C-band scatterometer σ0over Southern Ocean sea ice

In a continuing evaluation of the ERS-1 C-band scatterometer as a tool for studying polar sea ice, the authors evaluate the azimuthal modulation characteristics of Antarctic sea ice. ERS-1 AMI scatterometer mode data sets from several study regions dispersed in the Antarctic seasonal sea ice pack are evaluated for azimuthal modulation. When appropriate, the incidence angle dependence is estimated and removed in a study region before determining whether azimuthal modulation is present in the data. Other comparisons are made using the fore and aft beam measurement difference. The results show that over the ice pack, azimuthal modulation is less than 1 dB at the scale of observation of the ERS-1 C-band scatterometer     

Malignant lymphomas of various histological types in pike from the eastern portion of the Baltic Sea

Malignant lymphomas have been found in pikes (Esox lucius L.) caught in the eastern part of the Baltic Sea. The frequency of the disease has increased in recent years. Three different histological types of malignant lymphoma are described in 32 pikes: poorly differentiated diffuse lymphocytic lymphoma, mixed (histiocytoid-lymphocytic) diffuse lymphoma and undifferentiated (anisomorphic) diffuse lymphoma.     

Modeling the statistical time and angle of arrival characteristicsof an indoor multipath channel

Most previously proposed statistical models for the indoor multipath channel include only time of arrival characteristics. However, in order to use statistical models in simulating or analyzing the performance of systems employing spatial diversity combining, information about angle of arrival statistics is also required. Ideally, it would be desirable to characterize the full spare-time nature of the channel. In this paper, a system is described that was used to collect simultaneous time and angle of arrival data at 7 GHz. Data processing methods are outlined, and results obtained from data taken in two different buildings are presented. Based on the results, a model is proposed that employs the clustered “double Poisson” time-of-arrival model proposed by Saleh and Valenzuela (1987). The observed angular distribution is also clustered with uniformly distributed clusters and arrivals within clusters that have a Laplacian distribution     

Elevation angle dependence of fading for satellite PCS in urbanareas

Images of urban Japan taken vertically through a 180° fisheye lens were analysed to derive, as a function of elevation, the fractions of sky that are clear, shadowed by trees, or blocked by buildings. At a 32° elevation, the results match those derived from satellite measurements fitted to a three-state fade model. Using the same model, the elevation angle dependence of mobile satellite fading is predicted for the first time     

Frequency dependence of Rayleigh backscattering in bidirectional optical systems at 0.83 and 1.3 ?m

Measurements are presented of the frequency dependence of Rayleigh scattering in a bidirectional optical system at 0.83 and 1.3 ?m. The results are compared with a theoretical model. The functional forms of the frequency dependencies at both wavelengths are in good agreement with theory; however, the absolute magnitudes of the Rayleigh back-scattered light levels are lower than predicted.     

Method of moments analysis of the backscattering properties of a corrugated trihedral corner reflector

A method of moments (MoM) formulation is developed to analyze the backscattering properties of an anisotropic trihedral corner reflector, which is obtained by corrugating one or several of its interior faces. The proposed formulation treats the corrugated surface as ideally tuned to the incident wave frequency. The numerical analysis of the studied structures has been done using closed-form formulas and accurate numerical integration. The focus of the study reported in this paper has been the polarization responses of ideally tuned corrugated reflectors, which have interesting properties, particularly regarding elliptically or circularly polarized waves. We numerically verify that an appropriately corrugated reflector returns elliptically and circularly polarized waves with the same handedness as the incident wave. For a linearly polarized incident wave, the corner reflector is able to rotate them by 90/spl deg/. Also the effect of the direction of the corrugation to the backscattering properties is studied.     

Some statistical properties of mathematical morphology

Analyzes the statistical properties of the basic binary and multilevel morphological operations with both 1-D and 2D structuring elements. Very simple expressions for the output distribution of erosion and opening are derived in the case of any independent identically or nonidentically distributed inputs. The probability relations between erosion and dilation, also between opening and closing, are developed. The output expectation bias and variances are analyzed and computed to show the efficiency of morphological operations for noise supression. As applications of theoretical results, the effects of the morphological operations on noisy signals are illustrated by several examples. The study reveals certain interesting phenomena. For example, the output variances of opening for some input distributions are greater than those of erosion, and morphological operations perform better than median filters in edge preservation     

分形粗糙海面高斯波束散射特性模拟

利用波束模拟法研究了高斯波束入射下一维分形粗糙海面的电磁散射.通过与传统的矩量法计算进行比较,避免了矩量法在数值计算时因计算机内存限制而遇到的困难,分析了波束模拟法处理粗糙面散射问题的有效性,讨论了计算精度与子波束数目、极化特性和分维的关系.