共查询到20条相似文献，搜索用时 46 毫秒
1.
Baskakov A. Gagarin S. Kalinkevitch A. Kutuza B. Terekhov V. 《Oceanic Engineering, IEEE Journal of》1984,9(5):325-328
We discuss the advantages provided by the combined use of a polarization microwave radiometer and a short-pulse radar altimeter for sea roughness monitoring. A brief analysis of the potential of each device taken separately is carried out, which shows the advisability of their combination. The method and the results of the experiment performed with an airborneK -band radiometer and an altimeter are described. It is shown that, in regions of fully developed roughness, a correlation exists between the polarization characteristics of the microwave radiation by the sea surface and the rms sea waveheight as measured by the altimeter. Correlation is not found in regions where the roughness is not developed. Therefore, the combination of the two instruments makes it possible to sense the regions of fully developed sea roughness. 相似文献
2.
The present work describes the various corrections necessary in order to deduce ocean surface temperature fromS -band microwave radiometer measurements and applies these results to a series of data obtained with a high absolute accuracy radiometer. Measurements made with a 2.65 GHz radiometer from an aircraft flown over the Chesapeake Bay area are presented and compared in detail with accurately obtained sea truth data. For the calm sea, it was found that the observed brightness temperature agreed well with that calculated from the known sea surface and atmospheric properties over a fairly wide range of surface salinity values (0.2 per mille to 25 per mille). For cases where the surface wind speeds are of the order of 7 to 15 knots, an excess brightness temperature was observed which is attributable to surface roughness and microscale surface disturbances. The excess brightness temperature dependence on wind speed was found to correlate to a certain extent with the rms wave slope dependence on wind speed. 相似文献
3.
A number of models exist that attempt to explain wave imagery obtained with a synthetic aperture radar (SAR). These models are of two types; static models that depend on instantaneous surface features and dynamic models that employ surface velocities. Radar backscatter values (sigma_{0} ) were calculated from 1.3- and 9.4-GHz SAR data collected off Marineland, FL. Thesigma_{0} data (averaged over many wave trains) collected at Marineland can best be modeled by the Bragg-Rice-Phillips model which is based on roughness variation and the complex dielectric constant of oceans. This result suggests that capillaries on the surface of oceanic waves are the primary cause for the surface return observed by a SAR. Salinity and temperature of the sea at small and medium incidence angles produce little effect upon sea-surface reflection coefficients atX -band, for either of the linear polarizations. The authors' observation of moving ocean, imaged by the SAR and studied in the SAR optical correlator, support a theory that the ocean surface appears relatively stationary in the absence of currents. The reflecting surface is most likely moving slowly (i.e., capillaries) relative to the phase velocity of the large gravity waves. 相似文献
4.
A process of synthetic aperture radar imaging of ocean surface waves is considered on the basis of the two-scale model of microwave scattering by a disturbed sea surface. Analytical expressions are obtained to relate characteristics of a large-scale wave image, averaged over an ensemble of realizations of the small-scale ripple, with the wave, radar, and viewing scheme as parameters. It is shown that the wave image would be defocused as an image of a target moving in the along-track direction with a speed equal to a half of the wave phase speed projection on the line of flight. The defocusing magnitude was measured experimentally for the ocean swells images, obtained with an airborneS -band radar, and the results are found to be in satisfactory agreement with the model prediction. 相似文献
5.
A tide height measurement technique usingS -band radio waves in an oblique incidence interferometer is reviewed. Generalization of the technique is described which reduces the required bandwidth of the radio frequency adjustment and increases its efficiency. This generalization, however, introduces an ambiguity in the height determination and also requires specification of the phase shift of the radio waves specularly reflected from the sea surface. The ambiguity is shown to be easily removable given coarse information about the expected time derivative of tidal height. The influence of the phase shift which contains sea-wave information is studied analytically and requirement in its specification is evaluated to have an accuracy ofpm1deg . This corresponds to a tide height determination accuracy ofpm1 cm. The method is designed for coastal regions where a bistatic experiment geometry is feasible. 相似文献
6.
A method of determining sea-wave parameters from frequency characteristics of an RF signal scattered by the sea surface is considered. The method is based on the Doppler frequency shift due to orbital velocity of motion of long sea waves. It is shown that by measuring the frequency shift ofS -band signals scattered by a small (as compared to the sea-wave length) site on the sea surface, one is able to determine both integrated sea-wave parameters (e.g., rms waveheight and mean period) and the space-time structure of energy-carrying sea components. Results of field tests are presented substantiating the efficiency of the method and allowing measurement accuracy to be evaluated. The main systematic errors of the method are discussed. 相似文献
7.
The complex dielectric constant of snow at microwave frequencies 总被引：1，自引：0，他引：1
Tiuri M. Sihvola A. Nyfors E. Hallikaiken M. 《Oceanic Engineering, IEEE Journal of》1984,9(5):377-382
The complex dielectric constant of snow has been measured at microwave frequencies. New and old snow at different stages of metamorphosis have been studied. The results indicate that the complex dielectric constant is practically independent of the structure of snow. For dry snow, the dielectric constant is determined by the density. For wet snow, the imaginary part and the increase of the real part due to liquid water have the same volumetric wetness dependence. The frequency dependence of the complex dielectric constant of wet snow is the same as that of water. A nomograph for determining the density and wetness of wet snow from its dielectric constant is given. A snow sensor for field measurement of the dielectric constant has been developed. It can be used for determining the density and the wetness of snow by a single measurement. 相似文献
8.
A microwave technique for the measurement of ocean wave spectra has been compared with wave gauge output during extensive field testing. The method is based on the dual-frequency technique for detecting long ocean waves by matching the modulation of short waves with the beat wavelength between two transmitted microwave frequencies. The new method, however, utilizes three microwave frequencies in order to reduce mean backscatter not related to short-wave modulation. Two prototype scatterometers have been built using three frequencies at L -band and at K u-band. Wave spectra have been measured by both radar systems which, when properly normalized, agree well with simultaneous in situ measurements taken by conventional wave gauges at the pier site. Thirteen sets of spectra have been computed, five of which correspond to a situation in which a local wind sea was generated and then decayed. The present experiment does not demonstrate the directionality of this new technique 相似文献
9.
The nature and accuracy of ice-characterization measurements needed to test two microwave backscattering models are clarified by examining the sensitivities of these models to variations in the geophysical parameters they require as input. First, the Bragg, or small perturbation, model for rough surface scattering, which appears appropriate for backscattering from new ice types at L -band, is considered. The sensitivities of this model to variations in the dielectric constant of the ice and to the power spectrum of surface roughness are examined. The dense-medium radiation-transfer model at X -band is considered for backscattering from air bubbles embedded in multilayer ice. The sensitivities of this model to air-bubble size, air-volume fraction, and dielectric loss in the ice are examined. Based on these sensitivities, quantitative characterization guidelines for model testing are discussed 相似文献
10.
Experimental data on emissivity and backscattering properties of sea ice are presented. Measurements were conducted in East and West Soviet regions of the Arctic Ocean during recent years with the IL-18 airborne laboratory and the AN-2 aircraft. The equipment installed on board the aircraft provided simultaneousX -band side looking airborne radar (SLAR) images and radiometric data at wavelengths from 0.8 to 30 cm along the flight paths. Use of these measurements for sea ice studies is discussed. 相似文献
11.
A coherent, CW, dual-frequency,X -band radar was used to study microwave sea return from the Chesapeake Bay. It is shown that the product of the backseattered fields depends strongly on long surface wave properties. In particular, a sharp line is found in the product power spectrum whose frequency is that of the water wave whose wavelength is in resonance with the spatial period of the beat frequency between the two transmitted signals and whose wave vector is parallel to the horizontal line of sight. Thus, gravity wave dispersion relations can be obtained with the system. Furthermore, the degree of modulation of short waves by long ones is given by the intensity of the line. A broad background corresponding to the convolution of the single-frequency Doppler spectra is also seen in the product power spectrum. These results are shown to be interpretable by composite surface scattering theory. 相似文献
12.
13.
基于一维综合孔径微波辐射计的海面温度反演研究 总被引：1，自引：0，他引：1
Due to the low spatial resolution of sea surface temperature(T_S) retrieval by real aperture microwave radiometers,in this study, an iterative retrieval method that minimizes the differences between brightness temperature(T_B)measured and modeled was used to retrieve sea surface temperature with a one-dimensional synthetic aperture microwave radiometer, temporarily named 1 D-SAMR. Regarding the configuration of the radiometer, an angular resolution of 0.43° was reached by theoretical calculation. Experiments on sea surface temperature retrieval were carried out with ideal parameters; the results show that the main factors affecting the retrieval accuracy of sea surface temperature are the accuracy of radiometer calibration and the precision of auxiliary geophysical parameters. In the case of no auxiliary parameter errors, the greatest error in retrieved sea surface temperature is obtained at low T_S scene(i.e., 0.710 6 K for the incidence angle of 35° under the radiometer calibration accuracy of0.5 K). While errors on auxiliary parameters are assumed to follow a Gaussian distribution, the greatest error on retrieved sea surface temperature was 1.330 5 K at an incidence angle of 65° in poorly known sea surface wind speed(W)(the error on W of 1.0 m/s) over high W scene, for the radiometer calibration accuracy of 0.5 K. 相似文献
14.
蒸发波导是一种特殊的大气波导,在其中传播的电磁波信号会被陷获在近海大气层中,实现超视距传播。受海表面温度、湿度、风速、微波频率等因素的影响,海洋蒸发波导环境中的微波传播特性起伏变化很大,规律十分复杂。以往的工作主要通过计算这些气象因素对蒸发波导条件下大气折射率剖面的影响来分析它们对路径损失的作用,其结果与实验数据仍有较大差异。本文在一定的蒸发波导条件下,利用一维分形海面模型产生海面“地形”,将其作为抛物方程电磁波传播模型的边界条件进行计算,得到相应的路径损失,并与传统计算方法进行对比,分析了不同蒸发波导高度、不同频率及不同接收天线高度时的数值模拟情况,可为舰艇通信系统或者雷达系统的设计提供相应的依据。 相似文献
15.
The effect of a snow cover on sea ice upon radar backscatter at microwave frequencies (X - andKu -baud) can be important. The effect of scattering from the snow cover on thesigmadeg of first-year ice is shown to be severe (5 cm of dry snow can raisesigmadeg by 8 dB at 9 GHz), while that onsigmadeg of multiyear ice is shown to be smaller. The low thermal conductivity of snow compared to that of sea ice effectively raises the temperature of the upper surface of the ice, resulting in higher dielectric constants for the ice, thereby modifying the backscatter both from the ice surface and from the scattering volume. The temperature effect of a 10-cm snow cover on 3-m-thick multiyear ice is to lower thesigmadeg by only about 0.3 dB for air temperature of-20deg C. The effect on 1-m-thick first-year ice is even less. Hence, the volume-scattering effect of snow is more important than the temperature effect. The presence of a wet snow cover can block the volume-scattering contribution of the multiyear ice. The effect of wet snow cover on first-year ice should be smaller than that Of dry, snow, becausesigmadeg of wet snow is lower than that of dry snow. 相似文献
16.
Results from radar backscatter experiments conducted over the North Sea in Project Noordwijk in the years 1977, 1978, and 1979 are reported. For these measurements a short-rangeX -band FM/CW scatterometer was used. Data obtained were the average normalized backscattergamma(sigmadeg) of the sea as a function of grazing angle, windspeed, and look direction. The fading spectra and the autocorrelation function ofgamma(t) were also determined and compared with the output of the oceanographic sensors of the platform. 相似文献
17.
大气对微波散射计回波信号衰减的修正方法研究 总被引：2，自引：0，他引：2
为了使微波散射计测得的海面后向散射具有足够的精度，必须考虑大气对微波衰减的影响。大气对微波的衰减可以用微波射计来测定。本文将估算晴空、云和降雨天气下的衰减系，讨论计算海面发射率及用微波辐射计剩余亮温估算散射计工作频率下大气衰减的方法。 相似文献
18.
Kohtaro Hosoda 《Journal of Oceanography》2010,66(4):439-473
Satellite-based microwave radiometers can measure sea surface temperature (SST) over wide areas, even under cloud cover, owing
to the weak absorption of microwaves by cloud droplets. This advantage is not available in the case of infrared observations,
hence SST data derived from microwave radiometers have been widely used for operational and research purposes in recent years.
This paper reviews the significant algorithms, validations, and applications related to microwave observation of SST. The
history and specifications of past and present microwave radiometers are also documented. Various physical properties, including
sea surface salinity, sea surface wind, molecules in the atmosphere, and clouds, affect the accuracy of SST data estimated
by satellite-based microwave radiometers. Estimation algorithms are designed to correct these effects by using microwave measurements
in several frequency channels and by using data of ancillary geophysical parameters. Validation studies have shown that microwave
radiometer SST data have high accuracy that is comparable to the accuracy of data obtained from infrared measurements. However,
certain persistent problems, such as sea-surface wind correction, remain to be solved. 相似文献
19.
星载微波辐射计外定标的关键问题是通过辐射传输方程计算天线入瞳处亮温。根据辐射传输方程,海面成份对亮温的影响包括海面的微波辐射和对下行大气辐射的反射,其中的关键参数分别为海面发射率ep和海表面反射率R。文中对平静海面Fresnel反射率模式和粗糙海面反射率模式进行了研究分析,在此基础上着重研究了海面温度TS、海面盐度SS、海面风速W、以及观测角度θ等物理参数对海面发射率ep的影响,进而分析了这些物理参数的测量误差对亮温的计算精度的影响。 相似文献
20.
First results from a recently developed surface sensor for measuring the dielectric constant of snow at about 1 GHz are reported together with ground-based measurements of brightness temperatures between 4.9 and 94 GHz. The data are used to derive spectra of complex dielectric constants of wet snow for frequencies between 1 and 100 GHz. The result is simple: Debye relaxation spectra with a constant relaxation frequency of 9 GHz appear in contradiction to the mixing formula of Polder and van Santen. A way of resolving this discrepancy is presented. 相似文献