STUDY ON PASSIVE MICROWAVE REMOTE SENSING OF OIL POLLUTION ON SEA SURFACE

By using the model of air-oil slick-sea water system, the influence of the oil slick thickness, operating frequency of the radiometer and incidence angle on the effective emissivity are calculated and analysed. The optimum scheme for passive microwave remote sensing of oil pollution on sea surface is also proposed and used successfully for airborne microwave remote sensing experiments.     

Fusion of satellite active and passive microwave data for sea icetype concentration estimates

Young first-year sea ice is nearly as important as open water in modulating heat flux between the ocean and atmosphere in the Arctic. Just after the onset of freeze-up, first-year ice is in the early stages of growth and will consist of young first-year and thin ice. The distribution of sea ice in this thickness range impacts heat transfer in the Arctic. Therefore, improving the estimates of ice concentrations in this thickness range is significant. The NASA Team Algorithm (NTA) for passive microwave data inaccurately classifies sea ice during the melt and freeze-up seasons because it misclassifies multiyear ice as first-year ice. We developed a hybrid fusion technique for incorporating multiyear ice information derived from synthetic aperture radar (SAR) images into a passive microwave algorithm to improve ice type concentration estimates. First, we classified SAR images using a dynamic thresholding technique and estimated the multiyear ice concentration. Then we used the SAR-derived multiyear ice concentration to constrain the NTA and obtained an improved first-year ice concentration estimate. We computed multiyear and first-year ice concentration estimates over a region in the eastern-central Arctic in which field observations of ice and in situ radar backscatter measurements were performed. The fused estimates of first-year and multiyear ice concentration appear to be more accurate than NTA, based on ice observations that were logged aboard the US Coast Guard Icebreaker Polar Star in the study area during 1991     

Retrieval of land and sea brightness temperatures from mixedcoastal pixels in passive microwave data

A technique is presented to separate uncontaminated land and sea brightness temperatures from mixed coastal pixels in 37-GHz vertically polarized passive microwave data from the Special Sensor Microwave Imager (SSM/I) instrument. Combining a mathematical model of the instrument response over several neighboring footprints with a GIS representation of the coastline yields a relationship between land and sea brightness temperatures and radiation measurements made at the satellite. Inverting this relationship allows separate land and sea brightness temperature values to be derived for each mixed coastal pixel in the original image. The technique has been successfully applied to 37-GHz vertically polarized SSM/I imagery for test areas covering the Gulf of Aden and the British Isles. Errors in the retrieved brightness temperatures were estimated to be of the order of 1-2 K     

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     

Report on an Arctic summer DTN trial

Delay- and disruption-tolerant networking (DTN) is an emerging area of networking research that will benefit from real-world trials and testbeds. We describe a week long DTN trial carried out during the summer of 2009 in the Laponia area of Northern Sweden that involved the provision of basic email and web services to users who were 57 km distant from any power or networking infrastructure. The trial validated our design and successfully demonstrated the use of email via helicopter-transported data-mules. With the aim of making it easier for others to replicate this kind of trial, the hardware and software used are described with references to full specifications, as are the results of the initial 2009 trial. We also describe plans for an extended trial in summer 2010 in the same area.     

海面目标星载微波辐射无源探测技术研究

为了全天时、全天候、隐蔽性探测海面舰船目标,提出将高分辨率综合孔径微波辐射计作为星载微波辐射无源探测系统,用于探测海面舰船目标.提出一种新方法用于定量化评估微波辐射无源探测系统探测目标的能力;建立系统关键指标、目标微波辐射截面和探测距离间的关系,分别推导微波辐射无源探测系统的探测概率方程和探测距离方程;开展仿真分析和机载验证实验,其结果均表明高分辨率星载综合孔径微波辐射无源探测技术探测海面舰船目标是可行的.高分辨率星载微波辐射无源探测系统可作为我国天基预警体系的重要补充.     

The statistical treatment of passive microwave data

A statistical treatment of microwave remote sensing data of the Earth's surface is described. The statistical characteristics of radiothermal emission from such surfaces as pure water, oil spills on water, soils, and forests are analyzed, and the relationships between the statistics of the radiothermal emission and surface parameters are discussed. As an example of the utility of the statistical approach of microwave retrieval the author suggests a method of determining the danger of fires in forests     

Multitemporal passive microwave mapping in MACHYDRO'90

MACHYDR0'90 was an experiment conducted in Pennsylvania in 1990 to study the synergistic use of remote sensors in multitemporal hydrologic studies. As part of this mission the pushbroom microwave radiometer was flown and used to produce brightness temperature maps. Verification studies and vegetation algorithms for mixed land cover areas are described     

基于CALIOP和MODIS的北极地区海雾检测研究

极地地区的海雾给极地科考和海冰研究带来了挑战,但由于相关监测数据较少,因此对极地地区海雾的研究还相对匮乏。基于CALIOP传感器可以观测垂直方向上云雾信息的特性,使用准同步观测的MODIS中分辨率成像光谱仪对北极地区的云雾信息进行分析。首先使用深度神经网络模型反演云顶高度,再根据云高确定是否为海雾。并且就不同波段对反演结果的影响进行了分析。结果显示使用深度神经网络反演的云顶高度平均绝对误差要比传统方法的结果低1774.280 m,可以更好地对云顶高度进行反演,提高了海雾检测精度。     

Synergy of active and passive satellite microwave data for the study of first-year sea ice in the Caspian and Aral seas

The paper discusses application of active and passive microwave data for assessment of time and space variations of first-year ice cover. The Caspian and Aral seas are chosen as main study areas. The Caspian Sea evolution is primarily climate driven, while for the Aral Sea there is a mix of anthropic and climate factors. We analyze ice cover conditions using a novel method that combines active and passive satellite measurements for ice discrimination. This method uses the synergy of simultaneous data from active (radar altimeter) and passive (radiometer) microwave instruments onboard the TOPEX/Poseidon (T/P) satellite, launched in 1992. The benefits, drawbacks, and potential of ice cover studies using the proposed method are discussed. We analyze in detail how this method is influenced by the difference in footprints of the T/P sensors and by the radiometric properties of ice and snow at different stages of ice cover evolution. In order to link the T/P-derived results to historical observations that end in the mid-1980s, long time series of passive microwave data from SMMR and SSM/I sensors have also been analyzed. Satellite time series of ice cover extent and duration of ice period have been obtained for the Caspian and Aral seas since 1978. A good agreement is obtained between historical and satellite data, with significant spatial and temporal variability of ice conditions. There is a marked decrease of both duration of ice season and ice extent during the winters 1998/1999-2001/2002. These satellite-derived time series of sea ice parameters are very valuable in view of the heterogeneous and mostly unpublished data on ice conditions over the Caspian and Aral seas since the mid-1980s.     

UWB passive microwave imagery from static discharge effects

It is well known that spark transmitters can be sources of ultra-wideband (UWB) radiation. It is also known that high-voltage low energy static discharges are ubiquitous in nature, whenever there is friction between surfaces. Provided is a simple electromagnetic model and it is suggested that it is feasible to construct an ultra-wideband correlator capable of imaging a region of space containing such sources. This would permit a new window of observation on several physical processes, with applications ranging from observations of ice flows to covert operations.     

Airborne active and passive microwave observations of Super TyphoonFlo

Airborne microwave measurements of precipitation associated with Super Typhoon Flo in the western North Pacific were conducted during September 16-18, 1990. The sensor package aboard the NASA DC-8 aircraft included a dual-frequency precipitation radar at 10 GHz and 34 GHz and a host of radiometers operating at 10 GHz, 18 GHz, 19 GHz, 34 GHz, and 92 GHz, as well as three frequencies near the strong water vapor absorption line of 183.3 GHz. The measurements were made during a few passes over the storm center, and active and passive microwave signatures of the rainbands were detected with a fine spatial resolution. The relationship between the measured brightness temperature and radar-estimated rain rate is examined at the frequencies between 10-92 GHz. At both 34 and 92 GHz this relationship is analyzed with the 10 GHz radar reflectivity factor measured at altitudes above the freezing layer as a further constraint. The results show that frozen hydrometeors strongly scatter radiation at these frequencies, especially at 92 GHz. It was shown from a close examination of both active and passive microwave signatures that a significant scattering of radiation at frequencies 118 GHz occurred in the inner eyewall at altitudes of 3-8 km. This scattering of microwave radiation by hydrometeors in both liquid and frozen forms is discussed under the authors' current understanding of the scattering mechanism     

Reflection profiling of Arctic lake ice using microwave FM-CW radar

X- and C-band FM-CW radar reflection profiles were obtained across frozen lakes in northern Alaska using a single elevated high-gain antenna. Clear returns were obtained from the air/snow, snow/ice, ice/water, and ice/ground interfaces. Surface-to-bottom signal intensity ratios are within ranges predicted by plane wave reflection theory, use of which also gives plausible permittivity values for the ice-rich bottom silts. Scattering losses are interpreted for the X-band ice-bottom signals, but evidence of increased volumetric scattering loss with increasing ice thickness may have been masked by changes in bottom dielectric contrasts. The results suggest that this type of radar is superior to conventional transient GPR systems for this application and ice grounded to almost any type of bottom sediments could be profiled from an airborne platform. Such a system could help inventory wetland water volume in northern regions     

Wind-speed dependence of small-grazing-angle microwave backscatterfrom sea surfaces

Results of X-band microwave backscatter from sea surfaces at a small-grazing angle for a range of wind speeds (3.8-10.3 m/s) are presented. The data indicate that the speed of faster-than-Bragg scatterers and their time-averaged polarization ratio both increase with wind speed. At a friction velocity above ~21 cm/s, super events (i.e., backscattering events where the horizontal-polarization power exceeds the vertical-polarization power) begin to appear. The fraction of fast scatterers which produce super events also increases with wind speed. The presence of super events indicates that in addition to scattering mechanisms, such as Bragg-resonant scattering, composite surface theory, wedge scattering, and specular reflection, other mechanisms which favor the horizontal-polarization returns must be considered     

微波无源器件的快速有限元全波分析

从电磁场有限元法出发,采用有限元撕裂对接法将大型复杂模型转化为若干个小型简单模型来进行分析,引入高阶传输条件和并行计算策略进一步提升了有限元撕裂对接法的性能。对基片集成波导和微带滤波器两种典型微波无源器件的S参数进行了仿真分析,数值结果表明了方法的正确性和有效性。     

High-resolution passive polarimetric microwave mapping of oceansurface wind vector fields

The retrieval of ocean surface wind fields in both one and two dimensions is demonstrated using passive polarimetric microwave imagery obtained from a conical-scanning airborne polarimeter. The retrieval method is based on an empirical geophysical model function (GMF) for ocean surface thermal emission and an adaptive maximum likelihood (ML) wind vector estimator. Data for the GMF were obtained using the polarimetric scanning radiometer/digital (PSR/D) on the NASA P-3 aircraft during the Labrador Sea Deep Convection Experiment in 1997. To develop the GMF, a number of buoy overflights and GPS dropsondes were used, out of which a GMF of 10.7, 18.7, and 37.0 GHz azimuthal harmonics for the first three Stokes parameters was constructed for the SSM/I incident angle of 53.1°. The data show repeatable azimuthal harmonic coefficient amplitudes of ~2-3 K peak-to-peak, with a 100% increase in harmonic amplitudes as the frequency is increased from 10.7 to 37 GHz. The GMF is consistent with and extends the results of two independent studies of SSM/I data and also provides a model for the third Stokes parameter over wind speeds up to 20 m/s. The aircraft data show that the polarimetric channels are much less susceptible to geophysical noise associated with maritime convection than the first two Stokes parameters. The polarimetric measurement technique used in the PSR/D also demonstrates the viability of digital correlation radiometry for aircraft or satellite measurements of the full Stokes vector. The ML retrieval algorithm incorporates the additional information on wind direction available from multiple looks and polarimetric channels in a straightforward manner and accommodates the reduced SNRs of the first two Stokes parameters in the presence of convection by weighting these channels by their inverse SNR     

Calibration of passive microwave polarimeters that use hybrid coupler-based correlators

Four calibration algorithms are studied for microwave polarimeters that use hybrid coupler-based correlators: (1) conventional two-look of hot and cold sources; (2) three looks of hot and cold source combinations; (3) two-look with correlated source; and (4) four-look combining methods (2) and (3). The systematic errors are found to depend on the polarimeter component parameters and accuracy of calibration noise temperatures. A case study radiometer in four different remote sensing scenarios was considered in light of these results. Applications for ocean surface salinity, ocean surface winds, and soil moisture were found to be sensitive to different systematic errors. Finally, a standard uncertainty analysis was performed on the four-look calibration algorithm, which was found to be most sensitive to the correlated calibration source.     

海上运动辐射源单站纯方位无源定位分析

针对海上运动辐射源单站纯方位无源定位过程中辐射源运动参数对定位性能的影响进行分析,提出利用对目标的航向分析改进定位性能的方法,分析其性能改善程度及局限性。