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首页> 外文学位 >Sea ice radar backscatter modeling, measurements, and the fusion of active and passive microwave data.
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Sea ice radar backscatter modeling, measurements, and the fusion of active and passive microwave data.

机译：海冰雷达反向散射建模，测量以及有源和无源微波数据的融合。

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The polar oceans play a key role in our climate because of the complex interactions between sea ice, open water and the atmosphere. Because of the persistent cloud cover and darkness in the Arctic for roughly half the year, the most viable means for monitoring sea ice on a global basis is with satellite microwave remote sensing instruments. The development of techniques for utilizing microwave remote sensing data depend on our understanding of the backscatter and emission properties of sea ice. Seasonal transitions are particularly difficult for interpretation of microwave scattering and emission from sea ice, due to the rapidly changing environmental conditions.; We investigated several key issues concerning the radar backscatter signatures of Arctic sea ice during the summer-to-fall transition and examined the potential for fusing active and passive microwave data for ice type concentration estimation.; To improve measurements made with short-range FM and step-frequency radar systems we developed coherent noise reduction techniques. We have demonstrated that these techniques are useful for a number of the systems designed for exploring the backscatter properties of sea ice. These coherent noise reduction methods improve the sensitivity of single-antenna radar systems by as much as 25 dB.; We obtained C-band measurements of radar backscatter from multiyear ice during the onset of freeze-up in the Arctic. Through the use of measurements of ice and snow physical properties and electromagnetic scattering models we determined the scattering mechanisms responsible for the observed changes in radar backscatter. The refreezing of moisture on or near the ice surface of multiyear ice causes a decrease in the lossy part of the permittivity of the ice. This allows more energy to penetrate into the sea ice volume, which results in increased volume scattering. This results in a dramatic increase in the radar backscatter from sea ice at the onset of freeze-up. We demonstrated that these changes are also observed on a large scale from satellite synthetic aperture radar (SAR) data and can be used to detect the onset of freeze-up in the Arctic.; Finally, we utilized a technique to combine active and passive microwave data for estimating ice type concentration during the freeze-up season. This technique uses multiyear ice concentrations, obtained by analysis of ERS-1 SAR data. The multiyear ice concentration, derived from the SAR data, is used to constrain a multispectral algorithm for determining ice type concentration from satellite passive microwave data. According to ship-based ice observations the "fused" estimates of first-year ice concentration appear to be more accurate than estimates based on the SSM/I data alone.
机译：由于海冰，开放水域与大气之间的复杂相互作用，极地海洋在我们的气候中起着关键作用。由于北极地区持续约半年的持续云层覆盖和黑暗，全球范围内监测海冰的最可行方法是使用卫星微波遥感仪器。利用微波遥感数据的技术的发展取决于我们对海冰的反向散射和发射特性的理解。由于瞬息万变的环境条件，季节转换对于解释微波散射和海冰发射特别困难。我们研究了从夏季到秋季过渡期间北极海冰的雷达反向散射特征的几个关键问题，并研究了将主动和被动微波数据融合以进行冰类型浓度估算的潜力。为了改善使用短距离FM和步进频率雷达系统进行的测量，我们开发了相干降噪技术。我们已经证明，这些技术对许多设计用于探索海冰反向散射特性的系统很有用。这些相干降噪方法可将单天线雷达系统的灵敏度提高多达25 dB。在北极冻结期间，我们获得了多年冰层雷达反向散射的C波段测量值。通过使用冰雪物理性质和电磁散射模型的测量，我们确定了引起雷达反向散射变化的散射机制。多年制冰的冰表面上或附近的水分的重新冻结导致冰的介电常数的有损部分减小。这允许更多的能量渗透到海冰体积中，从而导致体积散射增加。这导致冻结开始时海冰对雷达的反向散射急剧增加。我们证明了从卫星合成孔径雷达（SAR）数据还可以观察到这些变化，并且可以用来检测北极地区冻结的发生。最后，我们利用一种技术来组合主动和被动微波数据，以估计冰冻季节的冰种浓度。该技术使用多年冰浓度，这是通过分析ERS-1 SAR数据获得的。从SAR数据得出的多年冰浓度用于约束从卫星无源微波数据确定冰类型浓度的多光谱算法。根据基于船的冰观测，第一年冰浓度的“融合”估计似乎比仅基于SSM / I数据的估计更准确。

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