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首页> 外文期刊>Journal of Geophysical Research, C. Oceans: JGR >Whitecap lifetime stages from infrared imagery with implications for microwave radiometric measurements of whitecap fraction
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Whitecap lifetime stages from infrared imagery with implications for microwave radiometric measurements of whitecap fraction

机译：红外图像中的白帽寿命阶段，对微波辐射测量白帽级分有影响

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摘要

Quantifying active and residual whitecap fractions separately can improve parameterizations of air-sea fluxes associated with breaking waves. We use data from a multi-instrumental field campaign on Floating Instrument Platform (FLIP) to simultaneously capture the signatures of active and residual whitecaps at visible, infrared (IR), and microwave wavelengths using, respectively, video camera, mid-IR camera, and a radiometer at 10 GHz. We present results from processing and analyzing IR images and correlating this information with radiometric time series of brightness temperature at horizontal and vertical polarizations T_(BH) and T_(BV). The results provide evidence that breaking crests and decaying foam appear in mid-IR as bright and dark pixels clearly distinguishing active from residual whitecaps. We quantify the durations of whitecap lifetime stages from the IR images and identify their corresponding signatures in T_B time series. Results show that T_(BH) and T_(BV) vary in phase during the active and in antiphase during the residual whitecap stages. A methodology to distinguish active and residual whitecaps in radiometric time series without a priori IR information has been developed and verified with corresponding IR and video images. The method uses the degree of polarization P (the ratio between the sum and difference of T_(BV) and T_(BH)) to capture whitecaps as prominent spikes. The maximum and zero-crossing of the first derivative of P serve to identify the presence of active whitecaps, while the minimum of dP marks the transition from active to residual whitecap stage. The findings have implications for radiometric measurements of active and total whitecap fractions.
机译：分别量化有效白帽和残余白帽的比例可以改善与破碎波相关的海-气通量的参数化。我们使用来自浮动仪器平台（FLIP）上的多仪器野外活动的数据，分别使用摄像机，中红外摄像机，在可见光，红外（IR）和微波波长下同时捕获有效和残留白帽的信号，和10 GHz的辐射计。我们介绍了处理和分析红外图像并将此信息与水平和垂直极化T_（BH）和T_（BV）下的亮度温度辐射时间序列相关的结果。结果提供了证据，表明破裂的波峰和腐烂的泡沫出现在中红外，因为明暗像素清楚地区分了活性成分和残留的白帽成分。我们从红外图像中量化了白帽生命阶段的持续时间，并在T_B时间序列中标识了它们的相应特征。结果表明，T_（BH）和T_（BV）在活动期间的相位变化，在剩余白帽阶段的相位变化。已经开发出一种方法，该方法可以在没有先验IR信息的情况下区分辐射时间序列中的有效白帽和残留白帽，并已通过相应的IR和视频图像进行了验证。该方法使用极化度P（T_（BV）和T_（BH）之和与差之比）捕获白帽作为突出的尖峰。 P的一阶导数的最大值和零交叉点用于识别活动的白帽的存在，而dP的最小值则指示从活动的白帽阶段过渡到残留的白帽阶段。该发现对活性白总级分和总白帽级分的辐射测量具有重要意义。

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