A model for Brewster angle damping and multipath effects on the microwave radar sea echo at low grazing angles
A model for Brewster angle damping and multipath effects on the microwave radar sea echo at low grazing angles
复制标题
DOI：
10.1109/36.628790
复制
发表时间：
1997-09
期刊：
影响因子：
--
通讯作者：
D. Trizna
中科院分区：
文献类型：
--
作者：
D. Trizna
布鲁斯特角阻尼和局部多径效应被认为是低掠角海面散射特性中极化差异的来源。作者表明，至少有五个观测到的偏振差异可以解释为由于离散的非线性海洋表面特征，如钻孔和小尺度破碎波的照明而发生的局部多径干扰效应。照明增益因子（IGF）在空间中的一点处被定义为相对于入射平面波中的功率的该点处的总功率。从离散散射体前方的海面的局部多径产生的IGF产生强的干涉图案，其可以随掠射角和散射体高度而变化。因此，当干扰为相长干扰时，水平极化（HH）的IGF值可高达16倍（12 dB）;相消干扰会产生相应的强抵消。这些极端的变化可能会导致强烈的HH NRCS振幅调制，由于本地波斜率的变化或散射体形状随时间的变化。然而，对于垂直（VV）偏振，对于低于20/spl deg/的掠射角，前向散射路径的布鲁斯特角阻尼发生，并且减小了VV IGF的幅度和动态范围，消除了这种强调制。这种效应与雷达波长成比例，并且需要更高的波特征来产生远低于10 GHz的雷达频率的等效效应。作为说明，比较了海水电介质的六个雷达波段：L（1.4 GHz）、S（3.5 GHz）、C（5 GHz）、X（10 GHz）、K/sub u/（15 GHz）和K/sub a/（35 GHz）。X波段的结果表明，12分贝IGFs可以发生的水面特征，只是一厘米以上的平均表面。作为这些结果的应用，这些HH和VV IGF模式的影响建模为离散散射体均匀分布沿着海洋重力波。的动态范围的HH IGF的孔散射高达5厘米高的分布被发现他显着大于VV在长波的所有位置。此外，IGF HHVV极化比向前的波峰，其中出现最大数量的小尺度破碎波散射体，是大于在所有其他区域的长波，20分贝的顺序。这些结果表明，HH偏振可能是敏感的小尺度破碎功能的海洋表面在低掠角，因此可能是一个敏感的措施的海气通量。
Brewster angle damping and local multipath effects are considered as sources of polarization differences in low grazing angle sea scatter characteristics. The authors show that at least five observed polarization differences can be explained by local multipath interference effects that occur due to the illumination of discrete nonlinear ocean surface features, such as bores and small scale breaking waves. The illumination gain factor (IGF) is defined at a point in space, as the total power at that point relative to the power in the incident plane wave. The IGF resulting from local multipath from the sea surface forward of a discrete scatterer produces strong interference patterns that can vary both with grazing angle and scatterer height. As a result, IGF values up to a factor of 16 (12 dB) can occur for horizontal polarization (HH) when the interference is constructive; a corresponding strong cancellation occurs for destructive interference. These extreme variations can cause strong HH NRCS amplitude modulations due either to a change of local wave slope or a change of scatterer shape with time. However, Brewster angle damping of the forward scatter path for grazing angles below 20/spl deg/ occurs for vertical (VV) polarization, and reduces the VV IGF in magnitude and dynamic range, eliminating such strong modulations. This effect scales with radar wavelength, and higher wave features are required to produce equivalent effects for radar frequencies far below 10 GHz. As an illustration, six radar bands are compared: L (1.4 GHz), S (3.5 GHz), C (5 GHz), X (10 GHz), K/sub u/ (15 GHz), and K/sub a/ (35 GHz), for a sea water dielectric. X-band results indicate that 12-dB IGFs can occur for water surface features just a centimeter above the mean surface. As an application of these results, the influence of these HH and VV IGF patterns is modeled for discrete scatterers distributed uniformly along an ocean gravity wave. The dynamic range of the HH IGF for a distribution of bore scatterers up to 5 cm high is found to he significantly larger than for VV at all locations on the long wave. Moreover, the IGF HHVV polarization ratio forward of the crest, where the largest number of small scale breaking wave scatterers occurs, is larger than at all other regions of the long wave, of the order of 20 dB. These results suggest that HH polarization may be sensitive to small scale breaking features on the ocean surface at low grazing angles, and thus may be a sensitive measure of air-sea fluxes.