Sentinel-1 sar observations of peak wavelength and dominant wave direction in the marginal ice zone of the barents sea
Sentinel-1 sar observations of peak wavelength and dominant wave direction in the marginal ice zone of the barents sea
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Sentinel-1 sar对巴伦支海边缘冰区峰值波长和主波方向的观测
DOI：
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
H. Johnsen
中科院分区：
文献类型：
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作者：
D. Monteban;R. Lubbad;H. Johnsen
合成孔径雷达(SAR)已被证明是极地地区非常重要的数据来源，因为它连续覆盖大片区域，与天气和一天中的时间无关。在这项研究中，我们利用Sentinel-1干涉宽幅(IW)条带SAR图像来研究长波通过巴伦支海冰水的峰值波长和主波方向的变化。我们通过将Sentinel-1合成孔径雷达的结果与现场浮标测量结果进行比较，验证了我们对公开水域峰值波长和主波方向的估计，浮标测量是巴伦支海冰洋网络(BaSMIN)测量活动的一部分。我们发现，当波传播到海冰中时，峰值波长增加。这与我们关于海浪穿透Miz的知识非常一致，在Miz，海冰扮演着海浪的天然低通过滤器的角色。其结果是在海冰上，特别是在离冰缘一段距离的地方，从合成孔径雷达图像中消失了高频波。由于高频波的存在使合成孔径雷达图像变得模糊，海冰中的合成孔径雷达图像变得比开阔海洋上的图像质量更高。因此，观测到的峰值波长在开阔水域的扩散比在海冰内要大得多。此外，相对于冰缘，主波方向向法线方向变化。这可能是由斯内尔定律推动的，并与之前研究的结果一致。在冰缘附近发现了主导波方向的巨大移动，这部分是由于波折射造成的物理原因，部分是成像伪影。后者源于这样一个事实，即海冰的方位截止点(即沿航迹的空间分辨率损失)比开阔水域的小得多，因此在开阔水域上空的图像中看不到的波可能出现在海冰上方的图像中。这纯粹是由于合成孔径雷达成像导致了靠近冰缘的波方向发生了明显的变化。我们用我们处理过的图像演示了这一效果。
Synthetic aperture radar (SAR) has proven to be a very important source of data in the Polar regions because it covers large areas continuously, independent of the weather and time of day. In this study, we make use of Sentinel-1 Interferometric wide (IW) swath SAR images to study the change in peak wavelength and dominant wave direction of long waves traveling through icy waters in the Barents Sea. We verify our estimates of the open water peak wavelength and dominant wave direction by comparing the results from the Sentinel-1 SAR with in-situ buoy measurements, which are part of the Barents Sea Metocean and Ice Network (BaSMIN) measurement campaign. We find that the peak wavelength increases as waves propagate into the sea ice. This agrees well with our knowledge of wave penetration into the MIZ, where the sea ice acts as a natural low pass filter on the ocean waves. A consequence of this is the disappearance of the high frequency waves from SAR images over the sea ice especially at a distance from the ice edge. Since the presence of high frequency waves blur the SAR images, SAR images in sea ice become of higher quality compared to images over the open ocean. As a result, the spread in observations of the peak wavelength is much larger in the open water than within the sea ice. Further, the dominant wave direction changes towards the normal, relative to the ice edge. This can be motivated by Snell’s law and agrees with findings from previous studies. A large shift of the dominant wave direction is found in the vicinity of the ice edge, which is partly physical due to wave refraction and is partly an imaging artefact. The latter stems from that fact that the azimuth cut-off (i.e., loss of spatial resolution along track) is much smaller in the sea ice than in open water and thus waves that were not visible in images over the open water may appear in images over the sea ice. This causes an apparent shift in wave direction close to the ice edge that is purely due to SAR imaging. We demonstrate this effect with our processed images.