Modelling Sea Surface Wind Vectors with Coherent Dual Polarization Synthetic Aperture Radar

加拿大是一个海洋国家，其经济和总体福祉与海洋密切相关。加拿大北极地区的海冰继续达到超过历史水平的年度最低水平，增加了船舶交通量和资源开采，同时延长了加拿大东部的冰山季节。大型游轮开始在西北航道和巴芬湾的水域穿梭，为北部社区带来了新的经济机会。然而，全球变暖造成了这些无冰条件，也导致了极端天气，这增加了北方海上作业的风险。本研究的总体目标是提高加拿大对加拿大北部风场的监测能力，包括北极岛屿之间的通道以及格陵兰岛和纽芬兰岛之间的水域。成像雷达是在加拿大北部水域收集信息的完美工具，因为它能够在任何天气（包括厚厚的云层）日夜成像。成像雷达可以发送和接收特定偏振的微波，就像偏振太阳镜可以阻挡从具有特定偏振的水中反射的光一样。加拿大航天局正准备发射新一代成像雷达卫星，称为雷达卫星星座任务（RCM）。这些新卫星将能够传输一种偏振，并在传输的同一偏振上生成一幅图像，再加上在完全相反的偏振上生成第二幅图像。这就是所谓的双极化。在这项研究中，我将探索使用海洋的双偏振雷达图像来创建风速和风向的地图。为了做到这一点，我将观察每张图像中的能量强度，并将其与每张图像中的多普勒频率结合起来。多普勒效应是移动的接收器接收到的波的频率变化。当一辆消防车从你身边驶过时，你就会听到这种效果——当它驶近时，它发出的声音是高音，当它驶离时，它发出的声音是低音。当雷达接近一片海面时，它的频率更高，当它飞过时，频率就会降低。这种情况随着接收者的移动而变得更加复杂，例如，当你骑着自行车时，消防车向你驶来。接近时的频率甚至更高，当雷达经过时，频率甚至更低。这种效应是可以预测的（每种极化都是不同的），并且与海面的运动有关，反过来又与风速和风向有关，这是我将要估计的。

Canada is a maritime nation, whose economy and general well-being is closely tied to the sea. The sea ice in Canada's Arctic continues to reach annual minima that exceed historical levels, increasing ship traffic and resource exploitation, as well as extending the iceberg season in eastern Canada. Massive cruise ships are starting to ply the waters of the Northwest Passage and Baffin Bay exposing northern communities to new economic opportunities. Yet, global warming, which has created these ice-free conditions, has also led to extreme weather, which increases the risks of maritime operations in the North.The overall objective of this research is to improve Canada's capability of monitoring the wind field in Canada's north, including the channels between the Arctic islands, and the waters between Greenland and Newfoundland.An imaging radar is the perfect instrument for gathering information over Canada's northern waters as it is capable of imaging night or day and in all weather, including thick clouds. Imaging radar can transmit and receive microwaves at certain polarizations, like polarizing sunglasses can block out light reflected from the water that has a certain polarization. The Canadian Space Agency is preparing to launch a new generation of imaging radar satellites, called the Radarsat Constellation Mission or RCM. These new satellites will be able to transmit one polarization, and create one image, at the same polarization that was transmitted, plus a second image at the exact opposite polarization. This is called dual-polarization.In this research I will explore the use of dual-polarized radar images of the sea to create maps of wind speed and direction. To do this I will look at the intensity of the energy in each image, and I will combine this with the Doppler frequency in each image. The Doppler effect is the change in frequency of a wave that is received by a moving receiver. You hear this effect when a fire engine drives past you - it is a high pitched sound as it approaches, and a lower pitched sound as it drives away. As the radar approaches a patch of sea surface it is at a higher frequency, and as it flies past the frequency gets lower. This situation gets more complicated as the receiver moves, e.g. if the fire engine is driving towards you as you are riding your bike. The frequency on approach is even higher and gets even lower as the radar passes by. This effect is predictable (and different for each polarization), and is related to the movement of the sea surface, and in turn to both the wind speed and direction, which is what I will estimate.