EAGER: Collaborative Research: Mapping Melting Glacial Surfaces with GNSS Reflectometry

第一部分：非技术性的全球导航卫星系统(GNSS)，如全球定位系统(GPS)，正在不断地向地球传输信号。虽然许多人可能熟悉使用GPS信号进行定位和导航，但这些信号也可用于感知地球环境。来自全球导航卫星系统的无线电信号不断地淹没着冰雪表面。当信号从冰或雪表面反弹，然后到达接收器时，它就像一种雷达，雷达发射器是免费的，覆盖全球，始终开启，不受降水的影响。这项工作将建造和部署专门用于探测冰川表面反射的全球导航卫星系统(GNSS-R)。这项工作的目标是找出信号如何随着地表类型的变化而变化，具体地说，就是利用全球导航卫星系统作为雷达，是否可以有效地监测冰川表面的冰雪融化和冻结。在这个系统中，将使用两个GNSS天线和接收器，一个向上定位，另一个向下定位以收集表面反射。将GNSS-R系统安装在南极洲麦克默多冰架上靠近美国麦克默多站的冰面跑道附近，该系统将监测信号的变化，因为它交替反射表面的冰、融水和雪。在现场进行相机图像和激光雷达测量将把全球导航卫星系统的“雷达”信号及其反弹区域(从几何学上可知，因为全球导航卫星系统卫星和接收器的位置已知)与地表类型联系起来。如果GNSS-R发展到可与现有的表征冻结表面的方法相媲美或更好的程度，它将在从局部烧蚀监测到飞机跑道安全评估的各种应用中找到一席之地。第二部分：技术描述拟议的研究渴望回答这样一个问题：全球导航卫星系统(GNSS-R)能否用于在恶劣的冰川环境中以高时空分辨率可靠地绘制积雪、冰和地表水的地图？我们的工作假设是，GNSS-R可以区分冷雪、湿雪、裸冰、湿冰和地表水，这种方式将产生一种观测，可以告知冰川表面是如何积累和消融的。该项目将通过进行GNSS-R仪器设计、现场试验和信号处理，并与其他方法进行比较，包括目前使用的单天线干涉反射法(GNSS-IR)来验证这一假设。其目标是开发全球导航卫星系统-R仪器和数据处理技术，作为描述南极冰盖上与气候变化有关的积雪、积雪和融化冰面成分的一种有效的高时空分辨率方法。GNSS-R接收器系统将在它与表面(在这种情况下是冰川的)相互作用后捕获信号，以便推断表面的不同成分。被动雷达回波强度将被用来表征地表类型，无论是雪、雪、冰还是水。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Part I: Nontechnical Global navigation satellite systems (GNSS) such as the Global Positioning System (GPS) are continuously transmitting signals toward Earth. While many people may be familiar with using the GPS signals for positioning and navigation, these signals are also usable for sensing Earth’s environment. Ice and snow surfaces are continuously awash with radio signals broadcast from GNSS. When the signal bounces off the ice or snow surface and then arrives at a receiver, it acts as a form of radar, in which the radar transmitter is free, covers the globe, is always on, and is unaffected by precipitation. This work will build and deploy a GNSS reflectometry (GNSS-R) system specifically to detect reflections off glaciated surfaces. The goal of the work is to find out how the signal changes depending on surface type, and specifically, whether using GNSS as a radar can be effective for monitoring snow and ice melt and freeze on a glaciated surface. In this system, two GNSS antennas and receivers will be used, one facing upward for positioning, and one directed downward to collect the surface reflections. Setting up the GNSS-R system near the ice runways on the McMurdo Ice Shelf, near to the US McMurdo Station, Antarctica, the system will monitor for variations in the signal as it reflects off alternately surface ice, meltwater, and snow. With camera images and lidar surveys at the site will relate the GNSS “radar” signal and the area it bounced from (knowable from geometry because the GNSS satellite and receiver locations are known) to the surface type. If GNSS-R is developed to the point of being comparable to or better than existing ways of characterizing frozen surfaces, it would find a niche in applications ranging from local ablation monitoring to assessment of aircraft runway safety. Part II: Technical Description The proposed research aspires to answer the question: Can global navigation satellite system (GNSS) reflectometry (GNSS-R) be used to reliably map snow-cover, ice, and surface water in a harsh glaciated environment at high spatio-temporal resolution? Our working hypothesis is that GNSS-R can differentiate among cold snow, wet snow, bare ice, wet ice, and surface water in a way that will yield observations that can inform how glacial surfaces accumulate and ablate. This project will test this hypothesis by conducting GNSS-R instrument design, field trial and signal processing, and comparison with other methods, including the single-antenna interferometric reflectometry (GNSS-IR) method currently in use. The objective is to develop GNSS-R instrumentation and data-processing techniques as an effective high-spatiotemporal-resolution method of characterizing the composition of snow, firn and melting ice surfaces relevant to climate change on the Antarctic Ice Sheet. The GNSS-R receiver system will capture the signal after it has interacted with the surface (glaciated in this case), in order to infer variable compositions of the surface. Passive radar return intensity will be used to characterize the surface type, whether snow, firn, ice, or water.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.