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

第一部分：全球定位系统（GPS）等非技术全球导航卫星系统（GNSS）不断向地球发射信号。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。冰雪表面不断充斥着来自全球导航卫星系统的无线电信号。当信号从冰雪表面反射回来，然后到达接收器时，它就像雷达的一种形式，雷达发射器是免费的，覆盖全球，永远开着，不受降水的影响。这项工作将建立和部署一个GNSS反射测量（GNSS- r）系统，专门用于检测冰川表面的反射。这项工作的目标是找出信号如何随地表类型而变化，特别是使用GNSS作为雷达是否可以有效地监测冰雪融化和冰川表面的冻结。在该系统中，将使用两个GNSS天线和接收器，一个向上定位，一个向下收集表面反射。在靠近美国南极洲麦克默多站的麦克默多冰架冰面跑道附近设置GNSS-R系统，该系统将监测信号在表面冰、融水和雪交替反射时的变化。通过现场的相机图像和激光雷达调查，将GNSS“雷达”信号及其反射区域（由于GNSS卫星和接收器位置已知，因此可以从几何图形中得知）与地面类型联系起来。如果GNSS-R发展到与现有的冻结表面表征方法相当或更好的程度，它将在从局部烧蚀监测到飞机跑道安全评估等应用中找到一个合适的位置。提出的研究旨在回答以下问题：能否使用全球导航卫星系统（GNSS）反射测量（GNSS- r）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，从而产生可以告知冰川表面如何积聚和消融的观测结果。本项目将通过GNSS-R仪器设计、现场试验和信号处理，以及与包括目前使用的单天线干涉反射（GNSS-IR）方法在内的其他方法的比较来验证这一假设。目标是开发GNSS-R仪器和数据处理技术，作为一种有效的高时空分辨率方法，表征与南极冰盖气候变化有关的雪、雪和融化冰表面的成分。GNSS-R接收系统将在信号与地表（在这种情况下为冰川）相互作用后捕获信号，以便推断地表的可变组成。无源雷达回波强度将用于表征表面类型，无论是雪、雪、冰还是水。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.