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

点击翻译按钮获取中文摘要

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.