Tutorial on Remote Sensing Using GNSS Bistatic Radar of Opportunity

TLDR

Traditional GNSS receivers suffer from multipath interference that degrades positioning accuracy, prompting researchers to explore reflected GNSS signals for remote‑sensing applications. The tutorial aims to describe the GNSS bistatic radar of opportunity technique, review existing results, and overview current and planned missions. By pairing a GNSS transmitter with a receiver that processes scattered signals, the system functions as a bistatic radar that can serve as an altimeter or scatterometer to estimate surface height, roughness, dielectric properties, and derive geophysical parameters such as ocean topography, winds, soil moisture, vegetation, snowpack, and sea ice, with capabilities varying by platform. It highlights interesting results already obtained with this remote‑sensing approach.

Abstract

In traditional GNSS applications, signals arriving at a receiver's antenna from nearby reflecting surfaces (multipath) interfere with the signals received directly from the satellites which can often result in a reduction of positioning accuracy. About two decades ago researchers produced an idea to use reflected GNSS signals for remote-sensing applications. In this new concept a GNSS transmitter together with a receiver capable of processing GNSS scattered signals of opportunity becomes bistatic radar. By properly processing the scattered signal, this system can be configured either as an altimeter, or a scatterometer allowing us to estimate such characteristics of land or ocean surface as height, roughness, or dielectric properties of the underlying media. From there, using various methods the geophysical parameters can be estimated such as mesoscale ocean topography, ocean surface winds, soil moisture, vegetation, snowpack, and sea ice. Depending on the platform of the GNSS receiver (stationary, airborne, or spaceborne), the capabilities of this technique and specific methods for processing of the reflected signals may vary. In this tutorial, we describe this new remotesensing technique, discuss some of the interesting results that have been already obtained, and give an overview of current and planned spacecraft missions.