Tutorial on Remote Sensing Using GNSS Bistatic Radar of Opportunity

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.

The Impact of Inter-Modulation Components on Interferometric GNSS-Reflectometry

“…The general expression for BPSK and BOC modulations could be written as BPSK(n) and BOC(n, m), in which n and m refer to the code chipping rate of n × 1.023 MHz and the subcarrier frequency of m × 1.023 MHz. Thus, the C/A code, P code and M code could be expressed as BPSK(1), BPSK(10) and BOC(10, 5) respectively, and the IM component as BOC (10,10) [23]. Figure 2 summarizes the ACFs of the different signal components in the GPS modernized L1 band.…”

“…During the past two decades, several theoretical and experimental studies have been performed to demonstrate the feasibility of ocean altimetry using reflected GNSS signals, e.g., in [2][3][4][5][6][7][8][9], and several studies have been performed on scatterometric applications, such as sea surface wind, sea ice and soil moisture. A comprehensive tutorial of GNSS-R technique and its applications can be found in [10].…”

Efficient Folding Processor for Direct Precision Code Acquisition in Global Positioning System Sensors

“…(1)(2)(3) To estimate the distance from the satellites, the GPS sensor performs code acquisition. In the GPS, the precision code (P code) is employed to provide a high degree of positioning accuracy owing to its long period (one week).…”

Low-Cost GPS Receivers for the Monitoring of Sunflower Cover Dynamics

“…One of the most outstanding examples is the GNSS reflectometry (GNSS-R), where the navigation signals are used in a bistatic radar configuration [7] to sense oceans, soil moisture, snow and ice, vegetation, and forest characteristics [8,9]. In the specific case of vegetation measurements, several GNSS-R techniques have demonstrated their potential: a single antenna approach with dedicated linearly polarized receivers [10] or commercial geodetic receivers [11].…”