Review of crop growth and soil moisture monitoring from a ground‐based instrument implementing the Interference Pattern GNSS‐R Technique

TLDR

Reflectometry using GNSS signals has evolved over the past decade into a promising tool for retrieving geophysical parameters such as soil moisture, vegetation height, and topography from land, ocean, and ice surfaces. This study evaluates the Interference Pattern Technique (IPT) for land‑based retrievals of soil moisture, vegetation height, and topography, with a detailed analysis of soil moisture across irrigation–drying cycles in a maize field. IPT measures the power fluctuations of the interference between simultaneous direct and reflected GNSS signals, enabling real‑time retrievals from a ground‑based instrument. The experiment over a 300‑cm‑tall maize crop demonstrated that IPT accurately retrieved soil moisture and vegetation height, matching probe measurements and confirming its effectiveness in dense, water‑rich vegetation.

Abstract

Reflectometry using Global Navigation Satellite Systems signals (GNSSR) has been the focus of many studies during the past few years for a number of applications over different scenarios as land, ocean or snow and ice surfaces. In the past decade, its potential has increased yearly, with improved receivers and signal processors, from generic GNSS receivers whose signals were recorded in magnetic tapes to instruments that measure full Delay Doppler Maps (the power distribution of the reflected GNSS signal over the 2‐D space of delay offsets and Doppler shifts) in real time. At present, these techniques are considered to be promising tools to retrieve geophysical parameters such as soil moisture, vegetation height, topography, altimetry, sea state and ice and snow thickness, among others. This paper focuses on the land geophysical retrievals (topography, vegetation height and soil moisture) performed from a ground‐based instrument using the Interference Pattern Technique (IPT). This technique consists of the measurement of the power fluctuations of the interference signal resulting from the simultaneous reception of the direct and the reflected GNSS signals. The latest experiment performed using this technique over a maize field is shown in this paper. After a review of the previous results, this paper presents the latest experiment performed using this technique over a maize field. This new study provides a deeper analysis on the soil moisture retrieval by observing three irrigation‐drying cycles and comparing them to different depths soil moisture probes. Furthermore, the height of the maize, almost 300 cm, has allowed testing the capabilities of the technique over dense and packed vegetation layers, with high vegetation water content.