An Improved Method of Multiple RFI Intensity Estimation for Synthetic Aperture Interferometric Radiometer

L-band radio frequency interferences (RFIs) seriously contaminate remote sensing data. This poses a major challenge in processing microwave radiometric data and can substantially degrade the quality of the data. There is an urgent need to estimate RFI intensity to mitigate Gibbs errors caused by RFIs along the sidelobes. The traditional CLEAN algorithm is limited in its ability to account for the interactions among multiple RFIs, which results in biased intensity estimations. In this article, the RFI brightness temperature (BT) model is modified to incorporate the interactions among multiple RFI sources. Building upon this modified model, we establish fundamental equation sets and propose a numerical solution method for calculating RFI intensity. Experiments and simulations based on soil moisture and ocean salinity (SMOS) data confirm that the method presented in this article, which we have named multiple source intensity decoupling (MUSID), outperforms the traditional CLEAN algorithm.

I. Introduction

In the 1.4-GHz frequency band, also known as the L-band, the radiometric brightness temperature (BT) is sensitive to the variations in surface salinity over the oceans. The sensitivity of this frequency makes it highly valuable for monitoring and measuring changes in ocean salinity levels [1], [2]. However, due to the longer wavelength associated with this frequency band, there is a need for improved spatial resolution in the antenna aperture to meet the higher demand. This demand has led to the introduction of the synthetic aperture interferometric radiometer (SAIR), which provides enhanced resolution capabilities [3]. The concept of “aperture synthesis” not only improves spatial resolution but also addresses the limitation of finite aperture in traditional radiometers. This means that it can overcome the challenges posed by the physical size of the antenna, allowing for better data capture and higher quality imaging [4]. The SAIRs use interferometric measurements to operate spatial frequency sampling, also known as visibility sampling, and SAIRs retrieve the BT through Fourier transformation and other algorithms [5]. Microwave imaging radiometer using aperture synthesis (MIRAS), specifically designed for observing sea surface salinity and soil moisture, is an airborne SAIR [6].