# Resource-Efficient FPGA Architecture for Real-Time RFI Mitigation in Interferometric Radiometers
## 1 Introduction  
Microwave radiometry has established itself as a cornerstone of Earth Observation (EO) systems, providing precise data for monitoring critical environmental parameters such as soil moisture, ocean salinity, and atmospheric conditions [1]. Current operational satellites employing microwave radiometers, including Soil Moisture and Ocean Salinity (SMOS) [2] and Soil Moisture Active Passive (SMAP) [3], have demonstrated the technology's capabilities for global environmental monitoring. These instruments operate in protected frequency bands theoretically reserved for passive observations. However, the exponential growth of wireless communications, coupled with unauthorized transmissions and out-of-band emissions, has led to an increase in Radio Frequency Interference (RFI) incidents [4, 5, 6]. The proliferation of RFI sources compromises data quality and scientific observations, presenting a significant challenge for current and future Earth observation missions. RFI can originate both from external sources and from conducted or radiated interference within the satellite itself [7]. The impact of RFI on radiometric measurements manifests in various forms, ranging from subtle biases that distort scientific data to complete data loss in severely affected regions. Analysis of SMOS mission data has revealedsignificant RFI contamination patterns, particularly over densely populated regions in Asia and Europe [8]. In some areas, persistent interference has rendered measurements completely unusable, necessitating extensive data filtering and correction procedures [9]. Similar challenges have been documented for the SMAP mission [10] and other radiometric systems, highlighting RFI as a critical concern that must be addressed to ensure the viability of future Earth observation missions [11]. The scientific community has responded to these challenges by developing increasingly sophisticated RFI detection and mitigation strategies [12; 13; 14]. These approaches have evolved from simple threshold-based techniques to complex multi-domain analysis methods. After the key lessons learnt from SMOS [15], a new architecture for advanced L-band radiometers using 1-bit quantization at a higher sampling rate was proposed [16]. As part of the technology activities, the RFI detection algorithm presented in [17] was developed. The algorithm processes the 1-bit quantized signals and employs innovative techniques such as frequency-domain cross-correlation computation and Polarimetric Kurtosis, offering promising results in theoretical and simulation studies. The challenges of RFI detection with highly quantized data are illustrated in Figure 1, which shows a chirp interference signal before and after 1-bit quantization. The quantization process introduces several critical effects: signal clipping fundamentally alters both temporal and spectral properties, generating harmonics at integer multiples of the RFI's fundamental frequency, some of which manifest as aliases in the frequency domain. Despite these distortions, the temporal and spectral signatures of the RFI remain detectable, motivating detection algorithms that exploit these preserved characteristics while accounting for quantization effects. Microwave radiometers must detect extremely weak signals, often below \(-100\) dBm [18], making them particularly susceptible to electromagnetic interference. The loss of sensitivity due to the 1-bit sampling, since the hard decision threshold between 0 and 1 means that any interference above the noise floor can directly impact the quantization decision, can potentially corrupt measurements more severely than in systems with higher bit depth that provide amplitude information. However, the transition from theoretical algorithms to space-qualified implementations presents a formidable set of challenges. Space missions demand highly optimized hardware implementations that must operate reliably for years with minimal intervention.