Compact front-end prototype for next generation RFI-rejecting polarimetric L-band radiometer

Interferometric synthetic aperture radiometry is a relative new technique in the area of microwave earth observation to measure the brightness temperature distribution of the earth. It can enhance the spatial resolution of the passive microwave remote sensing effectively. Steady progresses of this technology have been achieved in both one dimensional and two dimensional cases since 1990's. In this paper, the technique development of the interferometric synthetic aperture radiometry in the past ten years was reviewed. The imaging principle of the aperture synthesis was introduced. Both of the two most common means of the aperture synthesis, one dimensional and two dimensional, were described. Another aperture synthesis means based on antenna array rotating was also described as the latest progress. Then the existing and proposed instruments were reviewed, including ESTAR, 2D-STAR, GeoSTAR from the US, MIRAS of the ESA mission SMOS, HUT-2D developed by Helsinki University of Technology, and the C-band and X-band systems developed by Center for Space Science and Applied Research, Chinese Academy of Sciences, etc. Finally, the application prospect of the interferometric synthetic aperture technology was discussed, especially in the area of earth observation, space exploration, reconnaissance and some security imaging application.

Initial examination of ALOS PALSAR synthetic aperture radar (SAR) data has indicated significant radio frequency interference (RFI) in several geographic locations around the world. RFI causes significant reduction in image contrast, introduces periodic and quasi-periodic image artifacts, and introduces significant phase noise in repeat-pass interferometric data reduction. The US National Research Council Decadal Survey of Earth Science has recommended DESDynI, a Deformation, Ecosystem Structure, and Dynamics of Ice satellite mission comprising an L-band polarimetric radar configured for repeat-pass interferometry. There is considerable interest internationally in other future L-band and lower frequency systems, as well. Therefore, the issues of prevalence and possibilities of mitigation of RFI in these crowded frequency bands are of considerable interest. RFI is observed in ALOS PALSAR in California and Hawaii, USA, and in southern Egypt in data examined to date. Application of several techniques for removing it from the data prior to SAR image formation, ranging from straight-forward spectral normalization to time-domain, multi-phase filtering techniques, are considered. Considerable experience has been gained from the removal of RFI from P-band acquired by the GeoSAR system. These techniques applied to the PALSAR data are most successful when the bandwidth of any particular spectral component of the RFI is narrow. Performance impacts for SAR imagery and interferograms are considered in the context of DESDynI measurement requirements.

Compared with the traditional microwave radiometer, one dimensional synthetic aperture microwave radiometer can effectively improve the spatial resolution of sea surface temperature retrieval. However, the spaceborne one dimensional synthetic aperture microwave radiometer is multiple incidence angle observation for the sea target and the incidence angle changes from 0° to 55°. In order to develop sea surface temperature inversion algorithms suited to one dimensional synthetic aperture microwave radiometer, it is necessary to evaluate the sensitivities of brightness temperature to oceanic and atmospheric environmental elements. Using the sea surface emissivity model and the atmospheric radiative transfer model, we construct a oceanic and atmospheric radiative transfer mode suited to the one dimensional synthetic aperture microwave radiometer. In this paper, the sensitivity changes of C-band vertical and horizontal polarization brightness temperature to oceanic and atmospheric environmental elements at different incidence angles are studied, and the corresponding sensitivity coefficients are calculated. The results indicate that the sensitivities of vertical and horizontal polarization brightness temperature to oceanic and atmospheric environmental elements show different characteristics. With the increase of the incidence angle, the sensitivity of the vertical polarization brightness temperature to the sea surface temperature is enhanced, and the sensitivity to the sea surface wind field is relatively weakened; but the horizontal polarization brightness temperature is opposite. The vertical and horizontal polarization brightness temperature errors caused by the errors of atmospheric water vapor content and cloud liquid water content increase with the increasing of the incidence angle, however, even at a large incidence angle of 55°, the errors of vertical and horizontal polarization brightness temperature are still less than 0.12 K. If the accuracy of sea surface temperature inversion is higher than 1 K, the calibration precision of one dimensional synthetic aperture microwave radiometer should be better than 0.6 K. Overall, the results of this paper are of great significance to the research of sea surface temperature retrieval with multiple incidence angle for one dimensional synthetic aperture microwave radiometer.

Synthetic aperture radiometer imaging use sparse antennas array for reducing the cost.In this process,phase errors of the visibility function will sharply degrade the imaging quality.This paper presents a detailed analysis of system imperfections and a calibration modeling.Meanwhile,we introduce a real time calibration method-Redundant Spacing Calibration(RSC).And its simulation result proves that this calibration method is very efficient under the two kinds of antenna arrays.

In common with all wideband ionospheric sounding systems the backscatter technique is susceptible to contamination by radio frequency interference. The eradication of such interference is imperative in systems required to automatically interrogate the backscatter sounder data base. This paper presents the results of the development of an algorithm designed for that purpose. The philosophy guiding the design is presented, together with the results of a computer simulation designed to simultaneously validate the proposed approach and derive an appropriate threshold. Details of the implementation are provided together with data demonstrating the effectiveness. The algorithm is capable of being implemented in any backscatter sounder system featuring an adequate digital signal processing capability.

Due to its conceptual simplicity and its proven effectiveness in real-time detection and removal of radio frequency interference (RFI) from radio astronomy data, the spectral kurtosis (SK) estimator is likely to become a standard tool of a new generation of radio telescopes. However, the SK estimator in its original form must be developed from instantaneous power spectral density estimates, and hence cannot be employed as an RFI excision tool downstream of the data pipeline in existing instruments where any time averaging is performed. In this Letter, we develop a generalized estimator with wider applicability for both instantaneous and averaged spectral data, which extends its practical use to a much larger pool of radio instruments.

The observation of surface water bodies in all weather conditions and better knowledge about inundation patterns are important for water resource management and flood early warning. Microwave radiometers at 37 GHz were applied to observe and study the inundation pattern in large subtropical floodplains in China, i.e. the Poyang Lake and Dongting Lake floodplains, due to the trade-off between the capability to penetrate hydrometeors and vegetation, revisiting time, and spatial coverage and resolution. Taking the shallow sensing depth at 37 GHz into account, open water, inundated area and water saturated soil surface all determine the surface emittance measured by the radiometer. Thus, Water Saturated Surface (WSS) is defined as the combination of these three land surface elements. In subtropical regions, seasonal changes in vegetation cover and various surface roughness conditions are the major challenges for the observation of surface water bodies with microwave radiometers. Atmospheric attenuation, observation gaps and errors in the microwave observations reduce the quality of daily radiometric observations. To deal with the attenuation due to vegetation and surface roughness, a two-step model was developed: the first step is to retrieve the polarization difference emissivity from Polarization Difference Brightness Temperature (PDBT) at 37 GHz with the simplified radiative transfer model and the vegetation optical thickness at 37 GHz parameterized from Normalized Difference Vegetation Index (NDVI) ; the second step is to retrieve the fractional area of WSS from the emissivity difference with a linear model, which can be parameterized according to the Qp surface roughness model. To remove the noise and extract the surface signal (including surface emittance and vegetation attenuation) from the daily PDBT time series, the Time Series Analysis Procedure (TSAP) was developed to identify the spectral features of noisy components in the frequency domain and remove them with a proper filter. The overall method combined the TSAP and the two-step model to derive daily observation of WSS area. The retrieved WSS area in the Poyang Lake floodplain was in a good agreement with the lake area observed from MODerate-resolution Imaging Spectroradiometer (MODIS) and Advanced Synthetic Aperture Radar (ASAR). The observations and analysis of the inundation patterns in the Poyang Lake and Dongting Lake floodplains with this method illustrated the close relationship between inundated area, precipitation and stream flow. Furthermore, a lumped hydrological model, named the discrete rainfall-runoff model, was developed to fully use the retrieved WSS area and to study the role of inundated area in stream flow production. This model simulates stream flow as the integration of contributions of antecedent precipitation in a certain period. Three implementations of the model were developed with the help of ground water table depth and the retrieved WSS area. The case study in the Xiangjiang River basin (upstream catchment of the Dongting Lake floodplain), China, illustrated that: 1) the longest duration of antecedent precipitation is a key parameter to determine model performance; 2) long duration would increase the model uncertainty and lead to overfitting; 3) the application of the WSS area can reduce the duration required to achieve a reasonable accuracy. The model parameters indicated the interaction between stream flow and various water storages, and the calibration results of three implementations implied the recharge period of ground water.

This paper deals with the susceptibility to radio frequency interference (RFI) of the analog front ends embedded in smart power integrated circuits. The case of RFI injected in the power transistor terminals that propagates to the analog front ends of the same integrated circuit is investigated using equivalent circuits that include the silicon substrate. The demodulation of the interference that takes place in the analog front-end circuits is evaluated by means of an approximate nonlinear method. In particular, it is shown that the demodulation of the substrate interference in a MOS differential input stage depends on the asymmetry of the circuits connected to the input terminals. Based on this, a simple method to increase the immunity to such interference is presented and its effectiveness is proved through computer simulations and through measurements carried out on a test chip.

In order to meet the spatial resolution requirement of passive microwave remote sensing from space, aperture synthesis radiometer is used. An antenna array is an important part in synthetic aperture radiometer. A Sparse Antenna Array with Parabolic Cylinder Reflector at Millimeter Wave Band is presented in this paper. The overall requirements for antenna array are listed, followed by design and characterization of the entire antenna array architecture and each part of it including offset reflector geometry, sparse feed array and support structures. The theoretical computation and measured results of electrical parameters of the antenna array are also summarized.

Radio astronomical data is increasingly corrupted by human telecommunication activities. It is becoming particularly difficult to work at frequencies between 1100–1300 MHz that are rapidly filling up with satellite navigation signals. Therefore, Radio Frequency Interference (RFI) mitigation becomes an important step in the data processing flow. As to the telescopes based on Antenna array, RFI mitigation can be conducted in spatial domain using the sampled covariance matrix. In this paper, a subspace tracking RFI approach has been proposed based on the power method. The RFI spatial signature estimations provided by the reference antenna are used to initialize the power method to support a faster convergence and more accurate estimation. In addition, the reference antenna sequentially steers at the multiple interferences, thereby acquires new updates of each RFI spatial signature successively. Then, the Interference can be mitigated individually by applying the orthogonal projection. The simulation results validate the effectiveness of the proposed algorithm.

The European Space Agency (ESA) successfully launched the Soil Moisture and Ocean Salinity (SMOS) mission in November 2, 2009. SMOS uses a new type of instrument, a synthetic aperture radiometer named MIRAS that provides full-polarimetric multi-angular L-band brightness temperatures, from which regular and global maps of Sea Surface Salinity (SSS) and Soil Moisture (SM) are generated. Although SMOS operates in a restricted band (1400–1427 MHz), radio-frequency interference (RFI) appears in SMOS imagery in many areas of the world, and it is an important issue to be addressed for quality SSS and SM retrievals. The impact on SMOS imagery of a sinusoidal RFI source is reviewed, and the problem is illustrated with actual RFI encountered by SMOS. Two RFI detection and mitigation algorithms are developed (dual-polarization and full-polarimetric modes), the performance of the second one has been quantitatively evaluated in terms of probability of detection and false alarm (using a synthetic test scene), and results presented using real dual-polarization and full-polarimetric SMOS imagery. Finally, a statistical analysis of more than 13,000 L1b snap-shots is presented and discussed.

Fully polarimetric radiometer plays an important role in measuring and researching of the ocean surface wind field.Fully polarimetric radiometer can get target's all polarization information by measuring the full set of the Stokes parameter,which is an useful implement of the measuring of the ocean surface wind field.There are two main types of the fully polarimetric radiometer:polarization combining radiometer and correlation radiometer.This paper focuses on the correlation radiometer.At last,we discuss the calibration of the fully polarimetric radiometer.

Photoacoustic (PA) imaging and sensing based on optical excitation and acoustic detection are emerging recently. The main issue of the PA systems is the poor SNR at the output of the sensors. The power consumption and size of the receiver are also crucial for the systems. Thus, several techniques are proposed in the analog front-end (AFE) and the analog-to-digital convertor (ADC) to improve the output SNR and power efficiency of the receiver. A resonant noise matching (RNM) technique is proposed to improve the sensitivity of ultrasound transducers. Diverse from the power matching which aims to maximize the output power from transducer in conventional electrical impedance matching (EIM) technique, the RNM maximizes the output voltage. The advantage of RNM is that it can also equivalently reduce the LNA’s input-referred noise and thus minimize the noise figure (NF) of the ultrasound receiver. Measurement results show that, the output signal is improved by 5 times through the proposed RNM technique, which is 66.7% larger than that of conventional methods. In addition, the sensitivity of the receiver is significantly improved by more than 10.4 dB which is beneficial for a variety of applications of piezoelectric ultrasound transducers. Thereafter, a high sensitivity and high dynamic range AFE is developed and fabricated in TSMC 65 nm CMOS process. An LNA with 30 dB gain and low input-referred noise (1 nV/Hz) is designed to amplify the input signal and suppress the noise from subsequent stages. Then a 3rd order Butterworth low-pass filter (LPF) with 5-20 MHz cut-off frequency is connected behind the LNA to reduce the out-of-band noise. Finally, a variable gain amplifier (VGA) which covers a gain range 0-45 dB with 20 MHz bandwidth are implemented in the AFE. The AFE is also applied in a photoacoustic sensor system which can achieve coherent lock-in function to detect weak PA signals noninvasively at in-vivo environments. An asynchronous SAR ADC with a novel mismatch error shaping (MES) technique is designed and fabricated. The power dissipation of the SAR ADC is dominated by the comparator, DAC and digital logic circuits. To reduce digital power consumption, the asynchronous timing sequence is adopted. As known, the resolution of SAR ADC is limited by the non-linearity of DAC and noise of comparator. The linearity of the DAC can be efficiently improved by the MES technique. The proposed novel MES technique can remove the flash ADC and DWA digital circuits in the convention MES technique, and thus improve the power efficiency. Noise shaping technique is also applied in the SAR ADC to reduce the comparator noise and improve the output SNR. In addition, another MES technique based on a double input range SAR ADC is also proposed. Through this method, the input signal is not necessary to be reduced by 2 times, which happens in the first proposed MES. Consequently, the output SNR can be improved by 3 dB. Overall, the main contributions of the thesis are: a) the RNM technique which is designed to improve the sensor’s sensitivity, b) A 0.18µVrms super-sensitivity photoacoustic imager based on coherent detection for deep in-vivo imaging and c) a low power and high-resolution SAR ADC with improved MES technique.

Radio spectrum bands allocated to spaceborne synthetic aperture radar (SAR) imagery are shared by multiple missions. In practical radio spectrum environments, these bands are also used by some ground radars, e.g., C-band weather radar. Due to this fact, radio frequency interference (RFI) may occur for a spaceborne SAR when its received signals contain the transmitted waveforms from another SAR or radar operating at the same frequency band. This particular class of RFI is usually linear-frequency-modulation (LFM) signals, which can cause bright radiometric artifacts in focused SAR images. Most existing signal processing approaches designed for addressing this problem belong to the class of preprocessing methods, which removes RFI in level-0 raw radar data before SAR focusing. In this article, we propose a postprocessing kernel—2-D SPECtral ANalysis (2-D SPECAN) filter, for removing the class of LFM RFI in level-1 SLC images. The filtering consists of three main steps: Step 1: focus LFM RFI artifacts in SLC images as point-like responses in the spectral domain via 2-D SPECAN; Step 2: perform 2-D notch filtering in the spectral domain to remove the most contribution of the RFI responses; and Step 3: transform the filtered spectrum back into the SLC image domain using the inverse operation of the 2-D SPECAN. For computation efficiency, we design a simplified processing flow and adopt a blockwise processing strategy. Experiments with several Sentinel-1 SLC images demonstrate that severe RFI artifacts in SLC images can be removed significantly by the proposed method.

This paper presents a low noise wearable wireless Electrocardiogram (ECG) system used for long term homecare and noninvasive monitoring three Leads ECG signals. An ac coupling circuit is implemented to remove the dc offset component created by the body movement and employs a high common mode rejection ratio (CMRR) instrumentation amplifier to reduce electromagnetic interference (EMI). The analog front end is connected to the End-Device which samples the three Leads signals with 200 Hz sampling frequency and sends data to a Coordinator on the PC using ZigBee protocol. A QRS and heart rate detection algorithm is implemented on a GUI data acquisition host. The system is evaluated when the body is walking and running. A reasonable performance is achieved even under body motion.