Radio Frequency Interference (RFI) is a significant limiting factor in the retrieval of geophysical parameters measured by microwave radiometers. Microwave Imager Combined Active and Passive (MICAP), which is a package of active and passive microwave instruments including L/C/K-band Microwave Interferometric Radiometer (MIR) and L-band scatterometer, has been approved to be taken on-board in the Chinese Ocean Salinity Mission. RFI is a serious threat to MICAP, especially to the L-band MIR. In the first part of this paper, on-orbit RFI mitigation method in MICAP L-band MIR is proposed, which is detected in time domain, frequency domain, probability spectrum, polarization domain, and RFI is removed in time domain and frequency domain. Secondly, desktop experiment of this RFI mitigation method is proposed based on MICAP L-band MIR. Thirdly, a flight experiment of this RFI mitigation method is demonstrated before MICAP launch. As shown in this paper, MICAP L-band MIR will be the first MIR with on-orbit RFI mitigation capacity.

The Chinese Ocean Salinity Mission was officially initiated in 2020. In July 2023, a flight campaign was conducted to assess the system design, data processing methodologies, and performance criteria. This paper discusses the system architecture of the L/C/K-band one-dimensional microwave interferometric radiometers (MIR) tested in the flight campaign and presents the performance evaluations derived from imaging results.

A cross beam correlation microwave radiometer (CBCR) using two orthogonal subarrays is introduced. It consists of two spatially orthogonal subarrays and a correlation receiver, where a pencil beam is realized by the coherence of two orthogonal fan beams. However, the differences between the two orthogonal fan beam patterns lead to gain loss and negative sidelobes. The gain loss (effective aperture reduction) of cross arrays has been proven to lead to deterioration in radiometric resolution. But the properties of negative sidelobes and their impact on observations have not been fully investigated. In this article, the performance of the cross array is comprehensively analyzed, and the systematic expressions of beam characteristics and radiometric resolution are proposed. The main beam efficiency (MBE) is redefined to prevent it from exceeding unity. Two novel factors, namely the spatial sparsity factor and phase influence factor, are introduced to quantitatively assess the influence of the cross array on radiometric resolution. In addition, a planar cross antenna array is proposed to remedy the shortcomings of Mills cross in small radiometer applications, and the performance of the two cross arrays is evaluated based on the above methods. Finally, the numerical simulations and hardware experiments with an L-band prototype are conducted to verify the theoretical results.

Digital correlator is the central signal processing unit for an interferometric radiometer system. The core function of the digital correlator is to quantitatively measure the correlation coefficients of all the receiver output combination pairs, and then generate the visibility functions together with the system noise temperatures obtained by single-channel total-power measurements. In this letter, a comprehensive quantitative characterization method is proposed for a 30-channel, three-level quantized digital correlator unit (DCU), which will be used for the microwave imager combined active and passive (MICAP) C- and K-bands radiometers, on-board Chinese ocean salinity mission (COSM). First, several key performance characteristics of DCU, including correlation offset and correlation efficiency, are defined and discussed based on a segmented error model. Second, a test platform based on an arbitrary waveform generator (AWG) is established and applied for the test and evaluation of the DCU engineering model (EM). Orthogonal in-phase and quadrature bandlimited noise signals are generated via a newly proposed approach based on Hilbert transform, facilitating the joint tests of correlation efficiency and phase error. Moreover, the influences of the correlator’s input power level on correlation offset and correlation efficiency are also investigated during the test of DCU. DCU test results show that the correlation offset is smaller than −40 dB, the correlation efficiency is better than 0.996, and the phase error is less than 5°. The result can provide an important reference for the digital correlator test in COSM.

Radio Frequency Interference (RFI) is a significant limiting factor in the retrieval of geophysical parameters measured by microwave radiometers. Microwave Imager Combined Active and Passive (MICAP), which is a package of active and passive microwave instruments including L/C/K-band Microwave Interferometric Radiometer (MIR) and L-band scatterometer, has been approved to be taken on-board in the Chinese Ocean Salinity Mission. RFI is a serious threat to MICAP, especially to the L-band MIR. In the first part of this paper, RFI mitigation strategy combined on-board processing and on-ground processing is proposed based on MICAP structure. Secondly, RFI side lobe blanking criteria is proposed to clarify the requirements for on-board RFI detection capabilities, which indicate a trade-off between detection sensitivity and false alarm rate. Thirdly, a verification experiment of RFI mitigation method is demonstrated for on-board RFI detection.

Microwave Imager Combined Active and Passive (MICAP), which is a package of active and passive microwave instruments including L/C/K-band radiometers and L-band scatterometer, has been chosen as one of the primary payloads for the Chinese Ocean Salinity Mission (COSM). The L-band one-dimensional synthetic aperture radiometer (L-Rad) is the key part of MICAP to measure sea surface salinity (SSS). As radio frequency interference (RFI) has been reported as a severe threat to L-band radiometry, it can be foreseen that MICAP L-Rad will encounter RFI contaminations unavoidably. Due to the conflict between the huge transmission data volume and the limited downlink budget, it is challenging for MICAP L-Rad to transmit all rapidly sampled sub-band data products and conduct on-ground RFI processing like Soil Moisture Active Passive (SMAP) microwave radiometer. The onboard real-time RFI detection and mitigation strategy is proposed accordingly for MICAP L-Rad. It is designed based on the distributed digital processing structure and the synthetic-aperture feature. The proposed RFI processing strategy is evaluated and verified by the system simulations and hardware experiment, demonstrating its RFI detection capability and low false alarm rate performance.

Person re-identification is a popular research topic which aims at matching the specific person in a multi-camera network automatically. Feature representation and metric learning are two important issues for person re-identification. In this paper, we propose a novel person re-identification method, which consists of a reliable representation called semantic region representation (SRR), and an effective metric learning with mapping space topology constraint (MSTC). The SRR integrates semantic representations to achieve effective similarity comparison between the corresponding regions via parsing the body into multiple parts, which focuses on the foreground context against the background interference. To learn a discriminant metric, the MSTC is proposed to consider the topological relationship among all samples in the feature space. It considers two-fold constraints: the distribution of positive pairs should be more compact than the average distribution of negative pairs with regard to the same probe, while the average distance between different classes should be larger than that between same classes. These two aspects cooperate to maintain the compactness of the intra-class as well as the sparsity of the inter-class. Extensive experiments conducted on five challenging person re-identification datasets, VIPeR, SYSU-sReID, QUML GRID, CUHK03, and Market-1501, show that the proposed method achieves competitive performance with the state-of-the-art approaches.

The Geostationary Interferometric Microwave Sounder (GIMS) is millimeter wave imaging sounder concept proposed for China's next generation geostationary meteorological satellite (FY-4M). GIMS is supposed to utilize a rotating circular thinned array, instead of a stationary Y-shape array, to reduce the required number of the antenna elements. A proof-of-concept 53GHz ground-based GIMS demonstrator with 28 elements has been successfully developed and tested during 2009~2012. A new GIMS demonstrator development plan has been approved for further risk mitigation. A 70 element demonstrator is foreseen to be finished before the end of first quarter of 2017. In this paper, recent progresses on the ongoing demonstration activities will be summarized. The preliminary imaging and performance evaluation results of the GIMS-II demonstrator will also be presented.

This paper presents the design and preliminary performance tests of an L-band synthetic aperture interferometic radiometer using the new sampling concept of clock scan. With the advantages of simple and deployable array structure, the concept of Clock Scanning Microwave Interferometric Radiometer (CS-MIR) has much potential to apply for the future Solar Polar Orbit (SPO) and Geostationary Earth Orbit (GEO) missions, where large antenna array with high angular resolution is the prime requirement. This L band demonstrator is developed to validate the concept of CS-MIR and solve the related technical problems.

Water Cycle Observation Mission (WCOM) is an earth science mission proposed and focused on the research of water cycle under global change. With its three dedicated designed main payloads, WCOM can achieve synchronized observation on a group of global water cycle key parameters, including soil moisture, ocean salinity, snow water equivalent, soil freeze-thaw, atmospheric water vapor, precipitation and other associated parameters. One of the three WCOM main payloads names IMI (Interferometric Microwave Imager), which is a newly designed L/S/C tri-frequency radiometer aiming to provide advanced measurement capability on soil moisture and ocean salinity. In this paper, the instrument concept and preliminary system design of WCOM/IMI will be introduced. Recent progresses on the filed experiments of an L-band demonstrator will also be introduced.

A combined L-band active and passive sensor for space-based ocean salinity observation has been proposed in MIRSlab, CAS [1] [2]. A ground-based prototype has been developed to demonstrate the concept and performance of the instrument. The experimental result of the passive part of the prototype, the L-band 1-D synthetic aperture radiometer, has been introduced in this paper.

The Geostationary Interferometric Microwave Sounder (GIMS) is a new concept of atmospheric microwave sounder for China's future geostationary Earth orbit meteorological satellite (FY-4). A novel self-calibration method for interferometric radiometers with a rotating thinned array, particularly for GIMS, has been proposed in this letter. Compared with the traditional relative phase calibration approach, neither dedicated hardware nor dedicated calibration working model is needed to achieve the relative phase calibration in this novel interelement phase calibration. The self-calibration approach is inherently merged with the nominal observation working model of GIMS, owing to the continuous array rotating of the GIMS instrument. A running average scheme has been introduced into the self-calibration approach to enhance the signal-to-noise ratio of the calibration data, which is normally very low with the natural earth scene. The method is demonstrated by both simulation and field imaging experiment.

Sea surface salinity (SSS) plays an important role in global water cycle. In recent years, satellite based remote sensing has proven to be a promising approach for global SSS observation. A new payload concept, named MICAP (microwave imager combined active and passive), has been introduced in this paper. MICAP is a suit of active/passive instrument package, which includes L/C/K band one-dimensional MIR (microwave interferometric radiometer) and L-band DBF (digital beamforming) scatterometer, sharing a parabolic cylinder reflector. MICAP has been selected to be a candidate payload for future Chinese ocean salinity mission. In this paper, the MICAP instrument concept, specification and preliminary system design will be introduced.

The Geostationary Interferometric Microwave Sounder (GIMS) is a new concept of atmospheric microwave sounder for China's future geostationary Earth orbit meteorological satellite (FY-4). It is a microwave interferometric radiometer (MIR) using aperture synthesis and working in rotating time-sharing mode with a circular antenna array. A GIMS proof-of-concept demonstrator operating in the temperature sounding bands of 50-56 GHz has been successfully developed. The instrument uses a circular array with 28 elements (including one in the center of the array). It is capable of imaging a scene with an angular resolution of about 0.08° and a radiometric resolution of less than 1 K with 5-m integration time within a 5° field of view (FOV). Some theoretical aspects of the imaging characteristics of GIMS are discussed, such as the alias-free FOV, angular resolution, radiometric resolution, and imaging algorithm. Some early tests and preliminary imaging experiments of the GIMS demonstrator are also presented.

A new ocean salinity mission concept has been proposed and a ground-based prototype is being developed in MIRSlab, CAS. The passive part of the combined instrument is a one-dimension synthetic aperture radiometer. A critical technical challenge is that the radiometer needs to have very high sensitivity and high calibration stability. In this paper, theoretical analysis is given to high stability radiometer, and a high stability L-band radiometer has been developed to demonstrate its performance.

The recent progress of the potential main payload of the Solar Polar ORbit Telescope (SPORT) mission, a space weather mission proposed by the National Space Science Center, is introduced in this paper. The main payload of SPORT is essentially an interferometric radiometer using synthetic aperture technique, and the time sharing clock rotation to implement the visibility sampling. The progress on system design, including frequency selection, payload configuration, rotation scan schemes and image retrieval are presented in this paper.

System study and development of an L-band one-dimensional synthetic aperture radiometer, or microwave interferometric radiometer (MIR), has been introduced in this paper. This radiometer is the passive part of a combined active/passive instrument for space-based ocean salinity observation. Recent progresses on radiometer hardware development and system simulation have been introduced.

The concept of a new type combined L-band active and passive sensor for soil moisture and ocean salinity measurement has been proposed in this paper. The passive part of this combined system is a one-dimensional synthetic aperture radiometer, while the active part is a digital beam forming scatterometer. Preliminary considerations for space-borne system design and performance evaluation has also been introduced in this paper. A ground-based demonstrator is defined and under development.

The concept of Geostationary Interferometric Microwave Sounder (GIMS) has been proposed based on the rotating circular thinned array, aiming for China's next generation geostationary meteorological satellite (FY-4M). The space borne system design has been investigated. The tradeoff analysis between the system performance and system complexity has been studied. A full-scale ground-based 50~56GHz GIMS demonstrator with 28 elements has been defined and developed. Preliminary test results of the demonstrator will also be presented in this paper.

The Geostationary Interferometric Microwave Sounder (GIMS) is a new concept imaging radiometer proposed by CSSAR, aiming for China's next generation geostationary meteorological satellite (FY-4M). The concept of GIMS is based on aperture synthesis with a rotating circular thinned array. A three-element interferometer has been developed and tested to investigate the feasibility of the GIMS system design. A full-scale ground-based demonstrator with 27 elements is also under development, which is defined as a minimum system intended to fulfill the threshold application requirements. In this paper, the preliminary results of these activities will be reported.

In this paper, the authors will report some basic considerations on the synthetic aperture imaging radiometer for mm-wave sounding from GEO, especially for the China's next generation geostationary meteorological satellite (FY-4M).