This article proposes a method for calculating the millimeter-wave (MMW) radiation of chaff corridor-target-sea scene. This method is used to analyze the attenuation of target brightness temperature (TB) by chaff corridor. First, a numerical method is proposed to obtain the facet model of chaff corridor, which is then combined with the facet models of sea and target obtained by the traditional method. Second, the ray tracing method is carried out to obtain the MMW radiation TB of the scene. In ray tracing, the emissivity, reflectivity, and transmittance of chaff corridor facets are calculated by the generalized equivalent conductor (GEC) method and the calculation method of reflection and transmission by a layered medium (RTLM). The emissivity and reflectivity of sea and target facets are calculated by their permittivity. Finally, to verify the correctness of the MMW radiation calculation method, a method for measuring the emissivity, reflectivity, and transmittance of chaff corridor is proposed. The TB of chaff corridor-metal plate and chaff corridor-ship-sea scenes is simulated and measured to analyze the TB attenuation caused by the chaff corridor. The results show that the calculation method is effective and the attenuation by the chaff corridor decreases with the increase of TB.

Airborne passive interferometric microwave sensors (PIMSs) were proposed as a powerful complementary tool for ship detection, especially in low visibility and high sea clutter environments. At present, there is only one algorithm for ship detection by airborne PIMSs, and this algorithm is only based on the “cold” brightness temperature (TB) characteristic of metal ships with wakes in passive interferometric microwave images (PIMIs). Moreover, it has been found that ship wakes always exhibit a “hot” TB characteristic in PIMIs. In this article, an improved algorithm is innovatively proposed for ship detection by airborne PIMSs to improve detection performance, and it is simultaneously based on the “cold” and “hot” TB characteristics of metal ships with wakes. The microwave TB model of metal ships with wakes is established to analyze its TB characteristics. Given the TB model and its characteristics, an improved algorithm is introduced, which comprises five steps: searching targets, improving TB maps, clustering targets, estimating ship headings, and estimating ship trajectories. The improved algorithm can detect ships with a low false-alarm probability (FAR) and accurately estimate ship headings using only a single snapshot and the ship trajectory. The practicability and detection performance of the improved algorithm is verified by airborne experiments using an X-band PIMS. The experimental results demonstrate that the improved algorithm can accurately detect ships, estimate ship headings using only a single snapshot, and estimate ship trajectories. The impact of the algorithm parameters on the detection performance is analyzed and discussed. Moreover, the detection performance of the improved algorithm is analyzed and compared with the performance of the only existing algorithm, and the experimental results indicate that the improved algorithm has a better detection performance with a lower FAR value than the only existing algorithm, as expected.

The critical advantage of passive microwave imaging is that it can be used in all-day and in low visibility conditions, such as hazes, fogs, clouds, smokes, and sandstorms. In this article, the ground-based passive interferometric microwave sensor (PIMS) is proposed to detect civil aircrafts, especially in low visibility conditions. The fundamental of civil aircraft detection by a ground-based PIMS is introduced and analyzed. Numerical simulations are performed to assess its feasibility and detection performance, and the impact of the low visibility weather is analyzed and discussed. To verify the practicability of civil aircraft detection by the ground-based PIMS, a series of experiments have been performed by a ground-based X-band PIMS, and a data processing procedure is introduced, which contains a target detection algorithm. Experimental results have demonstrated that the civil aircrafts can be accurately detected and consecutively tracked by the ground-based PIMS using the target detection algorithm. Meanwhile, a mirrored TB phenomenon, the TB change, and an application scheme are analyzed and discussed. As a conclusion, the ground-based PIMS can be considered as a powerful complementary tool for civil aircraft detection.

Passive millimeter-wave (PMMW) imaging technology is widely used in civilian and military applications. However, there are reflections similar to the optical band in PMMW images, which have a negative influence on target detection and recognition. In this article, we present a reflection-based method to enhance the target features in PMMW images. The dividing line between the target and reflection is obtained by the similarity of brightness temperature (TB). By combining the similarity and reflection principle, we propose a new method to obtain the feature points of the target and reflection for registration. Then, the weighted method based on region TB is used to fusion target and reflection. Finally, to avoid interference with target detection and recognition, the reflection is removed. The experimental results show that the method can obtain higher contrast and more accurate target information.

Ship detection is important for a wide range of applications. In this article, an airborne passive interferometric microwave sensor (PIMS) is proposed as a powerful complementary tool for ship detection. The fundamental of ship detection by the airborne PIMS is introduced. A specification called “the detection factor” is addressed to quantitatively assess the performance of the airborne PIMS for ship detection. The detection probability is discussed and addressed based on the constant false-alarm rate (CFAR). Numerical simulations are performed to demonstrate the feasibility of ship detection by the airborne PIMS. The impacts of the atmosphere and the sea wind on the performance of the airborne PIMS for ship detection are also addressed in terms of theoretical analyses and numerical simulations. The airborne experiments are also carried out by an X-band PIMS to verify the practicability of ship detection by the airborne PIMS in a sunny weather and a cloudy weather. The data processing procedure and a ship detection algorithm in the experiments are introduced. The airborne experimental results reveal that the ships can be effectively detected and tracked by the airborne X-band PIMS in a sunny weather and a cloudy weather. It demonstrates the practicability of ship detection by the airborne PIMS. The ship detection probability is also analyzed, which agrees well with the theoretical detection probability.

The concept, principle, and method of microwave radiometric imaging with mirrored aperture synthesis (MAS) were proposed by the Huazhong University of Science and Technology (HUST), Wuhan, China. MAS can achieve higher spatial resolution without extending the size of the antenna array. However, the MAS principle has not been sufficiently validated by practical experiments. To solve this problem, an innovative experiment system of MAS at the V-band (MAS-V) has been developed by HUST. Experiments on the interference fringe pattern, spatial resolution, as well as the imaging of an electric warmer and the absorbing material in the styrofoam box filled with liquid nitrogen are performed. The initial experimental results demonstrate that MAS can achieve higher spatial resolution with the same antenna array compared with the conventional AS. For MAS, the experimental results are consistent with theory and simulation results.

A numerical simulator for analysis of the geostationary orbit multispectral passive microwave (Geo-MW) mapping and sounding is described, which mainly includes upwelling brightness temperatures forward, microwave radiometer payload simulation and atmospheric profile retrieval. This simulator allows evaluation and optimization of the ability of microwave sensors to retrieve atmospheric temperature and humidity profile. In this paper, end to end simulation study of a Geo-MW radiometer observation at selected frequencies from 50 to 425 GHz with a real-aperture antenna is performed and the accuracy of the brightness temperature measurement and the atmospheric temperature and humidity profile sounding are quantitatively analyzed and evaluated.

Mirrored Aperture Synthesis (MAS) was proposed to improve spatial resolution for passive microwave remote sensing. However, the MAS theory needs experimental verification. In this paper, an Experimental System of MAS (MAS-V) at V frequency band is introduced, which is developed for verifying the principle and performance of MAS. MAS-V is composed of an antenna array, reflectors, a receiving channel array, a synchronous acquisition subsystem, a computing server, and a rotatory platform. The initial experimental results demonstrate that the principle of MAS is valid. The experimental spatial resolutions are consistent with the theoretic spatial resolutions.

The passive microwave observations from geostationary earth orbit (GEO) are able to enhance the short-time forecasting of tropical cyclones (TCs) due to its ability to track and detect the internal structure of TCs. To assess the operational capabilities of the candidate GEO microwave instruments, the numerical simulations of GEO microwave observation for the three TC cases were carried out. This paper compares the abilities of 3 candidate passive microwave sensors, based on GEM/GOMAS, GeoSTAR and GIMS-II respectively, to observe the upwelling brightness temperatures of TCs at 50-57GHz band. The analysis is based on WRF model variables and radiative transfer mode DOTLRT.

The output signal of millimeter-wave (MMW) radiometer is usually affected by 1/f-noise that is characterized by self-similarity and non-stationary. Wavelet thresholding techniques are widely used to de-noise. However, soft-thresholding has good de-noising effect but is poor in details preservation, and hard-thresholding is good in details preservation but has poor de-noising effect. To eliminate 1/f-noise from white Gauss noise (WGN), an improved thresholding function is introduced in this paper. This method overcomes the permanent bias in soft-thresholding and the discontinuous point in hard-thresholding. Additionally, a least square estimation (LSE) is introduced to estimate 1/f-type parameters. Simulations and experiments have been carried out to validate this method.

For SMOS data, significant errors exist in coastal areas because of the contamination by the nearby land. In this paper, the analysis of SMOS brightness temperature (TB) data in coastal area of South China Sea (SCS) reveals a decreasing trend with the increase of the distance to coast. A SMOS TB measurement model according to geophysical parameters and SMOS/MIRAS antenna array is established. The simulation shows that TB is large within 40 km since land is much warmer than ocean and is observed by the mainlobe of the antenna array. Then the simulation result of land contamination is used for correction of SMOS measured TB data in coastal area of SCS. Then the corrected TB is applied for sea surface salinity (SSS) retrieval, which reduces SSS outliers and improves the accuracy of SSS in coastal area of SCS.

Scene imaging simulation is an indispensable work in passive millimeter-wave object detection and remote sensing. In this paper, a 3-D scene simulation model of passive millimeter-wave imaging based on ray-tracing is presented, with consideration of the essential affecting factors such as multiple reflections, sky radiation, polarization rotation and antenna pattern smoothing. In order to accelerate the ray-tracing process in simulation model, a fast ray-triangle intersection algorithm is adopted. The outdoor imaging experiment and scene imaging simulation are carried out to validate the presented method at 94GHz. From the results, it is shown that the speed of scene imaging simulation process is significantly improved and the simulated image is in good agreement with the measured brightness temperature image.

A general platform for millimeter wave synthetic aperture radiometers is introduced in this paper. The platform consists of hardware and simulation software, and has a flexible and open structure. Simulation and experiment results show the platform is suitable for simulation of synthetic aperture radiometer performance, algorithm performance, error influence on radiometer performance, and calibration performance. The platform can be used for radiometry simulation and design of synthetic aperture radiometers.