Passive interferometric microwave sensors (PIMSs) have been proposed for target detection, such as ships and aircrafts. However, the detection performance of the PIMSs has not been analyzed and discussed for target detection in detail before. In this letter, the detection performance of the PIMSs is analyzed in terms of detection probability at a constant false alarm rate (FAR). An end-to-end performance simulator is established to analyze the detection performance of the PIMSs in terms of detection probability at a constant FAR that 10-5in detail. Numerical simulations are performed to analyze the detection performance of the airborne PIMS for ship detection. The numerical results indicate that the detection performance depends on the height (distance), the targets, and the PIMSs, as expected.

The arrangement of the antenna array of the mirrored aperture synthesis (MAS) determines the transformation matrix for solving the cosine visibilities. When the transformation matrix is rank deficient, the solved cosine visibilities will introduce the rank-deficient error. For the two-dimensional mirrored aperture synthesis (2-D MAS), the existing literature has discussed the relationship between the arrangement of the antenna array and the rank-deficient error but has not proposed an array that can achieve a full rank transformation matrix, which is call the rank-full array (RFA). Based on a new method for calculating the rank of the transformation matrix and the literature on one-dimensional (1-D) RFAs, this paper proves that 2-D RFA cannot be obtained when the reflectors are all metal, and by introducing a reflector made of magnetic conductor, 2-D RFA can be obtained. Besides, this paper obtained the existence conditions for 2-D RFA. Based on those conditions, two methods are proposed to obtain 2-D RFAs.

Finding out and turning off the radio-frequency interference (RFI) sources as many as possible is an important work for synthetic aperture interferometric radiometer (SAIR). While the impact of strong RFIs on reconstructed brightness temperature (BT) image is clearly observable, the presence of low- or moderate-level RFIs is often hard to be aware of, leaving the RFI detection and localization a difficult problem. In this article, an improved RFI detection method is proposed by making use of the point-source ripple to give prominence to the RFIs presented in the SAIR imagery. The method tests based on Soil Moisture and Ocean Salinity satellite (SMOS) visibility samples and the performance evaluations by numerical simulations validate the correctness and effectiveness of the developed method.

Setting two reflectors perpendicular to each other and an array produces mirrored aperture synthesis (MAS), which obtains a higher spatial resolution than aperture synthesis (AS) for the same antenna array. The proposal of the MAS theory and the experimental verification suggest that the spatial resolution can be improved by setting the reflector. This paper proposes a method in which four tilted planar reflectors are set around an antenna array. This method is named two-dimensional (2-D) mirrored aperture synthesis with four tilted planar reflectors (2-D MAS-T). Because 2-D MAS-T uses more reflectors than MAS, the spatial resolution is further improved. The principle of 2-D MAS-T with an antenna array is given in this paper. The relationship between the size of the reflectors, the spatial resolution and the field of view (FOV) is obtained. The simulation and experimental results demonstrate that 2-D MAS-T can achieve a higher spatial resolution with the same antenna array than 2-D AS and 2-D MAS.

When observing from a spaceborne or unmanned airborne platform, aperture synthesis radiometric imaging (ASRI) is sometimes configured with an irregularly distributed array. In the previous study, the array factor forming (AFF) has been proposed to reconstruct the brightness temperature (BT) image of the observed scene. However, it is found that AFF is invalid when system noise is taken into account. In order to solve the problem, AFF with regularization is proposed in this letter. The reason why the conventional AFF becomes invalid is analyzed, and how AFF with regularization provides a stable solution is discussed. Numerical simulation and experimental results show that the BT image reconstructed by AFF with regularization is more accurate than that reconstructed by the conventional AFF, which demonstrates the validation of the method.

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.

Mirrored aperture synthesis (MAS) has been proposed to utilize a few antennas to provide high spatial resolution for atmospheric remote sensing. In order to verify the fundamentals of mirrored aperture synthesis (MAS) further, a prototype working at V band was developed in the past two years. In this paper, the prototype is briefly introduced, and then some indoor experiments and the experimental results for one-dimensional MAS based on the prototype are presented, mainly including the fringe pattern experiment for verifying the correlation output and the imaging experiment based on two point sources for evaluating the spatial resolution of MAS.

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.

Because the principle of mirrored interferometric aperture synthesis (MIAS) is different from that of the conventional interferometric aperture synthesis, the antenna array for 1-D MIAS should be redesigned. And in order to get a precise estimation of the cosine visibilities, the maximum rank of the transfer matrix should be set as the key constraint condition of the array optimization model, but this has not been clearly presented before. In this letter, the maximum rank of the transfer matrix is discussed and proved by the mathematical induction method. When the position of each antenna in the array is an even multiple of 0.5, the value for the maximum rank is proven to be M - 2, and when the position of each antenna is an odd multiple of 0.5, the value for the maximum rank is proven to be M - 1, where M is the number of the spatial frequencies provided by the array. This conclusion is significant for the array design of 1-D MIAS.

Mirrored interferometric aperture synthesis (MIAS) can reduce the complexity of large IAS systems. In this paper, UV sampling, spatial resolution, sensitivity, and image reconstruction of 1-D MIAS are analyzed, which are not addressed before. Numerical simulation and experiments are carried out to illustrate the performances of MIAS. The results demonstrate the validity of MIAS and the improvement of spatial resolution.

Aperture synthesis technique can provide high spatial resolution without requiring very large and massive real aperture. However, for a large aperture synthesis system, which will involve hundreds of antennas and thousands of correlators, system and its calibration are very complicated. In this letter, mirrored interferometric aperture synthesis (MIAS) is proposed, which can achieve the same spatial resolution as a large traditional aperture synthesis system but needs fewer antennas. First, the imaging principle of MIAS is presented. A new concept, named Cosine Visibility, is proposed to replace the visibility function used in traditional aperture synthesis. The relationship between the brightness temperature and the cosine visibility is a Cosine Transform. Inverse Cosine Transform can be applied to reconstruct the image of brightness temperature. Then, an example for MIAS is given, and a method is proposed to handle the problems of baselines missing and the rank defect associated with the underdetermined linear equations which relate the cross correlation between signals collected by pairs of antennas with the cosine visibility. Moreover, MIAS with a small array can provide higher and higher spatial resolution by combining more and more linear equations with the help of adjusting the distance from the array to the reflector. The simulation results demonstrate the validity of MIAS and the improvement of spatial resolution. The study in this letter provides a means to reduce the complexity of system and calibration of large traditional aperture synthesis systems.

The statistical characteristics of visibilities measured by digital complex correlators in aperture synthesis radiometry are investigated. First, the analytic probability density function of visibilities is derived under the assumption that the successive samples are Gaussian distributed and statistically independent. However, in practice, the assumption may be not satisfied due to non-Nyquist sampling and quantizing. Then, to account for such impacts, an effective sample size is proposed. By compensating with it, the statistical distribution of visibilities is well represented in closed form. The experimental results by using an aperture synthesis millimeter-wave radiometer demonstrate the validity of the improved distribution. The results of this letter can be applied to sensitivity estimation and high-accuracy image reconstruction in digital aperture synthesis radiometry.