Liang Lang

An aperture synthesis radiometer at millimeter wave band

Synthetic aperture radiometer has the potential to meet the spatial resolution requirement of passive microwave remote sensing from space. A one-dimensional prototype of aperture synthesis radiometer at millimeter wave band is introduced in this paper. It contains 16 antenna elements, 16 receiving channels, 16 ADCs, and image reconstruction part. Error correction is made in the image reconstruction. Experiment results show the radiometer can give good images of natural scenes.

A General Platform for Millimeter Wave Synthetic Aperture Radiometers

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.

Polarization-Based Method for Object Surface Orientation Information in Passive Millimeter-Wave Imaging

Surface orientation information is essential to depicting the 3-D structure of an object. This paper analyzes the linear polarization characteristics of several typical objects by simulations and measurements. Then, a polarization-based method is presented to acquire the object surface orientation information from three different linear polarization brightness temperature images by using a 94-GHz imaging radiometer. The experiments are conducted outside, where a wooden plate is placed obliquely on a metal box. Experimental results indicate that our method is capable of achieving the surface orientation information that is beneficial to recognizing the object. This method suggests possible applications for terrain models and object detections.

Wavelet-based 1/f-Noise elimination in millimeter-wave radiometer

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.

Passive millimeter-wave scene imaging simulation based on fast ray-tracing

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 novel Dicke microwave radiometer without temperature control for reference match load

Dicke microwave radiometer usually adopts one reference match load of constant desired temperature. In the paper, a novel Dicke microwave radiometer without temperature control for reference match load is presented. We choose to monitor the physical temperature of reference match load instead of to keep it constant, so the structure of the reference match load is simplified greatly. At the same time, the accuracy and stability of the radiometer are both improved because the accuracy of measuring reference match loads temperature is better than keeping its temperature nowadays. At last, an XC band Dicke microwave radiometer is designed, and some experiments of brightness temperature measurement are performed, which verified the principle of this kind of Dicke microwave radiometer.

Passive microwave imaging by aperture synthesis technology

In order to verify the theory of aperture synthesis at low expense, two-channel ka-band correlation radiometer which is basic part of synthetic aperture radiometer is designed firstly before developing the multi-channel synthetic aperture radiometer. The performance of two-channel correlation radiometer such as stability and coherence of visibility phase are tested in the digital correlation experiment. Subsequently all required baselines are acquired by moving the antenna pair sequentially, corresponding samples of the visibility function are measured and the image of noise source is constructed using an inverse Fourier transformation.

Accuracy Analysis of Full Digital Compensatory Millimeter Wave Radiometer

MMW radiometer is the core equipment of passive MMW remote sensing. As a new type of radiometer, full digital compensatory MMW radiometer can compensate system gain and receiver noise fluctuation by using digital compensatory algorithm. According to the designed full digital compensatory 8mm radiometer, the accuracy analytical method of the designed MMW radiometer system is put forward in this paper.

A novel two-channel correlation radiometer

A novel Ka-band two-channel correlation radiometer with independent local oscillator is constructed. To remain coherence in phase between two channels, the frequency of local oscillator must be very stable. The difference of phase between two channels, which is approximately invariable in a period of time, can be compensated by digital signal algorithm, so complexity of hardware can be reduced obviously.