Multistatic SAR offers a potential solution to overcome the limitations of conventional monostatic architectures. The imaging performance of multistatic SAR is greatly influenced by the observation geometry. However, due to the high degree of freedom, designing an efficient constellation is challenging. Through simulations, it has been confirmed that optimal image quality can be achieved by forming a seamless Doppler spectrum with an appropriate baseline value for the Along-Track Formation. Furthermore, the enhanced imaging performance of a well-designed multistatic constellation has been demonstrated by simulating distributed targets in complex terrains.

Microsatellite SAR systems are the centerpiece of the New Space era for the Synthetic Aperture Radar(SAR) field. However, compact and cost-effective architectures of microsatellite SAR are detrimental to overall system performance, especially with sensitivity. By taking advantage of mass production, the overall imaging performance of microsatellite SAR systems can be enhanced in a simple and intuitive manner with multistatic operation. This paper proposes a multistatic operation concept with an along-track constellation. With the image fusion technique, the sensitivity and resolution performance of the system can be designed more freely. A simulation was conducted to prove the concept.

In this letter, a forward-looking electromagnetic wave imaging method using radial scanning multichannel radar is proposed. Compared to the current forward-looking imaging systems, the method requires less hardware complexity due to the reduced number of channels, which is especially advantageous for millimeter-wave and higher frequency systems aiming for a high-resolution. By digitally processing the radially scanned radar data, a 3-D radar image is obtained. An image formation algorithm that exploits the computational efficiency of the fast Fourier transform is proposed. The effects of the radar parameters are discussed by analyzing the impulse response function. Moreover, the rotational sampling requirement, which relates to the field of view, is derived. A numerical simulation was performed to demonstrate the 3-D imaging capabilities of the proposed method. The results show that the proposed method enables radar imaging using a substantially fewer number of channels.

This study proposes a method for synthesizing 3-D microwave images using a multiple-input–multiple-output (MIMO) radar. Recent studies on MIMO radar technology have reported promising hardware that can be used in radar imaging. In particular, the increased amount of data acquired from MIMO radar is effective for 3-D radar imaging. Despite the demand for using 3-D radar imaging, the underlying technical challenges have not been addressed. Although the array synthetic aperture radar method is promising, realizing a multichannel radar with numerous channels requires significant effort in terms of hardware. Therefore, an MIMO radar can be used to effectively increase the number of channels with reduced hardware. Studies on beat frequency division (BFD) frequency-modulated continuous wave (FMCW) radars show that the simultaneously transmitted MIMO signal is suitable for radar imaging applications without hindering the along-track imaging performances. In this study, the signal of a BFD FMCW radar mounted on a movable platform is modeled according to the imaging geometry, and a fast Fourier transform-based imaging algorithm is derived to efficiently process the multichannel data. This algorithm is applied to the simulated radar data to verify the effectiveness of the proposed method. The method is further assessed by applying the imaging algorithm to the radar data acquired from a functional W-band BFD FMCW radar hardware. The radar transceiver was mounted on a movable table, and the data are measured at an outdoor experiment site. The results verify that the proposed method can be used for various 3-D radar imaging applications.

A W-band multiple-input multiple-output (MIMO) radar imaging system has been proposed. The 4 × 4 radar system that forms a 2-D virtual array operates at a center frequency of 94 GHz and bandwidth of 1 GHz with frequency-modulated continuous wave. A hybrid scheme comprising time- and frequency-division multiplexing is introduced for establishing orthogonal waveforms, where the transmit channels perform alternate transmission in pairs. The proposed scheme can efficiently extend the number of MIMO channels utilizing the existing hardware with simultaneous transmission. The design, implementation, measurements, and imaging results of the proposed radar system have been presented. The imaging performance was tested through outdoor experiments. The high-resolution performance was shown with images generated using a synthetic aperture radar. The impulse responses of all channels were measured, and the resolution was confirmed to be 0.15 m in all the channels. In addition, a human and a car at 100-m range were imaged using the proposed radar system. The polarimetric and interferometric capabilities were tested for multimode imaging with the MIMO configuration. Overall, the measurements and experimental results verified the feasibility of the proposed MIMO radar with hybrid scheme as a high-resolution multimode imaging system.

The required accuracy performance of a high-precision oceanographic radar altimeter can be achieved by designing a height-tracking system. The optimal discriminator of the tracking system is synthesized in this letter, and the calculation methods for its discriminating characteristics and measurement error performance are investigated. The structure of the optimized tracking system is outlined. Using the obtained results, the dependence of the limiting accuracy of a single delay-time measurement on the signal-to-noise ratio is determined. The limiting accuracy obtained by the discriminator can be specified as the measurement performance of the altimeter system.

Radar signals are synthesized having a region of zero autocorrelation sidelobes with a relative width of 1/3 ≤ a <; 1 in the vicinity of the central peak of an aperiodic autocorrelation function. These signals represent a train of two binary phase-coded pulses encoded by pair of complementary sequences of length N = 2k, with an integer k ≥ 2. The correlation characteristics of the synthesized signal are analyzed. A compression algorithm for these signals, multichannel with respect to the Doppler frequency, is considered. It includes a combined algorithm for fast Walsh and Fourier transforms.

When designing a high-precision airborne radar altimeter, the approach of an analysis of the characteristics of radio signals reflected from a statistically rough sea surface based on its steady-state model becomes invalid. In the measurement of the sea surface profile, a characteristic of the reflection properties is the local backscattering pattern of the radar cross section, which depends on the time and the relative position of the low-altitude carrying vehicle from the surface. The effective width of the local backscattering pattern is determined by the statistical characteristics both of the small-scale roughness and the large-scale roughness of the surface. The location of the maximum value of the local backscattering pattern depends on the derivative of the large-scale roughness of the sea surface, i.e., the shifts in proportion to the slopes of the large-scale surface roughness. These effects must be considered when analyzing the measurement errors of a low-altitude radar altimeter.

An algorithm of optimal Neyman-Pearson detection for a high-precision spaceborne radar altimeter is synthesized, and its detection performance in the case of sea surface returns is evaluated. One result of the synthesis is that the new detector incorporates a filter with time-varying signal-to-noise-ratio-dependent parameters. A simplified (near-optimal) detector considered in this letter loses only 2 dB in the threshold signal with respect to that of the optimal Neyman-Pearson algorithm.

In this letter, we introduce the possibility of the sea-surface slope measurements using second-order statistics of return waveforms from sea surface in a continuous-wave radar scatterometer. It has been shown that the estimation of the variance of sea-surface slopes can be obtained by measuring the signal power or the power-spectrum width of return waveforms. We found that the power-spectrum-width-based estimation approach is more sensitive to the variance of the sea-surface slope for weak sea-surface disturbances in contrast to the power-based one.

A simple statistical extension at the individual tree level for an earlier-developed very high frequency forest backscatter model is proposed. This extended model treats trunk volumes as random quantities. A concept of random forest reflection coefficient is also introduced to characterize radar returns from individual trees. Based on the extended model, a set of algorithms for estimating the mean trunk (stem) volume from synthetic aperture radar data at the individual tree level is developed assuming that the areal tree density is known. The algorithms are specified for different scenarios related toa prioriinformation on parameters of statistical distributions for the trunk volume and fluctuations of the forest reflection coefficient. An approximate lower bound on the standard deviation in the unbiased estimation of the mean trunk (stem) volume is proposed. This bound can be readily obtained by means of computer simulation for any specified statistical distribution for the trunk volume and fluctuations of the forest reflection coefficient. Performance analysis for the proposed algorithms is numerically performed by means of Monte Carlo simulation for a variety of scenarios. This analysis has shown that the algorithms provide nearly unbiased and efficient estimates, and the proposed lower bound is a very accurate approximation. The results of the study have demonstrated that the approach and methods developed in this paper suggest promising solutions in accurate forest parameter retrieval.

A readily computable formula to perform versatile analysis of the nonstationary pulse-to-pulse correlation properties of ocean altimeter returns is presented. Using this formula, the correlation coefficient and correlation interval depending on the reference time, sea state, and system parameters have been analyzed. The results have suggested that the pulse repetition frequency should adaptively be adjusted to the sea state to ensure precise altitude measurements.

The effect of look angle on the accuracy performance of fixed-baseline interferometric synthetic aperture radar is studied. It is shown that there exists an optimal look angle that minimizes the variance of the surface height estimate for a resolution cell, and it depends upon the system as well as surface parameters. Numerical analysis confirming the existence of the optimal look angle is presented