Multistatic Method Research Articles

Cone-Shaped Space Target Inertia Characteristics Identification by Deep Learning With Compressed Dataset

An effective method for identifying inertia characteristics of cone-shaped space target based on deep learning is proposed. The inertia ratio is determined by the time-varying scattering fields from the cone-shaped targets. The multistatic method is introduced to reduce the evaluation time of time-varying scattering fields. The micro-Doppler spectrogram (MDS) dataset is constructed by the time–frequency analysis with numerical simulation method, point scattering model, and experimental tests. The compressed dataset is further achieved by truncated singular value decomposition (SVD). Finally, the micromotion parameter identification model is constructed to identify the inertia ratio for the cone-shaped space target. The interaction loss function and the feedforward denoising convolutional neural networks (DnCNNs) are employed to improve the identification accuracy. Parameters identification of the precession frequency, precession angle, spin frequency, and inertia ratio with both simulation and experiment datasets demonstrate the validity of the proposed method.

Neodymium isotope heterogeneity of ordinary and carbonaceous chondrites and the origin of non-chondritic 142Nd compositions in the Earth

We present high-precision Nd isotope compositions for ordinary and carbonaceous chondrites determined using thermal ionization mass spectrometry with dynamic and multistatic methods. The ordinary chondrites had uniform and non-terrestrial μ142Nd, μ148Nd, and μ150Nd values, with data that plot along the mixing line between s-process and terrestrial components in μ150Nd versus μ148Nd and μ142Nd versus μ148,150Nd diagrams. In contrast, the carbonaceous chondrites were characterized by larger anomalies in their μ142Nd, μ148Nd, and μ150Nd values compared to ordinary chondrites. Importantly, the data for carbonaceous chondrites plot along the s-process and terrestrial mixing line in a μ150Nd versus μ148Nd diagram, whereas they have systematically lower μ142Nd values than the s-process and terrestrial mixing line in μ142Nd versus μ148,150Nd diagrams. This shift likely results from the incorporation of calcium- and aluminum-rich inclusions (CAIs), indicating that the Nd isotopic variability in the ordinary chondrites and CAI-free carbonaceous chondrites was caused solely by the heterogeneous distribution of s-process nuclides. The isotopic variation most likely results from nebular thermal processing that caused selective destruction of s-process-depleted (or r-process-enriched) dust grains in the inner Solar System where the parent bodies of ordinary chondrites formed, whereas such grains were preserved in the region of carbonaceous chondrite parent body formation. The Nd isotope dichotomy between ordinary and bulk aliquots of carbonaceous chondrites can be related to the presence of Jupiter, which may have separated two isotopically distinct reservoirs that were present in the solar nebula. After correcting for s-process anomalies and CAI contributions to the Nd isotopes observed in the chondrites, we obtained a μ142Nd value (−2.4±4.8 ppm) that was indistinguishable from the terrestrial value. Our results corroborate the interpretation that a missing reservoir (e.g., a hidden enriched reservoir, erosional loss of crust) is not required to explain the observed differences in 142Nd/144Nd ratios between chondrites and terrestrial materials.

Evaluation of the long-term fluctuation in isotope ratios measured by TIMS with the static, dynamic, and multistatic methods: A case study for Nd isotope measurements

We investigated the long-term fluctuation in high-precision Nd isotope measurements by using a modern thermal ionization mass spectrometer (Triton plus) to evaluate the effect of Faraday cup deterioration caused by the accumulation of strong ion beams into the cups. A number of measurements (n=76) were conducted by applying three distinct methods (static, dynamic, and multistatic) during an eight-month analytical period, which was further divided into seven short analytical campaigns. The reproducibilities of 142Nd/144Nd ratios for campaigns 1–4 were 23, 6.4, and 17ppm (2 SD) for the static (Jump 1), dynamic, and multistatic methods, respectively. After the replacement of six out of nine Faraday cups (campaigns 5–7), the reproducibilities of 142Nd/144Nd ratios were improved to 18, 4.1, and 5.4ppm (2 SD) for the static, dynamic, and multistatic methods, respectively. This implies that high-precision Nd isotope analysis with not only the static but also the multistatic method is susceptible to the deterioration of Faraday cups. Consequently, the dynamic method is the most effective to minimize the influence of Faraday cup degradation, although it is recommended to ensure that Faraday cups are as fresh as possible to avoid small, but resolvable, shifts in isotope ratios obtained by this method. In addition to 142Nd/144Nd, we demonstrate that it is possible to determine 148Nd/144Nd and 150Nd/144Nd ratios with the dynamic method. The reproducibilities of 148Nd/144Nd and 150Nd/144Nd for campaigns 5–7 were 6.3 and 8.8ppm, respectively, which are 1.5–4.1 times better than those obtained in previous studies.

Hilbert space inverse wave imaging in a planar multilayer environment

Most diffraction tomography (DT) algorithms use a homogeneous Green function (GF) regardless of the medium being imaged. This choice is usually motivated by practical considerations: analytic inversions in standard geometries (Cartesian, spherical, etc.) are significantly simplified by the use of a homogeneous GF, estimating a nonhomogeneous GF can be very difficult, as can incorporating a nonhomogeneous GF into standard DT algorithms. Devaney has circumvented these issues by developing a purely numerical DT inversion algorithm [A. J. Devaney and M. Dennison, Inverse Probl. 19, 855-870 (2003)] that is independent of measurement system geometry, number of frequencies used in the reconstruction, and GF. A planar multilayer GF has been developed for use in Devaney's "Hilbert space" algorithm and used in a proof-of-principle nondestructive evaluation (NDE) experiment to image noninvasively a flaw in an aluminum/copper planar multilayer medium using data collected from an ultrasonic measurement system. The data were collected in a multistatic method with no beamforming: all focusing through the multilayer was performed mathematically "after-the-fact," that is, after the data were collected.

Multistatic refraction-error compensation in radar and satellite navigation systems

A multistatic method compensation of positioning errors caused by refraction is proposed that does not require a model of the atmosphere's refractive-index profile and can be used in radar and satellite navigation systems.