We demonstrate a 3D multiple-input multiple-output (MIMO) terahertz (THz) imaging system. It uses an optoelectronic architecture comprising two continuous-wave lasers to generate and detect the THz field. Frequency tuning is achieved by sweeping the output frequency of one laser and mixing it with a fixed frequency laser. The optical output is fiber coupled, amplified and split into 16 channels which are used to illuminate an array of eight continuous wave THz transmitters and eight THz receivers. Each transmitter can be switched on and off individually via the applied bias voltage such that parallel sampling of the intermediate frequency (IF) at the receivers allows to record every transmitter and receiver combination individually. Numerical postprocessing of this data on a general purpose graphics processing unit (GPGPU) allows the reconstruction of the entire scene as a 3D-voxel array.
Automotive radar is becoming increasingly popular for enhanced driving safety and autonomous driving. However, the increasingly severe mutual interference problems can cause the commercially available linear frequency-modulated continuous-wave (LFMCW) automotive radar to become the victim of its success. Phase-modulated continuous-wave (PMCW) automotive radar systems can be used to mitigate the mutual interference problems. To attain this goal, long binary periodic probing sequences with low correlation sidelobes, arbitrary period lengths, and ample diversity are needed by PMCW radar systems. To further reduce the sidelobe levels, at the slight loss of the signal-to-noise ratio (SNR), mismatch receive filters are also viable options for PMCW radar. We introduce herein the joint design of probing sequences and mismatched receive filters, under the constraint of maximum allowable SNR loss, for PMCW radar.
This paper presents a novel method for the identification and resolution of targets with ambiguous velocities within a single measurement cycle of a phase-modulated continuous wave (PMCW) radar system based on multi-hypothesis Doppler shift compensation. The Doppler shift is first compensated by assuming that the velocities of all targets are unambiguous. Since targets with velocity ambiguity cannot be perfectly compensated in their range profiles based on this assumption, ambiguities can be identified after the range correlation processing. The range correlation processing for ambiguous targets is then repeated under multiple velocity hypotheses. The velocity hypothesis with the best sidelobe suppression is considered the correct velocity. As a result, the Doppler shift compensation in the range profile is achieved as well. Simulation results show that the proposed method can simultaneously resolve velocity ambiguities and compensate for the Doppler shift induced increased sidelobe level in the range profile.
Due to numerous benefits, radar is considered as an important sensor for human activity classification. The problem of classifying continuous sequences of activities of unconstrained duration has been studied in this work. To tackle this challenge, a radar data processing method utilizing point transformer networks has been proposed. The method has been experimentally verified on a dataset of human activities, and experiments have been performed to determine its optimal implementation. Promising preliminary results on a 9-class dataset show test accuracy and macro F-1 scores in the range of 83% and 73% respectively.
In 2010 the first formation flying radar system was built by extending the TerraSAR-X synthetic aperture radar mission by a second, TerraSAR-X-like satellite called TanDEM-X. The resulting large single-pass radar interferometer features flexible baseline selection. This enables the acquisition of highly accurate cross-track interferograms not impacted by temporal decorrelation and atmospheric disturbances. The primary objective of the mission – the generation of a global digital elevation model with unprecedented accuracy – was achieved in 2016. Up to 2020 the mission acquired data for a global change layer (TanDEM-X DEM 2020) revealing the height changes relative to the first dataset. After so many years in orbit both spacecraft show aging effects. There are already several redundant units in operation on both satellites, but they are still fully functional and have enough consumables for several additional years. Repeated height measurements allow the observation and quantification of dynamic processes on the Earth’s surface such as deforestation or melting of glaciers and ice sheets. Therefore, bistatic operations continue in the TanDEM-X 4D Phase with a focus on changes in the cryosphere, biosphere and densely populated areas and regions with larger height changes.
