G-band FMCW Doppler radar for sea clutter and target characterisation

Funding: UK Engineering and Physical Sciences Research Council under grant EP/S032851/1.Marine autonomy is a field receiving a high degree of interest for its many potential applications in terms of commerce, crew safety, and the military. A successful autonomous vessel depends on a sophisticated degree of situational awareness facilitated by sensors. We are investigating sub-THz radar sensors for this purpose, with the primary goal being the characterization of sea clutter and targets in terms of both amplitude and Doppler statistics at frequencies spanning 24 to 350 GHz, where presently there is a lack of data. Sub-THz frequencies are of particular interest due to improved range and Doppler resolutions, and reduced sensor size, factors expected to be critical in enabling anomaly detection in the dynamic marine environment. As part of this work, a new 207 GHz frequency modulated continuous wave (FMCW) radar is being developed for the collection of clutter and target phenomenology data. The architecture uses a direct digital synthesis (DDS) generated chirp which is upconverted onto a low phase noise microwave LO then frequency multiplied by 24 to the carrier frequency. Twin Gaussian optics lens antennas (GOLAs) are used for transmit and receive with beamwidths of 2° , with adjustable linear polarization. The radar head is gimbal mounted for raster scanning RCS maps or for use in staring mode Doppler measurements. A chirp bandwidth of 4 GHz enables range bins of a few centimeters and high speed chirps enable a maximum unambiguous velocity of ±5 m/s.Publisher PD

Doppler characteristics of sea clutter at K-band and W-band : results from the St Andrews and Coniston water trials

Funding: UK Engineering and Physical Sciences Research Council under grant EP/S032851/1.This study reports on the experimental results from two field trials conducted by the University of St Andrews, focusing exclusively here on Doppler data. The first trial was at the Bruce Embankment in St Andrews, UK (winter 2020) and the second one was at Coniston Water in the Lake District, UK (autumn 2022). A 24 GHz K-band radar and a 94 GHz W-band radar were used in both trials to collect sea clutter data for phenomenology studies. As very few sea clutter data and analysis of these are available in the literature at these high frequencies, the results are expected to be of general interest within this field of study. The data collection at both trials was done for low grazing angles in the littoral zone. The datasets are quite varied in terms of wave direction, polarization and wind speed. The Doppler signatures and corresponding statistical parameters for these various conditions are reported here. The spectral analysis of different wave types (burst, whitecap, rough surface scattering) along with the combined spectra are also discussed. It is anticipated that these empirical results will be the precursor for improving upon the frequency ranges of existing sea clutter Doppler models

Millimetre wave radar signatures of sea lions

Funding: This work was supported by the UK Engineering and Physical Sciences Research Council under grant EP/S032851/1.This study reports the millimetre wave radar signatures of sea lions collected from three animals in the outdoor seal pool available at the Sea Mammal Research Unit in St Andrews in the Autumn of 2021. The objective is to study the radar signatures of the animals when their full body or part thereof is above water. The data was collected using a 77 GHz Frequency Modulated Continuous Wave (FMCW) radar with linear polarisation. Both Horizontal-Horizontal (HH) and Vertical-Vertical (VV) polarisation data have been stored and analysed. It has been demonstrated that the sea lions were very clearly detected by the radar with SNR greater than 30 dB at a range of 40 m. The calculated radar cross section (RCS) of the sea lions in HH polarisation varies from −50 to −19 dBsm (modal) and −28 to −2 dBsm (maximum), corresponding to the different body parts and the amount of exposure to the radar beam. In VV polarisation, the modal RCS value range is from −47 to −25 dBsm and the maximum RCS varies from −26 to −15 dBsm. It is also shown that the recorded Doppler features have the potential for target classification, essential for autonomous operation of marine vessels.Postprin

Amplitude distribution of low grazing angle G-band littoral sea clutter

G-band radar sensing of the marine environment is of interest for maritime autonomy, however at present, no phenomenological data of low grazing angle sea clutter at this frequency is available in the literature. Future sensor design is contingent on the modeling of empirical data, with polarization expected to be a key parameter. This paper presents the results of an analysis of data of radar returns from the water’s surface gathered in 2022 at Coniston Water, UK. The difference in amplitude distribution and normalized radar cross section (NRCS) between HH (horizontal-horizontal) and VV (vertical-vertical) polarization is shown for two 0.5° wide grazing angle swaths centered at 2° and 4°. HH is seen to produce longer-tailed distributions than VV for both swaths, with a mean NRCS for thresholded data (i.e. for wave signal peaks) of -33.3 dB (HH) and -35.2 dB (VV) for the swath centered at 2°, and -38.6 dB (HH) and -41.6 dB (VV) for the swath centered at 4°

Amplitude Characteristics of Littoral Sea Clutter Data at K-band and W-band (dataset)

Files correspond to data used for the generation of the figures in this manuscript. In each dataset, each column contains the log magnitude values of a single range profile and successive columns correspond to the subsequent range profiles. Dataset_1 and Dataset_2 are 24 GHz radar data looking towards the shore and looking at the open sea respectively. Dataset_3 and Dataset_4 are the corresponding 94 GHz data

Machine learning based approach for maritime target classification and anomaly detection using millimetre wave radar Doppler signatures (dataset)

Raw radar dat

Millimetre wave radar signatures of sea lions (dataset)

Raw radar data file of the Sea Lion signatures processed and analysed in the paper