Paul V. Brennan

FMCW radar is a popular technique for radar sensors. A Direct Digital Synthesiser (DDS) is commonly used to generate the required linear frequency sweep. DDS devices are widely‐available and easy to configure in terms of the key radar parameters of sweep bandwidth and pulse duration. They generate a step‐approximation to a linear frequency sweep for which the frequency increment parameter also needs to be defined. However, there is little information available in the literature to guide radar designers on the choice of this parameter. As a result, most designs are based on an empirical estimate of the DDS frequency increment. The aim is to provide an analytic basis and design rules for the choice of this parameter. Two principal types of FMCW radar (direct sampling and deramp) are studied to determine the effect on the range profile of the finite DDS frequency increment. It is shown that a set of spurs appears around each target response. Analytic expressions are derived to quantify the amplitude and distribution of these spurs from which simple design rules are presented to allow an informed choice of DDS frequency increment. These analytic results are convincingly validated using numerical simulations and experimental measurements.

Polarimetric Airborne Scientific INstrument, mark 2 (PASIN2) is a 150 MHz coherent pulsed radar with the purpose of deep ice sounding for bedrock, subglacial channels and ice‐water interface detection in Antarctica. It is designed and operated by the British Antarctic Survey from 2014. With multiple antennas, oriented along and across‐track, for transmission and reception, it enables polarimetric 3D estimation of the ice base with a single pass, reducing the gridding density of the survey paths. The off‐line data processing stream consists of channel calibration; 2D synthetic aperture radar (SAR) imaging based on back‐projection, for along‐track and range dimensions; and finally, a direction of arrival estimation (DoA) of the remaining across‐track angle, by modifying the non‐linear MUSIC algorithm. Calibration flights, during the Antarctic Summer campaigns in 16/17 and 19/20 seasons, assessed and validated the instrument and processing performances. Imaging flights over ice streams and ice shelves close to grounding lines demonstrate the 3D sensing capabilities. By resolving directional ambiguities and accounting for reflector across‐track location, the true ice thickness and bed elevation are obtained, thereby removing the error of the usual assumption of vertical DoA, that greatly influence the output of flow models of ice dynamics.