Polarimetric airborne scientific instrument, mark 2, an ice‐sounding airborne synthetic aperture radar for subglacial 3D imagery

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

Polarimetric airborne scientific instrument, mark 2, an ice‐sounding airborne synthetic aperture radar for subglacial 3D imagery

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

Antarctic ice tomography with airborne MIMO synthetic aperture radar

The aim of the thesis is the software processing of data acquired by PASIN2 (Polarimetric Airborne Scientific Instrument, mark 2). It is a 150-MHz coherent pulsed synthetic aperture radar (SAR) for 3D imagery beneath the ice thickness of the Antarctic, designed and operated by the British Antarctic Survey (BAS) to map the overflown regions of the continent in a single pass. In conventional single SAR imaging (2D), along-track and range coordinates are obtained. For 3D mapping, the remaining across-track angle dimension is estimated after processing several SAR images, exploiting the multiple-input multiple-output (MIMO) capabilities, with 8 underwing elements (4 below each wing) switching between transmit- and receive-modes, and 4 receive-only below the fuselage. The array is non-uniformly distributed along the wing orientation, perpendicular to the aircraft trajectory. Using Matlab® software, the off-line processing of PASIN2 data consists firstly in amplitude, phase and delay calibration of the different channels; secondly, single SAR imaging resulting from Backprojection algorithm, assuming homogeneous ice medium, and electromagnetic propagation based on refraction and diffraction according to the surveyed area; and finally, the direction of arrival estimation, by combining the available images and applying a high-resolution non-linear technique called MUSIC. To deal with the spatial distribution of PASIN2 array, a pre-processing has been implemented to improve MUSIC outputs. The results lead to 3D map estimations of the bedrock, ice-water interface or subglacial channels, correcting the topography regarding models in which a vertical direction of arrival was wrongly assumed. These observations will be used by environmental scientist to design, optimise or validate climate models. The thesis is framed within a major project of the Natural Environment Research Council (NERC) called ‘Ice shelves in a warming world: Filchner Ice Shelf System, Antarctica’ (NERC reference NE/L013770/1), in which UCL and BAS participate, among others

Efficient path estimation through parallel media for wide-beam ice-sounding radar.

The authors propose an algorithm to estimate the path followed by refracted signals from a source to a target, through a medium formed by uniform parallel layers with known different refractive indices, a common model used for ice radioecho sounding. The analytical solution is a polynomial with a degree that exponentially depends on the number of layers, being computationally inefficient. For low incidence angles, the small-angle approximation can be used to avoid the polynomial. In their technique, they normalise the governing equations to obtain a framework where to find a narrow angular interval containing the solution, finally estimated interpolating the boundaries. The new approach improves the results regarding the small-angle approximation for a wider angular range at a slightly higher computational time. This method has been applied to focus airborne synthetic aperture radar images for deep ice sounding, reducing the calculation time and improving the detected response in wide beam and squinted geometries, used for high along-track resolution or the detection of sloping internal layers

Structural Control Method Research motivated for MAV Lift Force Modification

Micro Air Vehicle (MAV) is a group of unmanned aerial vehicles that is autonomous and with a size restriction. Thanks to its possible application ranging from civil search-and-rescue missions to military surveillance missions, there is rising interest in the MAV related topics. From the previous work of the Atlanta Project, a vehicle is designed that could generate upward lift force. However, for the agility of the vehicle, the ability of positioning and stabilizing is also required. Therefore, it is demanded there is a way to make the lift force on each wing unbalanced, which is also the aim of this thesis project. In this thesis project, the investigation is focused on what structure modification method is feasible to be applied on the vehicle. At first, different actuators and structural modification methods are analyzed and screened from perspective of effectiveness and weight. A passive stiffness method is nally selected as the best method among all methods, using piezo actuators. The mechanism of this method is that the piezo material's stiffness is different when electrodes of it is under open circuit and short circuit electrical condition. After the theoretical work, a test is done on a canti-lever beam for the verification of effectiveness of this method.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin