Robust visual odometry using uncertainty models

In dense, urban environments, GPS by itself cannot be relied on to provide accurate positioning information. Signal reception issues (e.g. occlusion, multi-path effects) often prevent the GPS receiver from getting a positional lock, causing holes in the absolute positioning data. In order to keep assisting the driver, other sensors are required to track the vehicle motion during these periods of GPS disturbance. In this paper, we propose a novel method to use a single on-board consumer-grade camera to estimate the relative vehicle motion. The method is based on the tracking of ground plane features, taking into account the uncertainty on their backprojection as well as the uncertainty on the vehicle motion. A Hough-like parameter space vote is employed to extract motion parameters from the uncertainty models. The method is easy to calibrate and designed to be robust to outliers and bad feature quality. Preliminary testing shows good accuracy and reliability, with a positional estimate within 2 metres for a 400 metre elapsed distance. The effects of inaccurate calibration are examined using artificial datasets, suggesting a self-calibrating system may be possible in future work

Calibrating and Stabilizing Spectropolarimeters with Charge Shuffling and Daytime Sky Measurements

Well-calibrated spectropolarimetry studies at resolutions of $R>$10,000 with signal-to-noise ratios (SNRs) better than 0.01\% across individual line profiles, are becoming common with larger aperture telescopes. Spectropolarimetric studies require high SNR observations and are often limited by instrument systematic errors. As an example, fiber-fed spectropolarimeters combined with advanced line-combination algorithms can reach statistical error limits of 0.001\% in measurements of spectral line profiles referenced to the continuum. Calibration of such observations is often required both for cross-talk and for continuum polarization. This is not straightforward since telescope cross-talk errors are rarely less than $\sim$1\%. In solar instruments like the Daniel K. Inouye Solar Telescope (DKIST), much more stringent calibration is required and the telescope optical design contains substantial intrinsic polarization artifacts. This paper describes some generally useful techniques we have applied to the HiVIS spectropolarimeter at the 3.7m AEOS telescope on Haleakala. HiVIS now yields accurate polarized spectral line profiles that are shot-noise limited to 0.01\% SNR levels at our full spectral resolution of 10,000 at spectral sampling of $\sim$100,000. We show line profiles with absolute spectropolarimetric calibration for cross-talk and continuum polarization in a system with polarization cross-talk levels of essentially 100\%. In these data the continuum polarization can be recovered to one percent accuracy because of synchronized charge-shuffling model now working with our CCD detector. These techniques can be applied to other spectropolarimeters on other telescopes for both night and day-time applications such as DKIST, TMT and ELT which have folded non-axially symmetric foci.Comment: Accepted to A&

Implementing a reference backscatter calibration technique on a multi-sector multibeam echosounder

Increasingly, national hydrographic agencies are committing to routine acquisition of seabed backscatter strength estimates from multibeam echosounders (MBES) as part of national programs for seabed characterization. As part of their bathymetric survey mandate, these agencies have a long history of sounding quality control utilizing absolute and relative calibration (reference surfaces and crossover comparisons). Equivalent quality control is, however, not yet in place for managing seabed backscatter strength measurements, as the majority of the collected data is not absolutely referenced.Herein, a new technique for cross-calibrating a MBES with a reference calibrated split beam echosounder (SBES) was implemented. Broadband reference bottom backscatter strength (45-450 kHz) from areas with different seafloor types, derived from data obtained with Simrad EK80 SBES, is used to adjust the received acoustic intensities acquired from the same areas with several multi-sector MBES (Kongsberg Maritime EM2040P, EM710 and EM712), thereby enabling the routine collection of absolutely referenced bottom backscatter strength measurements. Previous efforts to implement a similar cross-calibration only considered a simplified vertically referenced ensonification geometry, ignoring the dynamic variations due to vessel rotations and active stabilization. As a result, neither the rotation of the beam pattern with respect to the vertical reference nor the compensation due to active beam stabilization were accounted for. Furthermore, this method properly accounts for modern MBES which have multiple transmit sectors over multiple swaths with the associated changes in frequency and signal modulation. The main output of this research is a set of two-dimensional arrays of correctors, derived for each transmit sector - the correction heatmap - providing estimates of the necessary calibration, as a function of across- and along-track sonar referenced angles. To test the repeatability of the proposed technique, correction heatmaps derived for the same system (using the same settings), but with data from different reference areas, were compared, resulting in differences generally within ± ~2 dB. Finally, a pre-calibrated MBES was used to survey a different location and establish a reference area, enabling the subsequent calibration of sonars that use the same frequencies

Report of the Working Group on Fisheries Acoustics Science and Technology (WGFAST)[ 10–13 May 2011 Reykjavík, Iceland]

Contributors: Lucio Calise, Handegaard Nils Olav, Rolf Korneliussen, Gavin Macaulay, Egil Ona, Ruben Patel and Hector Pen

Optimization tools for Twin-in-the-Loop vehicle control design: analysis and yaw-rate tracking case study

Given the urgent need of simplifying the end-of-line tuning of complex vehicle dynamics controllers, the Twin-in-the-Loop Control (TiL-C) approach was recently proposed in the automotive field. In TiL-C, a digital twin is run on-board to compute a nominal control action in run-time and an additional block C_delta is used to compensate for the mismatch between the simulator and the real vehicle. As the digital twin is assumed to be the best replica available of the real plant, the key issue in TiL-C becomes the tuning of the compensator, which must be performed relying on data only. In this paper, we investigate the use of different black-box optimization techniques for the calibration of C_delta. More specifically, we compare the originally proposed Bayesian Optimization (BO) approach with the recently developed Set Membership Global Optimization (SMGO) and Virtual Reference Feedback Tuning (VRFT), a one-shot direct data-driven design method. The analysis will be carried out within a professional multibody simulation environment on a novel TiL-C application case study -- the yaw-rate tracking problem -- so as to further prove the TiL-C effctiveness on a challenging problem. Simulations will show that the VRFT approach is capable of providing a well tuned controller after a single iteration, while 10 to 15 iterations are necessary for refining it with global optimizers. Also, SMGO is shown to significantly reduce the computational effort required by BO.Comment: Preprint submitted to European Journal of Contro