Prediction of defensive success in elite soccer using machine learning - Tactical analysis of defensive play using tracking data and explainable AI.

The interest in sports performance analysis is rising and tracking data holds high potential for game analysis in team sports due to its accuracy and informative content. Together with machine learning approaches one can obtain deeper and more objective insights into the performance structure. In soccer, the analysis of the defense was neglected in comparison to the offense. Therefore, the aim of this study is to predict ball gains in defense using tracking data to identify tactical variables that drive defensive success. We evaluated tracking data of 153 games of German Bundesliga season 2020/21. With it, we derived player (defensive pressure, distance to the ball, & velocity) and team metrics (inter-line distances, numerical superiority, surface area, & spread) each containing a tactical idea. Afterwards, we trained supervised machine learning classifiers (logistic regression, XGBoost, & Random Forest Classifier) to predict successful (ball gain) vs. unsuccessful defensive plays (no ball gain). The expert-reduction-model (Random Forest Classifier with 16 features) showed the best and satisfying prediction performance (F1-Score (test) = 0.57). Analyzing the most important input features of this model, we are able to identify tactical principles of defensive play that appear to be related to gaining the ball: press the ball leading player, create numerical superiority in areas close to the ball (press short pass options), compact organization of defending team. Those principles are highly interesting for practitioners to gain valuable insights in the tactical behavior of soccer players that may be related to the success of defensive play.

Multiwavelength holography: height measurements despite axial motion of several wavelengths during exposure.

Interferometric measurements of rotating objects face an axial motion component if the optical axis of the measurement system is not pointing towards the axis of rotation. In a typical interferometer, axial motion of half a wavelength reduces the interference contrast to zero. Our setup compensates for this axial component by an adapted variation of the reference path length during exposure utilizing a piezoelectric actuator. We present off-center measurements on a cylinder, rotating with different angular velocities. The repeatability of these measurements is dominated by motion blur, which demonstrates that the compensation of the axial motion works accurately.

Multiwavelength digital holography in the presence of vibrations: laterally resolved multistep phase-shift extraction.

With the application of multiwavelength digital holography in rough environments, such as where machine tools are used, we cannot rely on the complete absence of vibrations. The evaluation of temporal phase shifting in multiple interferograms regions allows one to determine and take into account random subwavelength tilt changes during image acquisition of the sensor with respect to a work piece. In this regard, experimental data inside a controlled laboratory setup, as well as data acquired within a five-axis machine tool suffering from random vibrations, are evaluated and affirmed by a simulation model.

Inline application of digital holography [Invited].

We describe the inline integration of the digital holographic sensor HoloTop in a precision turning plant. A fully automated part-handling system that fulfills the requirements for cycle time and stability was built and integrated into the production process. The inspection system has been running in multishift operation since 2015. For the first time, to the best of our knowledge, the results of one-year, long-term height measurements of 10 million parts under rough production conditions are presented to verify the suitability for industrial use.

Digital holography on moving objects: interference contrast as a function of velocity and aperture width.

Digital holographic measurements on planar moving objects are investigated. We discuss the dependence of the interference contrast on velocity and aperture width for both diffusely and specularly reflecting objects. Using spatial phase shifting, the experimental results for motion in parallel and perpendicular to the optical axis are in good agreement with the theoretical considerations. Measurements with object velocities of up to 100 mm/s are conducted using only less than 1 mW of continuous-wave laser light. These considerations are used to determine the optimal angle between the direction of motion and the illuminating beam, resulting in the lowest decrease in contrast with increasing velocity.

Broadband infrared spectroscopy using optical parametric oscillation in a radially-poled whispering gallery resonator.

We demonstrate optical parametric oscillation in a millimeter-sized whispering gallery resonator suitable for broadband infrared spectroscopy. This nonlinear-optical process is quasi-phase-matched using a radial domain pattern with 30 µm period length, inscribed by calligraphic poling. The output wavelengths are selected in a controlled way over hundreds of nanometers. We achieve this by increasing the temperature of the resonator in steps such that the azimuthal mode number of the pump wave rises by one. As a proof-of-principle experiment, we measure a characteristic resonance of polystyrene in the spectral range of 2.25 - 2.45 µm.

Optimizing pump threshold and conversion efficiency of whispering gallery optical parametric oscillators by controlled coupling.

Threshold and efficiency of optical parametric oscillation in whispering gallery resonators have been predicted to depend strongly on the coupling strength. Our experiments, varying the coupling strength continuously over 3 orders of magnitude, confirm these predictions. The pump threshold changes by a factor of 20, allowing the adaptation of the system to a wide range of input powers. The minimum threshold of 0.20 mW occurs for significant pump undercoupling. The efficiency increases monotonically with coupling, spanning 4 orders of magnitude with a maximum efficiency of 30% in contact yielding output powers exceeding 1 mW.

Blue-pumped whispering gallery optical parametric oscillator.

We demonstrate a whispering gallery optical parametric oscillator pumped at 488 nm wavelength. This millimeter-sized device has a pump threshold of 160 µW. The signal field is tunable between 707 and 865 nm wavelength and the idler field between 1120 and 1575 nm through temperature variation. Although the conversion efficiency is fundamentally limited to several percent because of absorption loss for the pump wave, the results provide evidence that such oscillators will be able to cover finally the entire visible range.

Fabrication and characterization of whispering-gallery-mode resonators made of polymers.

High-quality whispering-gallery-mode resonators made of polymethylmethacrylate (PMMA) are fabricated by simple mechanical turning and polishing according to a technique used by Ilchenko et al. to produce crystalline whispering-gallery-mode resonators with high quality factors (Q-factors). The high-Q PMMA resonators are investigated in two wavelength regimes: in the near infrared between the wavelengths 1470 and 1580 nm and at the wavelength 635 nm. The Q-factor in the infrared regime is limited by material absorption to 3 x 10(5) At 635 nm the Q-factor is limited by surface scattering only and reaches 4 x 10(7), which is a new record for polymers.