Haritz Iribas

A novel processing and classification framework for the automatic detection and classification of pedestrians, bicycles, and cars in urban environments is proposed and experimentally demonstrated. The proposed processing pipeline combines high-sensitivity distributed acoustic sensing, automatic trajectory extraction, physically interpretable spectral feature extraction, and supervised machine-learning-based pattern recognition. The technique leverages pre-existing telecommunication fibers installed beneath or close to sidewalks and roadways. Coherent optical time-domain reflectometry enhanced with optical pulse compression provides the sensitivity and spatial resolution required to detect mobility-induced vibrations using these non-dedicated fibers, thereby avoiding sensing-cable deployment or pavement retrofitting. A detailed analysis of the signals extracted along the detected trajectories is performed in the spatial-frequency and equivalent-frequency domains. Controlled walking, running, and cycling measurements, together with passenger-vehicle observations under normal traffic conditions, reveal reproducible spectral characteristics associated with the underlying pavement-loading mechanisms. In particular, the analysis identifies four complementary properties: spatial loading periodicity, periodic loading peak prominence, initial spectral decay, and broadband spectral-energy distribution. Seven physically interpretable features derived from these properties are subsequently supplied to a support vector machine classifier. The processing and classification framework is evaluated using measurements acquired from an existing optical fiber in a real urban environment containing simultaneous sidewalk and road activity. When classification is restricted to manually verified bicycle, car, and pedestrian trajectories, a balanced accuracy of 98.3% is achieved. These results demonstrate the potential of physically interpretable spectral analysis of DAS measurements for continuous, spatially distributed, and privacy-preserving urban mobility monitoring.

The attempt to train undergraduate primary school teachers in STEM skills faces an evident handicap, since students enrolling Teacher Degrees usually have humanistic secondary school backgrounds. Attitudes towards STEM on a sample of 336 under-graduate teachers from two Spanish universities were analyzed. Students answered a questionnaire, and responses were analyzed qualitatively (open text questions) and quantitatively (Descriptive Statistics and Statistical Implicative Analysis). Results describe a young collective, with a clear majority of women, mostly interested in languages and history, with high vocation (rather spontaneous than hereditary) to work with children. There is evidence that school advice services fulfill a role to discourage certain students from STEM. These conclusions give valuable information that could be used to replace institutional practices and improve the perception future teachers have towards the teaching of STEM in Primary Education.

(AR) Derrigorrezko Bigarren Hezkuntzara bideratutako STEM proiektuen azterketa kuantitatiboa produkzioaren informazio-fitxa

In this paper, a number of STEM educational proposals are systematically analyzed from the lens of mathematics education. An extensive innovation project was implemented during the 2019/2020 academic year in a pilot study carried out in Schools and Teacher Training Programs in Navarre (Spain), comprising a bibliographical and source analysis as a previous step to characterize the existing material, and ultimately to design and test STEM projects at different educational levels from the point of view of mathematical education. All activities belong to international publications and widely used and contrasted web repositories, and seize the usual interval of compulsory education, i.e., from the beginning of Primary School (age 6/7) to the end of Secondary School (age 15/16). The findings draw a panorama of STEM activities where mathematics is mostly utilitarian, numbers and units are functionally used to measure quantities of magnitudes, and geometric contents serve the purpose of modeling a technological prototype. As it turns out, some STEM-labelled activities do not fulfill their principles and fundamental purposes. In lower levels, there is a common confusion between STEM activities and science laboratory projects; in higher levels, complex mathematical content could appear. Even though some activities are guided science laboratory projects, it is concluded that most STEM activities have the potential of a-didactical situations, i.e., contexts where students put into practice their personal problem-solving techniques before teachers formalize the mathematical content.

We review the latest developments in long-range Brillouin optical time-domain analysis sensors. The factors that impair the performance of these sensors, particularly in terms of their distance range, are discussed together with the latest methods to overcome them. We focus on our recent contributions based on the application of the probe dithering method, which is based on introducing a wavelength modulation to the probe wave. This technique is shown to effectively compensate nonlocal effects originated in the depletion of the pump pulse as well as of its pedestal. In addition, it can provide amplification to the pump wave with a slight modification of the setup. Furthermore, this method can be combined with pump pulse coding and a new technique for coding linearization that we have devised to further extend the sensing length into the hundreds of kilometers range.

We demonstrate a technique to compensate the nonlocal effects that appear in Brillouin optical time-domain analysis sensors when pump pulses with limited extinction ratio are deployed. These recently discovered nonlocal effects are originated in the interaction between the probe wave and the pulse pedestal. Hence, their compensation method is based on deploying a modulation (dithering) of the optical frequency of the probe and pulse pedestal waves that provides a reduction of the effective interaction length between them. This is implemented by taking advantage of the chirp associated to the direct current modulation of a semiconductor laser used as common source for both waves. The net effect of this procedure is that the probe and pulse pedestal waves display efficient Brillouin interaction just at correlation peaks along the fiber where the frequency difference between both waves remains constant. Proof-of-concept experiments in a 25-km sensing link demonstrate the performance of the technique, where large errors of more than 10 MHz in the measurement of the Brillouin frequency shift are completely compensated by introducing a sinusoidal dithering to the laser source.

We introduce a simple method to extend the performance of pulse coding techniques in their application to Brillouin optical time-domain analysis sensors (BOTDA). It is based on applying a simple logarithmic processing on the detected probe wave that compensates the deviation from linearity of the sensor response for long code lengths. The technique ensures that the accumulated effect of a sequence of pulses is equal to the linear addition of the effects of the individual components, which is the essential condition to ensure a correct decoding of the probe gain measurement. We experimentally demonstrate the compensation of the Brillouin frequency shift error induced by the accumulated gain nonlinearity. Furthermore, a proof-of-concept 80 km sensing link within a total 200 km fiber loop demonstrated a better than 2 MHz precision with 2 m spatial resolution.

This chapter focuses on Brillouin optical time-domain analysis (BOTDA) sensors because they are the most successful Brillouin distributed sensors (BDS) type in terms of performance and practical applications. Distributed sensor featuring can be done in the time, coherence, or frequency domains, giving rise to the three main analysis BDS types: BOTDA, Brillouin optical correlation-domain analysis (BOCDA), and Brillouin optical frequency-domain analysis (BOFDA). The distance range of measurements performed using a BOTDA sensor is given by the length of sensing fiber that the system is able to measure with a specified performance in terms of measurement precision and time. The chapter reviews the fundamentals and the research directions in BDSs. The applications of the technology are multiple and in diverse fields—for instance, in the oil and gas industry, where BDSs have been applied to measure temperature and strain along the umbilical cables used for subsea wells.

We report on two previously unknown non-local effects that have been found to impair Brillouin optical time-domain analysis (BOTDA) sensors that deploy limited extinction ratio (ER) pump pulses. The first one originates in the increased depletion of the pedestal of the pump pulses by the amplified probe wave, which in turn entails a reduced amplification of the probe and a measurement distortion. The second effect is due to the interplay between the transient response of the erbium-doped fiber amplifiers (EDFA) that are normally deployed to amplify the pump and the pedestal of the pump pulses. The EDFA amplification modifies the pedestal that follows the pulses in such a way that it also leads to a distortion of the measured gain spectra after normalization. Both effects are shown to lead to non-local effects in the measurements that have similar characteristics to those induced by pump pulse depletion. In fact, the total depletion factor for calculations of the Brillouin frequency shift (BFS) error in BOTDA sensors is shown to be the addition of the depletion factors linked to the pump pulse as well as the pedestal. A theoretical model is developed to analyze both effects by numerical simulation. Furthermore, the effects are investigated experimentally in long-range BOTDA sensors. The pedestal depletion effect is shown to severely constrain the probe power as well as the minimum ER of the pulses that can be deployed in BOTDA sensors. For instance, it is shown that, in a long-range dual-probe BOTDA, an ER higher that 32-dB, which is above that provided by standard electro-optic modulators (EOM), is necessary to be able to deploy a probe power of −3 dBm, which is the theoretical limit for that type of sensors. Even more severe can be the limitation due to the depletion effect induced by the EDFA transient response. It is found that the impairments brought by this effect are independent of the probe power, hence setting an ultimate limit for the BOTDA sensor performance. Experimentally, a long-range BOTDA deploying a 26-dB ER EOM and a conventional EDFA is shown to exhibit a BFS error higher than 1 MHz even for very small probe power.

We report on an additional limitation that has been found in Brillouin optical time-domain analysis (BOTDA) sensors due to the so-called second-order nonlocal effects (NLE). Second-order NLE appear in BOTDA setups that deploy a double probe waves to compensate the transfer of energy between the pump pulse and the probe wave, and are related to a spectral distortion of the pump pulse that leads to measurement errors and an effective limit on the maximum probe power that can be deployed in the sensor. We theoretically and experimentally demonstrate that the techniques that have been presented so far in the literature to compensate second-order NLE are only effective in the case that the Brillouin frequency shift (BFS) along the sensing fiber is uniform. However, this requirement for uniformity is not realistic in real world scenarios in which a variety of fibers with different BFS and subjected to different environmental conditions are typically deployed. Therefore, we demonstrate a new method to mitigate the effects of BFS variation in the BOTDA setups that compensate second-order NLE. This method is based on introducing an additional wavelength modulation to the probe wave so as to track the mean BFS changes along the sensing fiber link. With this method, we demonstrate a BOTDA setup that, without coding, distributed amplification, or any other form of performance enhancement, achieves a sensing length of 120 km with 3-m spatial resolution and 2-MHz measurement precision. Moreover, the setup demonstrates, to our knowledge, the largest probe power ever injected in a BOTDA sensing link.