Data Augmentation of Automotive LIDAR Point Clouds under Adverse Weather Situations.

In contrast to previous works on data augmentation using LIDAR (Light Detection and Ranging), which mostly consider point clouds under good weather conditions, this paper uses point clouds which are affected by spray. Spray water can be a cause of phantom braking and understanding how to handle the extra detections caused by it is an important step in the development of ADAS (Advanced Driver Assistance Systems)/AV (Autonomous Vehicles) functions. The extra detections caused by spray cannot be safely removed without considering cases in which real solid objects may be present in the same region in which the detections caused by spray take place. As collecting real examples would be extremely difficult, the use of synthetic data is proposed. Real scenes are reconstructed virtually with an added extra object in the spray region, in a way that the detections caused by this obstacle match the characteristics a real object in the same position would have regarding intensity, echo number and occlusion. The detections generated by the obstacle are then used to augment the real data, obtaining, after occlusion effects are added, a good approximation of the desired training data. This data is used to train a classifier achieving an average F-Score of 92. The performance of the classifier is analyzed in detail based on the characteristics of the synthetic object: size, position, reflection, duration. The proposed method can be easily expanded to different kinds of obstacles and classifier types.

Weather Classification Using an Automotive LIDAR Sensor Based on Detections on Asphalt and Atmosphere.

A semi-/autonomous driving car requires local weather information to identify if it is working inside its operational design domain and adapt itself accordingly. This information can be extracted from changes in the detections of a light detection and ranging (LIDAR) sensor. These changes are caused by modifications in the volumetric scattering of the atmosphere or surface reflection of objects in the field of view of the LIDAR. In order to evaluate the use of an automotive LIDAR as a weather sensor, a LIDAR is placed outdoor in a fixed position for a period of 9 months covering all seasons. As target, an asphalt region from a parking lot is chosen. The collected sensor raw data is labeled depending on the occurring weather conditions as: clear, rain, fog and snow, and the presence of sunlight: with or without background radiation. The influence of different weather types and background radiations on the measurement results is analyzed and different parameters are chosen in order to maximize the classification accuracy. The classification is done per frame in order to provide fast update rates while still keeping an F1 score higher than 80%. Additionally, the field of view is divided into two regions: atmosphere and street, where the influences of different weather types are most notable. The resulting classifiers can be used separately or together increasing the versatility of the system. A possible way of extending the method for a moving platform and alternatives to virtually simulate the scene are also discussed.

Dynamics of Isolated 1,8-Naphthalimide and N-Methyl-1,8-naphthalimide: An Experimental and Computational Study.

In this work we investigate the excited-state structure and dynamics of the two molecules 1,8-naphthalimide (NI) and N-methyl-1,8-naphthalimide (Me-NI) in the gas phase by picosecond time- and frequency-resolved multiphoton ionization spectroscopy. The energies of several electronically excited singlet and triplet states and the S1 vibrational wavenumbers were calculated. Nonadiabatic dynamics simulations support the analysis of the radiationless deactivation processes. The origin of the S1 ← S0 (ππ*) transition was found at 30, 082 cm(-1) for NI and at 29, 920 cm(-1) for Me-NI. Furthermore, a couple of low-lying vibrational bands were resolved in the spectra of both molecules. In the time-resolved scans a biexponential decay was apparent for both Me-NI and NI. The fast time constant is in the range of 10-20 ps, whereas the second one is in the nanosecond range. In accordance with the dynamics simulations, intersystem crossing to the fourth triplet state S1 (ππ*) → T4 (nπ*) is the main deactivation process for Me-NI due to a large spin-orbit coupling between these states. Only for significant vibrational excitation internal conversion via a conical intersection becomes a relevant deactivation pathway.

Time-Resolved Study of 1,8-Naphthalic Anhydride and 1,4,5,8-Naphthalene-tetracarboxylic Dianhydride.

We investigate the excited electronic states of 1,8-naphthalic anhydride (NDCA) and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) by time- and frequency-resolved electronic spectroscopy in the gas phase using picosecond lasers and by femtosecond time-resolved transient absorption in cyclohexane. The experiments are accompanied by calculations that yield the energy of the excited singlet and triplet states as well as by surface hopping dynamics simulations and calculations of spin-orbit couplings that give insight into the photochemistry. The origin of the A (1)A1 ← X (1)A1 (ππ*) transition in isolated NDCA was found at 30 260 cm(-1), and several low-lying vibrational bands were observed. The lifetime drops sharply from 1.2 ns at the origin to around 30 ps at an excess energy of 800 cm(-1). Both internal conversion (IC) and intersystem crossing (ISC) are possible deactivation pathways as found in coupled electron-nuclear dynamics simulations. In cyclohexane solution, two time constants were observed. Deactivation of the initially excited state by ISC seems to dominate as supported by computations. For NTCDA we observed a gas phase lifetime of 16 ps upon excitation at 351 nm.

Time-domain study of the S(3) state of 9-fluorenone.

We report a combined gas phase and solution phase study of 9-fluorenone. The structure and dynamics of isolated fluorenone in the S3-state were studied by resonant enhanced multiphoton ionization with picosecond pulses in a free jet of molecules excited between 285 and 312 nm. Ionization was performed with a second ps-pulse at 351 nm. The electronic spectrum is structured, and the origin of the C (1)B2 ← X (1)A1 transition was observed at 32,122 cm(-1). Several vibrational fundamentals appear in the spectrum. In the gas phase we observe a biexponential decay, which suggests an internal conversion to the coupled S1/S2-state within 10-40 ps. A further decay that is assigned to intersystem crossing was found to be longer than 500 ps. In addition to the gas phase measurements, we studied the photophysics of 9-fluorenone in cyclohexane by femtosecond-time-resolved transient absorption spectroscopy and observed very similar dynamics upon excitation to the S3 state: It deactivates within 8-11 ps by internal conversion, followed by intersystem crossing within 120-150 ps, forming a long-lived triplet state. Experiments in acetonitrile, however, showed marked differences. Intersystem crossing is ineffective in polar solvents because the lowest excited singlest state is of ππ* character and does not interact with the (3)ππ*.

Excited-state dynamics of the 2-methylallyl radical.

Radically exciting! The excited-state dynamics of the 2-methylallyl radical are studied by time-resolved photoionization. The radical, which is relevant for combustion processes, is generated by pyrolysis from the corresponding bromide. The lifetime of the electronically excited B state was measured to be 14 ps and shorter.

The electronic structure of pyracene: a spectroscopic and computational study.

We report a synthetic, spectroscopic and computational study of the polycyclic aromatic molecule pyracene, which contains aliphatic five-membered rings annealed to a naphthalene chromophore. An improved route to synthesize the compound is described. Gas-phase IR and solid-state Raman spectra agree with a ground-state D2h structure. The electronically excited S1 A(1)B3u state has been studied by resonance-enhanced multiphoton ionisation. An adiabatic excitation energy T0 = 30,798 cm(-1) (3.818 eV) was determined. SCS-ADC(2) calculations found a D2h minimum energy structure of the S1 state and yielded an excitation energy of +3.98 eV, including correction for zero point vibrational energy. The spectrum shows a rich low-frequency vibrational structure that can be assigned to the overtones of out-of-plane deformation modes of the five-membered rings by comparison with computations. The appearance of these modes as well as the frequency reduction in the excited state indicate that the potential in the S1 state is very flat. At higher excess energies most bands can be assigned to fundamentals, overtones and combination bands of either totally symmetric ag modes or of b2g modes that appear due to vibronic coupling. Lifetimes between 43 ns and 76 ns were measured for a number of vibronic bands. For the S2 state an equilibrium geometry with a non-planar carbon framework was computed. In addition a signal from the pyracene dimer was present. The spectrum shows several broad and structureless transitions. The origin band has a maximum at around 329 nm (30,400 cm(-1)). Again lifetimes between 60 ns and 70 ns were found. The dimer ion signal rises within less than 10 ps. Computations show that a crossed geometry with the long axis of one unit aligned with the short axis of the second constitutes the most stable structure. The broadening of the bands is most likely caused by excimer formation.