For at least 20 years, nadir altimetry satellite missions have been successfully used to first monitor the surface elevation of oceans and, shortly after, of large rivers and lakes. For the last 5–10 ...years, few studies have demonstrated the possibility to also observe smaller water bodies than previously thought feasible (river smaller than 500m wide and lake below 10km2). The present study aims at quantifying the nadir altimetry performance over a medium river (200m or lower wide) with a pluvio-nival regime in a temperate climate (the Garonne River, France). Three altimetry missions have been considered: ENVISAT (from 2002 to 2010), Jason-2 (from 2008 to 2014) and SARAL (from 2013 to 2014).
Compared to nearby in situ gages, ENVISAT and Jason-2 observations over the lower Garonne River mainstream (110 km upstream of the estuary) have the smallest errors, with water elevation anomalies root mean square errors (RMSE) around 50cm and 20cm, respectively. The few ENVISAT upstream measurements have RMSE ranging from 80cm to 160cm. Over the estuary, ENVISAT and SARAL water elevation anomalies RMSE are around 30cm and 10cm, respectively.
The most recent altimetry mission, SARAL, does not provide river elevation measurements for most satellite overflights of the river mainstream. The altimeter remains “locked” on the top of surrounding hilly areas and does not observe the steep-sided river valley, which could be 50–100m lower. This phenomenon is also observed, for fewer dates, on Jason-2 and ENVISAT measurements. In these cases, the measurement is not “erroneous”, it just does not correspond to water elevation of the river that is covered by the satellite. ENVISAT is less prone to get ‘locked’ on the top of the topography due to some differences in the instrument measurement parameters, trading lower accuracy for more useful measurements. Such problems are specific to continental surfaces (or near the coasts), but are not observed over the open oceans, which are flatter.
To overcome this issue, an experimental instrument operating mode, called the DIODE/DEM tracking mode, has been developed by CNES (Centre National d’Etudes Spatiales) and has been tested during few Jason-2 cycles and during the first SARAL/AltiKA cycle. This tracking mode “forces” the instrument to observe a target of interest, i.e. water bodies. The example of the Garonne River shows, for one SARAL ground track, the benefit of the DIODE/DEM tracking mode for a steep-sided river reach, which is not detected using the nominal instrument operating mode. Yet, this mode relies on ancillary datasets (a priori global DEM and global land/water mask), which are critical to obtain river valley observation. The ultimately computed elevations along the satellite tracks, loaded on board, should have an absolute vertical accuracy around 10m (or better). This case also shows, when the instrument is correctly observing the river valley, that the altimeter can detect water bodies narrower than 100m (like an artificial canal).
In agreement with recent studies, this work shows that altimeter missions can provide useful water elevation measurements over a 200m wide river with RMSE as low as 50cm and 20cm, for ENVISAT and Jason-2 respectively. The seasonal cycle can be observed with the temporal sampling of these missions (35 days and 10 days, respectively), but short term events, like flood events, are most of the time not observed. It also illustrates that altimeter capability to observe a river is highly dependent of the surrounding topography, the observation configuration, previous measurements and the instrument design. Therefore, it is not possible to generalize at global scale the minimum river width that could be seen by altimeters.
This study analyzes, for the first time, the potential of the experimental DIODE/DEM tracking mode to observe steep-sided narrow river valleys, which are frequently missed with nominal tracking mode. For such case, using the DIODE/DEM mode could provide water elevation measurements, as long as the on board DEM is accurate enough. This mode should provide many more valid measurements over steep-sided rivers than currently observed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Abstract The main objective of this study was to examine fronto-parietal networks underlying visual duration discriminations. Two types of interference tasks were used to augment cognitive load: line ...orientation associated with the right hemisphere and multiplication with the left. Both subtasks deteriorated duration discriminations, more severely for line orientation. Relative to the condition without interference, the dual task paradigm decreased amplitudes of the contingent negative variation (CNV) wave, predominant at frontal sites, and the P300 wave, predominant at parietal sites. Inversely, amplitudes of a later appearing positive component (LPC) and its parietal counterpart of opposite polarity (LNC) increased with spatial or numeric task interference. These results are concordant with the view that fronto-parietal networks underlying duration discriminations act in a concerted fashion, with the LPC/LNC waves acting as a warning signal to mitigate errors during high cognitive load.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Co-orbital objects, also known as trojans, are frequently found in simulations of planetary system formation. In these configurations, a planet shares its orbit with other massive bodies. It is still ...unclear why there have not been any co-orbitals discovered thus far in exoplanetary systems or even pairs of planets found in such a 1:1 mean motion resonance. Reconciling observations and theory is an open subject in the field. The main objective of the TROY project is to conduct an exhaustive search for exotrojans using diverse observational techniques. In this work, we analyze the radial velocity time series informed by transits, focusing the search around low-mass stars. We employed the alpha-test method on confirmed planets searching for shifts between spectral and photometric mid-transit times. This technique is sensitive to mass imbalances within the planetary orbit, allowing us to identify non-negligible co-orbital masses. Among the 95 transiting planets examined, we find one robust exotrojan candidate with a significant 3-sigma detection. Additionally, 25 exoplanets show compatibility with the presence of exotrojan companions at a 1-sigma level, requiring further observations to better constrain their presence. For two of those weak candidates, we find dimmings in their light curves within the predicted Lagrangian region. We established upper limits on the co-orbital masses for either the candidates and null detections. Our analysis reveals that current high-resolution spectrographs effectively rule out co-orbitals more massive than Saturn around low-mass stars. This work points out to dozens of targets that have the potential to better constraint their exotrojan upper mass limit with dedicated radial velocity observations. We also explored the potential of observing the secondary eclipses of the confirmed exoplanets to enhance the exotrojan search.
We investigate the left mini-neglect theory in phonological dyslexics and in normal readers in a visual matching task. Behavioral and electrophysiological results reveal two profiles of dyslexics but ...do not confirm this theory. However, a different mobilization of visuo-attentional abilities is suggested in dyslexic subjects. Adapted from the source document
Transit timing variations (TTVs) can provide useful information for systems observed by transit, as they allow us to put constraints on the masses and eccentricities of the observed planets, or even ...to constrain the existence of non-transiting companions. However, TTVs can also act as a detection bias that can prevent the detection of small planets in transit surveys that would otherwise be detected by standard algorithms such as the Boxed Least Square algorithm (BLS) if their orbit was not perturbed. This bias is especially present for surveys with a long baseline, such as Kepler, some of the TESS sectors, and the upcoming PLATO mission. Here we introduce a detection method that is robust to large TTVs, and illustrate its use by recovering and confirming a pair of resonant super-Earths with ten-hour TTVs around Kepler-1705. The method is based on a neural network trained to recover the tracks of low-signal-to-noise-ratio(S/N) perturbed planets in river diagrams. We recover the transit parameters of these candidates by fitting the light curve. The individual transit S/N of Kepler-1705b and c are about three times lower than all the previously known planets with TTVs of 3 hours or more, pushing the boundaries in the recovery of these small, dynamically active planets. Recovering this type of object is essential for obtaining a complete picture of the observed planetary systems, and solving for a bias not often taken into account in statistical studies of exoplanet populations. In addition, TTVs are a means of obtaining mass estimates which can be essential for studying the internal structure of planets discovered by transit surveys. Finally, we show that due to the strong orbital perturbations, it is possible that the spin of the outer resonant planet of Kepler-1705 is trapped in a sub- or super-synchronous spin-orbit resonance.
S-type planets, which orbit one component of multiple-star systems, place strong constraints on the planet formation and evolution models. A notable case study is Kepler-444, a triple-star system ...whose primary is orbited by five planets smaller than Venus in a compact configuration, and for which the stellar binary companion revolves around the primary on a highly eccentric orbit. Having access to the most precise up-to-date masses and orbital parameters is highly valuable to understand formation and evolution processes. We provide the first full dynamical exploration of this system, with the goal to refine those parameters. The planetary system does not appear in any of low-order two or three-planet mean-motion resonances (MMR). We provide the most precise up-to-date dynamical parameters for the planets and the stellar binary companion, using an approach that makes use of the Numerical Analysis of Fundamental Frequencies (NAFF) fast chaos indicator. The orbit of the latter is constrained by new observations from HIRES and Gaia, and also by the stability analysis. This update further challenges the planets formation processes. We also test the dynamical plausibility of a sixth planet in the system, following hints observed in the Hubble Space Telescope (HST) data. We find that this putative planet could exist over a broad range of masses, and with an orbital period roughly comprised between 12 and 20 days. We note an overall good agreement of the system with short-term orbital stability. This suggests that a diverse range of planetary system architectures could be found in multiple-star systems, potentially further challenging the planet formation models.
Over the past years, the amount of detected multi-planet systems significantly grew, an important sub-class of which being the compact configurations. A precise knowledge of them is crucial to ...understand the conditions with which planetary systems form and evolve. However, observations often leave these systems with large uncertainties, notably on the orbital eccentricities. This is especially prominent for systems with low-mass planets detected with Radial Velocities (RV), the amount of which is more and more important in the exoplanet population. It is becoming a common approach to refine these parameters with the help of orbital stability arguments. Such dynamical techniques can be computationally expensive. In this work we use an alternative procedure faster by orders of magnitude than classical N-body integration approaches. We couple a reliable exploration of the parameter space with the precision of the Numerical Analysis of Fundamental Frequencies (NAFF, Laskar 1990) fast chaos indicator. We also propose a general procedure to calibrate the NAFF indicator on any multi-planet system without additional computational cost. This calibration strategy is illustrated on HD 45364, in addition to yet-unpublished measurements obtained with the HARPS and CORALIE high-resolution spectrographs. We validate the calibration approach on HD 202696. We test the performances of this stability-driven approach on two systems with different architectures. First we study HD 37124, a 3-planet system composed of planets in the Jovian regime. Then, we analyse HD 215152, a compact system of four low-mass planets. We demonstrate the potential of the NAFF stability-driven approach to refine the orbital parameters and planetary masses. We stress the importance of undertaking systematic global dynamical analyses on every new multi-planet system discovered.
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