Abstract: We quantify errors on splitting intensity measurements produced by incoherent noise on horizontal components through a detailed analysis of synthetic seismograms and of SKS and SKKS waves recorded by four permanent broad-band stations. We find that these errors are quite significant, even on high-quality records, because the measurement procedure involves the comparison of radial and transverse components, which are both contaminated by noise. To decrease the level of noise in the data, it is thus recommended to average splitting intensities from waves coming from the same backazimuth. Alternatively, one can analyse stacked radial and transverse components after applying a Wiener filter, which standardizes the waveforms. This is found to be equivalent because the measure of splitting intensity is a linear process. The utilization of Wiener filters reduces variations of apparent splitting resulting from differences in frequency content of the waveforms. It is possible to determine splitting parameters (splitting delays and fast directions) from azimuthal variations of splitting intensity at a particular station. Tests on synthetic seismograms demonstrate that this approach gives unbiased and robust estimates of splitting parameters, in contrast to the Silver and Chan method, which only works on the rare records that have very large signals on their transverse components. The Wolfe and Silver method does not suffer from this limitation and gives the same results as the multichannel splitting intensity method. Analysis of splitting intensities at stations BDFB, BGCA, CAN and ERM gives fast directions that are generally in excellent agreement with those determined with the Wolfe and Silver method. However, at some stations, azimuthal variations of splitting intensities reveal features that are not well captured by the sinusoidal variation representing the average anisotropy beneath the station. This suggests that small-scale lateral variations of anisotropy are present in the subcontinental mantle, which remain to be imaged in detail.

Abstract: Understanding how marine top predators exploit their environment is a central topic in marine ecology. Among all methodologies used to investigate this part of ecology, electronic devices are very useful to track animals' movements and foraging habitats, but they do not provide any dietary information. Stable isotopes provide information on trophic levels but remain imprecise to identify small spatial-scale habitats. In this study, we combined the two approaches to obtain a synoptic view of the foraging behaviour variability of southern elephant seals Mirounga leonina. Our results suggested marked differences in distribution, diving behaviour, foraging habitats, trophic levels, and dietary habits of elephant seals according to their sex and age. Thus, we characterized main foraging habitats over the Kerguelen-Heard Plateau and the Antarctic shelf for juvenile males, while females foraged mainly in oceanic waters of the Polar Frontal Zone and the Antarctic Zone. In addition, we highlighted the ontogeny of niche partitioning in this sexually dimorphic species. While females did not exhibit a major dietary shift in relation to their age and their breeding status, a different picture emerged for males. Young males had a trophic level identical to that of all females. However, at 34yr of age, males showed a progressive increase in trophic level. The inter-annual combination of bio-logging and stable isotopes could provide a powerful tool to investigate possible shifts in ecological niche between years according to environmental changes.

Abstract: Context. Bolometric interferometry is a promising new technology with potential applications to the detection of B-mode polarization fluctuations of the cosmic microwave background (CMB). A bolometric interferometer will have to take advantage of the wide spectral detection band of its bolometers to be competitive with imaging experiments. A crucial concern is that interferometers are assumed to be significantly affected by a spoiling effect known as bandwidth smearing. Aims: We investigate how the bandwidth modifies the work principle of a bolometric interferometer and affects its sensitivity to the CMB angular power spectra. Methods: We obtain analytical expressions for the broadband visibilities measured by broadband heterodyne and bolometric interferometers. We investigate how the visibilities must be reconstructed in a broadband bolometric interferometer and show that this critically depends on hardware properties of the modulation phase shifters. If the phase shifters produce shifts that are constant with respect to frequency, the instrument works like its monochromatic version (the modulation matrix is not modified), while if they vary (linearly or otherwise) with respect to frequency, one has to perform a special reconstruction scheme, which allows the visibilities to be reconstructed in frequency subbands. Using an angular power spectrum estimator that accounts for the bandwidth, we finally calculate the sensitivity of a broadband bolometric interferometer. A numerical simulation is performed that confirms the analytical results. Results: We conclude that (i) broadband bolometric interferometers allow broadband visibilities to be reconstructed regardless of the type of phase shifters used and (ii) for dedicated B-mode bolometric interferometers, the sensitivity loss caused by bandwidth smearing is quite acceptable, even for wideband instruments (a factor of 2 loss for a typical 20% bandwidth experiment).