7 research outputs found
Integrated optics for astronomical interferometry - VI. Coupling the light of the VLTI in K band
Our objective is to prove that integrated optics (IO) is not only a good
concept for astronomical interferometry but also a working technique with high
performance. We used the commissioning data obtained with the dedicated K-band
integrated optics two-telescope beam combiner which now replaces the fiber
coupler MONA in the VLTI/VINCI instrument. We characterize the behaviour of
this IO device and compare its properties to other single mode beam combiner
like the previously used MONA fiber coupler. The IO combiner provides a high
optical throughput, a contrast of 89% with a night-to-night stability of a few
percent. Even if a dispersive phase is present, we show that it does not bias
the measured Fourier visibility estimate. An upper limit of 0.005 for the
cross-talk between linear polarization states has been measured. We take
advantage of the intrinsic contrast stability to test a new astronomical
prodecure for calibrating diameters of simple stars by simultaneously fitting
the instrumental contrast and the apparent stellar diameters. This method
reaches an accuracy with diameter errors of the order of previous ones but
without the need of an already known calibrator. These results are an important
step of integrated optics and paves the road to incoming imaging interferometer
projects
A method to assess annual average renewable groundwater reserves for large regions in Spain
This paper proposes a method for assessing the groundwater renewable reserves of large regions for an average year, based on the integration of the recession curves for their basins springs or the natural base flow of their rivers. In this method, the hydrodynamic volume (or renewable reserves), were estimated from the baseflow equation. It was assumed that the flow was the same as the natural recharge, and that the recession coefficients were derived by the hydrogeological parameters and geometrical characteristics of aquifers, and adjusted to fit the recession curves at gauging stations. The method was applied to all the aquifers of Spain, which have a total groundwater renewable reserve of 86,895 hm3 four times the mean annual recharge. However, the distribution of these reserves is very variable; 18.6% of the country aquifers contain 94.7% of the entire reserve
Evaluating Discharge Regimes of Karst Aquifer
Karst springs are typical for abrupt changes of discharge immediately following recharge events. Monitored discharges of springs are used to determine quantitative variability over the period of time, showing their reliability as dependable water sources. Karst aquifers also exhibit (at least) dual ground-water flow regimes, that is, fast (conduit-dominated) flow and slow (diffuse) flow. This is something that can be observed in nature as the fast change of water amount outflowing from the groundwater source, or described by rapidly responding hydrographs, recording water levels or discharges. Selection of proper investigative techniques characterizing discharge regime properties of a karst aquifer is therefore important in order to identify possible theoretical background models describing this behaviour. On this basis, we can also find a particular method of hydrograph separation into flow components linked to the fast-flow regime, slow-flow regime, or intermediate regimes as well. With this point in mind, several quantitative methods that might be particularly useful in hydrograph analysis of water outlets from the karst aquifer system are briefly discussed here