ABSTRACT. Synthetic-aperture radar interferometry data and airborne ice-sounding radar (ISR) data are employed to obtain modern estimates of the inland ice production from Nioghalvfjerdsbr× (NB) and Zachariae IsstrÖm (ZI), the two largest glaciers draining the northeast sector of the Greenland ice sheet. Ice fluxes are measured at the grounding line (14.2 AE1km 3 ice a^1 for NB and 10.8 AE1km 3 ice a^1 for ZI) with an ice thickness deduced from ice-shelf hydrostatic equilibrium, and along an ISR profile collected upstream of the grounding line (14.3 AE 0.7 km 3 ice a^1 for NB and 11.6 AE 0.6 km 3 ice a^1 for ZI). Balance fluxes calculated from a map of snow accumulation and model predictions of surface melt are 11.9 AE 2 km 3 ice a^1 for NB and 10.0 AE 2 km 3 ice a^1 for ZI at the grounding line, and 12.2 and 10.3 km 3 ice a^1, respectively, at the ISR line. The two glaciers therefore exhibit a negative mass balance equivalent to 14% of their balance flux, with a AE12% uncertainty. Independently, we detect a retreat of the grounding line of NB between 1992 and 1996 which is larger at the glacier center (920 AE 250 m) than on the sides (240 AE 50 m). The corresponding ice-thinning rates (2 AE1m a^1at the glacier center and 0.6 AE 0.3 m a^1on the sides) are too large to be accommodated by temporal changes in ablation or accumulation, and must be due to dynamic thinning.

The latest standardization DVB-S2X increases the achievable spectral efficiency of the satellite communications by around 15% in AWGN channel. In order to benefit from those improvements, the strong non-linear distortions introduced by the payload have to be overcome, mostly taking high back-off on the amplifier operation point. Nowadays, on-board amplifiers are linearized before being deployed, allowing low-complexity transmitters and receivers at the detriment of the payload's cost and reduced energy efficiency. In this paper, various techniques are investigated for the purpose of spectral efficiency improvement while releasing the amplifier linearization constraint. Iterative pre-distortion at the transmitter, turbo-equalization at the receiver and appropriate waveforms for transmission through non-linearized payload appear as strong candidates considering the results of this study.

The aim of this paper is to give a precise estimation of the extreme magnetic storms frequency per time unit (year) throughout a solar cycle. An innovative approach based on a proportional hazard model is developed. Based on the Cox model, this method includes non-stationarity and covariate influence. The model assumes that the number of storms during a cycle is a non-homogeneous Poisson process. The intensity of this process can be expressed as the product of a baseline risk and a risk factor. In the Cox model, the baseline risk is a nuisance parameter. In our model, it is a parameter of interest that will be estimated. The risk factor depends on a covariate, the solar activity index. As in Extreme Value Theory (EVT) and especially in Peaks Over Threshold (POT) modeling, all the high level events are used to make estimations and the results are extrapolated to the extreme level events. This study highlights a strong correlation between the occurrence intensity of magnetic storms and their position on the solar cycle. The model can be used to forecast occurrence intensity for the current 24th solar cycle.and the Log-likelihood for all the J cycles:The derivatives in α anb β respectively give:Replacing α by the solution of the first equation, we obtain:This implicit equation can be resolved only numerically (by the secant method). The Fisher information matrix is also computable:.The (2,2) coefficient of the inverse matrix of the Fisher information matrix provides the variance ofβ, used for the construction of a confidence interval.

Open Archive Toulouse Archive OuverteOATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible To cite this version:Abstract-In satellite communications, the non-linear distortions introduced by the amplifier in the payload have to be overcome. When advanced mitigation techniques are considered at the receiver side, the current channel model is often based on Volterra series derived from an approximation of the non linear transfer function of the on-board amplifier. This nonlinear model is conditioning the performance at the receiver side. In this paper, a new non-linear model is proposed, leading to improved receiver performances. The polynomial approximation is improved considering both the usual model truncation to the 3 rd order and the signal fluctuation at the input of the amplifier. First, the impact of the polynomial order of the AM/AM and AM/PM curve approximation is studied. Then, a non-linear model is derived based on a piecewise polynomial approximation of the amplifier response. Based on this refined nonlinear model, significant detection performance improvements are shown for both Nyquist and Faster-than-Nyquist rates.

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