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Current climate and weather changes urged the scientific community to find ways to observe and understand the relatively rapid land-atmosphere processes related to the water cycle. The HydroSoil project, funded by the European Space Agency, was proposed to experimentally assess the use of Synthetic Aperture Radar in future short revisit time missions based on Geosynchronous Orbital platforms. This article describes the HydroSoil facility providing continuous monitoring of an agricultural field with a 10-min temporal resolution and a spatial resolution in the order of 1 m2. Gathered data from the full Pol Ground-Based SAR are being used to investigate the capability of Geosynchronous SAR missions to retrieve soil moisture and to measure vegetation parameters. To achieve the project's objectives, intensive procurement of ground truth data encompassing continuous acquisition of relevant meteorological parameters such as air humidity, temperature, precipitation wind speed and direction, pressure, and solar irradiation together with other vegetation characteristics under study has been mandatory. The different densities, sizes, and water content of two different crops, barley and corn, together with the data generated, will enable the assessment of the missions’ ability to extract essential scene characteristics, such as soil moisture and crop water content, for use in future geostationary missions.

The TanDEM-X satellite mission has revolutionized DEM generation from spaceborne synthetic aperture radar. In addition to the primary objective of generating a consistent digital elevation model with global coverage and unprecedented accuracy, the mission has acquired time series of topographic data over several volcanoes, providing an excellent opportunity to test the use of this innovative dataset for volcano monitoring and research. In this article, we review the utilization of the single-pass TanDEM-X data for studying various kinds of volcanic activity, such as basaltic lava flows, the formation and destruction of lava domes and related pyroclastic density currents, and subsurface magma withdrawal and intrusion. We then consider the uses of these data for hazard assessment and forecasting. Our goal is to highlight the importance of timely and repeated topographic information in volcanology, and to suggest the development of future spaceborne bistatic synthetic aperture radar satellite missions, such as ESA's Earth Explorer 10 candidate mission, “Harmony.”

In this paper, a new two-steps design strategy is introduced for the optimal rational approximation of the fractional-order Butterworth filter. At first, the weighting factors of the summation between the ${n}^{\text {th}}$ -order and the $(n + 1)^{\text {th}}$ -order Butterworth filters are optimally determined. Subsequently, this model is employed as an initial point for another optimization routine, which minimizes the magnitude-frequency error relative to the $(n+\alpha)^{\text {th}}$ -order, where $\alpha \in (0, 1)$ , Butterworth filter. The proposed approximant demonstrates improved performance about the magnitude mean squared error compared to the state-of-the-art design for six decades of bandwidth, but the introduced approach does not require a fractional-order transfer function model and the approximant of the $s^\alpha $ operator. The proposed strategy also avoids the use of the cascading technique to yield higher-order fractional-order Butterworth filter models. The performance of the proposed $1.5^{\text {th}}$ -order Butterworth filter in follow-the-leader feedback topology is verified through SPICE simulations and its hardware implementation based on Analog Devices AD844AN-type current feedback operational amplifier.

This paper describes the design of analog pseudo-differential fractional frequency filter with the order of $(2+\alpha)$ , where $0 < \alpha < 1$ . The filter operates in a mixed-transadmittance mode (voltage input, current output) and provides a low-pass frequency response according to Butterworth approximation. General formulas to determine the required transfer function coefficients for desired value of fractional order $\alpha $ are also introduced. The designed filter provides the beneficial features of fully-differential solutions but with a less complex circuit topology. It is canonical, i.e. it employs a minimum number of passive elements, whereas all are grounded, and current conveyors as active elements. The proposed structure offers high input impedance, high output impedance, and high common-mode rejection ratio. By simple modification, voltage response can also be obtained. The performance of the proposed frequency filter is verified both by simulations and experimental measurements proving the validity of theory and the advantageous features of the filter.

This paper introduces the generalization of the classical Transitional Butterworth-Butterworth Filter (TBBF) to the Fractional-Order (FO) domain. Stable rational approximants of the FO-TBBF are optimally realized. Several design examples demonstrate the robustness and modeling efficacy of the proposed method. Practical circuit implementation using the current feedback operational amplifier employed as an active element is presented. Experimental results endorse good agreement ( $\text {R}^{2} = 0.999968$ ) with the theoretical magnitude-frequency characteristic.