Wet Refractivity tomographic reconstruction over small areas using an ad-hoc GPS receivers network

One of the most attractive scientific issues in the use of GNSS (Global Navigation Satellite System) signal from a meteorological point of view, is the retrieval of high resolution tropospheric water vapour maps. The real-time (or quasi real-time) knowledge of such distributions could be very useful for several applications, from operative meteorology to atmospheric modeling. Moreover, the exploitation of wet refractivity field reconstruction techniques can be used for atmospheric delay compensation purposes and, as a very promising activity, it could be applied for example to calibrate SAR or Interferometric-SAR (In-SAR) observations for land remote sensing. This is in fact one of the objectives of the European Space Agency project METAWAVE (Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water vapour Effects), in which several techniques were investigated and results were compared to identify a strategy to remove the contribution of water vapour induced propagation delays in In-SAR products. Within this project, the tomographic reconstruction of three dimensional wet refractivity fields on a small atmospheric volume (16km x 20 km x 10 km height, from 2 km to 4 km horizontal resolution and 1 km vertical resolution), was performed considering real tropospheric delays observations acquired by a GNSS network (9 dual frequency GPS receivers) deployed over Como area (Italy), during 12–18 October, 2008. Acquired L1 and L2 carrier phase observations have been processed in terms of hourly averaged Zenith Wet Delays. These vertical informations have been mapped along the correspondent line of sights (by up-sampling at 30 second sample times the 15 minutes GPS satellites positions obtained from IGS files) and inverted using a tomographic procedure. The used algorithm performs a first reconstruction (namely, the tomographic pre-processing) based on generalized inversion mechanisms, in order to define a low resolution first guess for the following step. This second step inverts GPS observables using a more refined algebraic tomographic reconstruction algorithm, in order to improve both vertical and horizontal resolution. Despite limitations due to the network design, internal consistency tests prove the efficiency of the adopted tomographic approach: the rms of the difference between reconstructed and GNSS observed Zenith Wet Delays (ZWD) are in the order of 4 mm. A good agreement is also observed between our ZWDs and corresponding delays obtained by vertically integrating independent wet refractivity fields, taken by co-located meteorological analysis. Finally, during the observing period, reconstructed vertical wet refractivity profiles evolution reveals water vapour variations induced by simple cloud covering. Even if our main goal was to demonstrate the effectiveness in adopting tomographic reconstruction procedures for the evaluation of propagation delays inside water vapour fields, the actual water vapour vertical variability and its evolution with time is well reproduced, demonstrating also the effectiveness of the inferred 3D wet refractivity fields. Even if results obtained were satisfactory, limitations due to the observation geometry, to the GNSS propagation delay information extraction form observables and to the applied tomographic technique will be highlighted, in order to trace the road-map toward future improvements in this challenging field

Software Defined Radio system for GNSS-Refectometry: activities performed at the Politecnico of Turin (Italy)

The GNSS signals are an important active source for Earth’s remote sensing in L band. Experiments performed over sea and land surfaces demonstrated the capability of GNSS-Reflected signals (GNSS-R) for remote sensing purposes. Presently, many research groups are focusing their efforts in developing GNSS-R sensors for soil moisture, sea, sea-ice, and snow cover monitoring. Applications like drought monitoring, farm production, irrigation planning, flood protection, fire prevention, and meteorological forecasts can take advantage from retrieved soil moisture content. Detected sea-surface winds could help to identify adverse meteorological conditions far from coastal zones. Sea altimetry measurements could be used to monitor tides and to identify natural hazards (i.e. tsunamis). Sea-ice topographic changes in the Arctic and Antarctic regions and dry ice stratification could be monitored in order to improve polar climatology knowledge. Recently the Remote Sensing Group of Politecnico of Turin and NavSAS laboratory of ISMB (Istituto Superiore Mario Boella) starts the design and implementation of a fully reconfigurable GNSS-R instrument for research activities, following a Software Defined Radio approach. Using this solution, the hardware is reduced to the RF stages only (i.e. antennas, demodulation, sampling) and the processing starts from the IF (Intermediate Frequency) samples of the raw signal. This is a low-cost portable observing system, designed to be easily placed for example also on board small aircrafts (also unmanned). In this sense, the system components were carefully chosen to minimize size and weight of the complete observing system. Together with the system definition, a user interface is started to be developed. Actually the interface allows a quasi real time control of the received signal. The correct estimation of the whole correlation function profile (in range and frequency space) is achieved by keeping the noise level as low as possible and increasing the SNR. Therefore, it is important to optimally process signals even when long - non coherent integration time is necessary. The interface we developed is able to process such signals using FFT (Fast Fourier Transform) based acquisition algorithms. In addition, an optimized procedure is implemented to compensate for a residual code delay, enhancing the detection of weak signals. The interface allows also experimental activities planning, since it shows specular reflection points and isorange lines (inside receiver antenna’s footprint), computed knowing estimated or predicted satellite positions. All the information are georeferenced using UTM (Universal Transverse Mercator) coordinate system and projected on Google© static maps. Thus, this user friendly interface is a helpful tool able to generate all the necessary output for the geophysical applications performed exploiting GNSS-R signals. In order to test instrument and interface, some experimental activities were recently done by placing the instrument on a high cliff to collect some looks from the sea surface and on board an aircraft to collects measurements from soil reflections (rice fields water flooding, soil moisture, altimetry). Another important activity is to adapt our GNSS-R system for space-based measurements in the framework of an educational project which is being carried out by students belonging to the Aerospace and ICT Engineering faculties of Politecnico of Turin. This student project is going to be developed in the framework of an initiative offered by the Education Office of the European Space Agency. We are trying to design and develop on a system level a space-based test bed for an Earth’s Remote Sensing payload to be placed on-board a small Cubesat. This is the P-GRESSION payload (Payload for GNSS REmote Sensing and Signal detectION). It will try to demonstrate the feasibility of existing applications based on observations normally carried out by costly and operative space receivers. Two concepts will be tested. The first one is a twofold GNSS Remote Sensing experiment: 1) the GNSS Radio Occultation experiment, for the profiling of atmospheric refractivity, temperature, water vapour and electron density, which are very important for climate and meteorological purposes, and 2) The GNSS-R experiment for the land and sea surface parameters sensing. It is worth noting that, for both these GNSS-based experiments, global world coverage of observations is assured in all weather conditions. Finally, the current development/improvement of future global GNSS systems will enlarge the number of offered GNSS signals, improving consequently the resolution in time and space of the remote sensing observables. The second concept is based on signal identification. In particular P-GRESSION will acquire signals coming from ground-based radars, in C and/or X frequency bands, both for detection and for calibration purposes. All the experiments will be based on the same Software Defined Radio approach, since after standard radio acquisition with low cost front ends and antennas, all operations will be performed by softwar

Visuospatial exploration and art therapy intervention in patients with Parkinson's disease: an exploratory therapeutic protocol

Abstract Though abnormalities of visuospatial function occur in Parkinson's disease, the impact of such deficits on functional independence and psychological wellbeing has been historically under- recognized, and effective treatments for this impairment are unknown. These symptoms can be encountered at any stage of the disease, affecting many activities of daily living, and negatively influencing mood, self-efficacy, independence, and overall quality of life. Furthermore, visuospatial dysfunction has been recently linked to gait impairment and falls, symptoms that are known to be poor prognostic factors. Here, we aim to present an original modality of neurorehabilitation designed to address visuospatial dysfunction and related symptoms in Parkinson's disease, known as "Art Therapy". Art creation relies on sophisticated neurologic mechanisms including shape recognition, motion perception, sensory-motor integration, abstraction, and eye-hand coordination. Furthermore, art therapy may enable subjects with disability to understand their emotions and express them through artistic creation and creative thinking, thus promoting self-awareness, relaxation, confidence and self-efficacy. The potential impact of this intervention on visuospatial dysfunction will be assessed by means of combined clinical, behavioral, gait kinematic, neuroimaging and eye tracking analyses. Potential favorable outcomes may drive further trials validating this novel paradigm of neurorehabilitation

Population history from the Neolithic to present on the Mediterranean island of Sardinia: an ancient DNA perspective

Recent ancient DNA studies of western Eurasia have revealed a dynamic history of admixture, with evidence for major migrations during the Neolithic and Bronze Age. The population of the Mediterranean island of Sardinia has been notable in these studies –} Neolithic individuals from mainland Europe cluster more closely with Sardinian individuals than with all other present-day Europeans. The current model to explain this result is that Sardinia received an initial influx of Neolithic ancestry and then remained relatively isolated from expansions in the later Neolithic and Bronze Age that took place in continental Europe. To test this model, we generated genome-wide capture data (approximately 1.2 million variants) for 43 ancient Sardinian individuals spanning the Neolithic through the Bronze Age, including individuals from Sardinia{’}s Nuragic culture, which is known for the construction of numerous large stone towers throughout the island. We analyze these new samples in the context of previously generated genome-wide ancient DNA data from 972 ancient individuals across western Eurasia and whole-genome sequence data from approximately 1,500 modern individuals from Sardinia. The ancient Sardinian individuals show a strong affinity to western Mediterranean Neolithic populations and we infer a high degree of genetic continuity on the island from the Neolithic (around fifth millennium BCE) through the Nuragic period (second millennium BCE). In particular, during the Bronze Age in Sardinia, we do not find significant levels of the {“}Steppe{” ancestry that was spreading in many other parts of Europe at that time. We also characterize subsequent genetic influx between the Nuragic period and the present. We detect novel, modest signals of admixture between 1,000 BCE and present-day, from ancestry sources in the eastern and northern Mediterranean. Within Sardinia, we confirm that populations from the more geographically isolated mountainous provinces have experienced elevated levels of genetic drift and that northern and southwestern regions of the island received more gene flow from outside Sardinia. Overall, our genetic analysis sheds new light on the origin of Neolithic settlement on Sardinia, reinforces models of genetic continuity on the island, and provides enhanced power to detect post-Bronze-Age gene flow. Together, these findings offer a refined demographic model for future medical genetic studies in Sardinia