Towards a ground navigation system based in visual feedback provided by a mini UAV

This paper addresses initial efforts to develop a navigation system for ground vehicles supported by visual feedback from a mini aerial vehicle. A visual-based algorithm computes the ground vehicle pose in the world frame, as well as possible obstacles within the ground vehicle pathway. Relying on that information, a navigation and obstacle avoidance system is used to re-plan the ground vehicle trajectory, ensuring an optimal detour. Finally, some experiments are presented employing a unmanned ground vehicle (UGV) and a low cost mini unmanned aerial vehicle (UAV).

Ground cover and leaf area index relationship in a grass, legume and crucifer crop

Canopy characterization is essential for describing the interaction of a crop with its environment. The goal of this work was to determine the relationship between leaf area index (LAI) and ground cover (GC) in a grass, a legume and a crucifer crop, and to assess the feasibility of using these relationships as well as LAI-2000 readings to estimate LAI. Twelve plots were sown with either barley (Hordeum vulgare L.), vetch (Vicia sativa L.), or rape (Brassica napus L.). On 10 sampling dates the LAI (both direct and LAI-2000 estimations), fraction intercepted of photosynthetically active radiation (FIPAR) and GC were measured. Linear and quadratic models fitted to the relationship between the GC and LAI for all of the crops, but they reached a plateau in the grass when the LAI mayor que 4. Before reaching full cover, the slope of the linear relationship between both variables was within the range of 0.025 to 0.030. The LAI-2000 readings were linearly correlated with the LAI but they tended to overestimation. Corrections based on the clumping effect reduced the root mean square error of the estimated LAI from the LAI-2000 readings from 1.2 to less than 0.50 for the crucifer and the legume, but were not effective for barley.

Seismic Hazard and Ground Motion Characterization at the Itoiz Dam (Northern Spain).

This paper presents a new hazard-consistent ground motion characterization of the Itoiz dam site, located in Northern Spain. Firstly, we propose a methodology with different approximation levels to the expected ground motion at the dam site. Secondly, we apply this methodology taking into account the particular characteristics of the site and of the dam. Hazard calculations were performed following the Probabilistic Seismic Hazard Assessment method using a logic tree, which accounts for different seismic source zonings and different ground-motion attenuation relationships. The study was done in terms of peak ground acceleration and several spectral accelerations of periods coinciding with the fundamental vibration periods of the dam. In order to estimate these ground motions we consider two different dam conditions: when the dam is empty (T = 0.1 s) and when it is filled with water to its maximum capacity (T = 0.22 s). Additionally, seismic hazard analysis is done for two return periods: 975 years, related to the project earthquake, and 4,975 years, identified with an extreme event. Soil conditions were also taken into account at the site of the dam. Through the proposed methodology we deal with different forms of characterizing ground motion at the study site. In a first step, we obtain the uniform hazard response spectra for the two return periods. In a second step, a disaggregation analysis is done in order to obtain the controlling earthquakes that can affect the dam. Subsequently, we characterize the ground motion at the dam site in terms of specific response spectra for target motions defined by the expected values SA (T) of T = 0.1 and 0.22 s for the return periods of 975 and 4,975 years, respectively. Finally, synthetic acceleration time histories for earthquake events matching the controlling parameters are generated using the discrete wave-number method and subsequently analyzed. Because of the short relative distances between the controlling earthquakes and the dam site we considered finite sources in these computations. We conclude that directivity effects should be taken into account as an important variable in this kind of studies for ground motion characteristics.

Comparative assessment of global irradiation from a satellite estimate model (CM SAF) and on-ground measurements (SIAR): a Spanish case study

An analysis and comparison of daily and yearly solar irradiation from the satellite CM SAF database and a set of 301 stations from the Spanish SIAR network is performed using data of 2010 and 2011. This analysis is completed with the comparison of the estimations of effective irradiation incident on three different tilted planes (fixed, two axis tracking, north-south hori- zontal axis) using irradiation from these two data sources. Finally, a new map of yearly values of irradiation both on the horizontal plane and on inclined planes is produced mixing both sources with geostatistical techniques (kriging with external drift, KED) The Mean Absolute Difference (MAD) between CM SAF and SIAR is approximately 4% for the irradiation on the horizontal plane and is comprised between 5% and 6% for the irradiation incident on the inclined planes. The MAD between KED and SIAR, and KED and CM SAF is approximately 3% for the irradiation on the horizontal plane and is comprised between 3% and 4% for the irradiation incident on the inclined planes. The methods have been implemented using free software, available as supplementary ma- terial, and the data sources are freely available without restrictions.

Comparative assessment of global irradiation from a satellite estimate model (CM SAF) and on-ground measurements (SIAR): a Spanish case study

An analysis and comparison of daily and yearly solar irradiation from the satellite CM SAF database and a set of 301 stations from the Spanish SIAR network is performed using data of 2010 and 2011. This analysis is completed with the comparison of the estimations of effective irradiation incident on three different tilted planes (fixed, two axis tracking, north-south hori- zontal axis) using irradiation from these two data sources. Finally, a new map of yearly values of irradiation both on the horizontal plane and on inclined planes is produced mixing both sources with geostatistical techniques (kriging with external drift, KED) The Mean Absolute Difference (MAD) between CM SAF and SIAR is approximately 4% for the irradiation on the horizontal plane and is comprised between 5% and 6% for the irradiation incident on the inclined planes. The MAD between KED and SIAR, and KED and CM SAF is approximately 3% for the irradiation on the horizontal plane and is comprised between 3% and 4% for the irradiation incident on the inclined planes. The methods have been implemented using free software, available as supplementary ma- terial, and the data sources are freely available without restrictions.

Observation and Detection of Underground Cellars in the Duero Basin By GNSS, Lidar and Ground Penetrating Radar Techniques

The underground cellars that appear in different parts of Spain are part of an agricultural landscape dispersed, sometimes damaged, others at risk of disappearing. This paper studies the measurement and display of a group of wineries located in Atauta (Soria), in the Duero River corridor. It is a unique architectural complex, facing rising, built on a smooth hillock as shown in Fig. 1. These constructions are excavated in the ground. The access to the cave or underground cellar has a shape of a narrow tube or down gallery. Immediately after, this space gets wider. There, wine is produced and stored [1]. Observation and detection of the underground cellar, both on the outside and underground, it is essential to make an inventory of the rural patrimony [2]. The geodetection is a noninvasive technique, adequate to accurately locate buried structures in the ground. Works undertaken include topographic work with the LIDAR techniques and integration with data obtained by GNSS and GPR.

On the use of trenches and walls on the control of ground transmitted railway vibrations

An actual case of an underground railway in the neighbourhood of habitation buildings has been analyzed. The study has been based on a twodimensional BEM model including a tunnel and a typical building. The soil properties were obtained using geophysical techniques. After a sensitivity study, the model has been simplyfied and validated by comparison with "in situ" measurements. Using this simplyfied model, a parametric study has been done including trenches and walls of different materials and different depths at two different distances from the tunnel. The reductions obtained with the different solutions can then be compared.

Expectations from EMET and OESEE ground listening of possible EM events generated by the TSS 1R

On 22nd February '96, the space mission STS 75 started ,from the NASA facilities at Cape Canaveral. Such a mission consists in the launch of the shuttle Columbia in order to carry out two experiments in the space: the TSS 1R (Tethered Satellite Sistem 1 Refliight) and the USMP (United States Microgravity Payload). The TSS 1R is a replica of a similar mission TSS 1 '92. The TSS space programme is a bilateral scientific cooperation between the USA space agency NASA (National Aeronautics and Space Agency) and the ASI (Italian Space Agency. The TSS 1R system consists on the shuttle Columbia which deploys, up-ward, by means a conducting tether 20 km long, a spherical satellite (1.5 mt diameter) containing scientific instrumentation. This system, orbiting at about 300 km from the Earth's surface, represents, presently, the largest experimental space structure, Due to its dimensions, flexibility and conducting properties of the tether, the system interacts, in a quite complex manner, wih the earth magnetic field and the ionospheric plasma, in a way that the total system behaves as an electromagnetic radiating antenna as well as an electric power generator. Twelve scientific experiments have been assessed by US and Italian scientists in order to study the electro dynamic behaviour of the structure orbiting in the ionos phere. Two experiments have been prepared in the attempt to receive on the Earth's surface possible electromagnetic events radiated by the TSS 1R. The project EMET (Electro Magnetic Emissions from Tether),USA and the project OESEE (Observations on the Earth Surface of Electromagnetic Emissions) Italy, consist in a coordinated programme of passive detection of such possible EM emissions. This detection will supply the verification of some thoretical hypotheses on the electrodynamic interactions between the orbiting system, the Earth's magnetic field and the ionospheric plasma with two principal aims as the technological assesment of the system concept as well as a deeper knowledge of the ionosphere properties for future space applications. A theoretical model that keeps the peculiarities of tether emissionsis being developed for signal prediction at constant tether current. As a step previous to the calculation of the expected ground signal , the Alfven-wave signature left by the tether far back in the ionosphere has been determined. The scientific expectations from the combined effort to measure the entity of those perturbations will be outlined taking in to account the used ground track sensor systems.

Ice volume changes (1936-1990-2007) and ground-penetrating radar studies of Ariebreen, Hornsund, Spitsbergen

Ariebreen is a small (0.37 km2) valley glacier located in southern Spitsbergen. Our ground-penetrating radar surveys of the glacier show that it is less than 30 m thick on average, with a maximum thickness of 82 m, and it appears to be entirely cold. By analysing digital terrain models of the ice surface from different dates, we determine the area and volume changes during two periods, 1936-1990 and 1990-2007. The total ice volume of the glacier has decreased by 73% during the entire period 1936-2007, which is equivalent to a mean mass balance rate of -0.6190.17 m/yr w.eq. The glacier thinning rate has increased markedly between the first and second periods, from -0.5090.22 to -0.9590.17 m/yr w.eq.

Ice volume estimates from ground-penetrating radar surveys, western Nordenskiöld Land glaciers, Svalbard

As part of ongoing work within the SvalGlac project aimed to obtain a reliable estimate of the total ice volume of Svalbard glaciers and their potential contribution to sea level rise, in this contribution we present volume calculations, with detailed error estimates, for ten glaciers on western Nordenskiöld Land, central Spitsbergen, Svalbard. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 1999-2012, all of them except one within 2010-2012. The total area and volume of the ensemble are 113.38±0.09 km2 and 10.439±0.185 km3, respectively, while the individual areas, volumes and average ice thickness lie within 2.5-49.1 km2, 0.08-5.48 km3 and 29-108 m, respectively. The maximum recorded ice thickness, 265±15 m, corresponds to Fridtjovbreen, which has also the largest average thickness (108±1m). Available empirical formulae for Svalbard glaciers overestimate the total volume of these glaciers by 24% with respect to our calculation. On the basis of the pattern of scattering in the radargrams, we also analyse the hydrothermal structure of these glaciers. Nine out of ten are polythermal, while only one is entirely cold.

Ice volume estimates from ground-penetrating radar surveys, Wedel Jarlsberg Land glaciers, Svalbard

One of the aims of the SvalGlac project is to obtain an improved estimate, with reliable error estimates, of the volume of Svalbard glaciers and their potential contribution to sea level rise. As part of this work, we present volume calculations, with detailed error estimates, for eight glaciers on Wedel Jarlsberg Land, southern Spitsbergen, Svalbard. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 2004-2011. The total area and volume of the ensemble are 502.9±18.6 km2 and 80.72±2.85 km3, respectively. Excluding Ariebreen (a tiny glacier, menor que 0.4 km2 in area), the individual areas, volumes and average ice thickness lie within 4.7-141.0 km2, 0.30-25.85 km3 and 64-183 m, respectively. The maximum recorded ice thickness, ca. 619±13 m, is found in Austre Torellbreen. To estimate the ice volume of small non-echo-sounded tributary glaciers, we used a function providing the best fit to the ice thickness along the centre line of a collection of such tributaries where echo-soundings were available, and assuming parabolic cross-sections. We did some tests on the effect on the measured ice volumes of the distinct radio-wave velocity (RWV) of firn as compared to ice, and cold versus temperate ice, concluding that the changes in volume implied by such corrections were within the error bounds of our volume estimate using a constant RWV for the entire glacier inferred from common mid-point measurements on the upper ablation area.

Evaluation of the Grounding Circuit Measurements for Stator Ground-Fault Location of Synchronous Generators

Locating stator-winding ground faults accurately is a very difficult task. In this paper the grounding circuit measurements are evaluated in order to obtain information about the stator ground-fault location in synchronous generators. In power generators grounded through a high impedance, the relation between the neutral voltage and the phase voltage provide a first estimation of the fault location. The location error by using this ratio depends on the fault resistance and the value of the capacitance to ground of the stator winding. However, the error added by ignoring the value of the fault resistance is the most relevant term. This location estimation and the location error have been evaluated through the data of a real synchronous machine.

Ground-penetrating radar surveys and ice volume estimates of Wedel Jarlsberg Land glaciers, Svalbard

We present volume calculations, with detailed error estimates, for eight glaciers on Wedel Jarlsberg Land, southern Spitsbergen, Svalbard, and compare them to those obtained from area-volume scaling relationships. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 2004-2011.

Discrete element analysis for the assessment of the accuracy of load cell-based dynamic weighing systems in grape harvesters under different ground conditions

Dynamic weighing systems based on load cells are commonly used to estimate crop yields in the field. There is lack of data, however, regarding the accuracy of such weighing systems mounted on harvesting machinery, especially on that used to collect high value crops such as fruits and vegetables. Certainly, dynamic weighing systems mounted on the bins of grape harvesters are affected by the displacement of the load inside the bin when moving over terrain of changing topography. In this work, the load that would be registered in a grape harvester bin by a dynamic weighing system based on the use of a load cell was inferred by using the discrete element method (DEM). DEM is a numerical technique capable of accurately describing the behaviour of granular materials under dynamic situations and it has been proven to provide successful predictions in many different scenarios. In this work, different DEM models of a grape harvester bin were developed contemplating different influencing factors. Results obtained from these models were used to infer the output given by the load cell of a real bin. The mass detected by the load cell when the bin was inclined depended strongly on the distribution of the load within the bin, but was underestimated in all scenarios. The distribution of the load was found to be dependent on the inclination of the bin caused by the topography of the terrain, but also by the history of inclination (inclination rate, presence of static periods, etc.) since the effect of the inertia of the particles (i.e., representing the grapes) was not negligible. Some recommendations are given to try to improve the accuracy of crop load measurement in the field.