196,106 research outputs found
A semi-empirical approach for surface soil water content estimation from radar data without a-priori information on surface roughness
No full textIn this study, the spatial distribution of soil water content in an agricultural area of 30 km2 in Southern Italy has been estimated by using high-resolution space-borne Synthetic Aperture Radar data. Multi-polarised SAR images acquired during the SIR-C mission in April 1994 have been analysed by using the semi-empirical surface backscattering model derived by Oh et al. (1992). A site-specific calibration procedure of the cited model has been proposed to derive soil dielectric constant values without a-priori information on the surface roughness by using ground measurements on a regular grid in two bare-soil fields. The calibrated model applied to L-band data reproduced quite satisfactorily the spatial variability of the soil dielectric constant in the two fields. Diversely, C-band data gave poor results. Successively, the calibrated Oh’s model was applied to estimate the soil dielectric constant in bare soil and low vegetation fields of the entire irrigation district, where the output of a distributed simulation model of soil water balance were available. From the comparison between the Oh’s backscattering model and the soil water balance model, it was confirmed that, under bare soil conditions, the values of soil water content near the soil surface estimated from SIR-C L-band data differ by ± 20% from the simulated ones. Furthermore, as expected, the presence of a fractional vegetation cover, even if small, reduced the sensitivity of radar backscattering to soil moisture. The results of this study confirmed that L-band SAR data represent a minimum requirement for possible assimilation schemes in regional hydrological modelling
Spatial Sharpening of Land Surface Temperature for Daily Energy Balance Applications
No full textDaily high spatial resolution assessment of actual evapotranspiration is essential for water management and crop water requirement estimation under stress conditions. The application of energy balance models usually requires satellite observations of radiometric surface temperature with high geometrical and temporal resolutions. By now, however, high spatial resolution (~ 100 m) is available with low time frequency (approximately every two weeks); at the opposite daily acquisition are characterised by poor spatial resolution. The analysis of vegetation index (VI) and land surface temperature (LST) spatial relationship, shows in substance a scale invariant behaviour; this consideration allows the application of spatial sharpening algorithms of thermal data, by means of a combination of high spatial resolution data in VIS/NIR range with high temporal acquisition on TIR. In this paper, a sharpening algorithm was applied using the thermal bands of MODIS (MOderate resolution Imaging Spectroradiometer) and vegetation indices derived by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) sensor; the choice of this sensors is justified by the simultaneous acquisition time. The results of this sharpening process was firstly compared against LST estimation (at the same spatial resolution) by means of the ASTER simultaneous data; then the derived high spatial resolution LST distribution was used in order to investigate the effect of the disaggregation on the outputs of surface energy balance models. The above described application was performed on a Sicilian study area
Small Sats Lifecycle Management Through MBSE Aided Decision Making Tailored Tool
No full textTraditional System Engineering approaches highlight some bottlenecks whenever dealing with information exchange among stakeholders, typically producing many documents, difficult to trace and to keep harmonized. This is particularly true for space applications, which entail very complex systems conceivement, design, implementation and operation by a number of different players who grow with mission complexity. Model-Based Systems Engineering (MBSE) is intended to facilitate these activities, providing a common source of truth to the system engineering “ecosystem”, improving its efficiency and quality by applying a model that evolves along the entire product lifecycle. The paper proposes a critical analysis of an MBSE approach applied to real small sat mission currently under the European Space Agency (ESA) phase A study, demonstrating its potential and its gaps. All Systems Engineering phases are explored, from the high-level mission objectives definition, through the articulated external and internal functional analysis, down to concept of operations, ending up with the Assembly, Integration and Verification/Test plan definition; every modelling step is harmonized with proper requirements generation and their role in driving the logical and physical trade-off analyzes. The study is conducted according to the ARChitecture Analysis & Design Integrated Approach (ARCADIA) and adopting the Capella tool, being very effective in mastering different engineering levels with coherence and with an iterative information refinement. Despite the clear advantage of having a unique model in which a change is inherently shared with all stakeholders, saving up time in communication, MBSE still lacks intelligent support that could strongly help in addressing the best optimal architecture in line with the system functionalities, speeding up the alternatives selection process. This would be particularly useful during the preliminary design phases, in which the almost infinite design choices are skimmed by the only systems engineers’ knowledge, who may miss some solutions. A newly approach conceived to solve this issue is here presented in the form of a decision-making tool prototype, that correlates a set of functionalities with a set of available technologies, proposing one or more architectures that are coherent with what the engineers expect from the system behaviour; a first grid of requirements is also part of the tool output, in support of the previously described MBSE approach
A distributed agro-hydrological model for irrigation water demand assessment.
No full textThe actual irrigation water demand in a district in Sicily (Italy) was assessed by the spatially distributed agro-hydrological model SIMODIS (SImulation and Management of On-Demand Irrigation Systems). For each element with homogeneous crop and soil conditions, in which the considered area can be divided, the model numerically solves the one-dimensional water flow equation with vegetation parameters derived from Earth Observation data. In SIMODIS, the irrigation scheduling is set by means of two parameters: the threshold value of soil water pressure head in the root zone, hm, and the fraction of soil water deficit to be re-filled, Δ. This study investigated the possibility of identifying a couple of irrigation parameters (hm, Δ) which allowed to reproduce the actual irrigation water demand, given that the study area was adequately characterized with regard to the spatial distribution of the soil hydraulic properties and the vegetation conditions throughout the irrigation season. The spatial distribution of the soil and vegetation properties of the study area, covering an irrigation district of approximately 800 ha, was accurately characterized during the summer of 2002. The soil hydraulic properties were identified by an intensive undisturbed soil sampling, while the vegetation cover was characterized in terms of leaf area index, surface albedo and fractional soil cover by analysing multispectral LandSat TM imageries. Irrigation volumes were monitored at parcel scale.
A reference scenario with hm = −700 cm and Δ = 50% (corresponding to a mean actual to potential transpiration ratio of 0.95) allowed to reproduce the spatial and temporal distribution of the actual irrigation demand at the district scale. The spatial variability of the crop conditions in the considered area had much more influence to assess the irrigation water demand than the soil hydraulic spatial variability. The proposed approach showed that, under the agro-climatic conditions typical for the Mediterranean region, SIMODIS may be a valuable tool in managing irrigation to increase water productivity
Rethinking vineyard ground management to counter soil tillage erosion
No full textTillage erosion is a relevant process of soil redistribution in sloping arable land, but little research has analysed the effect of shallow tillage on soil erosion in vineyards. The goal of this study was to quantify the soil tillage effect on soil translocation and erosion at the territorial level in a large vineyard area in Sicily. The soil loss and soil erosion tolerance limits were compared to identify the vineyards with a high risk of soil degradation. An alternative management scenario to traditional tillage was proposed to evaluate the effectiveness of the best management practices on soil conservation. The experimental trials were conducted in 14 vineyards with different slopes and soil characteristics. Soil translocation after shallow tillage was determined using coloured sand as the tracer. Regression results between the slope and mean translocation distance (T) were used to estimate tillage erosion (Qplot) in 2840 vineyard plots within a Protected Designation of Origin (PDO) area, considering the number of inter-rows and the length of each plot. After a single tillage operation in the downslope direction, the mean translocation distance ranged from 0.22 m to 0.45 m in the slope of 4% and 32%, respectively. At the plot level (Mg yr−1 per plot), the size and shape of the field must be considered, and the number of inter-rows was the predominant factor in tillage erosion estimation in vineyards. When comparing tillage erosion of each inter-row and soil erosion tolerance, the findings showed that 94% of the analysed plots had a high tillage erosion risk. Therefore, more attention should be paid to tillage operations in terms of type and intensity. The plots with high erosion risk decreased to 74% when best management practices with a cover crop in the entire PDO area were adopted. This study highlights the contribution of high tillage erosion to overall soil erosion losses, suggesting specific attention should be paid to more sustainable practices in soil management
High resolution remote estimation of soil surface water content by a thermal inertia approach
No full textThe spatial distribution of soil surface water content in a bare soil was evaluated by a thermal inertia approach from high resolution visible/near infrared (VIS/NIR) and thermal infrared (TIR) airborne data. Given that the relationship between the thermal inertia and the soil water content strongly depends on the accurate estimation of the soil thermal conductivity, two different empirical models were applied to estimate it. Remotely estimated water contents were tested with time domain reflectometry (TDR) measurements collected on a 110 × 90 m2 bare field in coincidence with airborne over-flights. The thermal conductivity model by Johansen (1975) produced more accurate estimates of soil surface water content than that by Campbell (1985), especially for water content higher than 0.15 (m3 m-3). The considered thermal inertia approach allowed prediction of the spatial distribution of the soil water content with a satisfactory level of accuracy. In particular a relatively better accuracy was obtained when the remote sensing images were analyzed directly at the same scale of the field measurements
Detection of crop water status in mature olive orchards using vegetation spectral measurements
No full textLeaf/stem water potentials are generally considered the most accurate indicators of crop water status (CWS) and
they are quite often used for irrigation scheduling, even if costly and time-consuming. For this reason, in the last
decade vegetation spectral measurements have been proposed, not only for environmental monitoring, but also in
precision agriculture, to evaluate crop parameters and consequently for irrigation scheduling.
Objective of the study was to assess the potential of hyperspectral reflectance (450-2400 nm) data to predict the
crop water status (CWS) of a Mediterranean olive orchard.
Different approaches were tested and particularly, (i) several standard broad- and narrow-band vegetation indices
(VIs), (ii) specific VIs computed on the basis of some key wavelengths, predetermined by simple correlations and
finally, (iii) using partial least squares (PLS) regression technique.
To this aim, an intensive experimental campaign was carried out in 2010 and a total of 201 reflectance spectra,
at leaf and canopy level, were collected with an ASD FieldSpec Pro (Analytical Spectral Devices, Inc.) handheld
field spectroradiometer. CWS was contemporarily determined by measuring leaf and stem water potentials with
the Scholander chamber.
The results indicated that the considered standard vegetation indices were weakly correlated with CWS. On the
other side, the prediction of CWS can be improved using VIs pointed to key-specific wavelengths, predetermined
with a correlation analysis. The best prediction accuracy, however, can be achieved with models based on PLS
regressions.
The results confirmed the dependence of leaf/canopy optical features from CWS so that, for the examined crop, the
proposed methodology can be considered a promising tool that could also be extended for operational applications
using multispectral aerial sensors
Sulle tecniche di stima dell�indice di Area Fogliare da dati MIVIS: applicazione e confronto dei modelli SAIL e CLAIR
No full textMass and Surface Energy Balance Approaches for Monitoring Water Stress in Vineyards
No full textTree crops are representing one of most widespread agricultural systems in Mediterranean regions, thus contributing in a substantial way to the economy and productivity of primary sectors of the countries interested. Besides the aspects concerning their economical relevance, tree crops like vineyards, olive and orange orchards are also typical elements of the Mediterranean landscape, and their ecological role has been recently revitalised in consideration of their function as carbon sinks for the Kyoto agreement.
The environmental and economical sustainability of these agricultural systems in arid and semi-arid zones has to cope with the availability and management of water resources for irrigation. During recent years there has been a substantial progress in understanding the evolution of evapotranspiration processes in cropping systems, and detailed models and measurement techniques have been set-up for describing the mass and energy exchanges in the soil-plant- atmosphere continuum. However, due to the complexity of rooting systems and aerial parts further steps are needed for a full comprehension of hydrological processes in tree crop systems, with special regard to water stress conditions.
Within the research project P.R.I.N. 2008 “Assessment of mass and energy fluxes for the irrigation management of Mediterranean tree crops” different techniques for measuring evapotranspiration fluxes in tree crops will be developed and tested, from innovative methodologies based on remote sensing observations to in-situ observations (xylem-flow measurements and micro-meteorology). These data-sets have be interpreted by means of physical approaches, with a modelling perspective of the observed processes
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