1,720,980 research outputs found
Phenological indicators extraction from dense time-series of Landsat data
Full text linkTime series of remotely sensed vegetation indices are valuable data sets in various Earth science fields. In particular, they have been successfully used to map vegetation phenology. This information can be used into physically-based hydrological models to estimate crop water requirements (e.g. Pôças et al., 2015; Consoli & Vanella, 2014; Er-Raki et al., 2007).
Most of the phenology detection studies aimed to capture single seasonal crop growth cycles per year. However, the phenological variability in agriculture, especially connected with winter crops interposed to summer crops, demonstrates the necessity of deriving more than one crop cycle per year (e.g. Patel & Oza, 2014; Li et al., 2014). Moreover, remote sensing of phenology has been largely applied using MODIS normalized difference vegetation index (NDVI) data with a spatial resolution of 250 m, which is often not sufficient to resolve highly fragmented agricultural land surfaces. The opportunities for deriving phenological indicators at high spatial resolution improved radically in 2008 when the Landsat program opened its archive (Woodcock et al. 2008).
In this study, we present an approach to detect phenological indicators aimed to characterize vegetation dynamics in agricultural land surfaces. The proposed algorithm was applied to time series of bi-weekly smoothed and gapfilled Landsat Surface Reflectance Climate Data Record (CDR) data from 2012 to 2014 for a pilot area in the Marchfeld region, Lower Austria.
The analytic procedure can be summarized in the following steps. First, the surface reflectance of Landsat CDR data is smoothed and gap-filled using a state-of-the art Whittaker algorithm to create a time series of 24 images per year, regularly spaced in time (Vuolo et al., in preparation). NDVI and fAPAR (fraction of Absorbed Photosynthetically Active Radiation) are then derived and used as input to calculate phenology. Using a moving window approach, the multi-temporal time series are analysed to extract local maxima and minima for each pixel. The resulting values are automatically screened to identify the absolute maxima and minima for each crop cycle. Finally, the algorithm estimates the timing of key phenological periods (i.e. green-up, maximum and senescence) for each
pixel. Accuracy assessment is carried out through the visual interpretation of several crop growth curves and using a land cover/land use dataset to analyse the results.
The results show that the method can successfully extract phenological indicators from dense smoothed and gapfilled time series, both for summer and winter crops. In addition, the comparison between phenologies extracted from each vegetation indices (NDVI and fAPAR) shows a good agreement (R2 = 0.70).
Future effort will be dedicated to apply the proposed approach to Landsat time series for other areas of interest. Furthermore, the method will be improved by calibrating and validating the results for the pilot study based on ground truth data. The phenological indicators will be then assimilated into a hydrological model to estimate crop water requirements at basin scale
LAI retrieval by inverting a rt model and a simple empirical model with CHRIS/PROBA data from SPARC
No full textRetrieval of Leaf Area Index from CHRIS/PROBA data: an analysis of the directional and spectral information content.
No full textOperational irrigation services from remote sensing: the irrigation advisory plan for the Campania Region, Italy
No full textEvaluation of near-surface soil water status through the inversion of soil–canopy radiative transfer models in the reflective optical domain
No full textKnowledge of the spatial and temporal variability of surface soil water content (SWC) is important to understand the linkage between hydrological, ecological and geological processes in a region. Optical Earth observation (EO) data offer the pos-
sibility to retrieve surface soil water information, since an overall decrease of soil reflectance corresponds to increasing SWC. Sensitivity analysis of the combined leaf (PROSPECT) and canopy (SAILH) reflectance models (PROSAIL) to soil reflectance variations was carried out, and remote sensing and ground data from different experimental agricultural sites (ESA Spectra Barrax Campaigns (SPARC) 2004, ESA Airborne SAR and Optic Campaigns (AgriSAR) 2006 and participatory multi-level EO-assisted tools for irrigation water management and agricultural
decision-support (PLEIADeS) 2007) were exploited. A simple look-up table (LUT) inversion technique was implemented to estimate canopy and soil variables. High negative relationships (r = − 0.87) between the soil reflectance factor of the model
and the measured SWC were found for several crop types and different locations exhibiting a low fractional vegetation cover (fCover). Even though quantification of SWC is difficult, the method could be useful to obtain relative SWC information,
especially before the start and at the beginning of the growing season. Furthermore, the physically based estimation approach offers the possibility of getting information about soil and canopy characteristics concurrently from optical EO data. The methodology presented in this article may also represent a suitable complement in the retrieval of SWC from active microwave
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Spatial distribution of soil water content from airborne thermal and optical remote sensing data
No full textSpatial and temporal information of soil water content is of essential importance for modelling of land surface processes in hydrological studies and applications for operative systems of irrigation management. In the last decades, several remote sensing domains have been considered in the context of soil water content monitoring, ranging from active and passive microwave to optical and thermal spectral bands. In the framework of an experimental campaign in Southern Italy in 2007, two innovative methodologies to retrieve soil water content information from airborne earth observation (E.O.) data were exploited: a) analyses of the dependence of surface temperature of vegetation with soil water content using thermal infrared radiometer (TIR), and b) estimation of superficial soil moisture content using reflectance in the visible and near infrared regions acquired from optical sensors. The first method (a) is applicable especially at surfaces completely covered with vegetation, whereas the second method is preferably applicable at surfaces without or with sparse vegetation. The synergy of both methods allows the establishment of maps of spatially distributed soil water content. Results of the analyses are presented and discussed, in particular in view of an operative context in irrigation studies
Exploiting optical E.O. data for soil moisture retrieval
No full textIn the context of agricultural applications, the knowledge of soil moisture availability is an essential aspect for irrigation management. The microwave waveband region (SAR) has been primarily used to estimate soil moisture from Earth Observation (E.O.) data. However, the optical domain (0.4 - 2.5 μm) may as well offer the possibility to get information about soil moisture since an overall decrease of soil reflectance corresponds to increasing surface soil water content. Data from two different experiments (ESA SPARC and AgriSAR) have been exploited aiming at estimating soil moisture from optical E.O. data by using the radiative transfer model PROSAILH. A soil scale factor (α) was introduced into the model and estimated using a LUT inversion technique. Relatively high negative relationships between the α-factor and the measured soil water content (up to R2 = 0.73) could be found for several crop types with low vegetation cover. The results of this study indicate the potential to retrieve surface soil moisture information from optical E.O. data for similar soil types. The method gives the advantage of retrieving simultaneously soil and canopy characteristics from the same E.O. data sources by using a physical method of parameter estimation
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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