1,720,972 research outputs found
Comparison of Different Algorithms to Orthorectify WorldView-2 Satellite Imagery
No full textDue to their level of spatial detail (pixel dimensions equal to or less than 1 m), very high-resolution satellite images (VHRSIs) need particular georeferencing and geometric corrections which require careful orthorectification. Although there are several dedicated algorithms, mainly commercial and free software for geographic information system (GIS) and remote sensing applications, the quality of the results may be inadequate in terms of the representation scale for which these images are intended. This paper compares the most common orthorectification algorithms in order to define the best approach for VHRSIs. Both empirical models (such as 2D polynomial functions, PFs; or 3D rational polynomial functions, RPFs) and rigorous physical and deterministic models (such as Toutin) are considered. Ground control points (GCPs) and check points (CPs)-whose positions in the image as, well as in the real world, are known-support algorithm applications. Tests were executed on a WorldView-2 (WV-2) panchromatic image of an area near the Gulf of Naples in Campania (Italy) to establish the best-performing algorithm. Combining 3D RPFs with 2D PFs produced the best results
QGIS Use for IHS PAN-Sharpening Application to Landsat 8 OLI Images
No full textIHS Pan-sharpening is one of the most performed approaches to transfer the higher resolution of panchromatic images to the multispectral ones of the same scene. It requires basic operations that can be easily carried out using GIS software also in absence of specific tools for Pan-sharpening. The aim of this paper is to illustrate the steps to be realized in QGIS, a free and open source software that permits to operate with raster files, to implement IHS Pan-sharpening method. The procedure is applied to Landsat 8 OLI (L8 OLI) images so to reduce pixel dimensions of visible multispectral bands from 30 m to 15 m and produce RGB composition with higher spatial resolution. The quality of the results is tested using appropriate indices such as ERGAS (Erreur Relative Globale Adimensionnelle de Synthèse) and UIQI (Universal Image Quality Index)
QGIS use for IHS PAN-sharpening application to landsat 8 OLI images
No full textIHS Pan-sharpening is one of the most performed approaches to transfer the higher resolution of panchromatic images to the multispectral ones of the same scene. It requires basic operations that can be easily carried out using GIS software also in absence of specific tools for Pan-sharpening. The aim of this paper is to illustrate the steps to be realized in QGIS, a free and open source software that permits to operate with raster files, to implement IHS Pan-sharpening method. Particularly Map Algebra functions are applied using raster calculator: to facilitate the user approach the adopted formulas are included in a single process according to a workflow. Landsat 8 OLI (L8 OLI) images concerning Campania Region (Italy) are processed so to reduce pixel dimensions of visible multispectral bands from 30 m to 15 m and produce RGB composition with higher spatial resolution. The quality of the results is tested using appropriate indices such as ERGAS (Erreur Relative Globale Adimensionnelle de Synthèse) and UIQI (Universal Image Quality Index), both calculated using QGIS tools
Application of different pan-sharpening methods on worldview-3 images
No full textIn the field of the remote sensing, the introduction of high resolution satellite sensors has required the development of several data fusion approaches. Two kinds of images are usually acquired: Multispectral and panchromatic. The first group has a lower spatial resolution but accurate spectral information while the second presents a higher spatial resolution with a longer band acquisition range. Pan-sharpening permits to combine panchromatic and multispectral data to create new multispectral images with higher geometric resolution. In this paper nine different pan-sharpening methods are tested on WorldView-3 images: Brovey, Weighted Brovey, Gram Schmidt, IHS, Fast IHS, Multiplicative, Principal Component Analysis (PCA), Simple Mean and Zhang. With the aim to rank the techniques efficiency, visual inspections combined with quantitative evaluations are performed to test spectral qualities of the fused images. This is a difficult task because the quality of the fused image depends on the considered datasets: RMSE (Root Mean Square Error) and ERGAS (Relative Dimensionless Global Error) are the accuracy indices used for this scope
Land Surface Temperature from Landsat 5 TM images: Comparison of different methods using airborne thermal data
No full textIn this study, several methods to compute land surface temperatures (LST) from Landsat TM5 data are compared. Two different approaches are considered. An image based approach that takes into account atmospherically corrected data by using a dark object subtraction model (DOS-1) and computes the emissivity as NDVI function. The emissivity of a surface is controlled by such factors as water content, chemical composition, structure and roughness; it can be determined as the contribution of the different components that belong to the pixels according to their proportions. NDVI method takes into account that vegetation and soils are the main surface cover for the terrestrial component. This emissivity is used to compute the LST by the inversion of Planck function. The other approach applies atmospheric correction to thermal infrared band and considers a constant emissivity of 0.95. Furthermore, the land surface temperature is computed by hybrid methods that result from the merger of the two initially considered approaches. These results are compared with the surface temperature measured by airborne Multispectral Infrared and Visible Imaging Spectrometer (MIVIS). The LST measured by MIVIS sensor can be considered closer to the real surface temperature because the data are acquired at an altitude of 1500 m and are not affected by significant atmospheric effects such as for satellite data, acquired at 705 km from the Earth's surface. The best results are obtained by considering variable emissivity
Assessing Crop Water Requirement and Yield by Combining ERA5-Land Reanalysis Data with CM-SAF Satellite-Based Radiation Data and Sentinel-2 Satellite Imagery
No full textThe widespread development of Earth Observation (EO) systems and advances in numerical atmospheric modeling have made it possible to use the newest data sources as input for crop-water balance models, thereby improving the crop water requirements (CWR) and yield estimates from the field to the regional scale. Satellite imagery and numerical weather prediction outputs offer high resolution (in time and space) gridded data that can compensate for the paucity of crop parameter field measurements and ground weather observations, as required for assessments of CWR and yield. In this study, the AquaCrop model was used to assess CWR and yield of tomato on a farm in Southern Italy by assimilating Sentinel-2 (S2) canopy cover imagery and using CM-SAF satellite-based radiation data and ERA5-Land reanalysis as forcing weather data. The prediction accuracy was evaluated with field data collected during the irrigation season (April-July) of 2021. Satellite estimates of canopy cover differed from ground observations, with a RMSE of about 11%. CWR and yield predictions were compared with actual data regarding irrigation volumes and harvested yield. The results showed that S2 estimates of crop parameters represent added value, since their assimilation into crop growth models improved CWR and yield estimates. Reliable CWR and yield estimates can be achieved by combining the ERA5-Land and CM-SAF weather databases with S2 imagery for assimilation into the AquaCrop model
Processing Very High-Resolution Satellite Images for Individual Tree Identification with Local Maxima Method
No full textIn the last decades, different Remote Sensing (RS) techniques and instruments were developed and utilized to manage and monitor the natural and semi-natural resources. Increasing the number of the sensors with the high spatial and spectral resolution, the remote sensing techniques and the Geographic Information System (GIS), provide more and detailed information, required for the precision agriculture tasks, and support, where possible, the decision-making process. The aim of this study is to develop a chain process, to obtain by using Earth Observation (EO) data, detailed information about the detection of the olive tree crowns. The Individual Tree Crown (ITC) detection process is implemented in a semi-automatic workflow based on Local Maxima Filter (LMF) applied on the Digital Aerial image and WorldView-2 (WV-2) images. The results indicate that the image data characteristics play a fundamental role to detect trees by EO data. For both datasets, the results show a higher accuracy achieved with the NDVI (Normalized Difference Vegetation Index), highlighting the spectral characteristics of the vegetation in the red and InfraRed domain
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
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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