scholarly journals 3D GLACIER MAPPING BY MEANS OF SATELLITE STEREO IMAGES: THE BELVEDERE GLACIER CASE STUDY IN THE ITALIAN ALPS

2020 ◽  
Vol XLIII-B2-2020 ◽  
pp. 1073-1079
Author(s):  
F. Giulio Tonolo ◽  
A. Cina ◽  
A. Manzino ◽  
M. Fronteddu
Keyword(s):  
Accuracy Assessment ◽  
Control Point ◽  
Surface Model ◽  
Stereo Pair ◽  
Italian Alps ◽  
Positional Accuracy ◽  
Multi Temporal ◽  
Fit For Purpose ◽  
The Impact

Abstract. The authors group is within the Glacier Lab of Politecnico di Torino (part of the CC-LAB, a laboratory for climate change monitoring), which is working on glacier monitoring since 2016, mainly exploiting Geomatics techniques to measure the extent and to model the surface of glaciers over the years. Measurement campaigns were carried out within the ASP (Alta Scuola Politecnica – Poliecnico di Torino e Milano) DREAM projects (Drone tEchnnology for wAter resources and hydrologic hazard Monitoring) The manuscript is focused on a specific case study related to the Belvedere glacier, a valley glacier located in northern Italy.In the framework of the Belvedere glacier monitoring, several Geomatics approaches have already been applied in the last four years by the cc-glacier-lab and DREAM Projects with the goal to monitor both the extent of the glacier and its surface. Such monitoring enables the multi-temporal comparison of the glacier digital surface model (DSM), highlighting areas of ice loss and gain. Considering the limitations of aerial surveys in high altitude environments, the authors started assessing the suitability of a satellite based approach, mainly focusing on positional accuracy assessment. The paper is focused on a monitoring based on a high resolution (0.5 m) satellite optical stereo pair. Several tests were carried out with the goal to test the 3D positional accuracies, assessing the impact of different configurations of Ground Control Point (GCP) in terms of numerosity and distribution and focusing on the DSM validation. The results demonstrated the fit-for-purpose of a satellite-based approach for glacier monitoring.

scholarly journals DSM Generation from Single and Cross-Sensor Multi-View Satellite Images Using the New Agisoft Metashape: The Case Studies of Trento and Matera (Italy)

2021 ◽  
Vol 13 (4) ◽  
pp. 593
Author(s):  
Lorenzo Lastilla ◽  
Valeria Belloni ◽  
Roberta Ravanelli ◽  
Mattia Crespi
Keyword(s):  
Case Studies ◽  
Accuracy Assessment ◽  
Stereo Pair ◽  
Commercial Software ◽  
Processing Module ◽  
Land Covers ◽  
Image Metadata ◽  
The Impact ◽  
The City ◽  
Reliable Software

DSM generation from satellite imagery is a long-lasting issue and it has been addressed in several ways over the years; however, expert and users are continuously searching for simpler but accurate and reliable software solutions. One of the latest ones is provided by the commercial software Agisoft Metashape (since version 1.6), previously known as Photoscan, which joins other already available open-source and commercial software tools. The present work aims to quantify the potential of the new Agisoft Metashape satellite processing module, considering that to the best knowledge of the authors, only two papers have been published, but none considering cross-sensor imagery. Here we investigated two different case studies to evaluate the accuracy of the generated DSMs. The first dataset consists of a triplet of Pléiades images acquired over the area of Trento and the Adige valley (Northern Italy), which is characterized by a great variety in terms of geomorphology, land uses and land covers. The second consists of a triplet composed of a WorldView-3 stereo pair and a GeoEye-1 image, acquired over the city of Matera (Southern Italy), one of the oldest settlements in the world, with the worldwide famous area of Sassi and a very rugged morphology in the surroundings. First, we carried out the accuracy assessment using the RPCs supplied by the satellite companies as part of the image metadata. Then, we refined the RPCs with an original independent terrain technique able to supply a new set of RPCs, using a set of GCPs adequately distributed across the regions of interest. The DSMs were generated both in a stereo and multi-view (triplet) configuration. We assessed the accuracy and completeness of these DSMs through a comparison with proper references, i.e., DSMs obtained through LiDAR technology. The impact of the RPC refinement on the DSM accuracy is high, ranging from 20 to 40% in terms of LE90. After the RPC refinement, we achieved an average overall LE90 <5.0 m (Trento) and <4.0 m (Matera) for the stereo configuration, and <5.5 m (Trento) and <4.5 m (Matera) for the multi-view (triplet) configuration, with an increase of completeness in the range 5–15% with respect to stereo pairs. Finally, we analyzed the impact of land cover on the accuracy of the generated DSMs; results for three classes (urban, agricultural, forest and semi-natural areas) are also supplied.

scholarly journals Love in the time of Covid-19: a case-study of the complex laws governing weddings

Legal Studies ◽  
2021 ◽  
pp. 1-17
Author(s):  
Rebecca Probert ◽  
Stephanie Pywell
Keyword(s):  
First Century ◽  
Marriage Law ◽  
England And Wales ◽  
General Law ◽  
The Social ◽  
The Future ◽  
Fit For Purpose ◽  
The Law ◽  
The Impact

Abstract During 2020, weddings were profoundly affected by the Covid-19 pandemic. During periods of lockdown few weddings could take place, and even afterwards restrictions on how they could be celebrated remained. To investigate the impact of such restrictions, we carried out a survey of those whose plans to marry in England and Wales had been affected by Covid-19. The 1,449 responses we received illustrated that the ease and speed with which couples had been able to marry, and sometimes whether they had been able to marry at all, had depended not merely on the national restrictions in place but on their chosen route into marriage. This highlights the complexity and antiquity of marriage law and reinforces the need for reform. The restrictions on weddings taking place also revealed the extent to which couples valued getting married as opposed to having a wedding. Understanding both the social and the legal dimension of weddings is important in informing recommendations as to how the law should be changed in the future, not merely to deal with similar crises but also to ensure that the general law is fit for purpose in the twenty-first century.

scholarly journals ASSESSMENT OF SOCIAL VULNERABILITY TO THE IMPACT OF FLOOD HAZARD: A CASE STUDY OF KOPILI RIVER BASIN, ASSAM, INDIA

2018 ◽  
Vol XLII-5 ◽  
pp. 455-460
Author(s):  
S. V. Shiva Prasad Sharma ◽  
P. S. Roy ◽  
V. Chakravarthi
Keyword(s):  
Social Vulnerability ◽  
Flood Hazard ◽  
Vulnerability Index ◽  
Social Vulnerability Index ◽  
The Social ◽  
Vulnerability Indicators ◽  
Multi Temporal ◽  
The Impact ◽  
Vulnerable Zones

<p><strong>Abstract.</strong> In the present study, an attempt is made to understand the impact on Social Vulnerability of the Kopili basin due to various severities of flood hazard. The flood hazard is generated using multi-temporal historical satellite based analysis and integration of annual flood inundation layers. The census of India data of 2001 and 2011 is spatially joined with village database to study the impact at village level. Using 5 Census variables from both Census 2001 &amp;amp; 2011 as vulnerability indicators, the Social Vulnerability Index (SVI) is derived and classified into various vulnerable zones namely Low, Moderate and High Vulnerable zones. The findings of the study show that the number of villages falling in Low and High Vulnerable zones had decreased during Census 2011 when compared to 2001 and a rise of 6% in villages falling in moderate vulnerable zones during 2011 is observed. The spatial database generated is useful to understand the impact of floods on the Social Vulnerability status of the basin and can be a useful input to further study the Physical, Economic and Environmental Vulnerabilities of the basin.</p>

scholarly journals Coupling Uncertainties with Accuracy Assessment in Object-based Slum Detections, Case Study: Jakarta, Indonesia

2017 ◽  
Author(s):  
Jati Pratomo ◽  
Monika Kuffer ◽  
Javier Martinez ◽  
Divyani Kohli
Keyword(s):  
Land Tenure ◽  
Classification Accuracy ◽  
Accuracy Assessment ◽  
False Negative ◽  
National Policy ◽  
True Positive ◽  
True Negative ◽  
Object Based ◽  
The Impact

Object-Based Image Analysis (OBIA) has been successfully used to map slums. In general, the occurrence of uncertainties in producing geographic data is inevitable. However, most studies concentrated solely on assessing the classification accuracy and neglecting the inherent uncertainties. Our research analyses the impact of uncertainties in measuring the accuracy of OBIA-based slum detection. We selected Jakarta as our case study area, because of a national policy of slum eradication, which is causing rapid changes in slum areas. Our research comprises of four parts: slum conceptualization, ruleset development, implementation, and accuracy and uncertainty measurements. Existential and extensional uncertainty arise when producing reference data. The comparison of a manual expert delineations of slums with OBIA slum classification results into four combinations: True Positive, False Positive, True Negative and False Negative. However, the higher the True Positive (which lead to a better accuracy), the lower the certainty of the results. This demonstrates the impact of extensional uncertainties. Our study also demonstrates the role of non-observable indicators (i.e., land tenure), to assist slum detection, particularly in areas where uncertainties exist. In conclusion, uncertainties are increasing when aiming to achieve a higher classification accuracy by matching manual delineation and OBIA classification.

scholarly journals Geometric Accuracy Assessment of Deimos-2 Panchromatic Stereo Pairs: Sensor Orientation and Digital Surface Model Production

Sensors ◽  
2020 ◽  
Vol 20 (24) ◽  
pp. 7234
Author(s):  
Manuel A. Aguilar ◽  
Rafael Jiménez-Lao ◽  
Abderrahim Nemmaoui ◽  
Fernando J. Aguilar
Keyword(s):  
Urban Areas ◽  
Satellite Images ◽  
Accuracy Assessment ◽  
Bare Soil ◽  
Surface Model ◽  
Stereo Pair ◽  
Rational Polynomial ◽  
Sensor Orientation ◽  
Vertical Accuracy ◽  
Land Covers

Accurate elevation data, which can be extracted from very high-resolution (VHR) satellite images, are vital for many engineering and land planning applications. In this way, the main goal of this work is to evaluate the capabilities of VHR Deimos-2 panchromatic stereo pairs to obtain digital surface models (DSM) over different land covers (bare soil, urban and agricultural greenhouse areas). As a step prior to extracting the DSM, different orientation models based on refined rational polynomial coefficients (RPC) and a variable number of very accurate ground control points (GCPs) were tested. The best sensor orientation model for Deimos-2 L1B satellite images was the RPC model refined by a first-order polynomial adjustment (RPC1) supported on 12 accurate and evenly spatially distributed GCPs. Regarding the Deimos-2 based DSM, its completeness and vertical accuracy were compared with those obtained from a WorldView-2 panchromatic stereo pair by using exactly the same methodology and semiglobal matching (SGM) algorithm. The Deimos-2 showed worse completeness values (about 6% worse) and vertical accuracy results (RMSEZ 42.4% worse) than those computed from WorldView-2 imagery over the three land covers tested, although only urban areas yielded statistically significant differences (p < 0.05).

scholarly journals DO OPEN GEODATA ACTUALLY HAVE THE QUALITY THEY DECLARE? THE CASE STUDY OF MILAN, ITALY

2016 ◽  
Vol XLI-B2 ◽  
pp. 609-614
Author(s):  
M. A. Brovelli ◽  
M. Minghini ◽  
M. E. Molinari ◽  
M. Molteni
Keyword(s):  
Spatial Data ◽  
Large Scale ◽  
Accuracy Assessment ◽  
Quality Parameters ◽  
Data Quality Control ◽  
Positional Accuracy ◽  
Systematic Assessment ◽  
Open Datasets ◽  
The Many

In the past number of years there has been an amazing flourishing of spatial data products released with open licenses. Researchers and professionals are extensively exploiting open geodata for many applications, which, in turn, include decision-making results and other (derived) geospatial datasets among their outputs. Despite the traditional availability of metadata, a question arises about the actual quality of open geodata, as their declared quality is typically given for granted without any systematic assessment. The present work investigates the case study of Milan Municipality (Northern Italy). A wide set of open geodata are available for this area which are released by national, regional and local authoritative entities. A comprehensive cataloguing operation is first performed, with 1061 geospatial open datasets from Italian providers found which highly differ in terms of license, format, scale, content, and release date. Among the many quality parameters for geospatial data, the work focuses on positional accuracy. An example of positional accuracy assessment is described for an openly-licensed orthophoto through comparison with the official, up-to-date, and large-scale vector cartography of Milan. The comparison is run according to the guidelines provided by ISO and shows that the positional accuracy declared by the orthophoto provider does not correspond to the reality. Similar results are found from analyses on other datasets (not presented here). Implications are twofold: raising the awareness on the risks of using open geodata by taking their quality for granted; and highlighting the need for open geodata providers to introduce or refine mechanisms for data quality control.

scholarly journals INTEGRATION OF TERRESTRIAL AND UAV PHOTOGRAMMETRY FOR THE ASSESSMENT OF COLLAPSE RISK IN ALPINE GLACIERS

2018 ◽  
Vol XLII-3/W4 ◽  
pp. 445-452 ◽  
Author(s):  
M. Scaioni ◽  
L. Barazzetti ◽  
M. Corti ◽  
J. Crippa ◽  
R. S. Azzoni ◽  
...  
Keyword(s):  
Global Warming ◽  
Structure From Motion ◽  
3D Model ◽  
Point Clouds ◽  
Italian Alps ◽  
Technical Aspects ◽  
Alpine Glaciers ◽  
Multi Temporal ◽  
Glacier Ice

<p><strong>Abstract.</strong> The application of Structure-from-Motion photogrammetry with ground-based and UAV-based camera stations can be effectively exploited for modeling the topographic surface of Alpine glaciers. Multi-temporal repeated surveys may lead to geometric models that may be applied to analyze the glacier retreat under global warming conditions. Here the case study of Forni Glacier in the Italian Alps is presented. Thanks to the integration of point clouds obtained from the independent photogrammetric processing of ground-based and UAV blocks of images (captured on 2016), a complete 3D reconstruction also including vertical and sub-vertical surfaces has been achieved. This 3D model, compared to a second model obtained from a ground-based photogrammetric survey on September 2017, has been exploited to understand the precursory signal of a big collapse that might have involved tourists and hikers visiting the glacier ice tongue during summer. In addition to some technical aspects related to the acquisition and processing of photogrammetric data of glaciers, this paper highlights how Structure-from-Motion photogrammetry may help evaluate the risk of collapse in Alpine glaciers.</p>

scholarly journals Analysis of the Impact of Positional Accuracy When Using a Block of Pixels for Thematic Accuracy Assessment

Geographies ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 143-165
Author(s):  
Jianyu Gu ◽  
Russell G. Congalton
Keyword(s):  
Spatial Scale ◽  
Accuracy Assessment ◽  
Block Size ◽  
Positional Error ◽  
Positional Accuracy ◽  
Landscape Characteristics ◽  
Sensing Applications ◽  
Assessment Unit ◽  
Thematic Accuracy ◽  
The Impact

Pixels, blocks (i.e., grouping of pixels), and polygons are the fundamental choices for use as assessment units for validating per-pixel image classification. Previous research conducted by the authors of this paper focused on the analysis of the impact of positional accuracy when using a single pixel for thematic accuracy assessment. The research described here provided a similar analysis, but the blocks of contiguous pixels were chosen as the assessment unit for thematic validation. The goal of this analysis was to assess the impact of positional errors on the thematic assessment. Factors including the size of a block, labeling threshold, landscape characteristics, spatial scale, and classification schemes were also considered. The results demonstrated that using blocks as an assessment unit reduced the thematic errors caused by positional errors to under 10% for most global land-cover mapping projects and most remote-sensing applications achieving a half-pixel registration. The larger the block size, the more the positional error was reduced. However, there are practical limitations to the size of the block. More classes in a classification scheme and higher heterogeneity increased the positional effect. The choice of labeling threshold depends on the spatial scale and landscape characteristics to balance the number of abandoned units and positional impact. This research suggests using the block of pixels as an assessment unit in the thematic accuracy assessment in future applications.

scholarly journals COMPARISON BETWEEN ABSOLUTE AND RELATIVE POSITIONAL ACCURACY ASSESSMENT - A CASE STUDY APPLIED TO DIGITAL ELEVATION MODELS

2019 ◽  
Vol 25 (1) ◽  
Author(s):  
Leandro Luiz Silva de França ◽  
Alex de Lima Teodoro da Penha ◽  
João Alberto Batista de Carvalho
Keyword(s):  
Thermal Emission ◽  
Accuracy Assessment ◽  
Digital Elevation Models ◽  
Shuttle Radar Topography Mission ◽  
Control Points ◽  
Positional Accuracy ◽  
Digital Elevation ◽  
The Absolute ◽  
Better Than

Abstract This paper presents a comparative study between the absolute and relative methods for altimetric positional accuracy of Digital Elevation Models (DEM). For the theoretical basis of this research, the definitions of accuracy (exactness) and precision, as well the concepts related to absolute and relative positional accuracy were explored. In the case study, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) DEM were used. In the analysis of the absolute accuracy, 6,568 ground control points from GNSS orbital survey were used, collected through relative-static method. In the relative accuracy, it was used as reference DEM with spatial resolution of 5 meters generated by stereophotogrammetrical process for the Mapping Project of Bahia (Brazil). It was concluded that, once the accuracy of the reference DEM is better than the other two evaluated DEM, the results of the classification for the PEC-PCD for the relative evaluation are equal to or better than the absolute evaluation results, with the advantage to being able to verify the pixel population of the evaluated models, which makes it possible to identify outliers, distortions and displacements, including delimiting regions, which is much less likely with a limited set of control points.

scholarly journals Impact of Multi-GNSS on Positioning Accuracy and Multipath Errors in High-Precision Single-Epoch Solutions – A Case Study in Ningbo China

2015 ◽  
Vol 68 (5) ◽  
pp. 999-1017 ◽  
Author(s):  
Lawrence Lau ◽  
Hiroaki Tateshita ◽  
Kazutoshi Sato
Keyword(s):  
High Precision ◽  
Positive Impact ◽  
Accuracy Assessment ◽  
Global Navigation Satellite Systems ◽  
Early Assessment ◽  
Positioning Accuracy ◽  
Single Epoch ◽  
The Impact ◽  
Multipath Errors

Real-Time Kinematic (RTK) Global Positioning System (GPS) carrier phase-based precise positioning has been widely using in geodesy and surveying applications, and other high accuracy positioning and navigation applications in the last two decades. More Global Navigation Satellite Systems (GNSS) are being developed and it is usually expected that combining GNSS will have a positive impact on positioning accuracy. This paper describes a case study carried out at Ningbo in China on the impact of multi-GNSS on RTK single epoch solutions. Both GPS and GLONASS are fully operational now. Moreover, the Quasi-Zenith Satellite System (QZSS) can be observed at Ningbo. Currently, only one QZSS satellite “MICHIBIKI” is operational. This paper carries out an early assessment of the impact of QZSS on GPS and GLONASS single-epoch high precision positioning (i.e., single-epoch positioning accuracy assessment) and investigates the multipath errors in the GPS, GLONASS and QZSS multi-frequency data.

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