The overall analyses are carried out by using averaged (multilook) InSAR interferograms with a spatial resolution of about 100 x 100 m. In addition, we present the results relevant to the cities of Istanbul (Turkey) and Roma (Italy). Etna volcano (Italy) and the Napoli Bay area (Italy), the latter including three volcanic systems (the Campi Flegrei caldera, the Somma-Vesuvio volcanic complex and the Ischia island) and the city of Napoli. In particular, we focus on the results obtained by retrieving ERS-ENVISAT deformation time-series from 1992 till today in selected case studies relevant to different scenarios. To achieve this result we take advantage of the Differential SAR Interferometry (InSAR) algorithm referred to as Small BAseline Subset (SBAS) technique (Berardino et al., 2002), which allows us to generate mean deformation velocity maps and corresponding time-series by exploiting temporally overlapping SAR dataset collected by the ERS and ENVISAT sensors (Pepe et al., 2005). We exploit in this work the availability of the large archives of spaceborne Synthetic Aperture Radar (SAR) data acquired by the ERS-1/2 and ENVISAT sensors of the European Space Agency (ESA) during the 1992-2009 time period, in order to investigate long term surface deformation of large areas. Type of measurement: What type of measurements need to be made? Depending on the type of measurement, different datums may be more appropriate.Satellite time series have already provided key measurements to retrieve information on the dynamic nature of Earth surface processes.Environment: What is the environment the part will be in? Different datums may be more or less suitable to different environments, such as extreme temperatures or hostile environments.Geometry: What is the geometry of the parts that must be measured? Different types of datums may suit different geometries better.Accuracy: How accurate does the datum need to be? If greater accuracy is required, then a different type of datum may be needed.The purpose of the datum: What is the purpose of the datum? Is it to locate a feature of a part, measure size, or measure orientation? Different datum types will be more appropriate for different tasks. ![]() When selecting a suitable datum in engineering, it is important to consider the application, accuracy needed, geometry of parts, environment, and the type of measurements that need to be made. The underside of the movable jaw is 10mm from the datum surface but it is in the opposite direction and hence is labelled '-10'.Ĭontinue reading here: Unacceptable dimensioning practice The 15mm dimension to the centre line of the bolt and the 30mm dimension to the top of the movable jaw are dimensioned from the datum surface. ![]() In the example shown in Figure 4.2, the datum faces are the flat faces where the underside of the hardened insert contacts the step in the movable jaw. The definition of a datum feature will be dependent upon the functional performance of a particular component. Thus, the various features on a component are dimensioned with respect to datum features. Reality datum features since it is with respect to features that other features relate. ![]() The datum point or points on a component are in ![]() A datum, is a point, line or surface of a component to which dimensions are referred and from which measurements are taken during inspection.
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