5,285 research outputs found
A comparison of various geometrical feature for damage assessment in VHR urban imagery
No full textUrban areas require scene interpretation tools with particular attention to geometric
features. Indeed, spatial analysis must be coupled to spectral characterization of ur-
ban materials if reliable and suitable land use or change detection maps needs to be
extracted. This is particularly true for Very High spatial resolution (VHR) imagery,
increasingly available both in the optical and the microwave regions of the electro-
magnetic spectrum.
In past work on spaceborne characterization of urban areas the most common geomet-
rical clues to scene interpretation in urban areas have always been segments, or edges.
They were used for instance for land use discrimination [1] or improved change detec-
tion techniques [2]. More complex geometrical features have been traditionally used
for aerial image interpretation, with a long experience due to the longer availability
of finer spatial resolution data. In the near future the availability of VHR data from
spaceborne platforms requires somehow a convergence of the two methodologies.
In this work, we try and analyze the possibility to exploit higher level geometrical
features, easily available in urban areas from VHR spaceborne imagery, to extract
information which not only improve change detection, but somehow allows a better
damage characterization than currently available. The methodology tries and exploits
the same clues to image interpretation that human interpreters usually look for in an
image. Examples are regular geometrical patterns (like rectangular shapes), pairs of
corresponding and parallel segments, corners with sufficient similarity. All of them
will be extracted and considered in the examples proposed in the final paper to improve
the possibility to detect or assess change due to destructive events in urban areas.
The algorithms developed in recent years by the group for geometrical scene analyysis [3] segment extraction [4] and junction detection [5] will be therefore revised
and jointly applied to improve the knowledge of pre-and post-event scenes in areas
affected by earthquakes, with particular stress on Quickbird data for the 2003 Bam
(Iran) event.
RE F E RE NCE S
1. J. Wang and P.J. Howarth: “Structural measures for linear feature pattern recog-
nition from satellite imagery,” Canadian Journal of Remote Sensing, vol. 17, pp.
294–303, 1991.
2. F. Dell’Acqua, P. Gamba, G. Lisini: “Change Detection of Multi-Temporal SAR
Data in Urban Areas Combining Feature-Based and Pixel-Based Techniques”,
IEEE Trans. on Geoscience and Remote Sensing, vol. 44, n.10, pp. 2820-2827,
Oct. 2006.
3. G. Lisini, F. Dell’Acqua, P. Gamba, W. Thompkinson: “Image interpreta-
tion through problem segmentation for very high resolution data”, Proc. of
IGARSS’05, Seoul (Korea), July 2005, pp. 534-5637.
4. F. Dell’Acqua, P. Gamba, G. Lisini: “Road map extraction by multiple detectors
in fine spatial resolution SAR data”, Canadian Journal of Remote Sensing, Vol.
29, n. 4, pp. 481-490, Aug. 2003.
5. F. Dell’Acqua, P. Gamba, G. Lisini, “Co-registration of multi-angle fine spatial
resolution SAR images”, IEEE Geoscience and Remote Sensing Letters, Vol. 1,
n. 4, pp. 237-241, Oct. 2004
The impact of social pressure on tax compliance: A field experiment
No full textWe study the effect of social pressure on tax compliance, focusing on the compliance of shop sellers to the legal obligation of releasing tax receipts for each sale. We carry out a field experiment on bakeries in Italy, where a strong gap exists between the legal obligation and the actual behavior of sellers. Social pressure is manipulated by means of an explicit request for a receipt when not released. We employ an innovative approach to the identification of the treatment effect. We find that a single request for a receipt causes a 17 per cent rise in the probability of a receipt being released for a sale occurring shortly thereafter, causing on average more than two receipts to be released. We also find strong evidence of persistence in compliance decisions
When the two ends meet: an experiment on cooperation across the Italian North-South divide
No full textWe study the behavior of individuals coming from different geographic regions of Italy, in a same public good game. We confirm previous findings according to which, faced with the same incentives and experimental conditions, Southern citizens exhibit a lower propensity to cooperate than Northern ones. This difference is mainly explained by a gap in the impact of coordination devices available to participants, as we show by manipulating them. Most importantly, when subjects with different geographic origins are teamed up together, their contributions decrease with respect to homogeneous groups, again because of a reduced effect of coordination devices. These findings reinforce the interpretation of the Italian South-North divide as related to trust, prejudice and a consequent path-dependence in levels of social capital, rather than due to the mere effect of differences in institutions and economic opportunities
COVID-19: R0 is lower where outbreak is larger
No full textWe use daily data from Lombardy, the Italian region most affected by the
COVID-19 outbreak, to calibrate a SIR model individually on each municipality.
These are all covered by the same health system and, in the post-lockdown phase
we focus on, all subject to the same social distancing regulations. We find
that municipalities with a higher number of cases at the beginning of the
period analyzed have a lower rate of diffusion, which cannot be imputed to herd
immunity. In particular, there is a robust and strongly significant negative
correlation between the estimated basic reproduction number () and the
initial outbreak size, in contrast with the role of as a emph{predictor}
of outbreak size. We explore different possible explanations for this
phenomenon and conclude that a higher number of cases causes changes of
behavior, such as a more strict adoption of social distancing measures among
the population, that reduce the spread. This result calls for a transparent,
real-time distribution of detailed epidemiological data, as such data affects
the behavior of populations in areas affected by the outbreak
When the two ends meet: an experiment on cooperation across the Italian North-South divide
No full textWe study the behaviour of individuals with different geographic
origins interacting in a same public good game. We exploit the peculiar composition of the experimental sample to compare the performance of groups where individuals have mixed origins to homogeneous
groups. We find that, despite the absence of any geographic framing, mixed groups exhibit significantly lower contributions. We also
find that cooperation levels differ significantly across geographic
origins, in line with the existing literature. This is explained by a different impact of coordination opportunities, such as communication,
as we show by manipulating them. Our results point towards integration as a crucial aspect for the economic development of intercultural
societies. They also confirm that, rather than being explained just by
the differences in institutions and economic opportunities, the Italian
North-South divide embeds elements of distrust, prejudice and a
consequent path dependence in the level of social capital
Improving Reliability in Nonlinear Hyperspectral Unmixing by Multidimensional Structural Optimization
No full textMapping vegetation in urban areas using Sentinel-2
No full textThe rapid expansion of cities globally leads to new challenges related to quality of life and health. The presence and fractional distribution of vegetation within urban cities directly impact the life and health of urban dwellers. This paper presents an approach to map urban vegetation from Sentinel-2 data. The twin Sentinel-2 satellites offer a 5-day revisit time global coverage at unprecedented spatial and temporal resolution. The temporal resolution allows for seasonal aggregation of the input data, thus providing phenological information. By considering seasonally aggregated Normalized Difference Spectral Vector (NDSV), a classification was performed using Random Forest (RF) and compared with Classification and Regression Trees (CART) and Support Vector Machines (SVM)
Possibilities and Limits of Urban Change Detection Using Polarimetric SAR Data
No full textThis paper introduces the topic of urban change detection by means of fully and dual polarized multitemporal spaceborne SAR data. The aim is to be able to detect not only urban extent expansion/shrinking phenomena, but changes that may affect both the two- and the three-dimensional landscape. For fully polarized SAR, we further validate and refine a recently introduced approach based on superpixel segmentation followed by the computation of selected polarimetric parameters and the analysis of the difference among feature vectors using specialized distance metrics. As for dual polarized SAR data, a combination of interferometric and polarimetric features within the same framework is proved to perform decently, but no real advantage if using polarimetry is obtained. Test cases using UAVSAR and Sentinel-1 data are presented in support of the proposed techniques
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