Marco Allegretti

A Network of Portable, Low-Cost, X-Band Radars

Radar is a unique tool to get an overview on the weather situation, given its high spatio- temporal resolution. Over 60 years, researchers have been investigating ways for obtaining the best use of radar. As a result we often find assurances on how much radar is a useful tool, and it is! After this initial statement, however, regularly comes a long list on how to increase the accuracy of radar or in what direction to move for improving it. Perhaps we should rather ask: is the resulting data good enough for our application? The answers are often more complicated than desired. At first, some people expect miracles. Then, when their wishes are disappointed, they discard radar as a tool: both attitudes are wrong; radar is a unique tool to obtain an excellent overview on what is happening: when and where it is happening. At short ranges, we may even get good quantitative data. But at longer ranges it may be impossible to obtain the desired precision, e.g. the precision needed to alert people living in small catchments in mountainous terrain. We would have to set the critical limit for an alert so low that this limit would lead to an unacceptable rate of false alarms

Preliminary analysis to design a 77 GHz weather radar

The European Telecommunications Standards Institute (ETSI) defines the frequency band around 77 GHz as the one dedicated to automatic cruise control long-range radars. This work presents the preliminary analysis for the design of a mini weather radar and/or a microwave rain gauge operating at such a frequency. Firstly, the Mie scattering formulation applied to a weather radar working in the W-band is briefly introduced, then the operative conditions are described in order to define the system functional requirements. Atmospheric attenuation, including the contribution due to water vapor, is estimated taking into account the ITU-T recommendations. The technical specifications are evaluated in order to meet the functional requirements, paying particular attention to the use of already developed components for radars installed on cars. A sensitivity analysis of the system is also given considering the proper relationship between the radar reflectivity factor Z and the rain rate R determined for a 77 GHz radar. Results provide the basis for the design and realization of a 77 GHz weather radar.

Identification of New Road Segments Using a Modified Version of the K-means Algorithm

The present work explains how to identify transformation and new road segments in existing electronic maps by using data coming from devices carried on board on different vehicles, by using a modified version of a standard clustering algorithm called k-means. The working dataset appears as sparse clouds of points with their centres over the road segments, including other different data. Because of the spatial distribution of the points and in order to allow the algorithm to converge in a short number of steps, a simple modification has been implemented. With respect to the standard k-means algorithm which works with a fixed number of clusters, the present modified version works with a large initial number of clusters, with sizes defined a priori on the basis of the smallest possible road segment. The number of clusters is progressively reduced considering, for each steps, only the clusters including a number of points above a specific thresholds. At the end of the algorithm, all the identified clusters are superimposed over a common map in order to validate if a new road segment is identified. The algorithm has been applied on different datasets acquired on the road network of Turin with good results allowing the identification of new road segments not present in the reference map and one-way roads (change in travel direction).