Geoscience Reference
In-Depth Information
7
A Network of Portable, Low-Cost,
X-Band Radars
Marco Gabella 1,2 , Riccardo Notarpietro 2 , Silvano Bertoldo 3 , Andrea Prato 2 ,
Claudio Lucianaz 3 , Oscar Rorato 3 , Marco Allegretti 3 and Giovanni Perona 3
1 Meteoswiss
2 Politecnico di Torino - Electronics Department,
3 Consorzio Interuniversitario per la Fisica delle Atmosfere (CINFAI) - Sede di Torino
1 Switzerland
2,3 Italy
1. Introduction
1.1 Excellent qualitative overview of the weather in space and time
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.
1.2 Range dependence of the results (range degradation)
Perhaps accurate quantitative precipitation estimation (QPE) can only be achieved at short
ranges from the radar. This is not because we miss careful investigations, but simply,
because radar can only see the hydrometeors aloft, while we would need to know what is
arriving at ground level. Obstacles as well as earth curvature lead to a limited horizon,
allowing us to see precipitation at variable height, often too far from the ground. All these
difficulties increase rapidly with range from the radar location. The situation becomes
obviously much more difficult in mountainous terrain, where weather echoes can only be
detected at high altitudes because of beam shielding by relieves: there, terrain blockage
combined with the shallow depth of precipitation during cold seasons and low melting
levels causes inadequate radar coverage to support QPE, especially in narrow valleys.
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