A Network of Portable, Low-Cost, X-Band Radars - Doppler Radar Observations: Weather Radar, Wind Profiler, Ionospheric Radar, and Other Advanced Applications - page 200

By the term “range degradation” we mean several important sources of uncertainty
regarding radar-based estimates of rainfall: beam broadening, non-homogeneous beam
filling, partial beam occultation, overshooting and, depending on the operating frequency,
attenuation. Such sources of uncertainty in general increase with increasing range. Current
approaches to operational weather observation are based on the use of physically large,
high-power, long-range radars, which are blocked from viewing the lower part of the
troposphere by the Earth's curvature combined with orography. Hence, range degradation
is one of the main problems in QPE and certainly a key factor in the underestimation of
rainfall accumulation at far ranges with conventional long-range radars (e.g. Kitchen and
Jackson [1993], Smith et al. [1996], Meischner et al. [1997], Seo et al. [2000], Gabella et al. [2000],
Chumechean et al. [2004], Joss et al. [2006]).

This Chapter describes an alternate approach based on networks of large number of small,
low-cost, X-band radars. Spacing these radars twenty kilometers apart defeats the Earth's
curvature problem and enables the sampling of the lowest part of the troposphere using
small antennas and low-power transmitters. Such networks can provide observing
capabilities which supplement the operational state of the art radar network satisfying at the
same time the needs of multiple users. Improved capabilities associated with this
technology include low-altitude coverage and high temporal resolution. This technology has
the potential to supplement the widely spaced networks of physically large high-power
radars in use today.

Indeed, short-wavelength low-cost radar is able to fill a remarkable gap in observational
meteorology: small, low-cost, radars can be used to supplement conventional, long-range
radar networks in complex orography regions (e.g. the Alps and the Apennines), in highly
populated areas (improving urban hydrology in major towns), in sensitive regions (areas
prone to hydro-geological hazards) and along technological networks (e.g. highways, gas
pipelines, …) New important spatio-temporal scales (see Table 7), which characterize the
highly variable precipitation field can now be investigated at affordable costs thanks to
portable, low-cost, X-band weather radar developed, among others, by the Remote Sensing
Group at Politecnico di Torino.

Type of device Band Cost Coverage Sampling vol. Temporal res.

TRMM (or future GPM)
spaceborne radar

Ku (Ka) global 510 9 -10 10 m 3 Once per day

Long-range, Doppler,
dual-pol radar

S (C) 1000 to 2000 k€ 200 000 km 2 10 5 -10 9 m 3 300 s

Medium-range dual-pol radar X 200 to 500 k€ 5000 km 2 10 4 -10 8 m 3 120 s

Short-range radar X 30 k€ 2000 km 2 10 4 -10 7 m 3 30 s

Rain Gauge --- point 50 m 3 600 s

Disdrometer --- point 10 m 3 1800 s

Table 7. The observational gap filled by the new portable, low-cost X-band weather radar
network.