Geoscience Reference
In-Depth Information
Antenna diameter (m)
4.2.
Antenna Gain (dB)
44.7
Beamwith (“)
0.9
Polarization
Linear hor/vert
Frequency (GHz)
5.60-5.65
Wavelenght (cm)
5.30-535
Peak power (kW)
250
Pulse lenght (µs )
0.5 - 2.0
PRF (Hz)
250, 900, 1200
MDS (dBm)
-114, -110, -109
Table 1. Cerro Catedral weather radar (Ericsson UBS 103 04, upgraded by Sigmet/Vaisala
technology) technical characteristics.
Such elevation has effects over the precipitation estimated at low level on Mexico Valley
Watershed. In order to get a good coverage of shallow rain, originating close to ground, it is
necessary to settle the elevation angles to negative value of around -1.5 degree. This has the
inconvenience of blockage, clutter and loss of signal. The weather radar usually suffers
partial or total blockade operating in mountain zones due to the complex topography
around it. This effect can limit the coverage of the radar when it use negative degrees and
affect the precipitation measurements (Joss & Waldvogel, 1990; Sauvageot, 1994; Collier,
1996 and Smith, 1998). The application of some blockage corrections to the observations
radar is worthwhile, in order to get quantitative estimation of the precipitation and it can be
combined with elimination of spurious echoes by two and three-dimensional analysis of the
topography and the storm (Krajewski &Vignal, 2001; Steiner & Smith, 2002). A promising
development in this field is related to the gradual change of weather radar concept, from a
tool for qualitative rainfall estimation to a tool for more quantitative rainfall measurement
(Borga et al., 1997).
Despite the drawback of the radar height site (1500 m above Mexico City) to follow
stratiform precipitation system, convective systems are adequately monitored. In fact, the
radar is capable of doing the full scan within convective clouds but no precipitation
estimates in clouds with a base height of less than 3500 m (Fig. 5).
Figure 6 shows the monitoring of three storm events within range of radar coverage. In
addition to tracking the storms, which would support decision makers in a warning system
in these figures one can see the fixed echoes caused by the presence of volcanoes on the
eastern side of Mexico City. This represents a serious problem in estimating precipitation,
both qualitatively and in its distribution and location, as it provides information on areas
where there is rain. Considering that the fixed echoes, whether caused by the interception of
the land or effect of the lateral lobes, they can be largely eliminated with the Doppler radar
function. However, despite all the Mexican radar, including that of Cerro Catedral, have this
feature is not used to remove these echoes.
The Doppler radar function is a great help to eliminate this kind of echo and it is important
for a better estimation of rainfall fields for hydrological or/and alert purposes. The cost of
sending false warning alerts to users, when these echoes are not removed, is high, because
once lost confidence in warnings of severe storms is difficult to recover it.
