| The goal of this paper is to present a methodology to calibrate the
reflectivity of the UHF Strato-Tropospheric (ST) radar located at NAIC in Puerto
Rico. The UHF lower relevant altitude is at 5.9km, the melting layer being
at around 4.8km. The data used for the calibration came from the
observations of clouds, carried out with Strato-Tropospheric dual-wavelength
(UHF and VHF) radars and a disdrometer; those instruments being located on
the NAIC site in Arecibo, Puerto Rico. The National Weather Service operates
other instruments like the radiosondes and the NexRad Radar in other sites.
The proposed method proceeds in two steps. The first consists of the
comparison between the NexRad reflectivity and the reflectivity computed
from the drop size distributions measured by the disdrometer for one day
with a noticeable rainfall rate. In spite of the distance of both
instruments, the agreement between the reflectivities of both instruments is
enough good to be used as a reference for the UHF ST radar. The errors
relative at each data set is found to be 2.75dB for the disdrometer and 4dB
for the NexRad radar, following the approach of Hocking et al. (2001). The
inadequacy between the two sampled volume is an important contribution in
the errors.
The second step consists of the comparison between the NexRad radar
reflectivity and the UHF non-calibrated reflectivity at the 4 altitudes of
common observations during one event on 15 October 1998. Similar features
are observed and a coefficient is deduced. An offset around 4.7dB is
observed and the correlation factor lies between 0.628 and 0.730. According
to the errors of the data sets, the precision on the calibration is of the
order of 2dB. This method works only when there are precipitation
hydrometeors above the NAIC site. However, the result of the calibration
could be applied to other data obtained during the campaign, the only
constraint being the same value of the transmitter power.
Key words. Meteorology and atmospheric dynamics (tropical
meteorology; remote sensing; instruments and techniques) |