Geoscience Reference
In-Depth Information
The radar is fully coherent pulsed Doppler and pertinent parameters are listed in Table 2
(see also Doviak & Zrnic, 2006 page 47). Each radar is assigned a fixed frequency in the band
(Table 2), hence some values like the beamwidth and unambiguous velocities (not listed)
depend on the exact frequency.
Frequency
Beamwidth
Antenna gain
2.7 to 3 GHz
1°
44.5 to 45.5 dB
Transmitter:
Pulse power
Pulse width
Rf duty cycle
PRFs (Hz, 5 sets of 8, variation ~3% )
Unambiguous range (km)
750 kW
1.57 μs and 4.57 μs
0.002
322, 446, 644, 857, 1014, 1095, 1181, 1282
466, 336, 233, 175, 148, 137, 127, 117
Receiver linear:
Dynamic range
Intermediate frequency (IF)
A/D converter at IF
Sampling rate
Noise figure
94 dB at 1.57 μs pulse and 99 dB at 4.57 μs
57.6 MHz
14 bits
71.9 MHz
-113 dBm at 1.57 μs and -118 dBm at 4.57 μs
Filter bandwidth or type:
Front end analogue
IF Digital matched, short/long pulse
Radial spacing in azimuth
6 MHz (3 dB bandwidth)
Output samples spaced at 250 m/500m
1
o
or 0.5
o
Table 2. Radar characteristics.
The data coming out of the RDA consist of housekeeping (time, pointing direction of the
antenna, status, operating mode, and fields of reflectivity factor, mean radial velocity, and
spread of velocities (designated as R, V, W in the console, Fig. 1), collectively called
spectral moments. A wideband communication link is used to exchange base data and
radar status/control between RDA and RPG. Depending on distance this link is by direct
wire (up to 120 m), microwave line-of-site (to 38 km), or telephone company T1 line
(unlimited).
Pulse of high peak power and narrow width (Table 2) generated at the output of the power
amplifier is guided to the antenna. It is radiated in form of electromagnetic (EM) field
confined within the narrow (1
o
) antenna beam. The propagating EM field interacts with
intervening scatterers (precipitation, biological, and other). Part of the field is reflected
forming a continuous stream at the antenna where it is intercepted and transformed for
further processing by the receiver. Concise mathematical expression for the magnitude of
the electric field at a distance
r
from the radar is
1/2
P
f
(,)
r
a
E
cos 2
f
t
U t
(
r
/ ),
c
(1)
t
2
r
c
