Term Term Name Description
3
rd
Term
20 log r : Range Normalization This term is the range normalization
expressed in dB form.
0
2
4
th
Term
ar: Gaseous Attenuation Correction This term accounts for gaseous attenuation.
The constant a is set in the RVP900
EEPROM since it is a function of
wavelength.
For a C-band system the default value is
0.016 dB per km (for two-way path
attenuation).
5
th
Term
CCOR: Clutter Correction This term corrects for the measured ground
clutter.
See 7.4.7 Clutter Correction (CCOR
threshold) (page 205).
7.4.3.1 Noise Correction to Reflectivity Calibration
The dBZ0 number in the above equation is the number which sets the sensitivity of the
radar. Lower numbers mean greater sensitivity. In =
2
=
0
2
2
0
2
0
it was
assumed that the noise level at calibration time is the same as the noise level at run time.
And that any changes in measured noise level were due to changes in receiver gain not
sensitivity.
Modern digital receivers and low-noise amplifiers are very gain stable, and this is generally
not true. One example of a relatively large noise level variation is the thermal noise from the
relatively warm earth and atmosphere. So, the bottom degree or so of elevation has a
dierent noise level, and thus a dierent sensitivity, and thus a dierent dBZ0. Normally we
calibrate while aiming the antenna up in the air in a direction away from the surface, or the
sun. For this discussion, let us define two new noise values:
N sub c
Noise level at calibration time.
N sub r
Noise level at ray processing time.
If we answer yes to "Enable noise power based correction of Z0" in the Mp
non-volatile setup section, then the new radar equation becomes:
=
2
=
0
2
2
0
2
0
In this equation, the dBZ0 is the term
0
2
RVP900 User Guide M211322EN-J
202
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