Micro Rain Radar on the CHN roof
This page provides easy access to the data of the MRR (Micro Rain Radar) situated on the roof of the CHN-building. The Radar has been installed in June 2015 and archived data is available after July 3, 2015.
The MRR is vertically pointing with a beam width of 2°. It operates with frequency modulated continuous wave radiation at about 24 GHz, which corresponds to a wavelength of 12.5 mm. A power spectrum is recorded with 10 Hz and averaged to about 10s to calculate the reflectivity spectrum, from which the Radar moments are calculated. This pre-processed data is logged every 10 seconds and aggregated to 1 and 5 minutes. The following Radar moments are available (for explanations, see below):
Radar Reflectivity (Z), Fall Velocity (W), Rain Rate (RR), Liquid Water Content (LWC) and Attenuated Radar Reflectivity (zatt).
Spectral Reflectivities (Fn), Drop Sizes (Dn) and Spectral Drop Densities (Nn) are also archived and are available upon request.
The MRR has a height resolution of 100m and measures 31 range bins, which correspond to 100 m to 3100 m above the Radar (~ 600 m to 3600 m above sea level).
Radar Moments:
Radar Reflectivity (Z)
Attenuation corrected Reflectivity.
$$ Z = \int_{0}^{\infty} N (D) D^6 dD $$
The Rayleigh approximation for small drops, which is used by pulsed Radars (e.g. Radar network of MeteoSwiss) is not valid here, since the wavelength of the MRR is rather small (12.5 mm).
Fall Velocity (W)
Each drop size bin has a different fall velocity. W is the characteristic falling velocity determined by the first moment of the Doppler spectra:
$$ W = \frac{\frac{\lambda}{2}\int_{0}^{\infty}\eta ( f ) fdf }{\int_{0}^{\infty} \eta ( f ) df } $$
In other words: W is the reflectivity-weighted mean Doppler Velocity towards the Radar.
Rain Rate (RR)
RR is calculated with the formula:
$$ RR = \frac{\pi}{6}\int_{0}^{\infty} N (D) D^3 \nu (D)dD $$
The rain rate estimation is only valid for liquid precipitation, i.e., below the bright band (melting layer). To estimate the surface rain rate, the 3rd lowest range bin (300 m above Radar) should be used, since the lowest two bins are usually biased by near-field effects of the Radar.
Liquid Water Content (LWC)
LWC is calculated with the formula:
$$ LWC = \rho_w \frac{\pi}{6}\int_{0}^{\infty} N (D) D^3 dD $$
The LWC estimation is only valid for liquid precipitation, i.e., below the bright band (melting layer).
Attenuated Radar Reflectivity (zatt)
zatt = Z - PIA (path integrated attenuation) is the radar reflectivity without attenuation correction.