The ZPHI ® software implements three patents brought by CNRS to NOVIMET, CNRS becoming a share holder of the company.
In 2017, NOVIMET set a fourth patent which improve the algorithm by a better consideration of the precipitations spatial variability.
ZPHI ® takes advantage of the “dual polarization” radar technology to extract the value of the intensity of rain with unprecedented precision.
ZPHI ® features are:
- MesMeasurement of the rain rate on the ground, with a precision better than a gauge.
- Separation of precipitation echoes from clutters (ground clutter or sea).
- Classification of different types of precipitations (rain, snow, sleet, hail).
The specific advantages of ZPHI ® lies in the fact that:
- It corrects the estimation of the rain rate from the attenuation effects (for C-band and X-band).
- It adapts itself to the natural variability of the rain, adjusting automatically the convertion “radar signal → rain intensity”, without degrading the spatial resolution of the input data…
- It allows you to check the internal absolute calibration of the radar.
- It has a module for classification of types of precipitations also suitable for attenuated band frequencies.
The ZPHI ® algorithm is applicable to X-band (~ 9 GHz), C-band (~ 5 GHz) and S-band (~ 3 GHz).
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Figure 1 : Internal calibration tool associated with the ZPHI ® operating system developed by NOVIMET. Left: before calibration, the scatterplot KDP / Z as a function of ZDR, whose average is shown in black, deviates from the theoretical curves (in color). Right: correcting the calibration of 3 dB, it refocuses the chart on the theoretical curves.
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Figure 2 : Verification of the effectiveness of the calibration correction by comparing the estimate data of the radar with the ground rain gauges. Before calibration (left diagram), the radar rain rate is overestimated compared to the rain gauges on the ground. After applying the correction of +3 dB, the bias disappears and the statistical scores have improved dramatically.
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Figure 3 : 24 hours precipitated rain before calibration correction (left) and after correction of +3 dB (right image). We note that the most intense rainfall is reduced, while low to moderate rainfall are amplified effect expected by the theory.
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Figure 4 : PPI at the 2.4 ° elevation in a squall line observed by X-band polarimetric radar (radar HYDRIX Mont Vial, 20km north of Nice). Left: field reflectivity (dBZ). Right: classification of type of precipitations (blue: rain, red: hail, violet: melting snow, white: snow, yellow: ground clutter).