1. Thies Laser Precipitation Monitor for precipitation type detection
H. Bloemink, E. Lanzinger
KNMI/DWD
06/05/05

2. Contents
Principle
Experiment
Results
Conclusions
Recommendation

3. Principle Disdrometer (Distribution Droplets)
IR light beam with 45 cm² measuring area
Extinction measurement
amplitude: diameter
duration: fall speed

4. Temperature constraints:
Comparison to known statistics of diameter and velocity of various precipitation types
Example:
Temperature constraints:
> 9 °C: liquid (exception: hail)
< - 4 °C: solid
Output: spectra, precip type, precip intensity

5. Experiment
Data from DWD test site at Wasserkuppe (Hessen)

6. Available data: 12-10-2003 – 31-11-2003 Some processing:
Observer: 1 minute interval
Reference: includes T, RH, PI, wind speed, precip detector
Disdrometer
FD12P present weather sensor (current KNMI sensor)
Some processing:
Precip detector used for precip/no precip distinction
Time synchronisation
Averaging

7. Results
10-minute
comparison

8. In terms of verification scores:

9. Optimisation Find best possible performance using
Averaging PW for rain & snow mixtures
Use wet-bulb temperature to distinguish freezing liquid precipitation
Use wet-bulb temperature to distinguish rain and snow mixtures vs. Rain
Results: no improvement compared to the observer
Possible causes:
Disdrometer tuned to Wasserkuppe conditions?
Changes tuned to Dutch conditions & FD12P

10. Conclusions
Thies disdrometer and Vaisala FD12P show similar results for precipitation type
Thies slightly better for liquid, FD12P for solid precipitation
Test of the Thies disdrometer in Dutch weather conditions
Possible use: precipitation type for smaller weather stations, or improved precipitation type by combination with FD12P
Future

11. Acknowledgements
Wiel Wauben
Manfred Theel
Eckhard Lanzinger