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

Thies Laser Precipitation Monitor for
precipitation type detection
H. Bloemink, E. Lanzinger
KNMI/DWD
06/05/05
Contents
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Principle
Experiment
Results
Conclusions
Recommendation
Principle
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Disdrometer (Distribution Droplets)
IR light beam with 45 cm² measuring area
Extinction measurement
 amplitude: diameter
 duration: fall speed
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Comparison to known statistics of diameter and
velocity of various precipitation types
Example: Diameter (mm) Fall speed (m/ s)
0.2 (drizzle)
0.3 (drizzle)
0.8 (rain)
0.9 (rain)
1.8 (rain)
2.2 (rain)
3.2 (rain)
5.8 (rain)
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Temperature constraints:
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0.73
1.2
3.3
3.7
6.1
6.9
8.3
9.2
> 9 °C: liquid (exception: hail)
< - 4 °C: solid
Output: spectra, precip type, precip intensity
Experiment
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Data from DWD test site at Wasserkuppe (Hessen)
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Available data: 12-10-2003 – 31-11-2003
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Observer: 1 minute interval
Reference: includes T, RH, PI, wind speed, precip
detector
Disdrometer
FD12P present weather sensor (current KNMI
sensor)
Some processing:
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Precip detector used for precip/no precip distinction
Time synchronisation
Averaging
Results
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Thies

10-minute
comparison
FD12P

Observer 
no
liquid mixed solid total
%
precip
5077
0
0
0 5077 100.0
no precip
398
339
33
14
784
43.2
liquid
0
0
12
3
15
80.0
mixed
89
2
3
230
324
71.0
solid
5564
341
48
247 6200
total
91.2
99.4
25.0
93.1
%
91.4
total %
Observer 
no
liquid mixed solid total
%
precip
5027
13
0
5 5045
99.6
no precip
51
356
29
2
438
81.3
liquid
0
1
8
3
12
66.7
mixed
439
21
11
299
770
38.8
solid
5517
391
48
309 6265
total
91.1
91.0
16.7
96.8
%
88.6
total %
FD12P 
Thies

no
liquid mixed solid total
%
precip
4722
32
0
329 5083
92.9
no precip
439
514
7
213 1173
43.8
liquid
0
6
4
8
18
22.2
mixed
85
2
2
380
469
81.0
solid
5246
554
13
930
6743
total
90.0
92.8
30.8 40.9
%
60.0
total %
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In terms of verification scores:
phase
liquid
mixed
solid
POD
0.99
0.25
0.93
FAR
0.57
0.2
0.29
FAR*
0.12
0.2
0.02
H SS*
0.84
0.36
0.93
H SS
0.57
0.38
0.80
Table 1. Verification scores for the Thies disdrometer.
phase
liquid
mixed
solid
POD
0.91
0.17
0.97
FAR
0.18
0.33
0.61
FAR*
0.08
0.33
0.10
H SS*
0.82
0.24
0.89
H SS
0.84
0.26
0.52
Table 2. The verification scores for the FD12P.
Observer 
Instrument

Y
N
Y
a
b
POD=a/ (a+b)
FAR=c/ (a+c)
H SS=(ad-bc)/ ((ad-bc)+ ½n(b+c) )
* : only cases obs reports precip
N
c
d
:0 –1
:1 –0
: -1 – 1, with 0 random
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Optimisation
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Find best possible performance using
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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:
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Disdrometer tuned to Wasserkuppe conditions?
Changes tuned to Dutch conditions & FD12P
Conclusions
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Thies disdrometer and Vaisala FD12P show similar
results for precipitation type
Thies slightly better for liquid, FD12P for solid
precipitation
Future
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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
Acknowledgements
Manfred Theel
Wiel Wauben
Eckhard Lanzinger