Title: WXT as a disdrometer?
1WXT as a disdrometer?
- Heikki Pohjola1) and Leila Konkola2)
- Vaisala Oyj
- University of Helsinki
2The opportunity
- Disdrometers are expensive and thus rare
- Global distribution of DSD is badly known
- Climatological research and radar measurements
could benefit of reasonably priced disdrometers - For example NASAs
- Global Precipitation Measurement (GPM) Program
- Satellite will be launched 2013 ?
- Understanding of clouds and rainfall processes
- Make frequent rainfall measurements on a global
basis. - FMI involved in ground validation with
HelsinkiTestbed and radar network
3Radar applications
- Set one or more WXTs toblocked sectors of radar
- combine dBZ valuesfor each image
- Gapfilling between radars
- Attenuation correction
- between the radar and the target, some microwave
power is lost. - (Barnes, S.L., 1964 A technique for maximising
details in numerical weather map analysis. Jour_.
AppI_Meteor., _3,396-409)
4Radars measurement volume, km3
0,5 km
0,5...1 km
5Radars measurement volume, km3
0,5 km
Raingauge e.g WXT, diameter 10 cm!!
0,5...1 km
6Radars measurement volume, km3
0,5 km
Raingauge, diameter 10 cm!
0,5...1 km
7Z from WXT measurement
Raincap sensor of WXT works as a disdrometer, and
measures N and D in time unit. Thus, we can
calculate reflectivity on ground Zg ?NiDi6
and avoid all fuzzy Z/R conversions
8Data
- Drop size distribution data from WXT, disdrometer
(RD-69) and POSS from Järvenpää, Sorto - WXT_Z 21.8. -gt
- RD-69 1.8. -gt
- POSS All Testbed campaings
DSD data from WXT_Z
Date Time D1.00 D1.25 D1.60 D2.00 D2.50 D3.20 D4.00 D5.00
2006-09-03 231500 10.9 57.6 23.2 9.4 3.1 0 1 1.3
2006-09-03 232000 21 44 27 3.6 2.9 0 0 2.3
2006-09-03 232500 24.9 44.6 27.6 13 1 0.7 0 0
2006-09-03 233000 16.3 41.5 18.1 2.7 1.1 0 0 0
2006-09-03 233500 4.9 15.9 7.7 6.8 1.7 0 0 0
2006-09-03 234000 15.7 49.1 63 20.7 4.6 0.7 0 0
2006-09-03 234500 25.4 57.7 34.7 11.5 1.8 0 0 0
2006-09-03 235000 3.6 6 1 0 0 0 0 0
9What next?
- Comparisons between disdrometer, WXT (and POSS)
DSD data. - If promising, first comparisons with radar
reflectivity data. - Challenges
- WXT data 5 min intervals, accuracy 5
- RD-69 data 1 min intervals, accuracy 1,4 !!!!
- Different drop diameter classes
10back up slides
11Defaults for WXT510 Disdrometer test units
- DSD test units transmit automatically in every
minute one message (so called auto composite
message) which includes wind, PTU and disdrometer
parameters in one string. - Disdrometer counters are automatically reset
after any output including disdrometer
parameters. - Example
- 0R0,Dm270D,Sm0.9M,Ta22.4C,Ua35.8P,Pa1009.7H,1
.0010.41n,1.2511.01n,1.606.45n,2.003.44n,2.50
2.98n,3.202.46n,4.000.51n,5.000.00n - Â