KNMI check gauge

Document Sample
KNMI check gauge Powered By Docstoc
					Investigations into
the improvement of
automated
precipitation type
observations at KNMI



Marijn de Haij
Wiel Wauben
KNMI
R&D Information and Observation Technology




TECO-2010, Helsinki | 31 August 2010
Contents

• The main issues

• Investigation of new sensors

• Conclusions and outlook




TECO-2010, Helsinki | 31 August 2010
Precipitation type observation
    Visual observations in SYNOP/METAR
    issued by KNMI fully automated using
    Vaisala FD12P scatterometers, with
    exception of 2 airports
    Combines optical (~size) and DRD12
    detector (~water content) signals
    Differences with human observer analyzed
    and reported to users (e.g. Wauben, 2002)

Most important issues:
- Discrimination of mixed/solid precipitation
- Classification of light precipitation events
- Detection of hail
- Precipitation detection in fog (MOR<400m)
                                                        FD12P De Bilt Test



3
                                     TECO-2010, Helsinki | 31 August 2010
Comparison with human observer
    Overlapping hourly observations at 6 KNMI stations in 2000-2002
    Correction rules and averaging applied on 1-min sensor data

        Precipitation            Liquid                 Freezing                 Solid
                 FD12P                    FD12P                  FD12P                   FD12P
        Obs      yes    no       Obs      yes    no     Obs      yes     no     Obs      yes     no
        yes       16729  3600    yes       15055  3650 yes         28      28   yes        808     466
        no         4224 117657   no         4261 119244 no         33    142121 no         181   140755

        POD              82%     POD               80%    POD             50%    POD              63%
        FAR              20%     FAR               22%    FAR             54%    FAR              18%
        CSI              68%     CSI               66%    CSI             31%    CSI              56%
        HSS              78%     HSS               76%    HSS             48%    HSS              71%
        BIAS             1.03    BIAS              1.03   BIAS            1.09   BIAS             0.78
        N               24553    N                22966   N                89    N                1455



    Poor skill scores found for freezing and solid precipitation
    Additional rules based on RH, TA, MOR evaluated with reference set
    Further improvement not likely -> test with „new‟ instruments

4
                                                          TECO-2010, Helsinki | 31 August 2010
Investigation of new sensors (2008-2010)
  KNMI selected four commercially available sensors:
- with the potential to improve the observation (combined w/ FD12P)
- which are suitable for use at AWS at an affordable price tag
         Ott Parsivel, Thies LPM, Lufft R2S, Vaisala WXT520

Setup:
 Field test in De Bilt September 2008-March 2010
 Additional data: FD12P (2x), rain gauge, wind, PTU, …
 Assessment of possibilities for indoor check
Reference:
 Evaluation by data validation specialists (10-min) and meteorologists
 (hourly) in a web tool
 Only precipitation type is used – wawa without intensity indication

5
                                   TECO-2010, Helsinki | 31 August 2010
  Sensors under test
Ott Parsivel                                           Thies LPM
Optical disdrometer                                    Optical disdrometer
51cm2 sheet, 650nm                                     46cm2 sheet, 785nm
Extinction-> D,v                                       Extinction-> D,v
8 types:                                               9 types:
L,LR,R,LRS,S,SG,SP,A                                   P,L,LR,R,LRS,S,IP,SG,A



Lufft R2S                                              Vaisala WXT520
24 GHz Doppler radar                                   RAINCAP Ø94mm
Frequency shift-> v                                    Drop impact-> volume
4 types:                                               Distinction rain/hail:
R,LRS,S,A                                              R,A




  6
                       TECO-2010, Helsinki | 31 August 2010
Example 16 January 2010: wintry precipitation

    Transition from liquid to solid
    precipitation around 19UT

    Captured well by disdrometers,
    2 FD12P sensors show difference

    R2S: mixture reported due to
    temperature threshold 4˚C

    Meteorologist confirms light
    drizzle detections of LPM



7
                                      TECO-2010, Helsinki | 31 August 2010
Example 16 January 2010: wintry precipitation (2)



                                                              First report LRS/S

                                                              R2S       1615
                                                              PAR       1842
                                                              LPM       1845
                                                              FD12      1853




8
                            TECO-2010, Helsinki | 31 August 2010
Example 15 December 2008: dense fog

    Dense fog event identified in the
    evening (MOR<200 m), just
    above 0˚C

    Both FD12Ps report snow and
    snow grains at max. 0.03 mm/h

    Other sensors do not report
    precipitation, as confirmed by
    meteorologist




9
                                        TECO-2010, Helsinki | 31 August 2010
Results: evaluation
 Hourly evaluation performed by meteorologist beside normal duties

 Selection of events where disagreement with FD12P was indicated
 Results (≠ skill scores):

             Hourly observations                                 10-min observations

            # obs.      # OK / N / NOK                         # obs.           # OK / N / NOK

     LPM     141          56 / 0 / 85        LPM                 269             232 / 7 / 30

 Parsivel    141          31 / 0 / 110     Parsivel              269             184 / 0 / 85

FD12oper     141          22 / 0 / 119    FD12oper               269            107 / 21 / 141




10
                                         TECO-2010, Helsinki | 31 August 2010
Results: general impression
 Technically OK for 18 months without maintenance
 Frequency distribution (10-min)


 LPM: UP due to spiders, some
 added value for hail and classification
 of light events, no detection in fog
 Parsivel: high FAR for hail types,
 insensitive to L/SG, solid “spider”
 reports (no T included)
 WXT520: no hail events reported,
 although 3 confirmed cases
 R2S: high FAR for LRS, insect
 detections, threshold D≥0.3mm


11
                                           TECO-2010, Helsinki | 31 August 2010
Conclusions and outlook
 None of the automated systems has perfect performance
 Thies LPM is able to partially solve the issues encountered with the
 precipitation type observation by the FD12P
 Analysis of the improvement limited due to availability of reference

Winter 2010-2011:
 Second test of LPM disdrometer at airports Schiphol and Rotterdam
 Entry of PW changes on a 1-minute basis by human observer
 Optimization of combination FD12P/LPM for precipitation type
LPM issues that still need to be addressed:
 Contribution of false reports by spider(web)s
 Sensitivity/threshold
 Wind effect on the determination of the precipitation type

12
                                   TECO-2010, Helsinki | 31 August 2010
     Thanks for your attention!
         See paper 3(2) for further details




13
                         TECO-2010, Helsinki | 31 August 2010
14
     TECO-2010, Helsinki | 31 August 2010
15
     TECO-2010, Helsinki | 31 August 2010
Indoor check
 Setup of test for homogeneity and                                                                                                                    Peristaltic
 reproduceability of disdrometers                                                                                                                       pump


 Prior to field test and after 1 year
 Problem: accurate positioning of drops
 in the light sheet!
                   LPM Tel3: average normalized drop volume (surface plot)                                                                             Droplet
                                                                                                                                                        plate

                                                                                               -10.0




                                                                                                       distance across beam (mm)
                                                                                               -5.0
                                                                                                                                                        Sensor
                                                                                               0.0


                                                                                               5.0


                                                                                               10.0                                                                       Scale
     L01    L02      L03    L04      L05         L06     L07       L08       L09     L10     L11
     14.0   34.0     54.0   74.0     94.0       114.0   134.0     154.0     174.0   194.0   214.0
                              position, distance along beam (mm)




                        0.00-0.20   0.20-0.40     0.40-0.60     0.60-0.80    0.80-1.00

       Good agreement with Thies factory calibration
16
                                                                                                                                   TECO-2010, Helsinki | 31 August 2010
Contingency table 2000-2002

                FD12P PWc
     Observer     N/A     C         P          L       LR      R      ZL         ZR        LRS       S        IP        SG       IC       SP       A       Sum
       N/A          719   7494       42         282     154     663        17         9        2         10               4                                  9396
         C         5230 117657      353        1234     248    2233        13         3       17         47        11    65                                127111
         P            2     25        3           1       7     253                            2          3                                                   296
         L          310   1535       46         987     121     465        1           1       5          3                                                  3474
        LR           98    182       20         760     365     940        2           2       3          2                                                  2374
         R          545   1722      106        2014    1694    7709                    1      13          4                                            2    13810
        ZL                  12        6           1                        6           3                  1               2                                    31
        ZR                   2                                    3        2          17                                  1                                    25
       LRS           11     20          14       32      19     107                    2      65      35            4     7                                   316
         S            5     64          22       10       4      22        1           1      81     442           26    59                                   737
        IP                                        1               3                    2               1                  1                                     8
        SG              7     20        2         3       2       1        4                     5    30           4     19                                    97
        IC                                                                                                                                                      0
        SP           8     16           15        6       6      54                           16         9         2         2                                134
         A           2      2                             1      10                                                                                            15
       Sum        6937 128751       629        5331    2621   12463        46         41     209     587           47    160          0        0       2   157824
       N/A       9.9%       Band0 89.5%      Band0*   47.3%   Band1 93.9%       Band1*     78.2%




17
                                                                                TECO-2010, Helsinki | 31 August 2010
         Amplitude  Diameter
         Duration  Velocity




18
     TECO-2010, Helsinki | 31 August 2010
 Classification FD12P vs disdrometer
         Vaisala FD12P                 Disdrometer (bv. Ott/Thies)




Optisch/DRD12 =                  + evt. temperatuur
“grootte”/”waterinhoud”
+ temperatuur
+ max. deeltjesgrootte
 19
                          TECO-2010, Helsinki | 31 August 2010
Intermezzo scores

                   other method

     event
                                       Probability of detection
                   yes      no
                                       POD = hit / (hit+miss)


                                       False alarm rate
             yes    hit    miss
                                       FAR = false / (hit+false)
referen
   ce
                                       Critical succes index
             no    false   none
                                       CSI = hit / (hit+miss+false)


20
                                  TECO-2010, Helsinki | 31 August 2010
Example 26 May 2009: hail event

 Parsivel and LPM report hail
 between 0215 and 0225UT

 Temperature drops 5˚C, radar
 summer hail chance >90%
 But unfortunately no evaluation

 Other sensors report heavy rain,
 including both FD12Ps




21
                                    TECO-2010, Helsinki | 31 August 2010
Overview
Precipitation type       PW                  NWS               METAR
                        code                 code               code
No precipitation         00                     C                -
Unknown precipitation    40                     P               UP
Drizzle                  50                     L               DZ
Freezing drizzle         55                    ZL              FZDZ
Drizzle and rain         57                    LR              DZRA
Rain                     60                     R               RA
Freezing rain            65                    ZR              FZRA
Drizzle/rain and snow    67                   LRS              RASN
Snow                     70                     S               SN
Ice pellets              75                    IP               PL
Snow grains              77                    SG               SG
Ice crystals             78                    IC               IC
Snow pellets             87                    SP               GS
Hail                     89                     A               GR

22
                        TECO-2010, Helsinki | 31 August 2010

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:36
posted:5/28/2011
language:Dutch
pages:22