Lysbilde by mikeholy

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									  Radar Data Quality – the Challenge
  of Beam Blockages and
                  Rissa
  Propagation Changes
Uta Gjertsen, met.no
Günther Haase, SMHI


 With thanks to Joan Bech, meteocat




Toulouse 5.9.-9.9.2005                 Meteorologisk Institutt met.no
  Why radar data quality?
Composite of
  radar-derived
  precipitation

Do we trust the
  spatial
  distribution?

What about
  blockages,
  overshooting,
  anaprop etc?

                            Meteorologisk Institutt met.no
Suggested NORDRAD quality projects:
a) Beam Propagation Project
b) VPR                    Background: Issues concerning          the
                               propagation of the radar beam are
                               identified as being of great importance
                               for the quality of radar reflectivity and
                               precipitation products.

                               Objective: The objective of the proposed
                               project is to coordinate the work carried
                               out in the NORDRAD member countries to
                               define common algorithms for addressing
                               these challenges.

                               Deliverables: site maps for each
                               NORDRAD radar in polar coordinates to
                               correct beam blockage

                               implementation of the correction fields
                               in the NORDRAD2 system to improve the
                               accuracy of precipitation estimates in
                               blocked regions

                                                            Meteorologisk Institutt met.no
    BPM output and 1-year
    accumulation for radar Bømlo




Height of lower beam edge 0.5   accumulated precipitation
degree elevation                   for 2004

                                            Meteorologisk Institutt met.no
Correction field for precipitation

                                                   y  * a2
                           y a 2  y 2  a 2 arcsin 
                      BB                          a   2
                                          * a2
                    (BB=beam blockage, y=distance center beam -
                    topography, a=radius radar beam cross section)


                                                            1
                                      1                   b
                             bcorr          
                                      1  BB 
   50%   1.54         (bcorr=correction factor for precipitation,
   60%   1.77         b=Marshall-Palmer b coefficient)

   70%   2.12
                                                  Meteorologisk Institutt met.no
                                 Radar Bømlo


                             *                          =

Uncorrected precipitation         Correction filed            Corrected precipitation




                             -                            =

   Corrected precipitation        Uncorrected precipitation          Corrected areas
                                                                             Meteorologisk Institutt met.no
Blockage correction at station 46610, 75
km from radar, daily accumulations 2004
                   uncorrected
                                         corrected
                   RMSf = 3.39
                                         RMSf = 2.65




                                                                               1
                                            1
                                                  n
                                                        Ri 
                                                                       2
                                                                           
                                                                           
                                                                               2
                                 RMSf  exp 
                                            N
                                                  ln  Gi 
                                                 i 1      
                                                                           
                                                                           
                                                                          



                                                 Meteorologisk Institutt met.no
40-100 km from radar

 14 stations




                       Meteorologisk Institutt met.no
100-160 km from radar

 24 stations




                        Meteorologisk Institutt met.no
RMSf and mean bias for different distances
and blockages

                    RMSf                bias(10*log10(radar/gauge)
      km   40-100   100-160   160-240         km   40-100   100-160 160-240
bb                                      bb
0%         1.73     3.45      14.58     0%         -2.33    -5.19          -11.17

1-         2.73     11.75     37.16     1-         -4.17    -9.33          -15
50%        2.19     9.7       30.7      50%        -3.22    -8.5           -14.17
50-        8.27     40.7      167.5     50-        -9.3     -14.96         -21.44
70%        4.57     22.75     97.19     70%        -6.5     -12.29         -19.05

Black=uncorrected
Blue= corrected




                                                             Meteorologisk Institutt met.no
  What about anaprop?
Radar Bømlo, Western Norway   Radar Hemse, Gotland, Sweden




                                             Meteorologisk Institutt met.no
Radar Bømlo and radiosonde Sola 1415




Time series of IDmax and IDmin for station Sola



                                    Radiosonde data from closest station is used to
                                      identify anaprop cases, the cases are studies
                                      to assess the influence of propagation
                                      changes on the degree of blockage
                                    The importance of using temporally/spatially
                                      variable correction fields

                                                                    Meteorologisk Institutt met.no
anaprop case 9.7.2005, 00:00 UTC
                        Precipitation intensity product




               Normal atmosphere                Radiosonde data




                                                    Meteorologisk Institutt met.no
               Summary and conlusions
Correction fields produced by BPM reduce the gauge/radar bias at
    radar Bømlo
The improvement is dependent on the distance from the radar and
    the degree of blockage
The BPM seems to give realistic output for normal conditions and
    cases with anaprop
The effect of anaprop on the degree of blockage will be
    investigated to see whether spatially/temporally variable
    correction fields are necessary
The use of radiosondes and NWP data (HIRLAM) as input to the BPM
    will be investigated
It is intended to integrate the blockage correction into the
    operational NORDRAD system



                                                    Meteorologisk Institutt met.no

								
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