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Since November 20, 2009 we measured at the Meteorological Observatory Lindenberg (Richard-Aßmann-Observatory) with the L52 Lightmeter (03.02 marks V05.05 S / N 908052.1382). The Lightmeter is located on the northwest side of the radiaton platform near two modified MOBOTIX - Hemispheric Q24 security cameras for sky monitoring.

Coordinates: 52°12'32" N 14°07'17" E

Height: 127 m asl (platform)

For the extension of the USB cable from the Lightmeter to the laptop (about 10m), we used the Lindy USB Extender PREMIUM.

Measurements (previous day)

Directory listing for DE_LINDENBERG_1

Calibration 21 Feb 2010

   X = c ( b (a exp (n/a) - 1) + n ) 
   n ... counts (sensor output)
   X ... physical quantity (total radiation in [W/m²] or horizontal illumination [Lux])  
  a = 9.776e+04,  b= 1.991e-04,  c= 2.662e-09    W/m²
  a = 9.776e+04,  b= 1.991e-04,  c= 2.538e-07    Lux

Data from morning twilight and daylight, Feb. 17th 2010 2:07 - 11:00 UTC

--GuentherWuchterl 18:43, 21. Feb. 2010 (UTC)

Improved calibration 24 Feb 2010

Checks with a total radiation sensor showed up to 40% deviations near noon. In a new fit the temperature dependence is included and the total radiation model is used for nominal site parameters (dew-point temperature, surface pressure). Data are the same as above (Feb 17th morning twilight to noon).

   X = c ( b (a exp (n(1+dT)/a) - 1) + n ) 
   n ... counts (sensor output)
   X ... physical quantity (total radiation in [W/m²] or horizontal illumination [Lux]) 
   a = 1.0118e+05,   b = 4.9571e-04,   c = 2.5688e-09, d = 2.3697e-03  [W/m²]
   a = 1.0118e+05,   b = 4.9571e-04,   c = 2.3298e-07, d = 2.3697e-03  [Lux]
   Background x0=6.3 mlx

Accuracy check with independent total radiation measurement shows the calibration to be accurate to 12%. Note that the Sun used as calibrator never rises higher than 30° during the calibration period and thus accuracy of the total radiation model used for calibration is necessarily limited and the likely accuracy limiting element in the calibration.

.zip with graphs relating to the calibration and its check by independent total /global radiation measurments

There is indication for some cloud towards the begin of the morning twilight near the background.

--GuentherWuchterl 01:25, 24. Feb. 2010 (UTC)

Check, Feb 27th, repetition of calibration procedure:

  5:03 - 11:18 UTC
  a = 1.0118e5,   b = 4.9571e-4,   c = 2.5754e-9, d = 2.3697e-3    [W/m²]
  a = 1.0118e5,   b = 4.9571e-4,   c = 2.3298e-7, d = 2.3697e-3    [Lux]
  X0 = -6.2552e-3 Lux
  Conversion Lux-model to Total-radiation model
     Lux     = 90.465    Watt/m²
     Watt/m² = 0.011054  Lux

copies from python-session

   In [9]: SJD=(X.JD > mx.DateTime.DateTime(2010,2,17,5,03).jdn) 
               & (X.JD < mx.DateTime.DateTime(2010,2,17,11,18).jdn)
   In [10]: X.fit_em1_to_natLight(JD_select=SJD,type='em1c0T')
   Out[10]: (array([  1.01179142e+05,   4.95712792e-04,   2.32981477e-07
                   , -6.25516123e-03,   2.36965039e-03]),
         ,'y,', label='DM model,P=998/T_d=-9/k=2.78')
    --> In [44]: 0.778/X.Watt_per_square_meter_per_Lux      Out[44]: 90.465116279069775
    --> In [45]: 1./(0.778/X.Watt_per_square_meter_per_Lux) Out[45]:  0.011053984575835474
    In [59]: plot_date(X.JD-X.pylab_JD0
                             ,1.01179142e+05,   4.95712792e-04, 2.57537e-09
                      ,'k,',label="a,b,c,d= 1.01e5, 4.96e-4, 2.58e-9, 2.37e-3"


For the measurement of global radiation on the observatory we use a CM22 pyranometer from Kipp & Zonen, which are used to measure the intensity of the radiation on flat surfaces.


22:16, 5. Mai 2011 AndreKnoefel 

WH --GW (talk) 15:27, 28 April 2016 (CEST)