Difference between revisions of "Kepler-Sternwarte Linz"

Revision as of 09:40, 30 June 2014

thumb|right|Kepler-Observatory Linz, seen from South-Southwest. The Lightmeter is mounted on top of the 3,5m pole at far right. thumb|right|Kepler-Observatory Linz, seen from South-Southeast The Lightmeter (Mark 2.2) at the Kepler-Observatory in Linz, Austria (48° 17' 36.3" North, 14° 16' 06.0" East [1], 344m ASL) is mounted on top of a 3,5m pole on the balcony of the observatory building, to avoid shading by the dome as much as possible. To connect the Lightmeter with the PC, a ~7m extension of the USB cable is necessary.

After some initial problems (see below), the lightmeter started continuous sky monitoring on 2009-04-21.

Preliminary Calibration

Accoring to Günther Wuchterl, the preliminary calibration for the Lightmeter #3 is:

• For < 1 lux: Lux = 3E-7 * counts (calibrated with a hand-held luxmeter)
• For > 1 lux to at least 20'000 lux: Lux = 2E-6 * (counts+exp(counts/8.7E4))

The latter is precise to ±10% on Lightmeter #2.

Final Calibration

Results of final calibration (described in detail here: Calibration example Linz):

   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 = 1.2835e+05,  b = 1.6468e-02,  c= 2.5778e-09  d= 3.4726e-03 W/m²
  a = 1.2835e+05,  b = 1.6468e-02,  c= 3.1887e-07  d= 3.4726e-03 Lux
 
  Background X0 = 6.741 mlx

Problems

There were two problems with Lightmeter in Linz. First, switching the fluorescent lamps on or off inside the observatory building crashes the Luxmeter driver. Second, due to the cable extension needed, the USB connection was unstable. A workaround for the first problem can be achived by setting up the software so that PC reboots every time the driver crashes. The solution for the second problem was found in using a USB-Extender USB-RJ45, which uses a 10m network cable to extend the original Lightmeter cable to the PC, and to use Jörg Weingrill's Skysensor-Software, which reboots the PC in case of USB errors.

For a more detailed description of the problems (in German language), see Lightmeter-Driver#USB-Fehler_am_Linzer_Luxmeter.

Sometimes, there is apparently a problem with the USB connection, no data is recorded, the Skysensor-Software does display "Error" in the status line, but still does not reboot the PC. On several occasions, this has gone unnoticed for several days, leading to long gaps in the measurements. To avoid this, we have installed a scheduled task which reboots the PC every day at 6:00, 12:00, 18:00 and 23:55 local time.

Data on public lighting in Linz

According to this article from Ausgust 2010, 20'624 luminaries with a total of 23'206 lamps are used for public lighting in Linz (189'311 inhabitants, as of Jaunuary 2010). The total power comsumption for the public lighting is 2.01 Megawatts. Not included in these figures is, of course, the public lighting of neighbouring municipalities. (Note that the Kepler observatory is located close to the western city limit of Linz, towards the city of Leonding [24.976 inhabitants]). --HerbertRaab 09:01, 3. Sep. 2010 (UTC)

Results

• Query data at the GAVO data center (Change parameters as necessary. Don't foget to select 'AT_LINZ_1' for the Staion ID. Set 'Output format' to 'VOPlot' to plot the data.)
• Directory listing

• 

  Kepler-Observatory and Lightmeter at night

• 

  All-sky image

• 

  First measurements, April 2009

• 

  April 23, 2009

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  April 23, 2009 (zoomed)

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  Night-Sky brightness in May 2009

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  Sky brightness at various locations (June 2009)

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  Example of fully calibrated data, Sept. 2009

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  October 2009