Kepler-Sternwarte Linz

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The Lightmeter station at the Kepler-Sternwarte Linz on 2017-03-17, after 8 years in operation
The sensor of the Kepler-Sternwarte Lightmeter. Number 3 of the Mark 2.2 prototype series after 8 years.
Luxmeter Kepler-Sternwarte 1.jpg
Luxmeter Kepler-Sternwarte 2.jpg

Link to the old station-page: --GW (talk) 10:52, 30 June 2014 (CEST)

General Description

Station Code AT_Linz, Sensor Mk 2.2, S/N L3

The Lightmeter is located at the Kepler-Observatory in Linz, Austria (48° 17' 36.3" North, 14° 16' 06.0" East [1], 344m ASL). It 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. As no permanent Internet connection is available in the observatory, the data is uploaded manually to the GAVO data center. Also, the clock is set manually from time to time.

The distance to the city center of Linz is ~1.9 km, to the city center of Leonding ~2.1 km, and to the industrial plants ~5 km (~4.5 km to the Chemiepark, ~5.5 km to the VOEST steel plant).

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

On 2014-06-29 the Windows PC running Jörg Weingrill's Skysensor-Software has been replaced by a Laptop running the Lightmeter Software under Unbuntu (see below). The Station code has been changed from AT_LINZ_1 to AT_LINZ_2 on that occasion.

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

Station History



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.

at_Linz_2 - Replacement of the Computer

Due to increasing downtime of the Lightmeter, the PC runnig Jörg Weingrill's Skysensor-Software under Windows XP has been replaced on 2014-06-29 by a Laptop running the Lightmeter Software under Unbuntu. The laptop was set up by Felix Linhardt. The Station code has been changed from AT_LINZ_1 to AT_LINZ_2 on that occasion.

The original sensor (Mark 2.2) is still in use. Also, data upload and clock check is still done manually at more or less regular intervals, usually once in a month.

--HerbertRaab (talk) 08:52, 1 July 2014 (CEST)

The Laptop failed in early September 2014 due to a hard disc crash. Unfortnately, all data collected after August 30, 2014 is lost. --HerbertRaab (talk) 14:36, 19 September 2014 (CEST)

at_Linz_3 - Netbook as Logger

On 2017-03-17 a Netbook ("Lighmeter 1") was installed as a logger.

The station responded immediately and data recording resumed 2017-03-17 13:50 CET. A few cycles of on/of switches of the lamps did not interrupt data-taking.

Configuration: Original sensor Mk 2.2, S/N L3 with Netbook (daily reboot at 14 UTC), time by internal clock;

To do:

  * there is a WLAN now at the observatory that is switched on if needed. The Lightmeter logger should do time synchro and upload the data if the WLAN is up.
  * the lightmeter could display data in real time with a python script (ipython is installed on the netbook
  * on/off photmetry with the TV-transmitter-lights;

Data Station is now running since 2009-04-21. It will by running

  * for 8 years on April 20th 2017
  * for 10 years in 2019.

--GW (talk) 15:45, 17 March 2017 (CET)

Light metering network of the state government

Lightmeter AT_LINZ (top) and L003 (below)

Since July 21, 2014, the Station L003 of the light metering network of the state government of Upper Austria is also located at the Kepler Observatory. This station runs independent from the Lightmeter.

--HerbertRaab (talk) 20:17, 3 August 2014 (CEST)

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)