Cloud+sensor


 * PAGE TO BE UPDATED WITH NEW DATWeather **

This page describes using a web cam as a 'Cloud sensor'. In truth it is really acting as a sky brightness monitor. I have used the Phillips ToUcam Pro as it is more sensitive than standard web cams.

Basically, in light polluted skies the sky is much brighter due to reflected light off clouds (orange clouds!). When clear it is darker. The images below show how 'bright' the sky gets in light polluted skies!

Using VB 2008 Express, GetBrightness will report the pixel value at defined positions. A matrix of pixels is selected and an average value obtained. When above a threshold, the sky is cloudy.

The threshhold is 'tunable' by entering set point values in a text box on the form. This uses a Vellerman KB8055 USB I/I board the same as used in the Observatory Auxiliary Control.

The output from the USB I/O card in series with the 24V weather loop that runs between each observatory. When this is open, the observatory will close.

So far, it works well! You can see increasing values as the weather gets worse. Last image it was raining. The time difference between first and last images was 10 minutes.

Other sensors have now been added (January 2011) since the images below were taken.

An LDR has recently been added and is quite sensitive also to background light increases. An infrared system is being developed also (November 2010) that uses a scrap car windscreen sensor.

Some sample images of the camera in position with a modified fish eye lens from Maplin (2.1mm Focal length with 150 degree field of view).

Hovering over the images above will state the conditions they were taken. The telescope was observing when clear and did close as the weather deteriorated. This was in 'advance' of the hardwired weather station sensors.



Links to some cloud sensors and code for driving web cams:-. [] [] []

=Web cam settings=

The screen shots below improve the low light level detection settings for the Phillips ToUcam Pro using the Amcap software programme.

Ensure IYUV and 640x480 is set as above. Setting frame rate to 5 from 15 does not apear to work, but set it anyway. This should be set first.

Ensure that the 'Outdoor' button is checked and that the exposure is Auto. This allows the web cam to be viewed during the day also.

This is the most important setting. Ensure that the frame rate in teh above screen is set to 5 manually. It will revert to 15 if set first before the above settings are completed.