One of the more useful instruments on the PTO’s sensor tower is the Sky Quality Meter (SQM). The device constantly measures how bright the sky is. Clouds and other particulate matter in the atmosphere reflect light from surface features and ‘brighten’ the sky. To evaluate how much the sky brightness is effecting each image, an SQM reading of the sky’s magnitude is taken and included in the accompanying metadata. This information is used to evaluate the accuracy of image measurements. High altitude clouds may not be visible to the naked eye but may be dense enough to effect the measurement of a star’s brightness.
Recently, I noticed the device had stopped working. I glanced up at the sensor tower prior to getting out the ladder to get an idea how easy the SQM would be to get to. I noticed the glass window of the external housing was offset so far from its normal location that it was visible from the ground. Not good news.
Once I got up to the device is was apparent that the adhesive that sealed the window was totally missing. I am pretty sure it wasn’t eaten by anything so my guess is the Sun’s UV radiation slowly degraded the marine grade adhesive and then one of our avian visitors nudged the window out of the recess and over to the edge of the housing. This is not the first time the window was left free. Several years ago I just happened to notice the absence of the sealant but at that time the window was still sitting in the recess. The manufacturer suggested the marine grade sealant that I used. They now recommend J-B weld for plastics.
Inside the housing there was evidence of the rain from a few days earlier. Testing showed the device still worked but the power over ethernet hardware was not working. So, right now the PTO awaits parts for the system to arrive from Canada. If you were wondering why the SQM trend chart has not changed since the 10th of June, this is the reason.