I had always been interested in cloud detectors for my imaging sessions, but since most of my imaging is done from my backyard (semi-remote), I figured a cloud detector wasn’t needed since I can “see” the sky conditions myself.
But after a few months of using the AAG CloudWatcher made by Lunatico, I now see the advantages of having one. I’ll be sharing my experience with it here.
Hardware & installation
Installation of the AAG CloudWatcher is easy. Just attach it to the side of your observatory, fence, post, or anything else convenient.
The AAG CloudWatcher consists of a plastic box with sensors on the side that faces the sky. Sensors include a cloud detector, rain sensor, light sensor, and, optionally, a wind speed anemometer.
The version I have has the relative humidity and atmospheric pressure sensors on the bottom, an option definitely worth the extra $65.
Only one cable is needed, with lengths available 3m to 10m, with the other end having:
- 12v power input jack
- RS232 serial port (for USB, you’ll need an RS232 serial-to-USB adapter)
- Relay: A pair of wires that act as a relay switch for (optionally) sending commands to devices like roof opening/closing motors.
Rain Sensor Options
There are two options for rain detection.
1 – Capacitive sensor
Capacitive sensor advantages:
- Integrated into the CloudWatcher box
- Stronger heater, so it can work with snow and heavy dew (tested with good results)
- Can indicate the approximate amount of rain
Capacitive sensor disadvantages:
- Needs to be kept relatively clean (bird droppings, etc.)
- Sensing surface could be scratched
- Calibration needed (2 minutes)
2- Hydreon RG-9 Sensor
This rain sensor uses infrared LEDs and a transparent dome-shaped plastic lens to detect rainfall ($70 option).
Hydreon RG-9 Sensor Advantages:
- Rugged and maintenance free
- Transparent dome can be replaced, if needed
- No calibration needed
Hydreon RG-9 Sensor Disadvantages:
- Weak heater, so it won’t work well in snow
- Not quantitative (Indicates only rain or no rain)
- Moving shadows (leaves, anemometer) can mislead the sensor
I have both sensors and I feel that provides the best of both worlds. The built-in capacitive sensor detects whatever threshold I consider unsafe (set in the software, described below) and closes the shutter or stops imaging. I like that it shows a value even with a single drop of water, before it really starts to rain.
The Hydreon sensor can be connected to the CloudWatcher, but mine was wired to my dome motor (the Lunatico Beaver) so it will trigger shutter closure even if no software or PC is present. This redundancy gives me extra peace of mind.
Wind Speed Sensor (Anemometer)
Lunatico also offer a wind speed sensor that connected to the CloudWatcher device ($145). I don’t have this sensor but I may try it later.
The software is straightforward and, while the user graphic interface isn’t aesthetically pleasing, it’s simple and gets the job fine. It was easy to install and understand.
The AAG CloudWatcher connects to a computer where the current sensor readings are displayed in the main panel, including environmental conditions such as temperature, relative humidity, sky brightness (darkness), wind speed and the presence of clouds or rain.
There is an optional standalone device – the SOLO – that eliminates the need for a PC and provides the readings over a network (the SOLO will be reviewed later).
Thresholds can be set for the levels of each parameter, such as defining what constitutes clear, cloudy, or overcast, and graph them against time. This provides a visual representation of ambient conditions.
The CloudWatcher’s main feature, detecting clouds, uses an infrared sensor and the temperature of the sky to detect the presence or absence of clouds. The measurement algorithm parameters can be tweaked by the user. I have found it to be accurate and responsive.
Temperature & Humidity
Below is an example of a rise in humidity detected by the CloudWatcher, allowing the user to take measures to avoid the formation of dew on the optics.
Similarly, ambient temperature changes are useful for monitoring things like temperature acclimatization inside the observatory compared to outside for telescope refocusing routine schedules.
The rain sensor is essential for safety, helping avoid potentially catastrophic situations such as a sudden shower that can damage the exposed equipment. Below is a real-life example from our backyard, showing how conditions can change from completely dry to heavy rain within minutes. In this case, the CloudWatcher triggered a dome shutter closure.
The light sensor has been useful for timing the start and end of data acquisition, down to the minute. Astronomical darkness varies in latitude and throughout the year. I find the sensor to be far more accurate than simply peeking out the window or using an all-sky camera.
The optional anemometer measures wind speed, allowing those in windy locations to shut down a session (automatically or manually) should wind speeds reach dangerous levels.
ASCOM Safety Monitor
This is something I really needed for my nightlong autonomous imaging sessions – a Go/No-Go switch using “Safe” and “Unsafe” conditions.
The user defines conditions for what to consider unsafe. The thresholds for each are adjustable. I selected “Overcast” or “Rain” or “Very Light” as “Unsafe”:
My imaging software, N.I.N.A., along with any other ASCOM-compliant imaging software, connects to the ASCOM Safety Monitor. Automatic imaging sequences continue to loop until an “Unsafe” command from the Safety Monitor triggers a shutdown.
For example, once clouds reach the “Overcast” level that I selected, indicating that rain may be imminent, the safety monitor switches to “Unsafe” and imaging stops. I program N.I.N.A. to terminate the session and close the observatory roof once an unsafe condition is detected. This process is independent of the Hydreon rain sensor that is hardwired to the dome motor, which can also trigger an unsafe condition.
The AAG CloudWatcher has been running nonstop on my observatory for several months and has been working well without any input from me. Having a clear picture of the weather conditions, I feel a lot more confident about my equipment being exposed to the elements.
The main advantage to me is the ASCOM integration, meaning my autonomous imaging sessions are much safer now.
I initially considered a CloudWatcher to be a “nice to have” accessory. Now, I feel I’d be flying blind without the weather conditions being monitored continuously.
- Lots of sensors and features
- Cloud detection works well
- The user can select what is or isn’t required
- Reasonably priced
- Software interface doesn’t look very appealing (though this doesn’t affect operation)
MSRP: $365 to $480
NOTE: Rouzbeh Bidshahri’s review of the Lunatico Solo, a standalone computer for the CloudWatcher, will be published on Saturday, April 9.