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NightMon-JV-JR-H

NightMon-JV-JR-H - A camera system to sample the hemisphere of light at night

This imaging system is aimed for professional astronomical site monitoring. It has the capacity of sampling the hemisphere under a variety of lighting levels in the R and V Johnson-Cousins bands.

Components

1. 2 Raspberry pi cameras HQ
2. 2 R and V Johnson filters
3. 1 Arducam Multi Camera Adapter Module V2.2 for Raspberry Pi
4. 2 Arducam 180 Degree Fisheye 1/2.3" M12 Lens with Lens Adapter for Raspberry Pi High Quality Camera
5. 1 Raspberry pi 4B computer with 8 Gb of RAM
6. 1 Raspberry Pi UPS HAT
7. 1 128 Gb microsd card U30
8. 1 512 Gb usb stick
9. M2.5 brass and nylon standoffs
10. 2 ez-tops transparent dome
11. 1 bud industries enclosure N3R-5805
12. 2 70mm ID C-bolt

Tools

Installation on site

The NigthMon needs to be leveled in order to have zenith not too far away from the images center. The back face of the enclosure (with anchors) must be pointing toward north. A few degrees away is not a problem but better results are when the alignment is accurate. This alignment has an impact on the capacity to recognize the stars in the images for the "stars" calibration mode.

The best way to install the instrument is by binding it to a 70 mm diameter vertical tube with two 70 mm ID U-bolts. If the tube is vertical then the only remaining alignment consist in rotating the enclosure around the tube to have the back face toward north.

Initial configurations

Once installed on site, it is necessary to obtain a first starry sky image in order to locate Polaris on the images. This will be used by the initial calibration software "FindShiftRotate.py" to determine once, after the installation, the shift and rotation to align the images according to the north. The Polaris positions (in super pixels) have to be provided in the cameraorientation_config file. So you need at least one clear sky nighttime image after installation. This file, once completed, need to be in the directory /home/sand. It contains the information on the geographical location of the observer along with the superpixel position of Polaris on both images (the V and R images). This position may be determined manually by opening the starry sky pictures with a imaging software like RawTherapee. The x and y position in original pixel have to be converted to the superpixel positions. This is easily done but dividing the pixel positions by two.

Sample cameraorientation_config file:

The other file to fill out is the basic configuration file nightmon_config. That file should also be in /home/sand This file contain again the position of the observer but also a sequence of 3 parameters to shift and rotate the images correctly for a good star field identification. These parameters (ShiftxA, ShiftyA, AngleA etc) are determined once with the program FindShiftRotate.py.

Sample nightmon_config file:

Operation mode

The system will record one image on each camera every 15 min. If the brightness is too high, the camera assembly will be retracted into the enclosure in order to prevent aging coming from Sun's UVs. In such a case, only the jpg images will be stored on the computer. Otherwise, both the jpg and raw dng images will be stored. There are two copies of the files, one on the web server tree (<IP_of_the_system>/data). The second copy is stored on a usb key at /home/sand/data. There is a script that will clean the directories to prevent the disks to be full. So it is important to make regular backup of the files.

The NightMon is a WIFI access point so that it is possible to access the data either by the web server or with a ssh file transfer with a mobile device. More details are given in the software page here.

There are two calibration modes available, one aimed for situations were the star field is not available (fixed mode). This may happens when the sky is cloudy or in highly polluted areas where almost no stars can be perceived. This mode need to use predefined zero points values in the nightmon_config file. The zero points for a specific system can be done by calibrating the unit once with a starry sky and with the proper atmospheric extinction values.

The normal calibration mode is the stars mode. In that mode the calibration will only be performed under clear skies and is made by using the SIMBAD stars database and an assumed knowledge of the atmospheric extinction. The software first produce a fake stars map and then search stars in the image and tries to associate the fake stars with the detected ones. Then a calibration constant is extracted and applied to the digital numbers of the image.

The calibration method (Calmet) and the zero points (ZpointA and ZpointB) can be provided on the command line with the ProcessNightMon.py script. If they are not provided to the command line, then the program will grab them in the nightmon_config file.

Software package

Software package and installation procedure is available here.

Pictures