CODE - Cloud detector.

Since 10 years ago, ITEC ASTRONOMICA S.L. is a dedicated company to astronomical and meteorological instrumentation developments for professional observatories and
institutions.

CODE (ClOud DEtector) is an instrument designed specifically to measure the daily cloud coverage under any weather conditions as high temperature, extreme low temperature, rain, snow or high humidity environments. It provides a full view of view of 180 degrees in all directions of the sky. Comparing with other similar instruments, CODE does not need any device to hide the sun projection onto the detector. Therefore, every part of the image is fully useful.

CODE is based on a fisheye objective attached to a color CCD system GRADE I. A neutral density filter is used to mitigate the sun light (in a factor of 1: 10000) while the cloud contrast over the blue sky is enhanced.

Figure 1: Left: CODE external view. Right: Detail of the protective dome with its ventilation holes.

CODE has been designed to be an autonomous system to work under any environmental circumstances. To do that, all the necessary elements have been integrated inside a whether proof housing (See figure 1). This housing is isolated from outside by a wall of 40mm width made of polyurethane and reinforced with aluminum (3mm width) in the external side. A transparent acrylic dome is located at the upper side to protect the fisheye objective and specially blackened to avoid any internal
reflection.

Moreover, two holes in the dome base of 20mm diameter allow a device to flow warm air into the dome to keep clear of condensation in high humidity conditions.
Figure 2 shows the internal view of the instrument. The CCD collects the image and sends it to the PC which is a industrial one able to support extreme conditions (temperature: -15 to 60C, humidity 0-95%). Appropriate conditions are kept inside and continuously checked by temperature and humidity sensors. The control software may
handle, if necessary, a drier to decrease the internal humidity values, a fan to evacuate air, or heater to increase the internal temperature.

Figure 2: Internal elements- (1) CCD+ fisheye. (2) Auxiliary CCD fan. (3) CCD power supply. (4) Industrial computer. (5) Drier. (6) Heater. (7) Main electronics. (8) External fan. (9) Temperature control. (10) Temperature and humidity sensors. (11) Power supplies (5,12V). (12) Electrical protection, circuit breakers, ground breakers, high voltage transient (storm protection).

The control algorithm designed by us runs in the internal computer to result in a image of 1008x1008 pixels which zero values correspond to a clear parts of the sky while 255 one correspond to cloudy ones. The output format is JPEG or FITS files. Figure 3 shows some actual examples.

The instrument has to be installed in a one squared meter leveled base and well orientated North-South. To do that, a level and compass may be used. The housing has 4 legs that allow slightly straighten the system.

Figure 3: Some detection examples. Left: Processed image, green pixels represent detected clouds in the image. Right raw image.

The system needs 220V and Ethernet connection to work (consult other possibilities). Weather proof connectors are installed.

The control software is written in C++ and contains more than 8000 code lines. It is designed to be a robotic system with barely human actions. To do that, it has to control all the internal devices to keep the good internal health of the system and to perform all the necessary processing routines to obtain the final cloud coverage image. This process runs every minute (user-defined) automatically from sun rise to sun set, when the software disables all the devices. Figure 4 shows a view of the main software.

A main display shows the raw, colored and processed images. This can be selected according to the options in Current image display. Available options are full color image, blue band, red band, green band, Color ratio (blue/red), cloud map. Display cursor provides:

Figure 4: CODE main software.
  • Cursor position, X-Y coordinates.
  • Sun distance from the cursor in Cartesian and Polar system.
  • Pixel value for every band.
  • Color ratio (Blue by red band).
  • Cloud threshold value.
  • Cloud value (Clear = 0, Cloud = 255).

Left button mouse over the display performs an intensity values plot of those pixels from the cursor position to the sun location.

Sequence contains Start and Stop buttons. According the current time, the system will decide to startup or wait. During the night, the main power of the CCD will be disabled but the temperature and humidity control routines will be continuously monitoring those variables. A dome heater will blow warm air into the dome to keep clear of strong condensation every time gap.

In the morning, the software will enable all the system power re-establishing the CCD link half hour previous to sun rise and starting all the processes.