Welcome on the user manual of the Sky Monitor, you will find all informations about the instrument in the sections below. For the installation procedure, troubleshooting and other questions, please contact us.
¶ Sky Monitor components
The Sky Monitor characterizes atmospheric turbulence, aerosols and cloud-cover. It is composed of several instruments:
- control unit, also referred as Sky Monitor
- weather station
- C-DIMM, for nighttime turbulence monitoring
- tracking mount for C-DIMM (optional)
- allsky LWIR thermal camera, for precise cloud-cover detection (optional)
- 4G modem, for data transfer (optional)
For the installation of the Sky Monitor, see the Installation guide.
The Sky Monitor and the other instruments must be set on a stable and flat surface, as close as possible to the optical ground station (or its potential location), with no obstacles for the observation of the sky (e.g. buildings, trees...).
Any vibrations of the mouting structure is likely to alter the quality of the measurements.
¶ Control Unit
The control unit of the Sky Monitor embeds a computer, a Gigabit Ethernet switch and various sensors:
- a visible allsky camera
- a Solar Scintillation Monitor (SSM) for daytime seeing and measurements
- an irradiance sensor
- two longwave infrared (LWIR) sensors, respectively pointing zenith and pointing the opposite direction of the equator at 52° elevation
- an optional thermal camera (see section LWIR thermal camera > Internal camera)
The housing presents several waterproof connection ports:
- a port for power supply, the overall consumption is about 25W
- a port for the weather station
- a USB port for Miratlas use
- several Ethernet ports for connecting the other instruments
The housing is weather-proof and designed to operate under all weather conditions. The orientation towards equator is engraved on the top on the control unit.
The C-DIMM, its optional motorized mount and the 4G router are connected to the control unit on the M12 weatherproof ethernet ports. Any of these devices can be connected on any port.
Dimensions (WxDxH): 272 x 169 x 141 mm
Weight: 15 kg
Power: 150 W
¶ Visible allsky camera
The allsky camera provides greyscale images in the visible spectrum, from 400 nm to 1000 nm. The images are 2064 x 2064 pixels, with a field of view of 185°.
The camera uses a Sony sensor IMX178, with 3088 x 2064 pixels of 2.4 x 2.4 μm. The general specifications of the sensor are presented in the table below.
| Quantum Efficiency | 81 % (typical) |
| Dark Noise | 3.2 e¯ (typical) |
| Saturation Capacity | 14.3 ke¯ (typical) |
| Dynamic Range | 73 dB (typical) |
| Signal-to-Noise Ratio | 41.6 dB (typical) |
¶ Solar Scintillation Monitor
The Solar Scintillation Monitor (SSM) measures the seeing in arcsec and the Fried parameter in cm during daytime, under direct illumination of the Sun. These two parameters are measured at 550 nm.
The input level and the internal gain are adjusted according to ambient conditions (see Data collection section).
¶ Irradiance
The irradiance sensor measures irradiance received in the visible range, at ground level in mag/arcsec2 with a field of view of 40°, pointing at zenith.
¶ LWIR sensors
The longwave infrared (LWIR) sensors are calibrated and measure temperature of the sky at zenith and at the opposite direction of the equator and an elevation of 52°. These acquisitions determine precipitable water column in cm and downwelling radiation in W/m2.
The precipitable water column represents the quantity of water of vapor in the atmosphere above the instrument. The downwelling radiation is the optical power reflected or scattered by the atmosphere towards the ground. Both parameters are correlated to the presence of clouds.
¶ Weather Station
The calibrated weather station provides basic weather parameters: ambient temperature, pressure, relative humidity, wind and rain.
It must be installed above surrounding obstacles (e.g. buildings or trees) and preferably towards the local prevailing wind, with a maximum distance of 10 meters to the control unit. The orientation towards North is engraved on the top of the device .
| Weather parameters | Unit | Range | Resolution | Accuracy |
|---|---|---|---|---|
| Temperature | °C | -40 to 85 | 0.1 | 0.3 |
| Relative humidity | % | 0 to 100 | 0.05 | 3% |
| Wind speed | m/s | 0 to 60 | 0.1 | 3% @10m/s |
| Wind direction | ° | 0 to 360 | 0.1 | 3% @10m/s |
| Pressure | hPa | 10 to 1100 | 0.1 | 0.5 |
| Cumulated Rain | mm | 0 to 500 | 0.1 | 4 |
| Rain rate | mm/h | 0 to 250 |
Dimensions (WxDxH): 160 x 160 x 263 mm
Weight: 2.6 kg
Operating temperature: -40 to 85 °C
¶ C-DIMM
The C-DIMM is a Compact Differential Image Motion Monitor. It measures nighttime seeing in arcsec, Fried parameter in cm, isoplanatic angle in arcsec, scintillation and transparence, from the observation of a star. Polaris star is well suited for the C-DIMM in the Nothern hemisphere. The field of view of the instrument (about 1°) is large enough to accomodate its yearly positions. For lattitude lower than 20°, the C-DIMM requires a motorized tracking mount to spot other stars at high elevation.
The C-DIMM can be placed up to 100 meters away from the control unit.
The C-DIMM without tracking mount must be mounted on a very stable support, any vibration or deformation is likely to alter the acquisitions.
Dimensions (WxDxH): 657 x 300 x 307 mm
Weight: 5 kg
¶ Tracking mount for C-DIMM (optional)
For lattitude lower than 20°, the C-DIMM requires a motorized tracking mount.
Dimensions (WxDxH): 725 x 265 x 686 mm
Weight: 33 kg
Operating temperature: -15 to 35 °C
Power: 12 W (idle), 100 W (max at slewing)
¶ LWIR thermal camera (optional)
Miratlas proposes two configurations for long wave infrared (LWIR) thermal camera: external or internal.
¶ External camera
The external configuration consists in a radiometrically calibrated LWIR camera placed above a gold coated spherical mirror. The camera enclosure presents a waterproof power supply connector and an Ethernet connector.
¶ Internal camera
In the internal configuration, the thermal camera is integrated in the control unit and requires no additional harware or installation structure. The camera delivers a map of temperature of the sky.
Resolution: 640 x 480
Bandwidth: 8 to 12 µm
Precision: +/- 5°C
Field of view: 180°
Operating temperature: -40 to 70°C
Radiometric calibration range: -20 to 45°C or -5 to 60°C
¶ 4G modem (optional)
An external 4G modem enables data to be transferred and instruments to be connected remotely.
Dimensions (WxDxH): 254 x 255 x 58 mm
Weight: 1.1 kg
Operating temperature: -40 to 60°C
¶ Physical parameters
| Class | Data | Unit | Range | Resolution | Accuracy | Periodicity | FoV | Availability |
|---|---|---|---|---|---|---|---|---|
| clouds | ||||||||
| allsky visible | ADU | 0 ~ 255 | 1 | < 1e— noise | 15s | 180° | always | |
| allsky LWIR | °C | -40 ~ 120 | 0.06 | 2% | 60s | 180° | always | |
| nighttime transparency | 0 ~ 1 | 0.004 | 60s | 180° | always | |||
| turbulence | ||||||||
| nighttime seeing | arcsec | 0.2 ~ 20 | 0.002 | 7% | 60s | Polaris | clear night | |
| nighttime Fried parameter | cm | 0.5 ~ 50 | 0.05 | 7% | 60s | Polaris | clear night | |
| nighttime isoplanatic angle | arcsec | 0.06 ~ 10 | 0.01 | 1% | 60s | Polaris | clear night | |
| nighttime scintillation | ADU | 0 ~ 255 | 0.004 | 1% | 60s | Polaris | clear night | |
| daytime seeing | arcsec | 0.2 ~ 20 | 0.01 | 11% | 2s or 60s | 180° | clear day | |
| daytime Fried parameter | cm | 0.5 ~ 50 | 0.05 | 11% | 60s | 180° | clear day | |
| aerosols | ||||||||
| downwelling infrared | W/m2 | 115 ~ 550 | 0.1 | 3.5 | 60s | 80° | always | |
| sky temperature | °C | -60 ~ 40 | 0.02 | 0.5 | 2s or 60s | 10° | always | |
| precipitable water column | cm | 0 ~ 15 | 0.003 | 20% | 60s | 10° | clear sky | |
| irradiance | mag/arcsec2 | 8 ~ 22 | 0.0001 | 2% | 60s | 40° | dusk & dawn | |
| weather | ||||||||
| temperature | °C | -40 ~ 85 | 0.1 | ±0.3 | 2s or 60s | always | ||
| pressure | hPa | 10 ~ 1100 | 0.1 | ±0.5 | 2s or 60s | always | ||
| humidity | % | 0 ~ 100 | 0.05 | ±3 | 2s or 60s | always | ||
| wind speed | m/s | 0 ~ 60 | 0.05 | ±3% @10m/s | 2s or 60s | always | ||
| wind direction | ° | 0 ~ 359.9 | 0.1 | ±3 @10m/s | 2s or 60s | always | ||
| rain | mm | 0 ~ 500 | 0.01 | ±4% | 60s | always | ||
| rain rate | mm/h | 0 ~ 500 | 0.01 | ±4% | 60s | always |