Paranal Ambient Query Forms

The Paranal ASM (Astronomical Site Monitoring) has been upgraded in April 2016 in order to solve some obsolescence issues of the old ASM system and to support new adaptive optics requirements. The measurements (seeing, coherence time, vertical profile of the turbulence, etc.) from the various instruments are accessible either graphically (see: ambient main page) or can be browsed/downloaded using dedicated archive query interfaces.

The table below provides access to the archive query interfaces and lists the main scientific parameters retrievable from each of them, usually along with various engineering parameters.

Detailed documentation is available in the Astronomical Site Monitor Data User Manual (v2.0).

A brief description of the new ASM subsystems and instrumentation follows.

From 1998 to March 2016 From April 2016 onwards
Historical Ambient Data (DIMM 1998) (Differential Image Moption Monitor)
  • Airmass
  • Coherence time
  • Isoplanatic angle
  • Relative Flux
  • Seeing
DIMM Seeing 2016 (Differential Image Moption Monitor)
  • Seeing
  • Relative Flux
  • Flux Variance integration time
  MASS (Multi-Aperture Scintillation Sensor)
  • Seeing (high atmosphere)
  • Coherence time
  • Isoplanatic angle
  • Turbulence Altitude
  • MASS-DIMM Cn2 fraction at ground
  • MASS-DIMM Seeing
  • MASS-DIMM Coherence time
  • MASS-DIMM Isoplanatic angle
  • MASS-DIMM Turbulence Altitude
  • MASS-DIMM Turbulence Velocity
  SLODAR (SLOpe Detection And Ranging)
  • Cn2 above equivalent VLT Unit Telescope height
  • Cn2 fraction below 300m
  • Cn2 fraction below 500m
  LHATPRO (Low Humidity And Temperature PROfiling microwave radiometer)
  • IR temperature at zenith
  • Liquid water path
  • Water Vapour
LHATPRO IR temperature
  • IR sky brightness temperature
LHATPRO profiles
  • Absolute humidity at different heights
  • Relative humidity at different heights
  • Brighness temperature at different heights
  • Ambient and Dew Temperatures
  • Relative Humidity
  • Air Pressure
  • Particle counts
  • Wind Speed and Directions

The new ASM is composed of various subsystems able to monitor different aspects of the observing conditions at Paranal:

* DIMM 2016: The new seeing measurements are taken by the new Differential Image Motion Monitor placed in location more representative of the observatory conditions. The ASM upgrade DIMM replaces the DIMM-1998. Data from April 2016 onwards.

* DIMM 1998: The measurements of the old DIMM are available from a separate interface. For a period of about 6 months starting from April 2016 the old and the new DIMMs operate in parallel so to allow comparison and to allow studying the long term evolution of Parnal observing conditions. Data from 1998 until about 6 months after ASM upgrade (April 2016).

* LHATPRO: The Low Humidity And Temperature PROfiling microwave radiometer provides Precipitable Water Vapor measurements. The instrument consists of a humidity profiler (183-191 GHz), a temperature profiler (51-58 GHz), and an infrared camera (~10 micrometers) for cloud detection. Data from April 2016 onwards.

* MASS: The Multi-Aperture Scintillation Sensor yields information of the vertical profile of the turbulence Cn2(h). It gives the Cn2(h) for 6 layers placed at 0.5, 1, 2, 4, 8 and 16 km above the telescope pupil. The combination of a DIMM and a MASS gives the possibility to measure both seeing and low-resolution turbulence profiles. Data from April 2016 onwards.

* METEO: The VAISALA METEOrological station provides: Wind speed and direction, Temperature, Humidity, Particle Count at different levels. The meteorological stations compute and store average, root mean square and extrema of each parameter during a preset averaging period (20 minutes). The sampling intervals are 2 seconds for digital sensors (wind speed and direction) and one minute for analog sensors (Temperature, Humidity). Data from 1998 onwards.

* SLODAR: (SLOpe Detection And Ranging) is optimised to measure the vertical profile of the turbulence in the first 500m above the site. The data is relevant to modelling and understanding the imaging performance of the VLT, both with and without adaptive optical correction. Data from April 2016 onwards.

To know more about the various instruments please refer to the Help page.