====== Ceilometer observations ======

{{:wiki:instruments:ceilo_jenoptik_05.jpg?direct&500|Ceilometer ©B. Pospichal}} \\
//Jenoptik (LUFFT) ceilometer CHM15k (left), Vaisala ceilometer CT25K (right) at JOYCE//


===== Principle =====
A ceilometer measures the cloud base height, called //ceiling// in aviation. It is based on the light detecting and ranging (LIDAR) principle, i.e. it sends laser pulses and measures the backscattered light. From travel time the distance of the back scattering object can be determined. From strength and attenuation of the backscattered signal the backscatter coefficient is determined. The instrument identifies cloud bases by caluclating visibility from the backscatter coefficient and identifying the height from which on you cant see the ground any more. If the lower clouds are transparent it can detect up to three distinct cloud layers. In cloud free cases we can use the backscatter profile for an estimate of boundary layer height.

At JOYCE, two different ceilometers are installed. One Vaisala CT25K and one Jenoptik/Lufft CHM15k instrument. 



===== Measurement modes =====

  * Vertically pointing observations with integration times of 15 seconds

===== JOYCE-CF Standard Operation Procedures =====
  * Standard measurement modes are 
  * Vertical resolution 15 m, maximum range 15 km  (CHM15k)
  * Vertical resolution 30 m, maximum range 7.5 km  (CT25K)





===== Data availability =====

Most of the following data products are provided via the SAMD database. If you would like to have additional data or recent data that have not been uploaded to SAMD yet, please fill the {{ :joyce_data_request_form.pdf |data request sheet}} and send it to [[mailto:info@joyce.cloud|info@joyce.cloud]]

 
^ Dataset     ^ Temporal resolution       ^ File size          ^ Filename   ^ Retrieval / Remarks   ^ 
| Uncalibrated attenuated backscatter (background corrected)   | 15 seconds    | 1 file per day (30 MB)     | //sups_joy_ceilo00_l1_beta_v00_YYYYMMDDHHMMSS.nc//  | from CHM15k, available on SAMD   |
| Mixing layer height   | 15 minutes    | 1 file per day (0.02 MB)     | //sups_joy_ceilo00_l2_zmlaa_v01_YYYYMMDDHHMMSS.nc//  | from CHM15k, available on SAMD   |
| Cloud base height   | 15 minutes    | 1 file per day (0.28 MB)     | //sups_joy_ceilo00_l2_zcb_v00_YYYYMMDDHHMMSS.nc//  | from CHM15k, available on SAMD   |
| Backscatter, cloud base height  | 15 seconds  | 1 file per day (25 MB)   | //YYYYMMDD_JOYCE_CHM120109_000.nc//   | from CHM15k    |
| Backscatter, cloud base height  | 15 seconds  | 1 file per day (6 MB)   | //YYMMDD_ct25k_jue_l0b.nc//   | from CT25K    |

===== Composite products using data from Ceilometer =====
  * **Cloudnet target classification** uses cloud base height observations from the CT25K-Ceilometer. Combined with cloud radar and microwave radiometer observation, clouds are characterized by their geometrical extent as well as their microphysical properties. Data are available via [[https://cloudnet.fmi.fi/|ACTRIS cloudnet website]] 

===== Link to current observations =====

Current observations at [[http://atmos.meteo.uni-koeln.de/~hatpro/dataBrowser/dataBrowser4.html?site=JOYCE&date=-1&UpperLeft=Ceilo_ct25k_Backscatter&UpperRight=Ceilo_ct25k_Boundarylayer-height&LowerRight=Ceilo_chm15k_raw&LowerLeft=Ceilo_chm15k_SNR|quicklook archive]]



===== Measurement examples =====

{{wiki:examples:200202_ct25k_jue_l0b.png?direct&400|CT25-K}}
{{wiki:examples:20200803_jenoptik_ceilo_snr_version1.png?direct&400|SNR CHM15k}} \\
//Left: Time series from CT25K (backscatter and cloud base height) on 2 February 2020, right: Time series from CHM15k (signal-to-noise ratio plus cloud and aerosol layers) on 3 August 2020 //



===== Instruments at JOYCE / University of Cologne =====

At JOYCE, two ceilometers are installed and running continuously. The CT25K has been installed since 2007, while the more powerful CHM15k was added in 2013. Please visit the sub-pages for more details. 

^ Instrument name      ^ current location       ^ in operation since          ^  features          ^
| [[ct25k|Vaisala CT25K]]    | JOYCE    | 2007   |     |
| [[chm15k|Jenoptik/Lufft CHM15k]]    | JOYCE    | 2013   | Level 2 products are derived from this instrument    |