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Table of Contents
Ceilometer
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.
Measurement modes
- Vertically pointing observations with integration times of 15 seconds
JOYCE-CF Standard Operation Procedures
- Standard measurement mode is vertically pointing, 1 second integration time
- Every 15 minutes one elevation scan with following angles: 42°, 30°, 19°, 10.2°, 5.4° (duration ~100 seconds) for improved resolution of temperature profiles in lowest 1000 m above ground
- Every 30 minutes one azimuth scan at 30° elevation angle with 5° azimuth resolution (duration ~3 minutes) for horizontal variability of IWV and LWP
Data quality assurance procedures
- Automatic rain detection (data are flagged in case of rain detected by rain sensor)
- Offset corrections for liquid water path
- O-B statistics from atmospheric models for brightness temperature offset correction available
- Spectral consistency checks
- Thresholds for Level 2 data products
- Housekeeping data analysis
- Visual data inspection
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 data request sheet and send it to 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 |
| Brightness temperatures 14 channel microwave, 6 elevation angles | 15 minutes | 1 file per day (0.07 MB) | sups_joy_mwr00BL_l1_tb_v00_YYYYMMDDHHMMSS.nc | |
| Brightness temperatures 2 channel infrared | 1 second | sups_joy_mwr00_l1_tb_v00_YYYYMMDDHHMMSS.nc | included in microwave brightness temperature file | |
| Level 2 | ||||
| Integrated water vapor (IWV) | 1 second | 1 file per day (3-4 MB) | sups_joy_mwr00_l2_prw_v00_YYYYMMDDHHMMSS.nc | Multivariate linear retrieval based on radiosoundings from De Bilt |
| Cloud liquid water path (LWP) | 1 second | 1 file per day (3-4 MB) | sups_joy_mwr00_l2_clwvi_v00_YYYYMMDDHHMMSS.nc | Multivariate linear retrieval based on radiosoundings from De Bilt including clear sky offset correction |
| Temperature profiles (from zenith pointing) | 1 second | 1 file per day (25-30 MB) | sups_joy_mwr00_l2_ta_v00_YYYYMMDDHHMMSS.nc | Multivariate linear retrieval based on radiosoundings from De Bilt |
| Temperature profiles (from elevation scans) | 1 second | 1 file per day | sups_joy_mwr00BL_l2_ta_v00_YYYYMMDDHHMMSS.nc | Multivariate linear retrieval based on radiosoundings from De Bilt |
| Humidity profiles (from zenith pointing) | 1 second | 1 file per day (25-30 MB) | sups_joy_mwr00_l2_ta_v00_YYYYMMDDHHMMSS.nc | Multivariate linear retrieval based on radiosoundings from De Bilt |
Composite products using data from HATPRO
- Cloudnet target classification uses LWP data from HATPRO. Combined with cloud radar and ceilometer observation, clouds are characterized by their geometrical extent as well as their microphysical properties. Data are available via ACTRIS cloudnet website
Link to current observations
Current observations at quicklook archive
Measurement examples
Time series of brightness temperatures (left) and Integrated Water Vapor / Liquid Water Path (right)
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 |
|---|---|---|---|
| Vaisala CT25K | JOYCE | 2007 | |
| LUFFT CHM15k | JOYCE | 2013 | Level 2 products are derived from this instrument |