cl2nc is an open source command line Python program for converting Vaisala CL51 and CL31 ceilometer DAT and HIS L2 files to NetCDF.

On the command-line:

cl2nc input.dat output.nc

where input.dat is a Vaisala CL51 or CL31 DAT file and output.nc is the name of a NetCDF output file.

See example.zip for an example input and output.

It is recommended to run cl2nc on Linux.

On Debian-derived distributions (Ubuntu, Devuan, ...), install the required system packages with:

sudo apt install python3 python3-pip pipx

On Fedora, install the required system packages with:

sudo yum install python3 pipx

Install cl2nc:

pipx install cl2nc
mkdir -p ~/.local/share/man/man1
ln -s ~/.local/pipx/venvs/cl2nc/share/man/man1/cl2nc.1 ~/.local/share/man/man1/

Make sure that $HOME/.local/bin is included in the PATH environment variable if not already. This can be done with pipx ensurepath.

You should now be able to run cl2nc and see the manual page with man cl2nc.

To uninstall:

pipx uninstall cl2nc
rm ~/.local/share/man/man1/cl2nc.1

Open the Terminal. Install cl2nc with:

python3 -m pip install cl2nc

Make sure that /Users/<user>/Library/Python/<version>/bin is included in the PATH environment variable if not already, where <user> is your system user name and <version> is the Python version. This path should be printed by the above command. This can be done by adding this line to the file .zprofile in your home directory and restart the Terminal:

PATH="$PATH:/Users/<user>/Library/Python/<version>/bin"

You should now be able to run cl2nc and see the manual page with man cl2nc.

To uninstall:

python3 -m pip uninstall cl2nc

Install Python 3. In the installer, tick Add python.exe to PATH.

Open Command Prompt from the Start menu. Install cl2nc with:

pip install cl2nc

You should now be able to run cl2nc.

To uninstall:

pip uninstall cl2nc

cl2nc is a command line program to be run a terminal (Linux and macOS) or the Command Prompt (Windows).

Synopsis:

cl2nc [-chq] [--debug] input output
cl2nc -h|--help

input is an input .dat or .his (L2) file. output is an output .nc file. If directories are supplied for input and output, all .dat, .DAT, .his and .HIS files in input are converted to .nc files in output.

Options:

• -c: Enable DAT checksum verification (slow).
• --debug: Enable debugging output.
• -h, --help: Show help message and exit.
• -q: Run quietly (suppress output).

On Linux and macOS, see also the manual page with:

man cl2nc

Please see Vaisala CL51 User's Guide for a complete description of the variables.

The DAT files can alternatively contain values in feet (instead of meters), in which case all values are converted by cl2nc to meters.

Time in DAT and HIS files is assumed to be UTC.

Missing values are encoded as NaN (floating-point variables) or -2147483648 (integer variables). The _FillValue attribute contains the missing value used in the given variable.

DAT files produce the following NetCDF output:

HIS L2 files produce the following NetCDF output:

Background light (mV)

Millivolts at internal ADC input.

Attenuated volume backscatter coefficient (km^-1.sr^-1)

Backscatter sum (sr^-1)

Sum of detected and normalized backscatter (0–0.0999 sr^-1).

Lowest cloud base height (m)

Second lowest cloud base height (m)

Highest cloud base height (m)

Ceilometer name (HIS L2 variable CEILOMETER).

Detection status

• 0 – no significant backscatter
• 1 – one cloud base detected
• 2 – two cloud bases detected
• 3 – three cloud bases detected
• 4 – full obscuration determined but no cloud base detected
• 5 – some obscuration detected but determined to be transparent
• / – raw data input to algorithm missing or suspect

Sky detection status

• 0-8 – cloud coverage of the first layer in octas
• 9 – vertical visibility
• -1 – data missing, sky condition option not active or ceilometer in standby mode
• 99 – not enough data (after start-up)

Highest signal detected

Laser temperature (°C)

Layer number

Layer cloud amount (octas)

Sky condition algorithm.

Layer height (m)

Sky condition algorithm.

Level number

Message number

• 1 – message without sky condition data
• 2 – message with sky condition data

Message subclass

• 6 – 10 m ⨉ 1540 samples, range 15400 m (msg1_10x1540)
• 8 – without a backscatter profile (msg1_base)

Period (HIS L2 variable PERIOD).

Pulse energy (% of nominal factory setting)

Pulse length

• L – long (100 ns)
• S – short

Pulse count

Receiver bandwidth

• N – narrow
• W – wide

Receiver gain

• H – high
• L – low

High by default, may be low in fog or heavy snow.

Self check

• 0 – self-check OK
• W – at least one warning active, no alarms
• A – at least one alarm active

Software level ID

Status alarm

Flags:

• 0x8000 – transmitter shut-off
• 0x4000 – transmitter failure
• 0x2000 – receiver failure
• 0x1000 – voltage failure
• 0x0400 – memory error
• 0x0200 – light path obstruction
• 0x0100 – receiver saturation

Status internal

Flags:

• 0x8000 – blower is on
• 0x4000 – blower heater is on
• 0x2000 – internal heater is on
• 0x1000 – working from battery
• 0x0800 – standby mode is on
• 0x0400 – self test in progress
• 0x0200 – manual data acquisition settings are effective
• 0x0080 – units are meters if on, else feet (note that units are always converted to m by cl2nc)
• 0x0040 – manual blower control
• 0x0020 – polling mode is on

Status warning

Flags:

• 0x8000 – window contamination
• 0x4000 – battery voltage low
• 0x2000 – transmitter expires
• 0x1000 – high humidity
• 0x0800 – blower failure
• 0x0100 – humidity sensor failure
• 0x0080 – heater fault
• 0x0040 – high background radiance
• 0x0020 – ceilometer engine board failure
• 0x0010 – battery failure
• 0x0008 – laser monitor failure
• 0x0004 – receiver warning
• 0x0002 – tilt angle > 45 degrees warning

Tilt angle (degrees from vertical)

Time (seconds since 1970-01-01 00:00:00 UTC, excluding leap seconds)

Time (UTC) (ISO 8601)

Unit identification character

Vertical resolution (m)

Vertical visibility (m)

Window transmission estimate (%)

90% to 100% means the window is clean.

cl2nc identification: cl2nc (https://github.com/peterkuma/cl2nc).

cl2nc version string. Follows semantic versioning.

Time when the NetCDF file was created (ISO 8601 UTC).

This software is open source and can be used, shared and modified freely under the terms of the MIT License (see LICENSE.md).

If you encouter any issues with cl2nc you can contact me at Peter Kuma <peter@peterkuma.net>, or submit a GitHub Issue.

There are many different undocumented variants of the CL31/CL51 format in use. cl2nc strives to support most of them, but if you encounter errors with your data files, it might be because it is yet another variant. In such a case, submit a GitHub Issue.

Please make sure you that the Python package netCDF4 is installed. If it still does not work for you contact me: Peter Kuma <peter@peterkuma.net>. There are small variations in the .DAT file format with instruments. cl2nc may need to be modified to be able to read a particular type of format.

Height can be determined from vertical_resolution. The instrument samples vertical bins on regular intervals.

MATLAB NetCDF implementation currently does not support reading NC_STRING variables. You can use the time variable instead or use the MATLAB HDF functions to read the file (you may need to change the file extension to .h5).

cl2nc follows semantic versioning.

• Added support for the HIS L2 format.

• Added support for a CL51 format as in R/V Polarstern data.

• Issue a warning when no output was created because an input file is empty.

• Fixed an issue of the last record in DAT files skipped.

• Fixed handling of certain types of time encoding.
• Issue a warning instead of an error when a line cannot be parsed.

• Fixed installation on Windows.

• Added manual page.

• Support for an alternative DAT format with UNIX timestamps.
• Improved error logging.
• New option: --debug.

• Support for Python 3.
• Accept directory input and output arguments.

• Changed time variable to contain time offset in seconds since 1970-01-01 00:00:00 UTC. time_utc contains the original time values (UTC as ISO 8601 strings).

• Fixed parsing on Windows (line endings).
• Added support for a specific CL31 format (timestamp line instead of checksum).

• Fixed writing of NA integer values.
• Fixed scale factor of backscatter_sum.

• Important: Fixed units conversion for sky condition height data and vertical resolution. In previous versions vertical_resolution is off by a factor of 0.3048 if input file units is ft. layer_height is off by a factor of 100 or 10 if units are ft or m, respectively.
• Added NetCDF file attributes: software, version, created.
• Format time with T as delimiter to conform to ISO 8601.
• Improved error handling.

ALCF, ccplot, ccbrowse, mpl2nc, mrr2c