cl2nc

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

Example

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.

Installation

Supported operating systems:

• Linux
• Windows
• macOS

Requirements:

• Python 2.7 or Python 3

On Windows and macOS Anaconda distribution of Python is recommended. On Linux, use Python which comes with your Linux distribution (either built-in, or installed through a package manager).

The following commands should be run in the Terminal (Linux and macOS) or Anaconda Prompt (Windows – you can find Anaconda Prompt in the Start menu). To install with Python 3 instead of Python 2, replace pip with pip3 and python with python3 in the commands below.

To install from the Python Package Index (PyPI):

pip install cl2nc

or to install in the user's home directory (make sure ~/.local/bin is in the PATH environment variable):

pip install cl2nc --user

Alternatively, to install from source, download and unpack the latest cl2nc archive, or clone the repository from GitHub (git clone https://github.com/peterkuma/cl2nc.git). In the package directory, run the following commands:

pip install netCDF4
python setup.py install

# or to install in the user's home directory
# (make sure `~/.local/bin` is in the `PATH` environment variable):

python setup.py install --user

You can also use the Python script cl2nc directly without installation (as long as netCDF4 is installed).

Once installed, you should be able to run cl2nc in the Terminal (Linux and macOS) or Anaconda Prompt (Windows).

Usage

cl2nc [-chq] [--debug] [--help] <input> <output>

<input> is an input .dat file. <output> is an output .nc file. If directories are supplied for <input> and <output>, all .dat and .DAT files in <input> are converted to .nc files in <output>.

Options:

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

A manual page is also available if cl2nc is installed on unix-like operating systems:

man cl2nc

Variables

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 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.

background_light

Background light (mV)

Millivolts at internal ADC input.

backscatter

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

backscatter_sum

Backscatter sum (sr^-1)

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

cbh_1

Lowest cloud base height (m)

cbh_2

Second lowest cloud base height (m)

cbh_3

Highest cloud base height (m)

detection_status

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

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

Highest signal detected

laser_temperature

Laser temperature (°C)

layer

Layer number

layer_cloud_amount

Layer cloud amount (octas)

Sky condition algorithm.

layer_height

Layer height (m)

Sky condition algorithm.

level

Level number

message_number

Message number

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

message_subclass

Message subclass

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

pulse_energy

Pulse energy (% of nominal factory setting)

pulse_length

Pulse length

• L – long (100 ns)
• S – short

pulse_count

Pulse count

receiver_bandwidth

Receiver bandwidth

• N – narrow
• W – wide

receiver_gain

Receiver gain

• H – high
• L – low

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

self_check

Self check

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

software_level

Software level ID

status_alarm

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

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

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

Tilt angle (degrees from vertical)

time

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

time_utc

Time (UTC) (ISO 8601)

unit

Unit identification character

vertical_resolution

Vertical resolution (m)

vertical_visibility

Vertical visibility (m)

window_transmission

Window transmission estimate (%)

90% to 100% means the window is clean.

Attributes

software

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

version

cl2nc version string. Follows semantic versioning.

created

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

License

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

Support

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

FAQ

cl2nc fails with an exception.

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.

Where is the height information?

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

MATLAB cannot read the time_utc variable.

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).

Changelog

cl2nc follows semantic versioning.

3.3.1 (2021-03-24)

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

3.3.0 (2020-08-27)

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

3.2.2 (2020-07-17)

• Fixed installation on Windows.

3.2.1 (2020-02-08)

• Added manual page.

3.2.0 (2020-02-08)

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

3.1.0 (2019-04-27)

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

3.0.0 (2018-08-20)

• 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).

2.1.0 (2017-11-25)

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

2.0.1 (2017-10-23)

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

2.0.0 (2017-10-19)

• 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.

See also

ALCF, ccplot, mpl2nc, mrr2c