ALCF-LIDAR(1)

NAME
alcf-lidar - Process lidar data.

SYNOPSIS
alcf lidar <type> [<options>] [<algorithm_options>] [--] <lidar> <output>

DESCRIPTION
The processing is done in the following order:

○   noise removal

○   calibration

○   time resampling

○   height resampling

○   cloud detection

○   cloud base detection

Arguments following -- are treated as literal strings. Use this delimiter if the input or output file names might otherwise be interpreted as non-strings, e.g. purely numerical file names.

ARGUMENTS

type
    Lidar type (see Types below).

lidar
    Input lidar data directory or filename. If a directory, only .nc files in the directory are processed. If the option -r is supplied, the directory is processed recursively.

output
    Output filename or directory.

options
    See Options below.

algorithm_options
    See Algorithm options below.

TYPES

blview
    Vaisala BL-VIEW L2 product.

chm15k
    Lufft CHM 15k.

cl31
    Vaisala CL31.

cl51
    Vaisala CL51.

cl61
    Vaisala CL61.

cosp
    COSP simulated lidar.

default
    The same format as the output of alcf lidar.

minimpl
    Sigma Space MiniMPL (converted via SigmaMPL).

mpl Sigma Space MPL (converted via SigmaMPL).

mpl2nc
    Sigma Space MPL and MiniMPL (converted via mpl2nc).

OPTIONS

align_output: <value>
    Align output time periods to the nearest multiple of output_sampling. Default: true.

altitude: <altitude>
    Altitude of the instrument (m). Default: Taken from lidar data or 0 if not available.

bsd: <value>
    Assume a given standard deviation of backscatter noise when detecting clouds or none to use the value calculated by the noise removal algorithm from observed backscatter if available (m^-1.sr^-1). The value applies at height bsd_z and is range-scaled for other heights. A suitable value can be taken from a plot generated by alcf plot backscatter_sd_hist. Default: none.

bsd_z: <value>
    Height at which bsd applies (m). Default: 8000.

calibration: <algorithm>
    Backscatter calibration algorithm. Available algorithms: default, none. Default: default.

couple: <directory>
    Couple to other lidar data. Default: none.

cl_crit_range: <range>
    Critical range for the fix_cl_range option (m). Default: 6000.

cloud_detection: <algorithm>
    Cloud detection algorithm. Available algorithms: default, none. Default: default.

cloud_base_detection: <algorithm>
    Cloud base detection algorithm. Available algorithms: default, none. Default: default.

--fix_cl_range
    Fix CL31/CL51 range correction (if noise_h2 firmware option if off). The critical range is taken from cl_crit_range.

keep_vars: { <... }
    Keep the listed input variables. The variable must be numerical and have a time dimension. The variable is resampled in the same way as backscatter along their time and level dimensions, its name is prefixed with input_, and its type is changed to float64. Default: { }.

lat: <lat>
    Latitude of the instrument (degrees North). Default: Taken from lidar data or none if not available.

lon: <lon>
    Longitude of the instrument (degrees East). Default: Taken from lidar data or none if not available.

noise_removal: <algorithm>
    Noise removal algorithm. Available algorithms: default, none. Default: default.

output_sampling: <period>
    Output sampling period (seconds). Default: 86400 (24 hours).

-r  Process the input directory recursively.

time: { <low> <high> }
    Time limits (see Time format below). Default: none.

tres: <tres>
    Time resolution (seconds). Default: 300 (5 min).

tshift: <tshift>
    Time shift (seconds). Default: 0.

zlim: { <low> <high> }
    Height limits (m). Default: { 0 15000 }.

zres: <zres>
    Height resolution (m). Default: 50.

CLOUD DETECTION OPTIONS

default
    Cloud detection based on backscatter threshold.

none
    Disable cloud detection.

CLOUD DETECTION DEFAULT OPTIONS

cloud_nsd: <n>
    Number of noise standard deviations to subtract. Default: 5.

cloud_threshold: <threshold>
    Cloud detection threshold (m^-1.sr^-1). Default: 2e-6.

cloud_threshold_exp: { <x> <y> <h> }
    Cloud detection threshold exponentially decaying with height (sr^-1.m^-1). If not none, this supersedes cloud_threshold. The threshold is <x> at surface level, decaying exponentially to <y> at infinite height with half-height <h>. Default: none.

CLOUD BASE DETECTION OPTIONS

default
    Cloud base detection based cloud mask produced by the cloud detection algorithm.

none
    Disable cloud base detection.

CALIBRATION OPTIONS

default
    Multiply backscatter by a calibration coefficient.

none
    Disable calibration.

CALIBRATION DEFAULT OPTIONS

calibration_file: <file>
    Calibration file.

NOISE REMOVAL OPTIONS

default
    Noise removal based on noise distribution on the highest level.

none
    Disable noise removal.

NOISE REMOVAL DEFAULT OPTIONS

○   noise_removal_sampling: <period>: Sampling period for noise removal (seconds). Default: 300.

○   near_noise: { <scale> <range> } : Assume additional exponentially-decaying near-range noise. The first argument is the value at zero range (sr^-1.m^-1). The second argument is range at which the function decays to a half (m). Default: { 0 0 }.

TIME FORMAT
YYYY-MM-DD[THH:MM[:SS]], where YYYY is year, MM is month, DD is day, HH is hour, MM is minute, SS is second. Example: 2000-01-01T00:00:00.

EXAMPLES
Process Vaisala CL51 data in cl51_nc and store the output in cl51_alcf_lidar, assuming instrument altitude of 100 m above sea level.

    alcf lidar cl51 cl51_nc cl51_alcf_lidar altitude: 100

COPYRIGHT
Copyright © 2019–2024 Peter Kuma, Adrian J. McDonald, Olaf Morgenstern, Richard Querel, Israel Silber and Connor J. Flynn.

BUG REPORTING
Report bugs to Peter Kuma (peter@peterkuma.net).

SEE ALSO
alcf(1), alcf-auto(1), alcf-calibrate(1), alcf-compare(1), alcf-convert(1), alcf-download(1), alcf-model(1), alcf-plot(1), alcf-simulate(1), alcf-stats(1)