Description

The BASIC code retrieves the extinction profile and the lidar ratio from combined lidar observations and aerosol optical depth measurements.

This program was initially developed by Augustin Mortier and Philippe Goloub at Laboratoire d’Optique Atmosphérique.

ICARE streamlined the original code for automatic processing and developed a command-line tool to facilitate manual runs. Also ICARE modified the code to support lidar data from the ORAURE network instruments including:

Inversion modes

Two inversion modes are currently available, each differs with the other by the nature measurements set as input:

  1. The algorithm expected naively lidar profile AND AOD measurements. Then it can benefit from miscellaneous physical properties contained in both files. This processing expects a NetCDF BALIA file as output.

  2. Otherwise the algorithm can also perform even if only the lidar profile is available. It needs assumptions about the lidar ratio over the time range. This processing expects a NetCDF BALI file as output.

Inputs

Lidar Pr2 signal

BASIC requires backscattered signal (or Pr2 signal) returned by LIDAR remote sensors.

In the frame of the french remote sensor network ORAURE, these measurements are gathered by the ICARE Data Center , and they are available through the web browser.

The name of variables containing the RCS values change depending on the data provider and the model of the lidar sensor.

Platform RCS Variable
SIRTA Palaiseau rcs_355_cop_an_l0_t0
  rcs_355_cop_ph_l0_t0
  rcs_355_crp_an_l0_t0
  rcs_355_crp_ph_l0_t0
LOA Photons Lille rcs_532_nop_ph_l0_t0
OPE Houdelaincourt rcs_355_cop_an_l0_t0
  rcs_355_cop_ph_l0_t0
  rcs_355_crp_an_l0_t0
  rcs_355_crp_ph_l0_t0
COPDD Puy-de-Dôme rcs_355_cop_an_l0_t0
  rcs_355_cop_ph_l0_t0
  rcs_355_crp_an_l0_t0
  rcs_355_crp_ph_l0_t0
  rcs_387_top_ph_l0_t0
  rcs_408_top_ph_l0_t0
QUALAIR Paris rcs_532
OPAR La Réunion rcs_355_cop_an_l0_t0

Aerosol Optical Depth

BASIC may also requires aerosol optical depth measurements (AOD) as input. These data are provided by the AERONET project and are also gathered in the frame of ORAURE project.

For each platform measurments are available in daily files and are computed for 3 different quality levels namely:

  • level 1.0: unscreened
  • level 1.5: cloud-screened
  • level 2.0: cloud-screened and quality assured

Refer to this data description in the AERONET web site for more information.

Besides the data quality the number of measurements may also strictly deacrease especially on a cloudy day.

Scientific settings

The BASIC algorithm needs miscellaneous scientific parameters to processing correlty. All of them are gathered in a unique file called the parameter file.

The unpacked BASIC archive contains samples of parameter files in the sub-directory parameters, such as <install-dir>/parameters/LOA-Photons_Lille.info.

For more information you can refer to the BASIC User Guide.

Outputs

Each run generates a NetCDF file as output. It contains values retrieved by the algorithm namely:

  • the lidar ratio: Lidar_Ratio
  • AODAeorosol_Optical_Depth_<WWW>nm
  • extinction coefficients: Extinction_Coefficient_<WWW>nm
  • the altitude of clouds along the lidar profile: Cloud_Base_Altitude_LidarCloud_Centroid_Altitude_LidarCloud_Top_Altitude_Lidar
  • the altitude of the boundary layer: Boundary_Layer_Altitude

with <WWW> the wavelength value required by the algorithm (in nm). It depends on the lidar remote sensor.

Refer to BALIA and BALI product descriptions for more information.

ICARE production

For each platform, the ICARE data center provides Level-2 daily files, formatted in the NetCDF standard format.

It provides 2 differents products which differ from their inversion mode:

  • BALIABASIC + LIdar + AERONET
  • BALIBASIC + LIdar

Then the BALIA file is generated in first. It requires both physical measurements:

  • Pr2 signal contained in lidar data files
  • AOD values (level 1.5) provided by the AERONET network

If one of these files is missing no BALIA can be produced.

Secondly the production process uses some retrievals contained is a previously generated BALIA file.

It make assumptions about the value of the lidar ratio along the time range. Indeed it directly extracts these data from the Time and the Lidar_Ratio variables contained in the BALIA file.

Then a new BASIC process can be launch using directly these assumptions, and the BALI is generated.

File Naming Convention

<PRODUCT_NAME>-L2_<YYYY>-<MM>-<DD>T00-00-00_<PLATFORM-NAME>_V<X-XX>.nc

with:

<PRODUCT-NAME> the name of product (BALIA or BALI)

<YYYY> the year of the acquistion (4 digits)

<MM> the month of the acquistion (2 digits)

<DD> the day of the acquisition (2 digits)

<PLATFORM-NAME> a standardized name of the platform, where each underscode character _ has been replaced by a minus character -

<X-XX> the product version

For example a BALI product came from the platform LOA-Photons_Lille with data measured the March 20th, 2012, and with 2-00 as product version, will yield the file:

BALI-L2_2012-03-2OT00-00-00_LOA-Photons-Lille_V2-00.nc