improve CL61 file format

[madrouin]

Improvement to apply to CL61 configuration file. Most parameters should already be available from the reader.

This issues gather the feedbacks

Feedbacks from Alexander

• Missing _FillValue for start_time, range_resol, l0_width, l0_beam_div, t0_fov, time_resol, l0_wavelength, l0_prf, station_latitude, station_longitude, station_altitude. (I removed dimension variables because dimensions shouldn't have missing value to be CF compliant)
• Laser, telescope and overlap are missing for rcs_0, rcs_1 and rcs_2. I can add these values. Could you provide them ?
• The background is not provided for rcs_1 and rcs_2. From the manual I understand that it’s not provided.

Feedbacks from Ina

• The long name of variables rcs_0, rcs_1, and rcs_2 are the same. It would be much better if the long names would be something like "calibrated range corrected signal", "calibrated parallel-polarized range corrected signal", "calibrated cross-polarized range corrected signal". Thus, the user would not need external documentation on which signal is what. Can easily be updated.
• Information about azimuth angle and tilt_angle_correction (whether the data have been corrected for tilt angle or not)
• The variables are important and missing in the proposed file format.
  • "cloud_calibration_factor"
  • "cloud_calibration_factor_user"
  • "fog_detection"
  • "cloud_thickness" and / or "cloud_penetration_depth"
  • "vertical visibility"
• the variable "linear_depol_ratio", I want to suggest a change of the long_name to "volume linear polarization ratio"

[madrouin]

I added most of the requested variables.

I couldn't find the values in CL61 documentations for the following variables:

• l0_width
• l0_beam_div
• t0_fov