Stratocumulus backscatter calibration

The SCCAL command allows a simple stratocumulus backscatter calibration of the scatter coefficient measurements. This requires a human observer to confirm a stable Stratocumulus cloud layer between 250 m (820 ft) to 2500 m (8202 ft) without holes, precipitation or reduced visibility, and has been stable for at least 10 minutes prior to running this command.

Set the Measurement_Period to 10 (see Summary of the terminal mode commands available).

A detailed description of this technique is given in: Ewan J. O’Connor, Anthony J. Illingworth, and Robin J. Hogan, 2004: A Technique for Autocalibration of Cloud Lidar. Journal of Atmospheric and Ocean Technology, 21, pp 777 – 786.

Enter terminal mode by typing Open 0 (for a sensor with an ID of 0)

This will return the prompt: CS135>

Type SCCAL

The SkyVue PRO will respond:

Stratocumulus calibration.

Enter height above sea level (m)? Press enter to continue:

Enter the sensor height above sea level, for example 70 m then type return.

The SkyVue PRO will respond: 70 m entered, is this correct? “Y”, “N” or “Q”

Type Y to confirm. If you have entered an incorrect number, type N and you will be able to replace it. Type Q to quit the calibration and return to the terminal command prompt.

The SkyVue PRO will respond:

For correct calibration a trained human observer must confirm that the layer is between 250 m (820 ft) to 2500 m (8200 ft) and has been stable for at least 10 minutes without drizzle. Has the Stratocumulus been stable for at least 10 minutes? “Y” or “N”

To confirm, type Y and the SkyVue PRO will respond:

Old Stratocumulus calibration = 0.0282

New Stratocumulus calibration parameters = 0.0258 70 1328

Do you want to apply this calibration? “Y” or “N”

In this example, 70 is the height of the sensor above sea level previously entered and 1210 is the cloud base in meters above the sensor.

As a rough guide, if the calibration factor has changed by less than 20%, there is no need to change. If it has changed by a factor of 2, it is wise to run the service routine on the sensor (see Service command).

Type Y to confirm and the SkyVue PRO will respond:

Calibration saved.

The following error messages may appear during the process.

  • Error ... Time out

  • Error ... Cloud not detected or height not within limits

    (250 m to 2500 m / 820 ft to 8200 ft)

  • Try again when layer is stable

  • Error ... Not enough data available try again in 10 minutes.