Configurations for Rayleigh fit

[HolgerPollyNet]

@ZPYin:
Which parameters can be “tuned” for finding the calibration height of the lidar signals for the backscatter retrieval, i.e. for the Rayleigh fitting procedure?

I.e.: which parameter can be used how to make the search retrieval more strict or to relax the finding criteria.
Simple example in FAQ style: "Often, no backscatter profiles at 355 nm are produced while they exist at 532 and 1064 nm - what can I do?"

[ZPYin]

There are 7 parameters can be tuned for Rayleigh fit, see as below:

1. decomSmoothWin{wavelength}
2. maxDecomHeight{wavelength}
3. maxDecomThickness{wavelength}
4. minDecomLogDist{wavelength}
5. minRefThickness{wavelength}
6. minRefSNR{wavelength}
7. minRefDeltaExt{wavelength}

They all have different influences on the final reference height. Details of these parameters can be found in polly_config.pdf and Picasso_Rayleigh_fit_algorithm.pptx.

Regarding finding more reference height at 355 nm, one should inspect the signal profile to exclude reasons like wrong laser pointing or extremely low signal strength. After that, maxDecomThickness can be tuned to be larger and minRefSNR can be tuned to be smaller, to relax the Rayleigh fit criteria. Usually, only these two parameters should be tried.

If this does not improve the results, you can contact the developer or raise issue/discussion with the polly config file attached.

[HolgerPollyNet]

Thanks, by increasing maxDecomHeight{wavelength}, do I incrase the maximum height considered for finding a reference range?

[ZPYin]

Yes. maxDecomHeight{wavelength} is the maximum height for searching reference height.