ECAC - Forum

Hello everybody,

I'm looking at the AE-33 lev0 data template. I see that attenuation coefficients are expected to be reported, even if they are not a direct output of the AE-33 instrument.
Do you calculate them with the following formula?

Att (λ) = eBC(λ)*sigma(λ)*C (1.57)

Is it correct?
Maybe it should be reported in the EBAS instructions/templates for data reporting.

Many thanks for your help

Best Regards
Angela

Hello Angela,

Since the ATN is an output of basic measurement data it would not be a good idea to perform a back calculation including undoing corrections. This is also not practicable because of the dual spot method, or the correction you describe would then have to be done for both spots WITHOUT dual spot correction. Would the leakage correction also have to be taken into account?
I myself have no experience whether this method is applicable. Have you compared the method via back calculation from eBC and a calculation directly from intensities?

The data loggers, which will soon be available for NRT, will also output the ATN.
There the ATN is calculated from the initial intensity and the current intensity with ATN = - 100 * ln (I/I0).
We will soon open a topic in the forum on these NRT data loggers.

Best regards,
Thomas

Thanks a lot Thomas for your reply.

Actulally, I was wondering if there was a nomenclature inaccuracy: with att1_1, att2_1, are defined as attenuation coefficient in the metadata, but we should report the attenuations. Is it correct? Should the metadata be changed from attenuation coefficien to attenuation?

Anyway, by applying the formula you suggested (ATN=-100*ln(sens/ref), to the values of the level0 template (downloaded by EBAS submission manual and related to Zeppelin station) the values are not corresponding. See below.

Were I am wrong?

Thank you very much for your help
Angela

Hi Angela,
I'm fighting with the same thing. I assumed (based on the suggested equation) that what was needed is attenuation, not coefficients. However, since our attenuation goes up to 120 before spot change, and the missing value flag in the template is 99.99999, I'm baffled again. Trying to sort this out with the ebas- team.

Best,
Antti

There is another small issue in the AE-33 metadata template; the green wavelength is typed 525 nm, although the instrument manual states 520 nm.