How to create wavelength and FWHM files

[reseadmin]

As the error message says, there is no fwhm tag in the ENVI header. You would need to add such a tag manually.
NOTE: In the latest release (7.0) of atcor4, this routine is obsolete - you may choose an ENVI header directly instead of the wavelength file when creating the response files. If no fwhm tag is found, a FWHM of 1.2* samling interval is assumed as a default.