An overview of the history and radiometric concepts of field spectrometry is given by @milton_progress_2009. Fundamental to the method is the concept of a 'reflectance factor' (RF) [@nicodemus_geometrical_1977], defined as;
“the ratio of the radiant flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal (lossless) perfectly diffuse (Lambertian) standard surface irradiated in exactly the same way as the sample.”
The typical metadata that should be collected for each RF measurement is summarised by (@milton_progress_2009, Table X);
Some of the items on this list require specialised equipment that may not be available at all field sites (such as meteorological parameters), for these cases, nearby meteorological stations may be used. For the description of sky conditions, standardised photographs are useful to augment written descriptions.
Using the OO SeaBreeze drivers https://github.com/ap--/python-seabreeze
Direct? python library: https://github.com/ap--/python-oceanoptics
http://lukemiller.org/index.php/2014/08/open-wave-height-logger/