Non-linear least squares fit oxygen optode against bottle oxygen.
Note: optode data that were obtained during bottle stops can be used for calibration
instead of density matching the downcast (see Uchida 2010, pg. 7).
Parameters:
btl_df (DataFrame) – CTD data at bottle stops
time_df (DataFrame) – Continuous CTD data
ssscc_list (list of str) – List of stations to process