There are many spectral indices in literature. However, the formulas mostly refer to landsat imagery, and thus the corresponding spectral bands.
Question: How can a formula that was originally designed for Landsat be converted into a Sentinel formula?
Problem: Not all Landsat and Sentinel bands seem to correlate well, as Sentinel has a higher number of bands that often also differ in the spread of wavelengths covered. These differences have to have some influence on the results when adjusting the formula from Landsat to Sentinel. I'm especially confused in Landsat8 Band 5, which is covered by Sentinel Band 8 and 8a. Furthermore, Sentinel data has Bands 5,6 and 7, which are not covered in Landsat8 data. Older Indices are missing these spectral bands completely.
In some bands they also strongly differ reflectance.
Example: Let's take the Enhanced Built-Up and Bareness Index (EBBI) formula as an example for discussion (As-syakur 2012). Band 4 and 6 are easy to pick (Sentinel 4 and 11, respectively)
Next, the formula states to take the Landsat 5 Band. When converting it to Sentinel, the question arises whether to take Band 8 or Band 8a.