The S2 Red Edge Position results from the following equation: S2REP = 705 + 35*( (Red+ VNIR3)/2 - VNIR) / (VNIR2-VNIR) using Sentinel-2 Bands 4 (Red), 5 (VNIR), 6 (VNIR2) Band 7 (VNIR3).
S2REP is sensitive to both (crop) chlorophyll content and growth status. Generally, the higher the S2REP value, the higher is the chlorophyll content.
This product is based on the open and free software suit Sentinel-2 Toolbox.
Relevant citation: Guyot, G., & Baret, F., 4th International Colloquium “Spectral signatures of objects in remote sensing”, p.279 (1988)