Plant Senescence Reflectance Index (PSRI) is a tool for identifying the stages of leaf senescence and fruit ripening with a higher degree of precision. It is sensitive to accumulation and/or retention of carotenoid in senescing leaves and ripening fruit.

PSRI = (red-blue)/nir08 Sentinel = (B04-B02)/B06
Landsat 8-9 = (red-blue)/nir08
Firefly = (B064-B009)/B086