crop-stress-multiindex

○unverified

Per-field crop stress diagnosis from a Sentinel-2 multi-index time series: EVI (canopy structure, saturation-resistant), NDRE (red-edge chlorophyll and nitrogen status), and NDMI (SWIR canopy moisture / water stress). Together the three indices separate stress TYPE that NDVI alone cannot resolve — a field with low NDRE is nitrogen-deficient; low NDMI flags water stress; both falling simultaneously indicates compound stress. For each clear S2 pass the recipe computes EVI, NDRE, and NDMI at field resolution, derives seasonal means per index, and flags per-field stress using a combined stress index (CSI = mean of z-scored deficits across the three indices). The per-field table is the deliverable; the index stacks and seasonal mean rasters are the "show your work" layers. The recipe extends crop-monitoring (NDVI harmonic phenology) by adding two diagnostic axes — chlorophyll/N (NDRE) and water (NDMI) — alongside a saturation-resistant canopy index (EVI). Together they allow a field scout to ask: "is this field stressed, and WHY?" Index formulas (Sentinel-2 band names, baseline >= 04.00 BOA reflectance): EVI = 2.5 * (B08 - B04) / (B08 + 6*B04 - 7.5*B02 + 1) [Huete 2002] NDRE = (B08 - B05) / (B08 + B05) red-edge NIR vs red-edge 705 nm [Gitelson 2003] NDMI = (B08 - B11) / (B08 + B11) NIR vs SWIR-1 1610 nm [Gao 1996]