9 cards showing.
NDVI typical value ranges by land cover?
likely vegBeyond standard VIs — two linear transforms?
maybe vegEVI — formula and coefficients?
essential vegThink of EVI as NDVI’s smarter cousin. It does two extra tricks:
Use EVI when NDVI flatlines — i.e., over thick rainforest canopy where every leaf already maxes NDVI out. EVI keeps climbing where NDVI gets stuck.
EVI = [(NIR − Red) / (NIR + C₁·Red − C₂·Blue + L)] · (1 + L)
C₁ = 6.0, C₂ = 7.5, L = 1.0 (MODIS standard). Corrects NDVI for atmosphere (blue band) and soil (L).
EVI = Enhanced with the Blue band. Coefficients 6-7-1 (six-seven-one). Doesn't saturate in dense canopy like NDVI does.
NDVI of AVHRR imagery — what does it show?
maybe vegContinental US NDVI through the seasons (Jan → Dec):
🛰️ AVHRR on NOAA polar orbiters, ~1 km resolution.
Why does EVI need blue, C1, C2, and L?
maybe vegResult: EVI doesn’t saturate in high-biomass canopies the way NDVI does.
Spectral signature of healthy vegetation?
essential vegThat contrast is why NDVI, SR, and EVI all work.
Leaves DRINK red (chlorophyll eats it), BOUNCE NIR. That 'red dip, NIR jump' is THE vegetation fingerprint.
Simple Ratio (SR) — formula and who’s credited?
essential vegThe first vegetation index. Divide NIR by Red — see how much more NIR came back. A jungle gives you 30+, a parking lot gives you 1. Simple but the number has no upper limit, so you can’t easily compare scenes against each other.
That’s why NDVI replaced it for most modern work — same idea, but locked between −1 and +1.
SR = NIR / Red. Cohen (1991) identified it as the first true vegetation index. On Landsat TM: Band 4 / Band 3.
Simple Ratio = Simple division. No subtraction, no normalization — just NIR/Red. Unbounded. Cohen 1991 (not Rouse, that's NDVI).
Phenology — definition and why it matters for RS?
likely vegPhenology — periodic biological phenomena tied to annual climate (🌱 planting → 🌿 greening → 🌾 senescence → 🚜 harvest).
Why it matters for remote sensing: - 📅 Imaging date changes what you see - 🌾 Peak biomass maximizes vegetation / soil contrast - 📊 Multi-date NDVI series separates crops that overlap when green
NDVI — formula and range?
essential vegPlants pull a sneaky trick with light: chlorophyll drinks red light for photosynthesis but bounces back invisible near-infrared. NDVI just compares the two bands — the bigger the gap, the healthier the vegetation. Numbers land between −1 (water / shadow) and +1 (lush rainforest). The middle is bare ground.
It’s basically a ‘how green is this place’ score that NASA, USDA, and every satellite ag company uses every day.
NDVI = (NIR − Red) / (NIR + Red). Range −1 to +1. Rouse et al. (1974).
NDVI = Normalized to −1..+1. Unlike SR which has no upper bound, and unlike EVI which adds the Blue band.