--- title: "NDVI, NDWI, NDMI: A Farm Manager's Guide to Satellite Health Maps" description: A plain-language guide to the satellite indices behind crop health maps — NDVI, SAVI, GNDVI, NDWI and NDMI — and how to combine them for better farm decisions. --- [Skip to content](https://horizonsatellite.net/en/satellite-services-ai-horizon-it/ndvi-ndwi-ndmi-a-farm-managers-guide-to-satellite-health-maps#main-content) [Contact us](mailto:contactus@horizonsit.net) [![Color logo with background-1](https://horizonsatellite.net/hs-fs/hubfs/Color%20logo%20with%20background-1.png?width=300&height=75&name=Color%20logo%20with%20background-1.png)](https://www.horizonsit.net) - Home - Products - Pricing - Blog - Company Open main navigation Close main navigation - Home - Products - Pricing - Blog - Company - [Contact us](mailto:contactus@horizonsit.net) Oct 5, 2026, 12:39:55 PM # NDVI, NDWI, NDMI: A Farm Manager's Guide to Satellite Health Maps [Horizon Satellite](https://horizonsatellite.net/en/satellite-services-ai-horizon-it/author/horizon-satellite) Share: [facebook-f icon](http://www.facebook.com/share.php?u=https://horizonsatellite.net/en/satellite-services-ai-horizon-it/ndvi-ndwi-ndmi-a-farm-managers-guide-to-satellite-health-maps) [linkedin-in icon](http://www.linkedin.com/shareArticle?mini=true&url=https://horizonsatellite.net/en/satellite-services-ai-horizon-it/ndvi-ndwi-ndmi-a-farm-managers-guide-to-satellite-health-maps) [Twitter icon](https://twitter.com/intent/tweet?url=https://horizonsatellite.net/en/satellite-services-ai-horizon-it/ndvi-ndwi-ndmi-a-farm-managers-guide-to-satellite-health-maps) [pinterest-p icon](http://pinterest.com/pin/create/link/?url=https://horizonsatellite.net/en/satellite-services-ai-horizon-it/ndvi-ndwi-ndmi-a-farm-managers-guide-to-satellite-health-maps) [envelope icon](mailto:?body=https://horizonsatellite.net/en/satellite-services-ai-horizon-it/ndvi-ndwi-ndmi-a-farm-managers-guide-to-satellite-health-maps) ![Satellite crop health map](https://horizonsatellite.net/hubfs/agriculture-environment03.jpg) A satellite crop report usually arrives as a set of coloured maps with short names: NDVI, SAVI, NDMI. Each one answers a different question. Read together, they explain what is happening in your field and why. Here is what each index measures, in plain language. ## How satellites "see" plant health Healthy leaves absorb red light for photosynthesis and strongly reflect near-infrared (NIR) light. Stressed or sparse vegetation reflects less NIR. Water, by contrast, absorbs shortwave-infrared (SWIR) light. Multispectral satellites such as Sentinel-2 record these bands every few days at 10–20 m resolution, and commercial satellites go much finer. Each index is simply a ratio of bands designed to highlight one property. ## The core indices - **NDVI — vegetation vigour.** Compares NIR and red light. Higher values mean denser, more active canopy. It is the starting point, but it can saturate over very dense crops and is affected by bare soil. - **SAVI — vigour on sparse fields.** A version of NDVI corrected for soil brightness. Useful for young crops, orchards and desert farms where a lot of soil is visible between plants. - **GNDVI — chlorophyll and nitrogen.** Uses green light instead of red, making it more sensitive to chlorophyll content. Helpful for spotting uneven nutrition. - **NDMI — water inside the plant.** Compares NIR and SWIR light to estimate canopy water content. Falling NDMI is often an early sign of water stress, before it shows in NDVI. - **NDWI — surface water.** Highlights open water and very wet surfaces. Useful for detecting waterlogging, leaks and ponding. ## Why one map is never enough A low NDVI tells you *where* plants are weak, not *why*. Combining indices narrows the cause: - **Low vigour + low plant moisture** → likely water stress. Check irrigation coverage and scheduling. - **Low vigour + high surface moisture** → likely drainage, waterlogging or salinity. More water will not help. - **Normal vigour + uneven GNDVI** → possible nutrition differences. Plan targeted soil and leaf sampling. - **Circular or linear patterns** → often infrastructure: a broken line, a blocked emitter, a faulty pivot nozzle. In one of our reports, a weak sector of a centre-pivot field turned out to have *more* moisture than the rest. The diagnosis moved from "add water" to "check drainage and salinity", which saved both water and money. ## Time is the most important band A single image is a snapshot. Comparing the same field across seasons and years shows whether a problem is new, recurring or spreading, and whether last season's fix actually worked. This is where satellites are hard to beat: the archive goes back years, at no extra field cost. ## What satellites cannot do Satellite indices point to where and roughly why. They do not replace an agronomist. The best results come from using the maps to decide **where to sample and inspect**, then confirming on the ground. ## Next Step Want to see these maps for your own farm? Book a short call and we will show you a sample report. [Book a Meeting](https://www.horizonsatellite.net/meetings/bassem-shaaban?hsLang=en) facebook-f icon linkedin-in icon Twitter icon instagram icon - Home - Products - Pricing - Blog - Company --- --- Building No. 3978, Abdullah Al Makhthob St. Al Wadi District, Riyadh 13313 Kingdom of Saudi Arabia 🌍 📞 +966 593755042 ✉️ [info@horizonsatellite.net](mailto:info@horizonsatellite.net) 🌐 [www.horizonsatellite.net](https://www.horizonsatellite.net?hsLang=en) © 2025 Horizon Satellite. 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