When you look at a healthy green field, your eyes perceive reflected light. But what if we told you plants reveal their true health status through light wavelengths you can't see? This is the science behind NDVI—technology that AgriSat uses to monitor crops across Ghana.
What is NDVI?
Normalized Difference Vegetation Index (NDVI) is a mathematical calculation that compares how a plant reflects near-infrared light versus visible red light. Healthy, photosynthetically active plants reflect more near-infrared and absorb more visible red light. Stressed or dying plants reflect less near-infrared.
NDVI values range from -1 to +1:
- +0.8 to +1.0: Dense, healthy vegetation
- +0.6 to +0.8: Healthy but less dense vegetation
- +0.4 to +0.6: Sparse vegetation or early growth
- +0.2 to +0.4: Stressed vegetation
- Below +0.2: Bare soil, water, or dead vegetation
The Mathematics Behind NDVI
NDVI = (NIR - Red) / (NIR + Red)
Where NIR = Near-Infrared reflectance, Red = Visible Red reflectance
How AgriSat Uses NDVI
Our satellites capture imagery of your farm multiple times per week. Each image is processed through AgriSat's algorithms to calculate NDVI values for every pixel. We then:
- Create NDVI maps showing crop health across your entire farm
- Track changes over time to detect emerging problems
- Compare current readings with historical averages
- Alert you when NDVI values drop unexpectedly
Early Warning System
NDVI can detect crop stress 10-14 days before visible symptoms appear, giving you precious time to take corrective action.
What NDVI Reveals
NDVI changes can indicate various problems:
- Water stress: NDVI drops as plants close stomata to conserve water
- Nutrient deficiency: Particularly nitrogen, causes visible yellowing and NDVI decrease
- Pest attacks: Infested areas show dramatically lower NDVI values
- Disease: Fungal and bacterial diseases reduce photosynthetic activity
- Compaction: Poor root development shows as patchy low-NDVI areas
Limitations of NDVI
While powerful, NDVI has limitations farmers should understand:
- Cannot identify specific diseases or pests—only general stress
- Affected by cloud cover (we use multiple satellites to minimize this)
- Soil background can influence readings in early crop growth stages
- Different crops have different optimal NDVI ranges
The Future: Enhanced Vegetation Index
AgriSat is developing enhanced indices that combine NDVI with other spectral bands for more specific crop health insights. Future updates will include disease-specific detection algorithms trained on thousands of crop disease images from Ghanaian fields.
See NDVI in Action
Request a demo to see how satellite monitoring can transform your farm management.
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