> ## Documentation Index
> Fetch the complete documentation index at: https://docs.agronome.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Viewing Vegetation Indices

> How to use the Analyze tab to view and compare vegetation index layers

# Viewing Vegetation Indices

The **Analyze** tab on each field's detail page provides a unified view of all imagery layers — drone flights and satellite passes — on an interactive map.

## Available indices

| Index     | Full Name                                    | Formula                                          | What it measures                                           |
| --------- | -------------------------------------------- | ------------------------------------------------ | ---------------------------------------------------------- |
| **NDVI**  | Normalized Difference Vegetation Index       | (NIR - Red) / (NIR + Red)                        | Overall vegetation health and density                      |
| **NDRE**  | Normalized Difference Red Edge               | (NIR - RedEdge) / (NIR + RedEdge)                | Chlorophyll content, nitrogen stress detection             |
| **GNDVI** | Green Normalized Difference Vegetation Index | (NIR - Green) / (NIR + Green)                    | Chlorophyll concentration, early stress                    |
| **SAVI**  | Soil-Adjusted Vegetation Index               | 1.5 × (NIR - Red) / (NIR + Red + 0.5)            | Vegetation in sparse canopy (reduces soil influence)       |
| **EVI**   | Enhanced Vegetation Index                    | 2.5 × (NIR - Red) / (NIR + 6×Red - 7.5×Blue + 1) | Vegetation in dense canopy (reduces atmospheric influence) |
| **CHM**   | Canopy Height Model                          | DSM - ground reference                           | Crop height and growth uniformity                          |

## Using the Analyze tab

### Layer selection

1. Navigate to a field and open the **Analyze** tab
2. The timeline at the bottom shows all available dates (drone flights and satellite passes)
3. Select a date to load its layers
4. Use the layer picker to switch between available indices

### Colormaps

Vegetation indices render with scientifically standard colormaps:

* **RdYlGn** (Red-Yellow-Green) — default for most indices. Red = low/stressed, green = healthy
* **Viridis** — perceptually uniform, colorblind-friendly alternative

Toggle between colormaps using the colormap selector above the map.

### Comparing layers

* Use the **opacity slider** to blend a vegetation index over the base map or orthomosaic
* Switch between drone and satellite layers for the same date range to compare resolution and coverage
* The timeline supports scrolling through historical data to track changes over the growing season

## Interpreting NDVI values

| NDVI Range  | Interpretation                                | Typical appearance    |
| ----------- | --------------------------------------------- | --------------------- |
| -1.0 to 0.0 | Water, bare soil, or non-vegetated            | Dark red              |
| 0.0 to 0.2  | Bare soil, residue, or very sparse vegetation | Red to orange         |
| 0.2 to 0.4  | Sparse vegetation, early growth stage         | Orange to yellow      |
| 0.4 to 0.6  | Moderate vegetation density                   | Yellow to light green |
| 0.6 to 0.8  | Dense, healthy vegetation                     | Green                 |
| 0.8 to 1.0  | Very dense, peak vegetation                   | Dark green            |

<Tip>
  NDVI is a good general indicator, but NDRE is more sensitive to nitrogen stress in mid- to late-season crops. Use NDRE when scouting for nutrient deficiencies.
</Tip>