## Overview

A **spectral index** (also called a spectral bandset) is a simple mathematical combination of a few spectral bands that highlights one specific characteristic of the landscape being imaged — for example, how healthy a crop is, how turbid a water body is, or whether a mineral deposit is present.

Satellite and hyperspectral sensors capture reflectance across dozens to hundreds of individual wavelength bands. On their own, these raw bands are hard for a non-specialist to interpret — a single band value doesn't tell you whether vegetation is stressed or a water body is polluted. Indices solve this problem by combining two or more bands into a single formula that produces one output value per pixel, which can then be visualized as a map or tracked over time.

In short, spectral indices:

- **Simplify interpretation** — instead of asking a customer to read raw reflectance values, Aurora shows them a single, purpose-built layer (e.g., "Vegetation Health" or "Water Turbidity").
- **Standardize comparison** — the same index calculated the same way lets customers compare one AOI (Area of Interest) to another, or the same AOI over time.
- **Map directly to business questions** — most indices exist because they answer a specific, well-established question in a given industry (agriculture, water management, mining, urban planning, and so on).

Aurora maintains a master table of these indices. This page explains how to read that table.
## Why Spectral Indices Matter

Every index on Aurora's list exists to isolate one signal from the noise of raw imagery. Conceptually, here's what that looks like across a few common domains:

- **Vegetation health** — Indices such as NDVI705, MTCI, and PSRI are built around how plants absorb and reflect light differently depending on chlorophyll content, water stress, and senescence (aging/dying-off). A healthier, greener canopy reflects light differently than a stressed or yellowing one, and vegetation indices are tuned to detect that difference.
- **Water quality** — Indices such as NDCI and CI are designed to pick up on chlorophyll and cyanobacteria concentrations in water bodies, which are strong proxies for algal blooms and eutrophication.
- **Mineral identification** — Certain indices are tuned to the specific absorption features of minerals (for example, iron oxides or clay minerals), which is why some of Aurora's indices are grouped under domains like Rare Earth or Transition Metals.
- **Urban materials** — Some indices help separate built-up, impervious surfaces (concrete, asphalt, rooftops) from vegetation or bare soil, which is useful for urban planning and infrastructure monitoring.
- **Environmental monitoring** — Many of the same vegetation and water indices double as environmental indicators — for example, tracking turbidity trends in a river or greenness trends in a protected area over months or years.

## Understanding the Bandsets Table

Aurora's spectral indices table has the following columns. Here's what each one means and how to read it:

| Column | What it tells you |
|---|---|
| **Index** | The short, commonly used name for the index (e.g., `NDVI705`, `PSRI`, `NDCI`). This is the name customers and the remote sensing community will recognize. |
| **Full Name** | The spelled-out name of the index (e.g., "Normalized Difference Chlorophyll Index"). Useful when a customer asks "what does NDCI stand for?" |
| **Required Bands** | The specific Pixxel HSI band IDs (e.g., `B060, B073`) that feed into the index's formula. More bands generally means a more specific or nuanced measurement. |
| **Formula (HSI)** | The exact calculation used when the index is generated from Pixxel's hyperspectral (HSI) imagery. |
| **Formula (Sentinel-2 MSI)** | The equivalent calculation using Sentinel-2 multispectral (MSI) bands, where such an equivalent exists. Marked `NA` when it doesn't (see [HSI vs MSI Availability](#hsi-vs-msi-availability) below). |
| **Application Categories** | A set of columns (Vegetation, Water, Urban, Rare Earth, Transition Metals, etc.) marked `YES` wherever that index is relevant to that domain. An index can apply to more than one domain. |


### Full Spectral Indices Table

This is the complete table as provided, with every index, its formulas, and its application categories.

| Index | Full Name | Required Bands | Formula (HSI) | Formula (Sentinel-2 MSI) | Application Categories |
|---|---|---|---|---|---|
| PSRI | Plant Senescence Reflectance Index | B009, B064, B086 | `(B064-B009)/B086` | `(B04-B02)/B06` | Vegetation |
| VARI | Visible Atmosphere Resistance Index | B005, B026, B059 | `(B026-B059)/(B026+B059-B005)` | `(B03-B04)/(B03+B04-B02)` | Water |
| CI | Cyanobacteria Index | B046, B060, B065 | `(B060-B046) + (B046-B065)*((45)/(61))` | NA | Water |
| NDCI | Normalized Difference Chlorophyll Index | B060, B073 | `(B073-B060)/(B073+B060)` | `(B05-B04)/(B05+B04)` | Water, Vegetation |
| NDVI705 | NDVI 705nm | B071, B086 | `(B086-B071)/(B086+B071)` | NA | Vegetation |
| MTCI | MERIS Terrestrial Chlorophyll Index | B064, B074, B086 | `(B086-B074)/(B074-B064)` | NA | Water, Vegetation |
| CRI1 | Carotenoid Reflectance Index 1 | B011, B022 | `(1/B011)-(1/B022)` | `(1/B02)-(1/B03)` | Trans. Metals, Vegetation |
| ARI | Anthocyanin Reflectance Index | B022, B071 | `(1/B022)-(1/B071)` | `(1/B03)-(1/B05)` | Vegetation |
| NDTI | Normalized Difference Turbidity Index | B026, B060 | `(B060-B026)/(B060 + B026)` | `(B04-B03)/(B04 + B03)` | Water |
| RENDVI | Red Edge NDVI | B074, B086 | `(B086-B074)/(B086+B074)` | `(B08-B05)/(B08+B05)` | Water, Vegetation |
| CRI2 | Carotenoid Reflectance Index 2 | B011, B071 | `(1/B011)-(1/B071)` | `(1/B02)-(1/B05)` | Vegetation |
| GCI | Green Chlorophyll Index | B022, B118 | `(B118/B022)-1` | `(B08/B03)-1` | Vegetation |
| GRVI | Green Ratio Vegetation Index | B022, B118 | `(B118/B022)` | `(B08/B03)` | Vegetation |
| GNDVI | Green Normalized Difference Vegetation Index | B022, B118 | `(B118-B022)/(B118+B022)` | `(B08-B03)/(B08+B03)` | Vegetation |
| REIP | Red Edge Inflection Point | B062, B071, B082, B095 | `700 + 40 * ((B062 + B095)/2 - B071) / (B082 - B071)` | `705 + 35 * ((B04 + B07)/2 - B05) / (B06 - B05)` | Vegetation |
| RedEdge 2 | Red Edge 2 | B062, B072 | `(B072-B062)/(B072+B062)` | `(B05-B04)/(B05+B04)` | Vegetation |
| TVI | Triangular Vegetation Index | B022, B062, B086 | `0.5*(120(B086-B022)-200(B062-B022))` | `0.5*(120(B06-B03)-200(B04-B03))` | Water, Vegetation |
| NDWIGreen | Normalized Difference Water Index Green | B022, B118 | `(B022-B118)/(B022+B118)` | `(B03-B08)/(B03+B08)` | Water |
| TCARI | Transformed Chlorophyll Absorption Ratio Index | B022, B062, B071 | `3*((B071-B062)-0.2*(B071-B022))*(B071/B062)` | `3*((B05-B04)-0.2*(B05-B03))*(B05/B04)` | Vegetation |
| MCARI | Modified Chlorophyll Absorption Ratio Index | B022, B062, B071 | `((B071-B062)-0.2*(B071-B022))*(B071/B062)` | `((B05-B04)-0.2*(B05-B03))*(B05/B04)` | Vegetation |
| MCI | Maximum Chlorophyll Index | B065, B073, B087 | `B073 - (B065 + (B087 - B065)*((28)/(72)))` | NA | Water |


## HSI vs MSI availability

Most rows in the table show two formulas: one for Pixxel's hyperspectral (HSI) imagery and one for Sentinel-2's multispectral (MSI) imagery. A few important patterns to know:

- **Both formulas exist** when the index only needs bands that are available (even if broader) on both sensor types. In these cases, Aurora can generate the same conceptual index whether the customer is using Pixxel HSI or Sentinel-2 MSI data, though the numeric output may differ slightly because the underlying bands are not identical in width or exact center wavelength.
- **The Sentinel-2 formula is marked `NA`** when the index depends on a narrow wavelength region that Sentinel-2 simply doesn't capture as a distinct band. Sentinel-2 has a fixed, limited set of broad bands, so if an index needs a very specific narrow slice of the spectrum (for example, a narrow red-edge band at a precise wavelength), there may be no Sentinel-2 band that corresponds to it.
- **Hyperspectral imagery enables additional indices** precisely because it captures many narrow, contiguous bands across the spectrum rather than a handful of broad ones. This gives Aurora the flexibility to build indices that target very specific absorption or reflectance features — features that would otherwise be "blurred together" inside one of Sentinel-2's wider bands.

For a deeper explanation of *why* HSI and MSI formulas differ mechanically, see the companion page: [Understanding HSI and MSI Bandsets](#).

## Application categories

The application category columns tell you which  use cases an index supports. Based on the categories used in Aurora's table:

- **Vegetation** — Crop health, forest condition, canopy stress, and general plant vigor monitoring. Relevant to agriculture, forestry, and land management conversations.
- **Water** — Water quality, turbidity, and algal/cyanobacteria bloom detection. Relevant to water utilities, environmental agencies, and coastal or inland water body monitoring.
- **Urban** — Distinguishing built-up or impervious surfaces from natural land cover. Relevant to urban planning, infrastructure, and land-use change conversations.
- **Rare Earth** — Detection of rare earth element signatures, relevant to exploration and mining customers.
- **Transition Metals** (labeled "Trans. Metals" in the table) — Detection of transition metal signatures, also relevant to mining and mineral exploration customers.

:::success
An index can be marked `YES` under more than one application category. For example, an index that measures chlorophyll can be relevant to both Water (algal blooms) and Vegetation (crop or plant chlorophyll) conversations, depending on what the customer is imaging.
:::

## Bandset compatibility reference

Knowing that an index exists is only half the picture — a given index can only be generated for a customer if the **Aurora bandset** they've tasked or ordered actually contains every band that index's formula requires. This table maps each index to the specific Aurora bandsets it is compatible with, and calls out which bandsets are missing the required bands (and which bands, specifically) when an index isn't supported.


| Index | Required Bands | Compatible Bandsets | Not Compatible (Missing Bands) |
|---|---|---|---|
| Simple Ratio (SR) | B118, B062 | Full Spectral Coverage | Water Analytics Bandset: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| Enhanced Vegetation Index (EVI) | B118, B062, B003 | Full Spectral Coverage | Water Analytics Bandset: missing B118, B003; Seagrass: missing B062, B003; Agriculture Subset 2: missing B118, B003; Intervals: missing B118, B062, B003; Three Signals: missing B118, B062, B003 |
| Atmospherically Resistant Vegetation Index (ARVI) | B118, B062, B003 | Full Spectral Coverage | Water Analytics Bandset: missing B118, B003; Seagrass: missing B062, B003; Agriculture Subset 2: missing B118, B003; Intervals: missing B118, B062, B003; Three Signals: missing B118, B062, B003 |
| Optimized Soil Adjusted Vegetation Index (OSAVI) | B118, B062 | Full Spectral Coverage | Water Analytics Bandset: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| Wide Dynamic Range Vegetation Index (WDRVI) | B118, B062 | Full Spectral Coverage | Water Analytics Bandset: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| Green Normalized Difference Vegetation Index (GNDVI) | B118, B022 | Seagrass, Full Spectral Coverage | Water Analytics Bandset: missing B118, B022; Agriculture Subset 2: missing B118; Intervals: missing B118, B022; Three Signals: missing B118, B022 |
| Green Chlorophyll Index (GCI) | B102, B022 | Seagrass, Agriculture Subset 2, Full Spectral Coverage | Water Analytics Bandset: missing B102, B022; Intervals: missing B102, B022; Three Signals: missing B102, B022 |
| Canopy Chlorophyll Content Index (CCCI) | B118, B074, B062 | Full Spectral Coverage | Water Analytics Bandset: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118, B062; Intervals: missing B118, B074, B062; Three Signals: missing B118, B074, B062 |
| NDWIGreen | B022, B118 | Seagrass, Full Spectral Coverage | Water Analytics Bandset: missing B118, B022; Agriculture Subset 2: missing B118; Intervals: missing B118, B022; Three Signals: missing B118, B022 |
| Red Edge NDVI (RENDVI) | B086, B074 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B086; Intervals: missing B086, B074; Three Signals: missing B086, B074 |
| NDVI 705 (ND705) | B086, B071 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B086; Intervals: missing B086, B071; Three Signals: missing B086, B071 |
| MERIS Terrestrial Chlorophyll Index (MTCI) | B086, B074, B064 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B086, B064; Agriculture Subset 2: missing B064; Intervals: missing B086, B074, B064; Three Signals: missing B086, B074, B064 |
| Modified Chlorophyll Absorption Ratio Index (MCARI) | B071, B062, B022 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B062; Intervals: missing B071, B062, B022; Three Signals: missing B071, B062, B022 |
| MCARI2 | B102, B062, B022 | Agriculture Subset 2, Full Spectral Coverage | Water Analytics Bandset: missing B102, B022; Seagrass: missing B062; Intervals: missing B102, B062, B022; Three Signals: missing B102, B062, B022 |
| Transformed Chlorophyll Absorption Ratio Index (TCARI) | B071, B062, B022 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B062; Intervals: missing B071, B062, B022; Three Signals: missing B071, B062, B022 |
| TCARI/OSAVI | B071, B062, B022, B118 | Full Spectral Coverage | Water Analytics Bandset: missing B118, B022; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B071, B062, B022, B118; Three Signals: missing B071, B062, B022, B118 |
| Modified Triangular Vegetation Index (MTVI) | B102, B062, B022 | Agriculture Subset 2, Full Spectral Coverage | Water Analytics Bandset: missing B102, B022; Seagrass: missing B062; Intervals: missing B102, B062, B022; Three Signals: missing B102, B062, B022 |
| Modified Triangular Vegetation Index 2 (MTVI2) | B102, B062, B022 | Agriculture Subset 2, Full Spectral Coverage | Water Analytics Bandset: missing B102, B022; Seagrass: missing B062; Intervals: missing B102, B062, B022; Three Signals: missing B102, B062, B022 |
| Renormalized Difference Vegetation Index (RDVI) | B118, B062 | Full Spectral Coverage | Water Analytics Bandset: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| Anthocyanin Reflectance Index 2 (ARI2) | B102, B022, B071 | Seagrass, Agriculture Subset 2, Full Spectral Coverage | Water Analytics Bandset: missing B102, B022; Intervals: missing B102, B022, B071; Three Signals: missing B102, B022, B071 |
| Carotenoid Reflectance Index 1 (CRI1) | B011, B022 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B011; Intervals: missing B011, B022; Three Signals: missing B011, B022 |
| Carotenoid Reflectance Index 2 (CRI2) | B011, B071 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B011; Intervals: missing B011, B071; Three Signals: missing B011, B071 |
| NDVI | B118, B062 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| PSRI | B064, B009, B086 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B064, B009, B086; Agriculture Subset 2: missing B009; Intervals: missing B064, B009, B086; Three Signals: missing B064, B009, B086 |
| EVI2 | B118, B062 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| VARI | B005, B026, B059 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B005, B026, B059; Agriculture Subset 2: missing B005; Intervals: missing B005, B026, B059; Three Signals: missing B005, B026, B059 |
| MSAVI | B118, B062 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| SAVI | B118, B062 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B062; Three Signals: missing B118, B062 |
| NDRE | B118, B072 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B072; Agriculture Subset 2: missing B118; Intervals: missing B118, B072; Three Signals: missing B118, B072 |
| RedEdge 2 | B072, B062 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B062; Intervals: missing B072, B062; Three Signals: missing B072, B062 |
| MTVI2 (duplicate entry) | B102, B022, B062 | Agriculture Subset 2, Full Spectral Coverage | Water Analytics: missing B102, B022; Seagrass: missing B062; Intervals: missing B102, B022, B062; Three Signals: missing B102, B022, B062 |
| TVI | B086, B022, B062 | Agriculture Subset 2, Full Spectral Coverage | Water Analytics: missing B022; Seagrass: missing B062; Intervals: missing B086, B022, B062; Three Signals: missing B086, B022, B062 |
| RECI | B118, B080 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B080; Agriculture Subset 2: missing B118; Intervals: missing B118, B080; Three Signals: missing B118, B080 |
| GCI (duplicate entry) | B118, B022 | Seagrass, Full Spectral Coverage | Water Analytics: missing B118, B022; Agriculture Subset 2: missing B118; Intervals: missing B118, B022; Three Signals: missing B118, B022 |
| CVI | B118, B022, B062 | Full Spectral Coverage | Water Analytics: missing B118, B022; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B118, B022, B062; Three Signals: missing B118, B022, B062 |
| Global Environmental Monitoring Index (GEMI) | B062, B118 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B062, B118; Three Signals: missing B062, B118 |
| IOI | B049, B002 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B049, B002; Agriculture Subset 2: missing B002; Intervals: missing B049, B002; Three Signals: missing B049, B002 |
| NDWI | B118, B026 | Seagrass, Full Spectral Coverage | Water Analytics: missing B118; Agriculture Subset 2: missing B118; Intervals: missing B118, B026; Three Signals: missing B118, B026 |
| CI (Cyanobacteria Index) | B046, B060, B065 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B046, B060, B065; Agriculture Subset 2: missing B046, B060, B065; Intervals: missing B046, B060, B065; Three Signals: missing B046, B060, B065 |
| NDCI | B060, B073 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B060, B073; Agriculture Subset 2: missing B060, B073; Intervals: missing B060, B073; Three Signals: missing B060, B073 |
| MCI | B065, B073, B087 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B065, B073, B087; Agriculture Subset 2: missing B065, B073, B087; Intervals: missing B065, B073, B087; Three Signals: missing B065, B073, B087 |
| GRVI | B118, B022 | Seagrass, Full Spectral Coverage | Water Analytics: missing B118, B022; Agriculture Subset 2: missing B118; Intervals: missing B118, B022; Three Signals: missing B118, B022 |
| PRI | B017, B029 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B017, B029; Agriculture Subset 2: missing B017, B029; Intervals: missing B017, B029; Three Signals: missing B017, B029 |
| RENDVI (duplicate entry, differing bands — see note below) | B118, B075 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B075; Agriculture Subset 2: missing B118; Intervals: missing B118, B075; Three Signals: missing B118, B075 |
| REIP | B062, B071, B082, B095 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B062, B071, B082, B095; Agriculture Subset 2: missing B095; Intervals: missing B062, B071, B082, B095; Three Signals: missing B062, B071, B082, B095 |
| ARI | B022, B071 | Water Analytics Bandset, Agriculture Subset 2, Full Spectral Coverage | Seagrass: missing B071; Intervals: missing B022, B071; Three Signals: missing B022, B071 |
| SI | B062, B118 | Full Spectral Coverage | Water Analytics: missing B118; Seagrass: missing B062; Agriculture Subset 2: missing B118; Intervals: missing B062, B118; Three Signals: missing B062, B118 |
| NDTI | B060, B026 | Water Analytics Bandset, Full Spectral Coverage | Seagrass: missing B060, B026; Agriculture Subset 2: missing B060, B026; Intervals: missing B060, B026; Three Signals: missing B060, B026 |


## Walkthrough Example: NDVI705

To make this concrete, here's how to read and explain one row from the table.

**Index:** `NDVI705` — "NDVI 705nm" (a red-edge variant of the standard NDVI vegetation index)

**What it measures:** A vegetation health indicator, similar in spirit to the standard NDVI, but tuned to a narrow band positioned in the red-edge region of the spectrum (the transition zone between visible red light and near-infrared light, roughly around 705 nm) rather than the broader red and near-infrared bands used by classic NDVI. This narrow-band positioning makes it more sensitive to subtle changes in chlorophyll content, which is useful for detecting early-stage plant stress before it becomes visible to the eye or shows up in standard NDVI.

**Which bands it uses:** Two Pixxel HSI bands — `B071` and `B086` — combined as `(B086 - B071) / (B086 + B071)`.

:::note
The exact center wavelength each Pixxel band ID (e.g., `B071`, `B086`) corresponds to should be confirmed against Aurora's band reference table before quoting specific nanometer values. This page describes the index conceptually rather than asserting precise per-band wavelength figures.
:::

**Why the HSI and MSI formulas differ:** The Sentinel-2 (MSI) formula for this index is marked `NA` in Aurora's table. That's because Sentinel-2's red-edge bands are broader and centered at different wavelengths than the narrow band this index depends on — Sentinel-2 doesn't have a band positioned narrowly enough at 705 nm to reproduce this specific calculation. This is a good example to use with customers who ask, "why can't I get this from Sentinel-2?" — the honest answer is that the sensor doesn't capture that particular slice of the spectrum narrowly enough.