authority: folia
slug: turbidity
name: Turbidity
domain: land
subdomain: water-quality
authority_id: folia:turbidity
aliases:
  - ntu
  - water-clarity
  - suspended-sediment
external_ids:
  cf_standard_name: sea_water_turbidity
canonical_units: NTU
external_validations:
  library:
    name: awesome-spectral-indices
    id: NDTI
    docs_url: https://github.com/awesome-spectral-indices/awesome-spectral-indices
  library_alt:
    name: acolite
    id: acolite-tur-nechad-dogliotti
    docs_url: https://odnature.naturalsciences.be/remsem/software-and-data/acolite
  sentinel_hub:
    processor: Sentinel-2 turbidity custom scripts (MODIS IDL / Imager)
    docs_url: https://custom-scripts.sentinel-hub.com/sentinel-2/turbidity_modis_idl_imager/
description: |
  Water clarity / suspended-sediment proxy. Standard operational measure
  is nephelometric turbidity units (NTU); satellite retrievals approximate
  this via the Dogliotti et al. 2015 single-band algorithm (red-band
  water-leaving reflectance mapped to NTU, with a near-infrared switch for
  high-turbidity waters), or via band-ratio indices such as NDTI (Lacaux
  et al. 2007, `(Red − Green)/(Red + Green)`) for relative comparison.
  Distinct from `chlorophyll-a-inland` — turbidity bundles sediment,
  plankton and CDOM together rather than isolating phytoplankton biomass.
  No clean GCOS parent: ocean-colour is adjacent but turbidity-specific,
  so this ships parentless in the operational tier. The CF standard name
  `sea_water_turbidity` is reused for inland waters by convention. Used
  by dredging-monitoring, watershed-erosion, post-flood water-quality,
  and EUDR-adjacent supply-chain ops.
theme: hydrology
example_recipes:
  - title: "NDTI on Sentinel-2 (Lacaux et al. 2007)"
    tool: gee
    requires: [s2-l2a-reflectance]
    snippet: |
      // NDTI = (Red - Green) / (Red + Green) — relative turbidity proxy
      var s2 = ee.Image('COPERNICUS/S2_SR_HARMONIZED/...');
      var ndti = s2.normalizedDifference(['B4', 'B3']).rename('ndti');
    docs_url: https://github.com/awesome-spectral-indices/awesome-spectral-indices
  - title: "Dogliotti 2015 single-band turbidity (ACOLITE)"
    tool: python
    requires: [s2-l1c-toa, s3-olci-l1]
    command: |
      # ACOLITE CLI — produces TUR_Nechad2009 / TUR_Dogliotti2015 bands (NTU)
      python launch_acolite.py --cli \
        --settings settings.txt \
        --inputfile S2A_MSIL1C_*.SAFE \
        --l2w_parameters TUR_Dogliotti2015 \
        --output ./acolite_out/
    docs_url: https://doi.org/10.1016/j.rse.2014.09.020
consumed_by: [imagery_radiometric_indices]
produced_by: []
demos: []
status: documented
sources:
  - https://github.com/awesome-spectral-indices/awesome-spectral-indices
  - https://odnature.naturalsciences.be/remsem/software-and-data/acolite
  - https://custom-scripts.sentinel-hub.com/sentinel-2/turbidity_modis_idl_imager/
  - https://doi.org/10.1016/j.rse.2014.09.020
  - Dogliotti, A.I., Ruddick, K.G., Nechad, B., Doxaran, D., Knaeps, E. 2015, Remote Sensing of Environment 156, 157-168 (single-algorithm turbidity retrieval, S2/S3/MODIS)
  - Lacaux, J.P., Tourre, Y.M., Vignolles, C., Ndione, J.A., Lafaye, M. 2007, Remote Sensing of Environment 106, 66-74 (NDTI, pond classification Sahel)