Published on 12 November 2025

swissEO NDVIz

The anomaly of the "Normalized Difference Vegetation Index" (NDVI) indicates the health status of forest areas, derived from satellite data.

NDVI anomalies provide insights into changes in vegetation vitality because the NDVI reflects the chlorophyll content (the “green”) of plants. Chlorophyll absorbs red light, as this wavelength is used for photosynthesis. The healthier and usually greener the plant, the higher its chlorophyll content and the stronger its absorption of red light. Healthy plants, on the other hand, reflect a larger portion of near-infrared light than stressed or diseased plants do.
From the ratio of red to near-infrared light, the NDVI can be calculated — it is higher for healthy plants than for stressed ones.

For practical use, the measured NDVI values are statistically classified. The current NDVI values are compared to the median value of the climate reference period from 1991 to 2020. The Z-score measures how far the current value deviates from the mean (or, in this case, the median). The larger the Z-score, the more extreme the deviation — and the rarer such a value is.
A positive Z-score indicates particularly vital vegetation showing growth and/or increased productivity. For example, a Z-score of +2 means that vegetation is more vital than in 95% of the comparison years.
A negative Z-score, on the other hand, indicates reduced vitality caused by management and/or natural disturbances (storm damage, drought, insect infestations, etc.). Thus, a negative Z-score may reflect either logging or premature autumn coloration.

Figure 1: Temporal progression of the NDVI with annual summer peak values for forests in the Franches-Montagnes region of the Jura.The ratio of a value to the climate reference period 1991–2020 determines the anomaly (Z-score). The greater the difference between a specific year’s measurement and the median value of the reference period, the higher the Z-score. The median values of the reference period are shown in the white-shaded area.A positive Z-score (NDVI values in the green range) indicates greener, more vital forests compared to 1991–2020.

Data representation and availability

The current dataset can be viewed in the BGDI map viewer via: https://map.geo.admin.ch/?layers=ch.swisstopo.swisseo_ndvi_z_v100 . In the BGDI WMS the dataset can be displayed by using the layer «ch.swisstopo.swisseo_ndvi_z_v100» .

To display older datasets in the BGDI map viewer, URL parameterization is required. Replace <id> in the following link with the end date of data acquisition in the format yyyy-mm-ddT235959 (example: 2023-09-30T235959):

https://map.geo.admin.ch/index.html?layers=WMS||ndvi_z_v100_<id>||https://wms.geo.admin.ch/?item=<id>||ch.swisstopo.swisseo_ndvi_z_v100||1.3.0

Example for the dataset of August/September 2023:

https://map.geo.admin.ch/index.html?layers=WMS||ndvi_z_v100_2023-09-30T235959||https://wms.geo.admin.ch/?item=2023-09-30T235959||ch.swisstopo.swisseo_ndvi_z_v100||1.3.0

Further information

• Technical details

  • Coordinate system: CH1903+ LV95 (EPSG:2056)
  • Resolution: 10 m
  • Temporal resolution: Monthly in summer (June/July, July/August, August/September)
  • Data format: Cloud Optimized GeoTIFF (COG)
  • Interfaces: STAC, WMS
  • Source code used for production: https://github.com/swisstopo/topo-satromo/

• Produktinhalte

  The swissEO NDVIz product contains seven elements, all available for direct download:*

  • FOREST-10M: Raster containing NDVI Z-score values masked for forest areas of Switzerland. Resolution: 10 m. (Preview, Sample)
  • PIXELCOUNT-10M: Raster showing the number of data records used to calculate the NDVI Z-score for each pixel. Resolution: 10 m. (Sample)
  • FOREST-WARNREGIONS-CSV: CSV file with the average NDVI Z-score and the percentage of valid data availability for forest areas per warning region. (Sample)
  • FOREST-WARNREGIONS-GEOJSON: GeoJSON file with the average NDVI Z-score and the percentage of valid data availability for forest areas per warning region, including coordinates and bounding boxes of the warning regions. (Sample)
  • FOREST-WARNREGIONS-PARQUET: Parquet file with the average NDVI Z-score and the percentage of valid data availability for forest areas per warning region, including coordinates and bounding boxes of the warning regions. (Sample)
  • METADATA: JSON file containing all necessary information for each product element. (Sample)
  • THUMBNAIL: A reduced-size JPEG image of the NDVI Z-score for quick preview. (Preview)

  *All sample data and previews refer to the latest product update.

• Detailed product information

  The swissEO NDVIz product is based on remote sensing data from polar-orbiting satellites. The optical data (Sentinel-2), processed in the "swissEO S2-SR" product, have a spatial resolution of 10 m and cover the entire area of Switzerland approximately every five days since spring 2017.
  The swissEO S2-SR product uses provided masks (cloud and terrain shadow) to exclude all clouds and cloud shadows. Pixels with illumination angles above 65° are identified and masked as potentially problematic, since their reflection values cannot be reliably interpreted due to extreme oblique lighting.

  From the swissEO S2-SR product, NDVI is calculated as the ratio of near-infrared to red light (Tucker, 1979): (Tucker, 1979):

  NDVI = (NIR - Red) / (NIR + Red)

  To analyze NDVI anomalies, a Z-score is calculated by subtracting the reference mean (ref) from the current mean (current) and dividing the difference by the standard deviation (e.g., Meroni et al., 2019).
  Swisstopo uses a modified Z-score based on median values instead of means. It employs the median absolute deviation (MAD) and a constant instead of the standard deviation. The modified Z-score is more robust against outliers and is calculated as:

  mod z-score = (NDVI_{current,median} - NDVI_ref,median) * 0.6745 / NDVI_ref,MAD

  For the "swissEO NDVIz" product, median values are calculated per pixel for each 10 m pixel over a two-month time window (e.g., June–July).
  The greater the variability of NDVI values for a pixel in this two-month window during the climate reference period, the less small changes matter — reflected by a Z-score near zero. Conversely, changes in areas with stable reference values and low variability are quickly considered extreme and yield high Z-scores.

  Because NDVIz was developed for forest areas, appropriate masking is applied. Based on category 6 (forests) of the Swiss Habitat Map, "swissEO NDVIz" includes only those 10 m pixels that are fully forest-covered. For the Principality of Liechtenstein, the corresponding category from the CLC+Backbone dataset was used.

  This dataset was developed in collaboration with the Bern University of Applied Sciences BFH-HAFL and the Federal Office for the Environment (FOEN) for waldmonitoring.ch.
  The vegetation data foundation is formed by optical satellite data from the European Space Agency (ESA – Sentinel-2) for the current "swissEO S2-SR" product values and from the National Aeronautics and Space Administration (NASA – Landsat 5, 7, 8) for the climate reference period values.

• Additional content information

  • swissEO NVDIz - Additional content info

    PDF401.52 kB30 October 2025

Access to raw data

The data can be accessed via the STAC Collection «ch.swisstopo.swisseo_vhi_v100» in the STAC interface of BGDI:

• Browser and download interface: swissEO NDVIz: NDVI anomaly (admin.ch)
• Download API documentation: REST Interface: Spatial Temporal Asset Catalog API (admin.ch)
• Google Earth Engine: VHI Image Collection (since April 2017) [projects/satromo-prod/assets/col/VHI_SWISS] / VHI Image Collection (1991-2020) [projects/satromo-prod/assets/col/VHI_HIST_SWISS]
• Accessing STAC via Python - Introduction (Jupyter Notebook)
• Image processing using Python with STAC (Jupyter Notebook)
• Streaming swissEO products in QGIS

Terms of use

swissEO may be used, distributed and made accessible. Furthermore,it may be enriched and processed and also used commercially. A reference to the source is mandatory. In the case of digital or analogue representations and publications, as well as in the case of dissemination, the following source references must be attached in any case:

© swisstopo, Contains modified Copernicus Sentinel data [Year]

Further information on the terms of use can be found on the terms of use webpage.