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STAR - Global Vegetation Health Products : Background and Explanation

Vegetation Health (VH) System: Background and Explanation

The satellite-based global VH System is designed to monitor, diagnose and predict long- and short-term land environmental conditions and climate-dependent socioeconomic activities. The System is based on satellite observations of the Earth, biophysical theory of vegetation response to the environment, set of algorithms for satellite data processing, interpretation, product development, validation, calibration and applications.

Satellite observations are principally represented by the Advance Very High Resolution Radiometer (AVHRR) flown on NOAA polar-orbiting satellites. Data are global with the resolution 4 km and 7-day composite. In addition, the System is using data and products from GOES, METEOSAT, MTSAT and DMSP. The System contains the following vegetation health indices and products: Vegetation Condition index (VCI), Temperature Condition index (TCI), Vegetation Health index (VHI), Soil Saturation index (SSI), No noise Normalized Difference Vegetation Index (SMN), No noise Brightness Temperature (SMT), Fire risk index (FRI); products - Drought, Malaria, Vegetation health, Ecosystems, Land sensitivity to ENSO.

Definition and Applications

Vegetation Condition index (VCI) - Global, 4 km, 7-day composite, validated.

VCI is based on the pre- and post-launch calibrated radiances converted to the no noise Normalized Difference Vegetation Index (NDVI=(NIR-VIS)/(NIR+VIS)). The VCI was expressed as NDVI anomaly relative to 25-year climatology estimated based on bio-physical and ecosystem laws (law-of-minimum, law-of-tolerance and carrying capacity). VCI is a proxy for moisture condition.

Temperature Condition index (TCI) - Global, 4 km, 7-day composite, validated.

TCI is based on 10.3-11.3 µm AVHRR's radiance measurements converted to brightness temperature (BT), which was improved through completely removed high frequency noise. BT was expressed as an anomaly relative to 25-year climatology estimated based on bio-physical and ecosystem laws (law-of-minimum, law-of- tolerance and carrying capacity). TCI is a proxy for thermal condition.

Vegetation Health index (VHI) - Global, 4 km, 7-day composite, validated.

VHI=a*VCI + (1- a)*TCI, where a is a coefficient determining contribution of the two indices. VHI is a proxy characterizing vegetation health or a combine estimation of moisture and thermal conditions.

Soil Saturation index (SSI) - Global, 4 km, 7-day composite, validated.

The SSI estimates vegetation depression due to soil saturation (excessive wetness) followed by abnormal rains and/or flooding. SSI is based on a rains, flash flood and VH products derived from sensor measurements on GOES, NOAA and DMSP satellites. The products are the Hydro Estimator (H-E), VCI, TCI, and snow cover (SC). If soil is saturated for a relatively long time vegetation is normally stressed similarly to other stressful events. SSI can be used to distinguish large area vegetation stress caused by soil saturation from that caused by drought.

No noise (smoothed) Normalized Difference Vegetation Index (SMN) - Global, 4 km, 7-day composite, validated.

The SMN is derived from no noise NDVI, which components were pre- and post-launch calibrated. SMN can be used to estimate the start and senescence of vegetation, start of the growing season, phenological phases.

No noise (smoothed) Brightness Temperature (SMT) - Global, 4 km, 7-day composite, validated.

The SMT is the BT with completely removed high frequency noise, SMT can be used for estimation of thermal condition, cumulative degree days and other.

Fire risk index (FRI) - Global, 4 km, 7-day composite, validated.

The FRI is based on drought intensity and duration estimated from VHI, TCI and VCI. FRI estimates condition potentially able to trigger open fire.

Drought (D) - Global, 4 km, 7-day composite, validated.

D assessment is based on VHI, VCI and TCI if their values are below 40. D is "Exceptional", If the indices are between 0 and 5; "Extreme" if they are 6-15; "Severe" 16-25; "Moderate" 26-35; "Abnormally dry condition" 35-40.

Malaria (M) - Africa, 4 km, 7-day composite, validated.

M assessment is based on VHI, VCI and TCI. M in different ecosystems can be monitored by either individual index or their combination. In dry ecosystems both VCI and TCI are normally used as predictors; in wet ecosystems, TCI is mostly used.

Vegetation health (VH) - Global, 4 km, 7-day composite, validated.

VH is a product estimating vegetation health (condition) base on moisture conditions (VCI), thermal conditions (TCI) and their combination (VHI). VH is used often to estimate crop condition and anticipated yield. If the indices are below 40 indicating different level of vegetation stress, losses of crop and pasture production might be expected; if the indices above 60 (favorable condition) plentiful production might be expected. VH is very useful for an advanced prediction of crop losses.

Ecosystems (E) - Global, 4 km, 7-day composite, validated.

E shows distribution of ecosystem. This information is often used for more accurate assessments of land surface condition.

Vegetation sensitivity to ENSO - Global, 4 km, 7-day composite, validated.

This information is used for assessment area, time and intensity of climate forcing impacts on vegetation, which is needed for one-three months predictions of vegetation health.