Agricultural Stress Index (ASI)

This map shows the actual situation of the vegetation, as reflected by the the Agricultural Stress Index (ASI)..

This index is available for different types of crops. Select the crop type of your interest in the Menu > Type of Crop.

Tabel 1: Interpretation of the ASI

How is the NDVI calculated?

The NDVI is calculated as:

Where VIS is the spectral reflectance in the visible region (red) expressed as ratio (reflectance/incoming) and NIR is the reflectance in the near infrared region (reflectance/incoming).

The figure below illustrates the calculation of the NDVI:

Figure 1: Example of NDVI calculation

What is the interaction between the vegetation and the spectral regions NIR and VIS?

Plants absorb and reflect particular regions of the light spectrum. Large part of the VIS is absorbed by plants and used in the photosynthesis process. Large part of the NIR is reflected by plants because it cannot be used in the photosynthetic process. When plants are in bad condition there is a change in the absorbance and reflectance of VIS and NIR.

Dataset Documentation

Data

16-day average estimates on a 1km lat/lon grid dataset

Data Source

United States Geological Survey, Land Processes Distributed Active Archive Center, Moderate Resolution Imaging Spectroradiometer USGS LandDAAC MODIS

Note:There is typically a 12- to 16-day delay between the end of the observation period for the latest data and the date when those data are received and displayed on this page.

Helpdesks

Contact mwar_lac@unesco.org with any technical questions or problems with this Map Room, for example, the forecasts not displaying or updating properly.

Instructions

The interface provides users with the ability to make graphs. The interface provides a contextual perspective of recent MODIS images by displaying an interactive map of the Normalized Difference Vegetation Index (NDVI). Time series analyses of NDVI are generated based on user-selected parameters.

Isolating a certain region of interest can be accomplished by clicking and dragging a rectangle across that region. The map will zoom to that area to allow for more precise variable. Any zoom level will allow for the user to click a location and generate 2 separate time series. Changing the area over which the spatial averaging is performed will modify the resolution of variable estimation.

Time series a: monthly estimates of NDVI for the selected region, commune or locality selected for the last 18 months.