Variable NDVI
Spatially Average Over district boundaries
Download as
Observations for


a)


b)

a) 16 day estimates of NDVI or EVI for Guatemala for the last 12 months.

b) The 16 day estimates of NDVI and EVI for the current and five most recent years are plotted for comparison. The thick black line is the same series shown in a.

Measures of Vegetation

This tool produces maps of estimated vegetation using data from NASA's MODIS sensor.

In some semi-arid regions of eastern Africa, precipitation has been found to have a 2-3 month lagged correlation with malaria incidence. Due to the lack of station data and because of the lagged nature of precipitation yielding lagged plant growth, vegetation indices have been used as a proxy measure to forecast malaria.

Two vegetation indices are provided: NDVI, EVI in addition to the reflectance values for the blue, red, near infrared and middle infrared channels. Each index is derived from data provided from The Moderate Resolution Imaging Spectrometer (MODIS), a key instrument aboard NASA's Terra and Aqua satellites.

NDVI
The Normalized Difference Vegetation Index (NDVI) is the ratio between the difference of red and near-Infrared (NIR) divided by the sum of red and near-Infrared reflectances. The index provides some information on healthy vegetation by examining their difference in wavelength absorption and reflectance. Healthy vegetation growth, such as forests, will yield high NDVI values closer to 1 while low vegetation will yield values close to 0.2.

EVI
The Enhanced Vegetation Index is provided as a complementary index to NDVI. EVI is an 'optimized' index designed to enhance the vegetation signal with improved sensitivity in high biomass regions and improved vegetation monitoring through a de-coupling of the canopy background signal and a reduction in atmosphere influences.

Reflectance
Using simultaneous exploitation of MIR, NIR, and Red wavelengths in a Red-Green-Blue color space, reflectance images allow for a more robust and reliable qualitative discrimination between land surfaces with sparse vegetation and those without vegetation. Land surfaces such as water bodies can also be accurately mapped. The user can follow the spatio-temporal dynamic of green vegetation and identify water bodies using the combination of MIR, NIR and Red channels.

NDVI and EVI are useful to estimate the presence of vegetation, but are subject to intrinsic commission and omission errors which lead to potential misrepresentation of land surfaces. To improve the retrieval of vegetation properties, reflectance values in the Blue, Red, near-Infrared (NIR) and Middle Infrared (MIR) channels can be used.

References:

Ceccato, P., et al. (2007). Malaria stratification, climate, and epidemic early warning in Eritrea. International Geoscience and Remote Sensing Symposium (IGARSS) pp. 178-192.5. American Journal of Tropical Medicine and Hygiene, 2007.

Dataset Documentation

Vegetation Estimates

Data
16 day estimates on a 250m lat/lon grid
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.

Dataset

Access the dataset used to create this map.

Instructions

The MODIS interface provides the ability to make graphs at a user-selected location across different resolutions of spatial averaging. The interface consists of a clickable map that allows users to generate customized time series graphs. When a desired location is clicked, 2 time series graphs will provide vegetation analyses of the past year and in comparison to the 5 most recent years.

By placing current vegetation in recent historical context, comparisons can be made to past outbreaks and useful early warning information can be developed for epidemic prone regions.

How to use this interactive map

Zoom Out Restores default view by removing any zoom requests. Note that the back button undoes the most recent zoom on modern browsers.
More Information Opens a page in the source data library which gives additional detail and options for the current image.
Independent Variables Controls the setting of the independent variables such as time or height. Only appears when there are choices to be made.
Layers Switches layers on and off in images that are displaying multiple layers of information. Only appears when there are choices to be made.
Share Allows sharing the current image with variable online tools and social media sites. Map-oriented tools are not given as options if the image is not a map.
Download Allows downloading the current image in various formats and protocols. The level of information varies depending on the format: only KML, WMS and PDF include links back to this page.
Multiple image sections Shows the currently-selected image with a black border when either sharing or downloading images. Clicking on another image will change the currently selected image.
Control Lock When this button is fully engaged, the controls remain visible; otherwise the controls appear and this button partially engages automatically when the image is active.

Helpdesks

Contact help@iri.columbia.edu with any technical questions or problems with this Map Room, for example, the forecasts not displaying or updating properly.