FAQ

What is Terra-i?

Terra-i is a near real time monitoring system for habitat loss in Latin America which is now being scaled for application across the entire tropics. It uses satellite data and computational neural networks in order to detect anthropogenic changes in the vegetation cover every 16 days in near real time.

Who developed Terra-i?

Terra-i has been developed by Louis Reymondin of the Decision and Policy Analysis program, led by Andy Jarvis, from the International Center for Tropical Agriculture based in Cali, Colombia. It has been developed in collaboration with the Nature Conservancy, Haute Ecole d'Ingénierie et de Gestion du Canton de Vaud, based in Switzerland and Dr. Mark Mulligan of the Department5 of Geography, King's College London.

Are the Terra-I data free of access?

Yes! Our data are totally free for non commercial use, all you need to do is to create an account by filling the registration form.

What's the spatial resolution of Terra-i?

Terra-i resolution is the same as the NDVI (Normalized Difference Vegetation Index) vegetation index from the MODIS product MOD13Q1 : 250m.

How does Terra-i work as early warning system?

Because the MODIS data used by Terra-i are available with a high temporal resolution and offer information about the vegetation cover every 16 days.

What kind of habitat is Terra-i working with?

Terra-i can be applied to all types of ecosystems from tropical forests and savannahs to dry forests and deserts. The system has so far been implemented throughout all of Latin America.

What are the input data used by the system?

● Vegetation Index Data: Data from the MODIS MOD13Q1 product with a spatial resolution of 250m and frequency of 16 days. The normalized difference vegetation index (NDVI) represents the amount and vigor of the vegetation. Its value is closely related to the type of vegetation present, the climatic conditions and the land use at the site.


● Rainfall Data: From the TRMM sensor data (Tropical Rainfall Monitoring Mission) with a spatial resolution of 28km and a frequency of 3 hours, it monitors in real-time the tropical and subtropical rainfall between 35 ° N and 35 ° S.


● The presence of waterbody data: Data from the MODIS product MOD35 that has a 1 km spatial resolution with which it is possible to filter the Terra-i detections due to changes in the behaviour of the vegetation caused by flooding or water bodies spreading.
 

How does Terra-i work?

Terra-i uses computational neural networks to detect or ‘learn’ how the vegetation vigour (measured as NDVI) behaves at each site over a period of time in relation to observed rainfall. This knowledge of historic vegetation response to rainfall is then applied to current measurements of rainfall to predict what the vegetation response should be. This prediction is then compared with NDVI data taken by the satellite and if the observed response is significantly different from the historic responses given the pattern of rainfall then the pixel is marked as one that may have changed through anthropogenic means. If this change remains two 16 day periods in a row then the event is confirmed. Much work is carried out to account for and remove the effects of drought, flooding and cloud cover or other image ‘noise’ that may produce false positives.

How can I access the data?

The portal has two systems which allow to access the data of habitat loss. One is the MapViewer where you can view the results of Terra-i for Latin America between 2004 and the current date in an ArcGIS Server application. On the other hand you can download the data by going to the download section. To access both the platform, you have to be logged in the portal. You can create an account by filling the registration form.

In what format are the data generated by Terra-i?

The data are available in gzip compressed ESRI ARCASCII grids. You can download data for each individual 16 day period or annual grids (from January 1 to December 31). Latin America has been split into different tiles which have the same extent and ID as the MODIS tiles. ***Give more on what the numbers in the files means****

How often are the data updated in the portal?

The data are updated monthly with a delay of only 15 days from the MODIS data collection, in order to fulfill the purpose of being an early warning system that allows environmental authorities to make timely decisions and set priorities for conservation.

What kind of data are available for downloads?

The data available are classified into three different products. The detections product provides the Terra-i detections that have likely been caused by human actions. The floods product provides the Terra-i detections that have likely been caused by floods or new dams. Finally the increase product provides the Terra-i detections that were due to an abnormal increase of the vegetation index (that could be the result of reforestation but also of the implementation of new irrigation systems in dry areas).

What does mean the values of the rasters?

• No Data (-9999) : The pixel was not analyzed. A pixel may not be analyzed for two different reasons: Firstly, because it is located within a water body such as lakes and rivers, and secondly, because there was more than 70% of bad quality data (mainly due to cloud cover) between 2000 and 2004.
• 0 : No change was detected within this pixel
• 1 – 353 : The Julian day when the pixel was detected as converted. If you find the value 49 within the raster for the year 2004 it means that the pixel was detected as converted the 18th of February 2004.