ENVIRONMENTAL MONITORING OF JAPAN

How to produce NDVI data ?

[JAPANESE]

Brief explanations on how to receive data from NOAA; how to correct image data received; and how to produce Normalized Difference Vegetation Index (NDVI) data are given here.

noaa-antenna

Geospatial Information Authority of Japan(GSI) received NOAA satellite data every day untill Dec. 2007. The receiving antenna was set up in the rooftop of the building of GSI (See left photo). The receive data was send to Earth Observation Data Analysis System (EODAS) and stored, and we produced NDVI data.

raw data corrected image

This is the data that NOAA AVHRR sensor observed directly. Part of Honshu Island is seen in the middle. As surface of the round earth was taken from an oblique direction, shape of Japanese Islands looks distorted. NOAA 14 takes images by flying from north to south above Japan, as a result, the north-south direction of the image becomes inverted.

Received raw data have a lot of distortions, such as ones resulted from taking the image of the round globe, from atmosphere and from blur of the satellite. The left image has these kinds of distortions. The distortions are resolved by being corrected by calculation. Errors typical of AVHRR sensor are also needed correction. At the GSI, distortions of the image are further corrected by referring to the coordinates based on the positions of distinctive coastlines. NDVI data are thus produced based on the corrected image.


NDVI data do not show an accurate value in the parts of the image where there are clouds. Therefore, the data cannot be produced from the above image at this stage. In order to remove the cloud influence, NDVI data are produced by extracting the maximum value from the NDVI data obtained in one month. The data produced in this process are open to the public on the Internet.

producing NDVI example of NDVI data

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