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Uruguay: spring and summer 1999-2000
Our country is affected by a severe drought anticipating serious damages in agricultural
production. Our ground station it has followed the evolution of this drought evaluating periodically the VEGETATION INDEXS
(NDVI = Normalized Differential Vegetation Index) also called sometimes
"GREEN IDEX". These indices have calculated at national coverage on the basis of received information of the polar orbit satellite
NOAA-14. The following figures, corresponding to dates 10/11/1999, 4/12/1999, 3/01/2000, 18-26/01/2000 and 7/03/2000 they allow to observe the general evolution of the vegetation index during the period
studied. Individually it can be observed that the vegetation more affected is throughout the coastal
west.
However, pay attention in the Laguna Merin
basin. There it's possible to be appreciated zones in which the vegetation index was from less to more during this
period: these zones are rice crops. Although this sector also was affected by the
drought, without doubts, has been one of the only season crops that have surpassed the
phenomenon. This, without doubt, it`s due to the existing water reserves in this influence
area. In other regions of the country dedicated to the rice culture they are insinuated also
growth, but not in the scale of the Laguna Merin basin. It's possible to extract of this analysis a very important conclusion about the remote sennsing agricultural
applications: being an cultivated area sufficiently extensive (in this case great rice
crops), its evolution can be monitored and analyzed with satellite like those NOAA series
NOAA, despite its low spatial resolution (1100mts per pixel). This tool it can be very useful not only for pursuit of extensive cultures in our country, but
also, to know the evolution of competitive areas at regional level (Brazil, Argentina). This is also valid for grass analysis
evolution.
DROUGHT EVOLUTION DYNAMICS.
The images displayed in our page offer, through the measurement of the vegetation
index, a multitemporary schema of the diverse states of the green cover in the course of the intense drought
period. In these images can be appreciated, when comparing different dates, that there are regions that evolve more quickly than
others, and even can exist between two dates, regions that evolve in opposite
sense, that is to say, while one of them makes worse, the other it improves it stress
situation. Also can occurs that given region don't show any changes in the vegetation index between consecutive dates. In order to visualize graphically and to quantify these variations we have developed
"slope maps". Between two consecutive multitemporary images the NDVI for an individual pixel of the image can to have decreased
(accentuates the state of stress vegetable), to have been equal or to have increased
(signal of certain recovery vegetable). If we assumed that the approach of these variations respond to a linear
model, thevalue of the corresponding slope it will constitute a measurement of the way of the change and its
intensity. The generalization of this approach to all the involved pixels in the images give the origin
in the mentioned "slope maps". In these, the digital numbers associated to each pixel is the slope of the function that link the values of NDVI for the equivalent pixels in the two taken multitemporary images as it bases. Using a color pallette we facilitated the visualization of the
changes.
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