2 Data

Two different sets of data are used to carry out the analysis. The first set is a time series of NDVI composite AVHRR images covering several countries in southwest Asia.
The second data set is a TM image (Landsat 7) from the southern Turkey.

AVHRR/NDVI Dataset

The bases of these classifications were 1 km x 1 km 10 day NDVI composite AVHRR images, geometrically registered and radiometrically calibrated by the USGS EROS data center (Eidenshank and Faundeen, 1994). The images were taken in the time between October 1992 and September 1993 in southwest Asia. The NDVI values of the images were re-scaled to 0-200, i.e. the value 200 is equivalent to a NDVI value of 1. The USGS EROS data center applied a land-sea mask to the data.

Several of the original composite images showed some severe errors. These errors included significant striping across the images, making it impossible to reliably compare different regions. Due to these errors, some of the images were excluded from any further analysis.

Image 4

Some less severe errors included lines with values of zero or ten. These errors were corrected by linear interpolation in time, using the same pixel of 10-day composite before and after.

The remaining data set consisted of 27 ten-day composite AVHRR NDVI images. The covered time frame is October 1992 to the beginning of November 1992; one image in the middle of December 1992; the middle and end of February 1993; and middle of March 1993 to September 1993. Thus the excluded images were mainly from the winter month, when vegetation is very low.

In order to be able to compute a sufficient number of repeated classifications, we used a 485 by 665 pixel subset of the above image that covers about a quarter of the full image.

TM/Landsat 7 Dataset

This dataset consists of one Landsat 7 TM image from 24 September 1999 (path 174, row 35). The area covers southern parts of Turkey and western parts of Syria. The thermal bands were omitted since the resolution of these bands is 60 by 60 meters compared to 30 by 30 meters for the other six bands. In order to allow repeat a sufficient number of classifications, a subset of 500 by 500 pixels was used for the analysis. This subset covers an area of 1.5 by 1.5 km north of Turkish city Antakya.