Land Cover Map of West Asia Using 1-Km AVHRR Data
Abstract
NOAA AVHRR data are regarded as one of the important tools that have been used in the exploration of natural resources especially vegetation resource at the regional and global levels. This paper addresses the fact that NOAA AVHR (30 second) could be used to develop land cover maps at regional level, which would lead to a balanced development in arid and semi-arid regions. This study falls into the following parts. (1) Cluster analysis of the NDVI 10 days composite data set for one year in total 36 data set. (3) Histograms analysis. (3) Ground truth collection and analysis. (4) Applying a supervised classification rules in form of three structure. As a result three of maps were produced. (1) Ground truth map contains all of the collected ground truth data. (2) Ground truth information sources map with text describing the source of each ground truth. (3) As a final result a 30 second Land Cover map of west Asia was produced, this map will be necessary as input data for a future desertification studies.
Introduction
The main purpose of this study is to produce land cover map of west Asia and demonstrate the role of NOAA AVHRR (NDVI 10-days composite data set for one year in total 36 data set and visible channels 1&2) data for vegetation monitoring and land cover classification at regional scale in arid and semi-arid environments like west Asia region.
West Asia generally characterized by arid climate, the southern part is extremely arid. However high precipitation occurs in coastal mountain ranges and in the extreme north and north east parts. The eastern Mediterranean countries are influenced Mediterranean frontal depressions, the average precipitation in this region ranges from 1500 mm to 70 mm. Egypt climate is extremely arid and average precipitation is about 10 mm. Arabian peninsula generally characterized by a ht dry climate. The morphology general of the study area is flat, though relatively narrow mountain ranges extend along the coastlines of the Red sea, the Mediterranean sea and the Gulf of Oman. Mountains and plateaus are found mainly in the north, they are mostly low relief features. West Asia region is intensive use of ground water which leads to land salinity of soil. Most of marginal lands in west Asia are permanent pastures and 85% of them are consider in danger to desertification. These marginal
land are susceptible to inappropriate land use practices, such as overgrazing, fuel cutting and inadequate cultivation. Vegetation degradation is widely found serious in these dry marginal lands. This study falls into the following parts: 1-Cluster analysis of the NDVI 10 days composite data set for one year in total 36 data set. 2-Histograms analysis. 3-Ground troth collection and analysis. 4-Applying a supervised classification rules in form of tree structure.
Data and Materials
The base data used in this study are the International Geosphere Biosphere Program (IGBP) 1- km NOAA AVHRR 10-days composite data sets for April 1992 through march 1993. While the 10-days maximum normalized difference vegetation index (NDVI) composite data are sued to classify the vegetation land cover features, the 10-days composite data set of the period 1 to 10 of June 1992, channel 1 and channel 2 are used t approve the discrimination of non-vegetation land cover features. Resurrs -1 data with it's wide swath width (600 km x 600 km) and medium spatial resolution (170m) is bridging the gap between AVHRR 1m resolution and Landsat TM. This data can be used for environmental monitoring of large areas and for agricultural classification. In our case the available images cover just a small part of the study area, so we used this data to defined ground truth data and in the visual interpreation at the post -classification level. And we use the several maps as resources information and ground truth collection data such as Land use map of Jordan, scale1:600,000. and Land cover map of Syria, scale 1:1,000,000. These data and others wee scanned and registered as image to image to the raw NDIV AVHRR 1 km data to fit the same geographic corrdinate of AVHRR data.
Pre-Processing of AVHRR data
The global 1 km 10-days composites AVHR data processed on Interrupted Goode Homolosine map projection (36 NDVI 10-days composites bands) were transformed into plate carray projection (latitude and longitude coordinates system). This transformation will locate easily the ground truth data and the usage of latitude and longitude corrdinates system is very practice and clear to view. We used this corredinates system to extract sub-images (of the 36 NDVI 10-days composites bands) representing the study area, the corrdinates of upper left corner are 40 degree northern latitude and 25 degree eastern longitude, the corrdinates of lower right corner are 10 of June 1992, channel 1 and channel 2 were extracted through the home page of the US geological Survey's (USGS), then these two channels were registered to the extracted NDVI data to fit their corrdinates system.
As much noise is involved in NOAA AVHRR data, noise free NDIV compiled on monthly base
should be used. This requires that the 36 NDVI 10-day composites data sets extracted for the study area are recomposed into 12 NDIV monthly composites data sets. This recomposing was generated using an algorithm based on the maximum NDVI value of the month.
