American-Eurasian Journal of Scientific Research 3 (1): 84-91, 2008 ISSN 1818-6785 © IDOSI Publications, 2008 Corresponding Author: Dr. Ali M. Qaid, Department of Studies in Geology, University of Mysore, Manasagangtri, Mysore- 750 006, India 84 Application of Optimum Index Factor Technique to Landsat-7 Data for Geological Mapping of North East of Hajjah, Yemen Ali M. Qaid and H.T. Basavarajappa Department of Studies in Geology, University of Mysore, Manasagangtri, Mysore-750 006, India Abstract: North east of Hajjah represents the southwestern extension of Nabitah belt which is a part of the Arabian Shield. The geology of the area is very complicated and exposed to the different tectonic movements. Landsat-7 Enhanced Thematic Mapper Plus (ETM+) provides six bands with 30 m resolution, one panchromatic band with 15 m and one thermal band with 60 m resolution. Optimum Index Factor (OIF) is one of the most common statistical methods which were applied in order to designate the most favorable three band combinations. It is based on the total variance within bands and correlation coefficient between bands. In this study OIF technique was applied to all bands of ETM+data. A number of 56 band colour combinations were produced and analyzed using OIF. The highest value of OIF is 45.65 with the first rank which is recorded the band combination 5-6-7. The aim of this study is to use OIF technique to rank all the possible band colour combinations of ETM+data for geological mapping of north east of Hajjah. The different analyses of all OIF values and their ranks showed that OIF technique is helpful for selecting the suitable combination for geological mapping of the study area. Key words: OIF • Yemen • Landsat-7 (ETM+) • geological mapping • combinations INTRODUCTION The study area represents the southwestern extension of Nabitah belt which is a part of the Arabian Shield. The Arabian Shield is a part of a larger geological ensemble, the Arabian-Nubian shield, which covers several countries, mainly Egypt, Eritrea, Ethiopia, Saudi Arabia, Somalia, Sudan and Yemen. The geology of the north east of Hajjah is very complicated due to the different tectonic events. The study area is located in the North East of Hajjah city, between 43°36' 47" to 43°40' 24" longitudes and 15°42' 18" to 15°50' 09" latitudes. The UTM between 351476.25 to 357860.25 E and from 1736760.00 to 1751268.00 N. Generally, the relief of the area is mountainous, moderate to steep slopes, sharp-ridges (Fig. 1). Buhe et al. [1] applied the OIF technique to ASTER bands for studying the land cover of oases and forest in XinJiang. Selecting of three bands for a colour composite (R-G-B) image is a tedious and time consuming business since many combinations have to be tried when working with ratio images. The OIF technique simplifies that selection by quantitative evolution of the scene statistics and avoids the time -consuming of visual analysis process of large numbers of potential R-G-B combinations. OIF is a statically calculation of every possible three-bands rendered as R-G-B. It is developed by Chavez et al. [2] and Chavez et al. [3]. Values of OIF were determined in order to designate the most favorable band combination [4] and rank the band subsets according to their information [5]. It is based on the amount of total variance and correlation between various bands [6, 7]. The used algorithm to compute the OIF for any subset of three bands is: () () n i1 n j1 i OIF Max rj = =   σ     =       ∑ ∑ [2] OIF is the optimum index factor. σ (i) is the standard deviation of k band. r (j) is the correlation matrix value. High value of OIF indicates, that the bands contain much information (e.g., high standard deviation) with little duplication (e.g., low correlation between the bands) [1]. Landsat-7 (ETM+) is a multispectral scanar which was launched on April 15, 1999, carrying the ETM+ sensor [8]. ETM+ has eight bands, bands 1 through 3