Comparative study on crown closure estimations using two different remote sensing data: Landsat ETM+ and IKONOS

Abstract

In this paper, we developed empirical relationships between crown closure and Landsat Thematic Mapper (TM) and IKONOS spectral response in a forest ecosystem in Turkey. The linear relationships between the crown closure and satellite images were examined and for that the normalized difference vegetation index (NDVI) was generated for correlation analysis. Satellite images were georeferenced with respect to corresponding forest stand type maps for the same area. The digital numbers (DNs) in all bands were positively correlated with the crown closure in Landsat-7 ETM image. Regarding the Landsat ETM+, the DN of NIR band (band 4) had the highest correlation coefficient value with the crown closure (r = 0.715), and the DN of blue band (band 1) had the lowest correlation value with the crown closure (r = 0.373) and explains 51.1% and 13.9% of data variability, respectively, in Landsat-7 ETM image. In IKONOS image, the DNs in three bands (red, green and NIR) were positively correlated with the crown closure at the level of r = 0.385, r = 0.359 and r = 0.829, respectively. The NIR band of the Landsat-7-ETM + image showed the highest correlation with the NDVI (r = 0.886) and the red band had the lowest correlation with the NDVI (r = 0.419), while the IKONOS image showed that the NIR band had the highest correlation with the NDVI (r = 0.781) and the green band resulted in the lowest correlation with the NDVI (r = 0.367). Results also indicated that the relationships between the crown closure and the NDVIs of Landsat-7 ETM and IKONOS were positively correlated with r = 0.794 and r = 0.871, respectively.