Contribution of spectral indices of chlorophyll (RECl and GCI) in the analysis of multi-temporal mutations of cultivated land in the Mostaganem plateau

The coastal strip of Mostaganem is an area with an agricultural vocation, characterized in recent decades by profound changes in land use, the results of biophysical processes and complex interactions between societies and their environment. These processes transform the landscape of several spatial and temporal scales. In this context, over the past few years, the evaluation of changes in cultivated areas has become one of the major priorities; it makes it possible to develop action plans and to propose management approaches that lead to sustainable agricultural development.Therefore, the use of remote sensing techniques and Landsat multispectral data for the diachronic mapping of agricultural land is a necessity. This work highlights the considerable contribution to the application of spectral indices of chlorophyll in the delimitation of cultivated areas and the analysis of their changes. In this work, we applied two spectral indices, on the one hand, the RECl index (Red-Edge Chlorophyll Vegetation Index) which shows the photosynthetic activity of the plant cover and, on the other hand, the GCI index (Green Chlorophyll Vegetation Index) Index which estimates the chlorophyll content of the leaves of various plant species and detects the physiological state of vegetation. These applications allow the evaluation of the state of vegetation growth and the monitoring of ecological changes in the environment of agricultural areas.The comparison between the results of the two indices shows that the GCI index is very effective in terms of automatic extraction of agricultural areas and discriminates between plant formations compared to the RECI index which includes all formations with important chlorophyll activity (agriculture, forest and natural vegetation).The analysis of the time series (1989, 2011, and 2021) globally confirms a trend of stability of the cultivated areas between "1989 to 2011" and a trend of improvement at the regional scale between "2011 to 2021" as a result of the improvement in rainfall conditions from 2011 and the application of effective action programs carried out by the state for the improvement of the agricultural sector.However, diachronic analyzes by the GCI index revealed significant increases in agricultural areas between 2011 and 2021 corresponding to 58% and stability between 1989 and 2011 with an increase of 0.17%. On the other hand, plant biomass grew by 22% between 1989 and 2011 and between 2011 and 2021 an increase of 7.25%.