Applied introduction of main procedures of spatio-temporal analysis of the bio-optical component of chlorophyll-a in the southern Caspian Sea

Since geographic issues and problems have large and variable dimensions over time series, it leads to the study of a geographic field while considering a variable during the time series. In recent decades, mankind has caused changes in land and sea, which have led to increased pollution and a subsequent increase in phytoplankton numbers. For this purpose, to understand and monitor these effects, there is a need for a link between scientific work in this field and its management. To manage these regions, strict approaches, stringent measures, infrastructure compliance, and finally modelling and prediction are required. The chlorophyll-a parameter is one of the most common elements which its value and changes over time and different parts of the area are determining the conditions for biomass and the development of flora and fauna in the marine environment. It has also played an important role in administrative and management programs such as finding suitable areas for establishing fishing shelves and finding suitable locations for protecting marine areas.

The purpose of this study is to explore the procedures and trends of time series in the two sectors, including the one-year procedure (2015), in the pixel range of 3*3 in order to perform calculations of procedures and the 18- year trend. For this purpose, chlorophyll-a from the MODIS Aqua and SeaWiFS Satellite data of the Caspian Sea were collected from January 1998 to December 2015. After pre-processing and extraction of time series using the Mann-Kendall test and Thiel-Sen test, trends were determined.

The results showed that the rate of changes in 2015 for the median and linear trends are minus 0.01 and minus 0.05, respectively. Also, the average change rate for the bio-optical component of chlorophyll-a using the linear and median trend in the overall southern basin of the Caspian Sea were 0.019 and 0.0187 g /m3 in 18 years and therefore has an annually increasing rate. In general, the amount of chlorophyll-a component in the eastern parts of the Caspian Sea has a rate of 0.058, 0.22 and 0.29 mg / m3, respectively. The ρ Value is < 0.001 and 0.01 in Mann-Kendall and Contextual Mann-Kendall tests which shows a fairly similar trend, but at ρ< 0.05, a significant increase was observed in the region because the Contextual Mann-Kendall test considered the variance of neighboring pixels.

The blocks that showed a non-significant trend with the Mann-Kendall test, once the impact of neighbor pixels were considered, showed to be significant at the confidence level. Also, the different results between the OLS and Thiel-Sen procedures in the southern basin of the Caspian Sea showed that the Thiel-Sen Procedure was less than the OLS procedure for the bio-optical component.