Click the “polygon button,” select the points to draw polygons in the target image, and double-click the left button to close the polygon automatically (Figure 2-34).
For the area corresponding to the irregular coastline, users can import the .txt file containing latitude and longitude coordinates of polygon corner themselves.
The software can generate histogram of the selected region and output statistical results, such as maximum, minimum, average, and standard deviation (Figure 2-35).
Figure 2‑34. Monthly average chlorophyll concentration of 4-km resolution in the Bohai Sea in February 2012 (a), and August 2012 (b), obtained from ESACCI data set. The green transparent polygon is imported by a pre-made .txt file containing Bohai coastlines.
Figure 2‑35. Polygon results. Results show that the average chlorophyll concentration in the Bohai Sea was 6.132 mg/m3 in February 2012 (a) and was 3.741 mg/m3 in August 2012 (b). According to the histogram and mean value, the chlorophyll concentration in the Bohai Sea was higher in winter than in summer, but the distribution of chlorophyll concentration was more uniform in summer than in winter.
