Click the “line” button to draw a polygonal line on the selected target image (Figure 2-28). The software uses the grid data along the polygonal line to generate a polygonal line graph, and calculates the statistical information (maximum, minimum, average, and standard deviation) of all grid points on the polygonal line. There are two categories of results: one with the x-axis of longitude through the polygonal line (Figure 2-29), and the other with the x-axis of distance between the points on the polygonal line and the starting point (Figure 2-30).
In addition, you can select other layers in the drop-down box and click the “analysis” button to output the analysis results of the same polygonal line position in other satellite data (Figure 2-31).
Figure 2‑28. The wind speed and direction image of Typhoon Morakot, the eighth typhoon of 2009, with a resolution of 25 km, on August 5, from the data set of CCMP wind field. The color represents the 10-m wind speed over the sea surface, and the arrow represents the wind direction. The white line is the selected line for line analysis.
Figure 2‑29. The longitude/latitude plot obtained by line analysis. The x-axis is the longitude of the polygonal line, and the y-axis is the latitude. The right column is the basic information of all grid points on the polygonal line. It shows that the maximum wind speed on the polygonal line is 17.6363 m/s, the minimum wind speed is 0.834288 m/s, and the average wind speed is 12.0919 m/s. The spatial variation of wind speed can be clearly seen by the latitude/longitude plot.
Figure 2‑30. The distance plot obtained by line analysis. The x-axis is the distance between the points on the polygonal line and the starting point, and the y-axis is the wind speed. The gradual increase of wind speed from the typhoon eye to the periphery is clearly shown by the distance plot.
Figure 2‑31. A comparison plot obtained by line analysis. The x-axis is the distance between the points on the polygonal line and the starting point, and the y-axis is the sea surface temperature (SST). The blue line represents SST of the grid points selected on August 5, and the red line represents the SST of the grid points on August 6. This comparison shows the SST decreased after the typhoon. By using the function of layer comparison, users can see the change of the selected polygonal line in different satellite images. It can be used to compare the variation of a parameter in the region of interest at different times, or show the variation of different parameters in the region of interest at the same time.
