The user-defined algorithm tab includes four modules: “formula editor,” “data gridding,” “data filter,” and “thematic maps” (as shown in Figure 2-50).
Figure 2‑50. User-defined algorithm tab
2.5.1 Formula editor
Click the "formula editor" button, and the calculator dialog will pop up. Click “add local layer,” “add layer,” and “remove” to select satellite data to be used in the calculation. The product parameters correspond to different satellite products, with symbols such as “A, B, C, D “ in the formula (Figure 2-51).
Click the satellite product, operator, and number to combine and build the user-defined calculation expression. After clicking the “calculation” button, you can select the area of your interest for calculation. The calculation result will be loaded into the 3D geosphere in a new grid layer (Figure 2-52). As the satellite data involved in the calculation may have different spatial resolutions, the software acquires the lowest resolution of the data involved in the calculation by default, and users can select the highest resolution for calculation.
Figure 2‑51. Calculation dialog box. Example: A is the monthly average SST data of 25-km resolution of AVHRR in November 1997, and B is the monthly average SST data of 25-km resolution of AVHRR in November 1998. The global mean SST difference in November was calculated using “B minus A.”
Figure 2‑52. Mean SST difference image for the Pacific region between November 1998 (La Nina year) and November 1997 (El Nino year). It shows that the equatorial Pacific Ocean in November 1998 was 7℃ lower than that in November 1997; the Northwest Pacific and Southwest Pacific were 5℃ higher. The SST in the eastern equatorial Pacific changed significantly from El Nino year to La Nina year.
