# Retrieval and Comparison of Multi-Satellite Polar Ozone Data from the EMI Series Instruments
## 4 Results and Discussions  
### Comparison between Multi-Satellite Total Ozone Columns  
Figure 2 shows the spatial distributions of the monthly mean global TOCs derived from the EMI-DQ01, EMI-GF5(01A), and EMI-GF5(02) instruments for November 2023. The capacity for monitoring changes in the global ozone distribution and the daily global coverage of the EMI series are shown in the figure. Figure 11 shows the daily spatial distributions of the EMI series and TROPOMI datasets for Antarctica (60\({}^{\circ}\)S-90\({}^{\circ}\)S latitude belts), which show an application example for analyzing the variation of the Antarctic ozone hole through EMI series measurements. Figure 3 shows the global maps of relative differences between EMI-GF5(01A), EMI-DQ01, and EMI-GF5(02) and TROPOMI TOC. Generally, the total ozone columns from the EMI and TROPOMI instruments show strong agreement, particularly in low- and mid-latitude regions. In comparison to the TROPOMI TOC, the EMI-GF5(01A) TOC exhibits a slight negative bias, with mean differences consistently below zero. However, these differences are generally less than \(-\)3% in both low- and mid-latitude regions. In addition, the Antarctic TOCs for the EMI series instruments had a resampled spatial resolution of 0.25\({}^{\circ}\)\(\times\) 0.5\({}^{\circ}\) (latitude \(\times\) longitude). As shown in Figures 2 and 4, high ozone values were concentrated between 30 and 60\({}^{\circ}\)S, while low ozone values were evident in the regions of Antarctica. The EMI series TOCs shown in Figure 2a-c are very similar to the overall spatial distribution of the TROPOMI TOCs shown in Figure 2d. This indicates that the EMI instruments have the capability of stably monitoring the Antarctic ozone hole on a daily basis. Figure 2 indicates that in the low and high latitudes of Antarctica, the ozone values were high and low, respectively, reflecting the daily variation of the ozone hole. In addition, the spatial distributions of TOCs in the EMI series datasets were highly consistent, which verified the stability of the EMI observations. This also provides a basis for mutual verification between EMI series instruments. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Node** & **Values** \\ \hline Month & 12 & 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 \\ Albedo & 9 & 0, 0.05, 0.1, 0.20, 0.30, 0.40, 0.60, 0.80, 1.0 \\ RAA (\({}^{\circ}\)) & 5 & 0, 45, 90, 135, 180 \\ Latitude (\({}^{\circ}\)) & 18 & \(-\)85, \(-\)75, \(-\)65, \(-\)55, \(-\)45, \(-\)35, \(-\)25, \(-\)15, \(-\)5, 5, \\  & 15, 25, 35, 45, 55, 65, 75, 85 \\ SZA (\({}^{\circ}\)) & 18 & 0, 10, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 72, 74, 76, 76, 78, 80, 82 \\ VZA (\({}^{\circ}\)) & 15 & 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 \\ Cloud pressure (hPa) & 9 & 1013, 795, 701, 616, 472, 356, 264, 164, 96 \\ VCD (DU) for AMF correction & 10 & 125, 175, 225, 275, 325, 375, 425, 475, 525, 575 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters for node settings in the AMF LUT. Figure 2: (**a**) Spatial distribution of the monthly mean global TOCs for the November 2023 EMIGF5(01A) data; (**b**) spatial distribution of the monthly mean global TOCs for the November 2023 EMI-GF5(02) data; (**c**) spatial distribution of the monthly mean global TOCs for the November 2023 EMI-DQ01 data; (**d**) spatial distribution of the monthly mean global TOCs for the November 2023 TROPOMI data. overall spatial distributions of the EMI-DQ01, EMI-GF5 (01A), and EMI-GF5(02) TOCs were very similar, with an average relative deviation of approximately 0.18%, indicating that the EMI observations were stable and consistent. The monthly mean TOCs of the EMI instruments (Figure 3a-c) exhibited an overall spatial distribution similar to that of the TROPOMI data (Figure 3), with an average relative deviation of approximately 0.18%. The mean relative difference between EMI-DQ01 and EMI-GF5(01A) TOCs is defined as:\(\Delta_{\text{rel}}=100\%\times\frac{\text{EMI-DQ01}-\text{EMI-GF5}(01A)}{\text{EMI-GF5}(01A)}\).