# Data-Free Area Detection and Evaluation for Marine Satellite Data Products
## 3 Results
### Data Product Analysis and Evaluation
#### 3.2.1 Integrity of Ocean Color Information
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Miss Rate (\%)** & **GOCI** & **MODIS** & **OLCI** \\ \hline _Jan._ & 43.63 & 39.23 & 13.24 \\ _Mar._ & 11.50 & 18.23 & 0.11 \\ _Apr._ & 28.05 & 38.79 & 6.72 \\ _May._ & 19.38 & 22.42 & 4.56 \\ _Jun._ & 32.13 & 34.79 & 16.20 \\ _Jul._ & 41.36 & 53.99 & 27.66 \\ _Aug._ & 18.15 & 15.58 & 6.36 \\ _Sept._ & 29.20 & 26.61 & 9.87 \\ _Oct._ & 21.81 & 23.55 & 6.21 \\ _Nov._ & 15.64 & 11.38 & 14.89 \\ _Dec._ & 23.10 & 12.90 & 4.75 \\ AVG & 25.81 & 27.04 & 10.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Month-by-month missing rate of the three products. Figure 9: Diagram of month-by-month missing rate: (**a**) box line diagram and (**b**) line graph. Table 6 particularly shows the total annual areas of the five common marine coverage objects in the product data-free area and their proportions. For GOCI and MODIS, the largest proportions of marine coverage objects in the data-free area are the clean water areas in the open ocean (both at approximately 47.7%), followed by those with cloud pixels (approximately 37.5%) of the data-free area. The difference between the two products and the OLCI product can be attributed to the presence of cloud pixels occupying 98.885% of the data-free area. Presumably, the composition of ocean-covered objects in the data-free area of OLCI was primarily clouds, a phenomenon that is consistent with the actual situation. The areas of each type of marine coverage object in the GOCI and MODIS data-free areas showed a concomitant increase or decrease (Figure 10). The trend indicates that the data are similar not only in their total missing rate but also in the missing rate of each type of marine object. The remote sensing information on the spatial locations of cloud pixels is inevitably lost after cloud detection and the cloud mask pre-processing of remote sensing data. Different satellites can hardly obtain data at the same time because of their respective but varying sensor imaging mechanisms and revisit cycles. Furthermore, cloud drifts are unavoidable. Clouds at the edges of an area disappear from the range of interest because of their movement, thus affecting the size of the data-free area. Here, we attempted to remove the cloud pixels in the ocean coverage type of the data-free area and evaluate the quality of \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Class**} & \multicolumn{3}{c}{**GOCI**} & \multicolumn{3}{c}{**MODIS**} & \multicolumn{3}{c}{**OLCI**} \\ \cline{2-10}  & **Area (km\({}^{2}\))** & **Percentage (\%)** & **Area (km\({}^{2}\))** & **Percentage (\%)** & **Area (km\({}^{2}\))** & **Percentage (\%)** \\ \hline Open Sea & 709,861 & 47.077 & 77.135 & 663,926 & 48.422 & 76.481 & 1683.18 & 0.302 & 27.044 \\ Turbid & 203,982 & 13.528 & 22.165 & 199,284 & 14.534 & 22.956 & 2536.92 & 0.455 & 40.762 \\ Green Tide & 3030.25 & 0.201 & 0.329 & 2676 & 0.195 & 0.308 & 599.85 & 0.108 & 9.638 \\ Sea Ice & 3413 & 0.226 & 0.371 & 2210 & 0.161 & 0.255 & 1403.82 & 0.252 & 22.556 \\ Cloud & 587,599.75 & 38.968 & & 503,038 & 36.688 & & 551,769.03 & 98.885 & \\ Abnormal & 920,286.25 & & 61.032 & 868,096 & & 63.312 & 6223.77 & 1.115 & \\ Missing & 1,507,886 & & 100 & 1,371,134 & 100 & 557,992.8 & 100 & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Status of the proportion of marine coverage objects in the data-free areas. Figure 10: Schematic diagram of the distribution of total missing marine coverage types for all seasons for the three products: (**a**) clean water, (**b**) turbid water, (**c**) green tide algae, (**d**) clouds and (**e**) sea ice. the products by using the abnormal missing indicator as a means of reducing the statistical error caused by cloud movement. It is shown in the second sub-column of the percentages in Table 6.  
As shown in Figure 6, the clean water of GOCI and MODIS has the largest proportion of anomalously missing information, even reaching 77%. The anomalous missing information of GOCI and MODIS are also extremely similar.