# 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  
The ecological environments of marine areas are complex, and remote sensing products with missing information are common in this case. Cloud occlusion is the main factor in the low spatial continuity of product data [56, 57, 58]. Moreover, the differences in algorithms for cloud detection or noise removal processes may result in missing normal pixels of the data product, thus greatly increasing the missing rate of the product. In this study, this loss of ocean color information corresponding to cloud-free pixels is called abnormal missing information. Table 5 shows the main types of marine coverage compositions and their area status in the product data-free areas. The area and missing rate are calculated as follows. \[A_{i}=S_{i}\cdot R_{i}^{2}, \tag{8}\]  
\[L_{i}=\frac{\sum_{i}^{n}A_{i}}{S}\cdot 100\%, \tag{9}\]  
where \(S_{i}\) (\(n=3\)) represents the number of image elements of each category in the recognition classification result, \(S\) is the total area size of the area of interest in a single view, \(R_{i}\) is the resolution size of a remote sensing image of GOCI (0.5 km), MODIS (1 km) and OLCI (0.3 km), \(A_{i}\) is the area size of each category and \(L_{i}\) is the missing rate of each image. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensors** & \begin{tabular}{c} **Producer** \\ **Accuracy (\%)** \\ \end{tabular} & \begin{tabular}{c} **User Accuracy** \\ **(\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Kappa** \\ **Coefficient** \\ \end{tabular} &
\begin{tabular}{c} **Overall** \\ **Accuracy (\%)** \\ \end{tabular} \\ \hline GOCI & 84.8 & 94.6 & 0.90 & 91.9 \\ MODIS & 92.4 & 90.7 & 0.86 & 89.3 \\ OLCI & 80.4 & 91.4 & 0.89 & 95.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Threshold values for each type of object accuracy evaluation of classification results. As shown in Table 5 and Figure 9, the missing rate of GOCI is mainly in the range of 15% to 30%, whereas that of MODIS is mainly in the range of 15% to 35%, with a large variation in missing rate per month. The missing rate of OLCI is mainly in the range of 4% to 15%, with less variation in the size of the missing rate per month. Its information is more complete and robust than those of GOCI and MODIS. Interestingly, the missing rates of the three products for January, June and July are larger than in the other months. MODIS products even lost half of their information in July. In addition, not only are the trends of the missing rates similar among the three products, but the monthly magnitudes of the missing rates of GOCI and MODIS are similar. With respect to the completeness of data, the information was judged based on the average annual missing rate indicator only. The quality of OLCI is better than the other two product data, followed by that of GOCI, whereas MODIS has the lowest quality. However, the three data missing rates are large, and the monthly missing rates of GOCI and MODIS products are similar to the inter-annual variations. The remote sensing information corresponding to the spatial location of Level 1 data in the product data-free area is complex. A single missing rate indicator cannot accurately describe the quality of the GOCI and MODIS products. Therefore, the remote sensing information of the products' data-free areas was mined to further obtain the missing information and improve the quality evaluation of the ocean color products. Level 1 data were mined for spectral information by using ISAM. The composition and distribution of the main marine objects in the product data-free area are shown in Table 6.