## 3 Results and Discussions
### Observation Results in the ECS
#### 3.3.2 Variation of the \(\chi_{p}\) Factor  
The \(\chi_{p}\) factor, defined as \(\chi_{p}=b_{bp}/(2\pi\beta_{p}(\theta))\), is an important factor relating \(b_{bp}\) with the particulate VSF measured at a single scattering angle and describing the shape of the particulate VSF in the backward direction [41; 42; 43]. Figure 9a shows the angular variation of the \(\chi_{p}\) factor using VSFlab data from all sites of the ECS. Similar to results measured in other coastal and oceanic areas, \(\chi_{p}\) of the ECS exhibited an increase from 90\({}^{\circ}\) to 120\({}^{\circ}\), a relatively flat shape at angles of 120\({}^{\circ}\) to 150\({}^{\circ}\) and an obvious decrease at angles greater than 150\({}^{\circ}\). The average and standard deviations (\(\sigma\)) of \(\chi_{p}\) from all sites are shown in Figure 9b. The variability in \(\chi_{p}\) was found to be less than 6% for most scattering angles within 90\({}^{\circ}\)-155\({}^{\circ}\). The average of \(\chi_{p}\) at 120\({}^{\circ}\) from the results in the ECS was 1.13 \(\pm\) 3.81%. Other mean \(\chi_{p}\) near 120\({}^{\circ}\) reported by [PERSON] et al. [42], [PERSON] et al. [43], [PERSON] et al. [44], [PERSON] et al. [36] and [PERSON] et al. [40] were 1.14 \(\pm\) 10%, 1.12 \(\pm\) 4.2%, 1.1 \(\pm\) 1.45%, 1.097 \(\pm\) 2.92%, and  
Figure 8: **(a)** Phase functions at 532 nm between 1\({}^{\circ}\) and 178.5\({}^{\circ}\) in the ECS. **(b)** Comparison of VSFs at 532 nm measured by VSFlab, POLVSM and MVSM between 170\({}^{\circ}\) and 178.5\({}^{\circ}\). All these VSFs were normalized at 170[PERSON]circ}\). \(1.1\pm 3.64\%\), respectively. Our result was very consistent with them. Another average of \(\chi_{p}\) at 140\({}^{\circ}\) in the ECS was 1.21 \(\pm\) 4.63\(\%\). Compared with other studies (\(\chi_{p}(140^{\circ})=1.18\pm 3.5\%\), 1.167 \(\pm\) 4.2\(\%\), and 1.15 \(\pm\) 3.48\(\%\)) [36; 40; 43], our \(\chi_{p}(140^{\circ})\) was only slightly higher. The conclusion proposed by [PERSON] et al. that the estimates of the particulate backscattering coefficient using single angle scattering measurements near 120\({}^{\circ}\) or 140\({}^{\circ}\) and suitable conversion factors [36], was justified in the ECS. Large variability in \(\chi_{p}\) factors could be observed at angles greater than 155\({}^{\circ}\), particularly greater than 170\({}^{\circ}\) (near 25\(\%\)). Such large variability at 170\({}^{\circ}\) was also pointed out by [PERSON] et al. [45], according to \(\chi_{p}\) of thirteen different algae, but few studies have given the variability of \(\chi_{p}\) after 170\({}^{\circ}\). Our results showed that the variability increased with the angle after 155\({}^{\circ}\) and reached the maximum value of 42.3\(\%\) at 178.5\({}^{\circ}\). Based on the different backscattering shapes at angles greater than 155\({}^{\circ}\), the VSFs measured in the ECS can be roughly classified into two types (type I and type II, see Figure 9). \(\chi_{p}\) of type I and type II was close between 90\({}^{\circ}\) and 155\({}^{\circ}\), but \(\chi_{p}\) of type I was smaller than that of type II after 155\({}^{\circ}\). The mean \(\chi_{p}\) for the two types and all observations are presented in Figure 9b, indicating that the most difference between these two types occurred at angles after 170\({}^{\circ}\). Such obvious deviation was closely associated with the particle size distribution, shape, and the real bulk index of refraction of the particles [46; 47; 48]. With the assistance of the BT-3000 micro imaging function, it could be found that the particles in type I and type II water had significant differences in particle size and morphology (see Figure 9c,d and Table 2). In terms of particle size, the average equivalent diameter of particles in type I samples (>10 um) was obviously greater than that of type II (near 8 um), and additionally, according to the \(\sigma\) calculation, type I samples had wider size distributions indicating that particles in these samples were more polydispersed.