## 3 Results and Discussions
### Observation Results in the ECS  
#### 3.3.1 VSF between 1\({}^{\circ}\) and 178.5\({}^{\circ}\)  
The VSFlab instrument was used in several cruises to carry out the VSF measurements in the ECS. The VSFs in the ESC are shown in Figure 8a. The \(\tilde{b}_{bp}\) derived from measured VSF was 1.25-2.83%. The \(c\) of all measured samples ranged from 0.62 m\({}^{-1}\) to 5.79 m\({}^{-1}\). The  
Figure 6: (**a**) Comparison of phase functions for 3 \(\upmu\)m beads at 532 nm obtained from the VSFlab (red line), redrawn from [PERSON]’s work (green line) and calculated by Mie theory (black line). (**b**) Same as (**a**) but for angles between 170\({}^{\circ}\) and 178.5\({}^{\circ}\).  
Figure 7: (**a–c**) VSFs for 2, 5, and 11 \(\upmu\)m beads at 520 nm. The blue line denotes the results measured by LISST-VSF, and the red line denotes the results measured by VSFlab. The black line corresponds to the theoretical curves calculated from Mie theory. (**d–f**) Same as (**a–c**) but for angles between 170\({}^{\circ}\) and 178.5\({}^{\circ}\).  
chlorophyll concentration ranged from 0.27 to 53.06 mg/m\({}^{3}\). For samples with \(c\) greater than 1.5 m\({}^{-1}\), the water samples were diluted in advance to meet the requirement of single scattering.  
The VSFs showed strong forward scattering. Forward and backward scattering differed by nearly five orders of magnitude. Past and recent studies about VSFs measurements that were performed in natural waters [13; 36; 37], showed a significant increase in the VSF in the backward direction at angles greater than 150\({}^{\circ}\). However, only a few instruments, such as POLVSM and MVSM, yielded the VSF measurements at the angles greater than 170\({}^{\circ}\)[21; 23; 38; 39], and there was large variability of VSF in this angle range. More than one order of magnitude increase in VSF from 170\({}^{\circ}\) to near 180\({}^{\circ}\) was sometimes observed. Hence, the comparison of the VSFs in the ECS with the results measured by POLVSM and MVSM at angles greater than 170\({}^{\circ}\) was made, which is shown in Figure 8b.  
POLVSM has been used to measure various types of VSFs including dust and algae. The measured VSFs increased by an average of five times at angles larger than 170\({}^{\circ}\)[23; 39]. The VSFs observed from MVSM in surface waters off the New Jersey coast showed even more increase by an average of 6.5 times, and the maximum growth exceeded 9.8 times [21; 38]. A field experiment in the northern Adriatic Sea indicated that the VSF measurements by the MVSM at angles > 175 are unreliable due to stray light contamination and / or difficulty in precisely calculating the scattering volume [40]. Therefore, it can be further found that the VSFs from VSFlab and MVSM were in good agreement with the range of 170\({}^{\circ}\) to 175\({}^{\circ}\), while a significant deviation was observed at an angle greater than 175\({}^{\circ}\). Different from other VSFs, the VSFs in the ESC increased relatively slowly from 170\({}^{\circ}\) to 178.5\({}^{\circ}\), about 1.24-3.97 times with an average of 2.19 times. In general, a moderate increase in VSFs at angles larger than 170\({}^{\circ}\) in the ECS was observed for the first time.