## 2 Materials and Methods
### Sun Clitter (SG) Geometry in Stereo Images  
The sun zenith angle and sun azimuth can be calculated by longitude, latitude, and time. Because multiple imaging times of multi-angle SG remote sensing are close, we believe that the angles associated with the sun have not changed, but SVA and sensor azimuth are significantly different. Referring to [PERSON] method (2017), [PERSON] et al. (2019) and [PERSON] et al. (2019) developed a method for calculating remote-sensing geometric parameters of pixel-by-pixel elements on both sides of the nadir. On this basis, we set the SVA positive and negative. Figure 1 shows the geometric model of multi-angle SG imaging.  
Regarding the calculation of geometric angles, the left and right sides of the nadir should be considered. In the calculation of SVA and the sensor zenith angle of any pixel, suppose each pixel between this pixel and the center of the scan line (where the pixel is located) is numbered \(n\), then \(n\) is positive when this pixel is at the left of the center and negative on the right side.  
In order to facilitate the description and calculation of geometric parameters, positive and negative SVA are added. With the sensor in the flight direction, the SVA is positive when the remote-sensing  
Figure 1: Observational geometry of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Sun zenith angle (\(\theta_{0}\)), sensor nadir-looking viewing angle (\(\theta_{b}\)), sensor forward-looking viewing angle (\(\theta_{c}\)), sensor backward-looking viewing angle (\(\theta_{a}\)), scene orientation angle (\(S\)), and pointing angle (\(P\)) is presented.  
image is acquired forward, corresponding to the position of c in Figure 1 (forward-looking); Conversely, the SVA is negative when the remote-sensing image is acquired backwards, corresponding to the position of a (backward-looking); b corresponds to the position of the ASTER 3N image (nadir-looking).  
The nadir-looking viewing angle (\(\theta_{b}\)) is given by:  
\[\theta_{b}=\left|n\times(IFOV)+P\right| \tag{13}\]  
where \(IFOV\) is the instantaneous field of view, and \(P\) is pointing angle.  
The azimuth angle is \(0^{\circ}\) in the north direction of the target and gradually increases in the clockwise direction within a range of \(0^{\circ}\)-\(360^{\circ}\). The sensor azimuth angle of a pixel in the nadir-looking direction is different on different sides of nadir. When the pixel is on the left side of nadir, the nadir-looking azimuth angle (\(\phi_{b}\)) is given by:  
\[\phi_{b}=270^{\circ}+S \tag{14}\]  
When the pixel is on the right side of nadir, \(\phi_{b}\) is given by:  
\[\phi_{b}=90^{\circ}+S \tag{15}\]  
The geometric parameters of the backward-looking (a) and forward-looking (c) views are calculated differently from the nadir-looking (b) view. The backward-looking viewing angle (\(\theta_{a}\)) and forward-looking viewing angle (\(\theta_{c}\)) are given by:  
\[\theta_{(ac)}=\tan^{-1}{(\frac{\sqrt{\left(h\tan{P+mn}\right)^{2}+\left(h\tan v /\cos{P}\right)^{2}}}{h})} \tag{16}\]  
where \(h\) denotes the satellite height, \(m\) denotes the image spatial resolution, \(V\) denotes the angle between the nadir-looking view and the current view. The positive and negative of \(V\) are consistent with the positive and negative of current SVA.  
The sensor azimuth angle of a pixel in the backward-looking or forward-looking view is also different on different sides of nadir. When the pixel is on the left side of nadir, we can obtain \(\phi_{a}\) and \(\phi_{c}\) through,  
\[\phi_{(ac)}=270^{\circ}-\tan^{-1}{\left(\frac{-1\times\tan v}{\tan(n\times( IFOV)+P)}\right)}+S \tag{17}\]  
When the pixel is on the right side of nadir, \(\phi_{a}\) and \(\phi_{c}\) are given by:  
\[\phi_{(ac)}=90^{\circ}-\tan^{-1}{\left(\frac{-1\times\tan v}{\tan(n\times( IFOV)+P)}\right)}+S \tag{18}\]