Arsia Mons cloud height estimation from shadow length
Figure 4: To the N of the cloud, a shadow can be seen on the martian surface. This can be used to estimate the altitude of the cloud above the surface using trigonometry. Using Celestia 1.6.0 the illumination angle was determined by highlighting the sun vector. The shadow length will be parallel to the sun vector. The thickest part of the cloud shadow falls at roughly [-8oS, 130oW] longitude following this vector. The shadow length at this point was measured to be 12 pixels. At this location, the MEX-VMC image is approximately 1.9 km/pixel along this latitude line. Thus the shadow length is approximately 22.8 km long at this location. From Celestia 1.6.0, the phase angle at [-8oS, 130oW] longitude was 78.5 degrees. This corresponds to an elevation of the sun above the surface of 12 degrees – early morning on the Arsia Sulci. The height of the cloud is related to the shadow length and phase angle by the equation:
Height above surface = cot(90-sun elevatoin) x shadow length along illumination vector
Using this relationship, the cloud is estimated to be approximately 4.6 km above the local martian surface. This is shown in the above graphic.
The Tharsis bulge is topographically high, at the location of the shadow [-8oS, 130oW], the elevation is 3.5 km above mean Mars radius. From the shadow calculation, the absolute elevation of the cloud is estimated to be 8.1 km above Mars’ mean radius.
Image credits: ESA/Mike Malaska
Arsia Mons cloud height estimation from shadow length
Figure 4: To the N of the cloud, a shadow can be seen on the martian surface. This can be used to estimate the altitude of the cloud above the surface using trigonometry. Using Celestia 1.6.0 the illumination angle was determined by highlighting the sun vector. The shadow length will be parallel to the sun vector. The thickest part of the cloud shadow falls at roughly [-8oS, 130oW] longitude following this vector. The shadow length at this point was measured to be 12 pixels. At this location, the MEX-VMC image is approximately 1.9 km/pixel along this latitude line. Thus the shadow length is approximately 22.8 km long at this location. From Celestia 1.6.0, the phase angle at [-8oS, 130oW] longitude was 78.5 degrees. This corresponds to an elevation of the sun above the surface of 12 degrees – early morning on the Arsia Sulci. The height of the cloud is related to the shadow length and phase angle by the equation:
Height above surface = cot(90-sun elevatoin) x shadow length along illumination vector
Using this relationship, the cloud is estimated to be approximately 4.6 km above the local martian surface. This is shown in the above graphic.
The Tharsis bulge is topographically high, at the location of the shadow [-8oS, 130oW], the elevation is 3.5 km above mean Mars radius. From the shadow calculation, the absolute elevation of the cloud is estimated to be 8.1 km above Mars’ mean radius.
Image credits: ESA/Mike Malaska