In principle you are good to do this, but would of course need to play close attention tot he physical attributes of the installation, interference, line-of sight etc...
At 9 miles, you need a total clearance at the midpoint of the link of 37ft.
The AP-175 Installation Guide below has details on this.
http://support.arubanetworks.com/DOCUMENTATION/tabid/77/DMXModule/512/Command/Core_Download/Default.aspx?EntryId=8939
snippet from the guide page 7/36:
A wireless bridge or mesh link requires a “radio line of sight” between the two antennas for optimum
performance. The concept of radio line of sight involves the area along a link through which the bulk of the
radio signal power travels. This area is known as the first Fresnel Zone of the radio link. For a radio link, no
object (including the ground) must intrude within 60% of the first Fresnel Zone.
If there are obstacles in the radio path, there may still be a radio link but the quality and strength of the
signal will be affected. Calculating the maximum clearance from objects on a path is important as it directly
affects the decision on antenna placement and height. It is especially critical for long-distance links, where
the radio signal could easily be lost. When planning the radio path for a wireless bridge or mesh link, consider these factors:
- Avoid any partial line of sight between the antennas
- Be cautious of trees or other foliage that may be near the path, or may grow and obstruct the path.
- Be sure there is enough clearance from buildings and that no building construction may eventually block the path.
- For very long distance links, the curvature of the earth (20 cm per km) may need to be considered in the calculation of relative heights.
- Check the topology of the land between the antennas using topographical maps, aerial photos, or even satellite image data (software packages are available that may include this information for your area)
- Avoid a path that may incur temporary blockage due to the movement of cars, trains, or aircraft.