  We determine the coronal magnetic field strength in the heliocentric distance
range 6 to 23 solar radii (Rs) by measuring the shock standoff distance and the
radius of curvature of the flux rope during the 2008 March 25 coronal mass
ejection (CME) imaged by white-light coronagraphs. Assuming the adiabatic
index, we determine the Alfven Mach number, and hence the Alfven speed in the
ambient medium using the measured shock speed. By measuring the upstream plasma
density using polarization brightness images, we finally get the magnetic field
strength upstream of the shock. The estimated magnetic field decreases from ~48
mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can
be described by a power law in agreement with other estimates at similar
heliocentric distances.
