Ionospheric refractivity

[Ian Culverwell]

Two here's a demand from EUM (AvE) for ionospheric refractivities to be handled by ROPP. This will allow comparison with EPS SG test data which will go up to 500 km. There are at least three aspects:

• Putting refrac_L1 and refrac_L2 (and errors, quality flags, altitudes (?) etc) in the ROprof structure, and making sure they're read and written OK. Easy.

• Adding in the -k₄ n_e(r)/f² term to the refractivity forward model. Easy.

• Including this in the Abel transform that produces the L1 and L2 bending angles. Might be done automatically, so need to ensure no clashes with the Chapman layer work (which this might supersede). Needs a bit of thinking about.