Add ne(LEO) effects

[Ian Culverwell]

For single and dual frequency work the effects of a non-zero electron density at the LEO should be included. These can change the bending angles by up to 30% at CHAMP altitudes of ~450 km, and 5% even at 800 km.

[Ian Culverwell]

Branch https://trac.romsaf.org/ropp/browser/ropp_src/branches/dev/Share/ic_neLEO has been set up to include these changes, which are basically those between r5335 and r5469 of https://trac.romsaf.org/ropp/browser/ropp_src/branches/dev/Share/sbh_LEO.

[Ian Culverwell]

First version committed to repos at r5490 and r5491.

[Ian Culverwell]

neLEO_effects_fm.png

[Ian Culverwell]

This version passes all the automatic buildpack tests, after the reference files have been updated of course.

Impact of changes on FM

Note the f ^-2 ratio between the L1 and L2 bangles (0.905*(1.575/1.228)² = 1.489), which is therefore almost entirely eliminated by the standard ionospheric correction method.

[Ian Culverwell]

neLEO_effects_1dvar.png

[Ian Culverwell]

Impact of changes on 1DVAR

We see the same f ^-2 impact on the bangles. The ne_LEO effects also cause differences in the retrieval of ~0.1K in T, 0.001 g/kg in q, 1 m in GPH and 0.1 hPa in p*. It also leads to the following differences in ionospheric retrieved parameters:

                 ROPP 9.0            ROPP 9.1   
                 --------            --------

H_peak            377912              394673  = +4.4%
H_width          77356.1             79671.6  = +3.0%
Ne_max       3.71549e+11         3.53006e+11  = -5.0%

Significant effects all round. All the above assumes a Metop altitude of 830 km. Impacts would be even larger for lower satellites, like CHAMP or GRACE.

[Ian Culverwell]

(The impact on the bending angles is ~ 3.5%.)

[Ian Culverwell]

Passing to Sean for review.

[Ian Culverwell]

The Test Folder tests IT-1DVAR-02 etc fail because

INFO (from ropp_1dvar_bangle):  Reading observation data for profile 1 from the file
       ROPP_testing/ropp_test_tmp/IT-1DVAR-02_y.nc.

WARNING (from ropp_fm_roprof2obs (1D bending angles)):  Cannot find LEO position and/or centre of curvature ... will try to estimate r_LEO from satellite ID.
 
WARNING (from ropp_fm_roprof2obs (1D bending angles)):  Unrecognised LEO satellite ID (9999) ... r_LEO cannot be estimated.
 
WARNING (from ropp_fm_roprof2obs (1D bending angles)):  Check that LEO POD and CoC positions, or LEO ID, are valid.
 
WARNING (from ropp_fm_roprof2obs (1D bending angles)):  Setting status flag obs%ok to FALSE

We therefore need to protest this piece of code by wrapping it in a IF ( ro_data%Lev2c%direct_ion ) THEN ... END IF condition. Do this in r5639. (Also take the opportunity to extend the set of LEOs whose radii are estimated in ropp_fm/common/ropp_fm_roprof2obs.f90.)

[Ian Culverwell]

With this fix the test folder runs OK. These changes are outside the mainstream of ROPP, so that's probably enough testing for now. Closing ticket.

[Ian Culverwell]

(For the record, the changes from ic_neLEO were merged into ROPP91_prototype at r5625.)