id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
197	Error covariance product	Huw Lewis	Ian Culverwell	"The GRAS SAF product list includes
'Covariance matrix for NRT sounding data products (GRM-07)' and
'Covariance matrix for Offline sounding data products (GRM-15)'.
These arrays will be provided as sample files on the GRAS SAF website.

These products will be based on the existing 'sample' observation error covariance (and sigma) files distributed as part of the 1dVar module. The SAF-specific file should be valid for the 247 observation levels supplied by the SAF (at least), and be compatible with the error model developed by Kjartan for use in the operational GRAS SAF processing chain. 

The file shall contain the following variables (perhaps latitudinally/seasonally varying at some point):
level(nob) - standard observation height levels
sigma(nob) - fixed standard deviation values for each ob level
corr(nobxnob) - packed error correlation array
frac_error(nob) - fractional/percentage error assumed at each ob level

Separate products should be made available for refractivity and bending angle observations.

The ropp_1dvar_read_cov() routines may need updating to read in fractional error and compute the covariances. Perhaps an extra 'VSDC, FSFC, FSDC' type option will be needed for reading in fractional errors and computing sigma values within the routine (rather than read those provided as variables bangle_sigma etc in the input file).





"	enhancement	closed	normal	6.0	ropp_1dvar	4.0	wontfix