*RTV Section

28JUN24
Type
Primary Section#5

Description
Retrieval grid, and list of parameters to be retrieved.

Format
Single record defining grid level indices for retrieval, then multiple fields of single type, any order.
Section structure
GRD1 GRD2 ... GRDn Retrieval Grid Indices, single record
RTV1[i:j:k] RTV2[i:j:k] ... Retrieval Parameters [retrieval grid subsets], multiple records
... RTVn[i:j:k]
Field Type ValueDescriptionUnitsRestrictions
GRD[1] Cn * Retrieve on all (NLev) grid levels Only item in record
0 Column retrievals Only item in record
i Retrieve on level i 1 : NLev
i:j Retrieve on all levels i:j inclusive 1 : NLev
i:j:k Retrieve on levels i:j with step k 1 : NLev
RTV C14 TEM Temperature [2] K
PRE Pressure [2] hPa Not on *PRE levels
CTM Continuum [3] km-1
AEROSOL Aerosol [4] km-1
SFCTEM Surface Temperature K
OFF Radiometric Offset [3] nW/(cm2.sr.cm-1)
[gas] Molecule VMR[5] ppmv from List of gases
Type: Cn=character string, length n.

Notes
  1. GRD lists the indices of the forward model grid (defined in the previous section) on which the retrieved profiles are represented (although individual species may be retrieved on subsets of this grid). Index 1 represents the lowest altitude level. Apart from the special cases of * and 0 this can be a list of increasing integers, a range expression (i:j or i:j:k), or any mix as long as these increase monotonically.

  2. The hydrostatic constraint is assumed whenever temperature (TEM) and pressure (PRE) are retrieved together in limb mode, or if temperature is retrieved on pressure surfaces in nadir mode.

  3. CTM and OFF are retrieved independently for each microwindow and therefore not included in the output unless the MWO Flag is set.

  4. AEROSOL differs from CTM in that a single profile is retrieved for all microwindows, rather than an independent profile for each microwindow separately. Effectively AEROSOL is treated just like any other retrieved gas. Note that the a priori covariances for AEROSOL and CTM differ, so even if AEROSOL is retrieved for a single microwindow over the same altitude range as CTM the results will differ.

  5. [gas] Molecules can either be specified by the chemical formula, HITRAN index or (for CFCs) 'F' number. However, internally these are stored as formulae or (for CFCs) 'F' number, all lower case.

Examples
Nadir-viewing (IASI)
*RTV 0 ! Column retrieval SFCTEM NH3 H2O ! Joint surface temperature, NH3 & H2O columns
Limb-viewing (MIPAS)
*RTV * ! Retrieve on all (17 here) tangent heights TEM PRE CTM[6:17] OFF ! Joint pT, MW continuum (scans 6-17 only) and offset
Text passed directly to output files as the second 'comment' record in the file headers, eg to identify driver table used to generate output files.

Format
Single record
FieldTypeDescription
HDRREC C79 Text for output file headers

Notes
  1. In the output file headers, an exclamation mark (!) is written as the first character (to identify a comment record), with the text string following, hence the truncation to 79 characters rather than the full 80 character length used for output files.
  2. Although the record is read as a single string, the usual rules for driver table entries still apply: completely blank records are ignored and the record is truncated at the first exclamation mark.
  3. Any tokens in the header are expanded once the L1C file is read (as in the Example below)
  4. The version of the MORSE software used (variable VIDHDR set at the start of module morse.f90) is automatically written into the first header record of output files so there is no need to include this information in the *RTV section.

Example

*RTV O3 Retrieval from Orbit#ORB ! this part won't be written

which will appear in the second record in output files (eg for orbit 12345) as

! O3 Retrieval from Orbit#12345