RFM File Formats

.grd File: Irregular Grid

02SEP17

Type
Input(s), mandatory if GRD Flag enabled without LUT Flag.

Description
Irregular grid for spectral calculations (MIPAS-specific format - the irregular spectral file is probably more convenient for other uses)

Filename
Specified in *GRD section of Driver Table

Structure
This file format is formally described in ESA document PO-TN-OXF-GS-0010
The following is the relevant structure for use in the RFM
CONFIG
ILSHDR
INTFNC
NPTS NUSE WNO1 WNOD
ALTMIN ALTMAX
HEXGRD(1:50)
HEXGRD(51:100)
...
HEXGRD(*:NPTS)
[eof]

Fields
FieldTypeDescriptionRange
CONFIG C*40 Configuration Info Passed directly to rfm.runlog
ILSHDR C*80 Header record from assumed AILS file
INTFNC C*3 Interpolation Function See table below
NPTS I*4 Number of points in full grid See Note 5
NUSE I*4 Number of points in irregular grid 1:MAXGRD (in rfmsiz.inc)
WNO1 R*8 Wavenumber [cm-1] of 1st point
WNOD R*8 Wavenumber spacing [cm-1]
ALTMIN R*4 Lower tangent altitude [km]
ALTMAX R*4 Upper tangent altitude [km]
HEXGRD Z*1 1 hex character=4 grid points
The INTFNC field (always lower case) may indicate any of the following interpolation methods :
INTFNCInterpolation Function
lin y = ax + b
qad y = ax2 + b + c
cub y = ax3 + bx2 +cx + d
1li y = 1 / ( ax + b )
1qa y = 1 / ( ax2 + b + c )
1cu y = 1 / ( ax3 + bx2 +cx + d )
1sq y = 1 / ( ax + b )2
lor y = 1 / ( ax2 + b )
lnl y = exp ( ax + b )
lnc y = exp ( ax3 + bx2 +cx + d )

Notes
  1. INTFNC: All MIPAS irregular grids use the lin function - simple linear interpolation.
  2. NPTS refers to the number of points in the reconstructed regular grid, NUSE is the number which are calculated in the irregular grid.
  3. HEXGRD is an array of hexadecimal characters, up to 50 per record, with the bit pattern of one character representing four grid points with the lowest wavenumber grid point corresponding to the most significant bit. Eg '8' means that only the lowest wavenumber in a group of 4 points is used for the irregular grid, '1' means that only the highest wavenumber is used, 'F' means that all 4 are used.
  4. If NPTS is not a multiple of 4, the last HEXGRD character represents the extra 1,2 or 3 'grid points' as set to 0.
  5. A negative value of NPTS is interpreted as defining spectral ranges in GHz rather than cm-1

Examples
PT__0039_lin_m_lut                                          
! MIPAS A-band nominal AILS supplied by H.Nett 22-DEC-00                        
lin   m   A    6.975   5.742                       ! Intpln. methd, band, tols  
   951   153    685.5250      0.0005               ! npts, nused, wn0, delta
  33  45                                           ! Altitude limits (km)
80000000000000000800000000000000000000000000000000
00000022000000000002000008429FF8AD4A56ED2822242204
404042FFEC892FFEBFFFBD5420008000008000012A44228FFF
FA92FFE4100400000004000000000000000020000000000000
00000000000000000000040000000000000002
[eof]