MORSE L1C Pre-processor

27AUG20

Contents

Introduction

MORSE requires a pre-processor to convert satellite spectra from their original format to a common input format: the MORSE L1C file (plain text format).

Currently there are two such pre-processors, both written in IDL

IASI_L1C

The program can be run just using the IASI .nat file as input, but also allows for two different types of colocated IASI L2 products (RAL and Eumetsat) to be used to provide additional information, in which case the output is further restricted to the L2 locations.
IDL Command line
The procedure would be run interactively from an IDL session as
IDL> IASI_L1C, INPFIL, OUTFIL, WNOBND, NPIX, $
     LAT=LAT, LON=LON, CLD=CLD, AVH=AVH, $
     EL2FIL=EL2FIL, EL2ATM=EL2ATM, EL2SFC=EL2SFC, $
     RALFIL=RALFIL, RALATM=RALATM, RALSFC=RALSFC, RALCLD=RALCLD
Arguments
ArgumentType I/O Description Notes
Mandatory
INPFIL STRING I Name of IASI .nat input file
OUTFIL STRING I Name of output MORSE .l1c file
WNOBND FLTARR(2,*) I Lower,Upper Wavenumber limits [cm-1] for each output band (1)
NPIX LONG O No. pixels in output file
Optional
LAT FLTARR(2) I Min,Max Latitude limits [-90:90 deg N]
LON FLTARR(2) I Min,Max Longitude limits [-180:180 deg E] (2)
CLD FLTARR(2) I Min,Max %Cloud cover [0:100%] (3)
AVH STRARR(*) I List of AVHRR channels for cluster data ['1','2','3A','3B','4' and/or '5'] (4)
EL2FIL STRING I Name of Eumetsat L2 file for colocated output (5)
EL2ATM STRING I Name of new orbital file (.orb file) containing colocated Eumetsat L2 profiles (6)
EL2SFC STRING I Name of new orbital file (.orb file) containing colocated Eumetsat L2 surface parameters (7)
RALFIL STRING I Name of RAL L2 netCDF file for colocated output (5)
RALATM STRING I Name of new orbital file (.orb file) containing colocated RAL L2 profiles (6)
RALSFC STRING I Name of new orbital file (.orb file) containing colocated RAL surface parameters (7)
RALCLD STRING I Name of new orbital file (.orb file) containing colocated RAL cloud parameters (8)
Notes
  1. WNOBND Usually this would just be a 2 element array giving the lower and upper wavenumber limits of the part of the IASI spectrum required. However it can also be used to extract multiple ranges.
  2. LON First element is west boundary of longitude limit so, for example, [170,-170] selects 20 degree span of Longitudes from 170E to 170W
  3. CLD The default is to include all pixels, but this argument can be used to exclude pixels where the cloud cover, as defined by the Cloud Fraction field in the IASI L1C .nat file, is above some threshold e.g. CLD=[0,50]. It could also be used to set the minimum cloud cover, eg CLD=[25,100], but that's probably less useful.
  4. AVH IASI .nat files contain cluster analyses from colocated AVHRR channels, which can be used by MORSE for modelling partly-cloudy fields-of-view. Select AVH=['4','5'] to extract cluster analyses for channels 4 (10.7μm) and 5 (12.0μm), which are the only two channels currently used by MORSE (data from any other channels is ignored).
  5. EL2FIL, RALFIL If either a Eumetsat L2 .nat file or RAL L2 netCDF file containing IASI L2 products is supplied, the L1C output will be limited to just those pixels where the L2 contains valid temperature retrievals.
  6. EL2ATM (requires EL2FIL) or RALATM (requires RALFIL) are the names of .orb format output files which will contain the profile information extracted from the Eumetsat/RAL L2 files, colocated with the L1C data.
  7. EL2SFC (requires EL2FIL) or RALSFC (requires RALFIL) are names of .orb format output files which will contain the surface information extracted from the Eumetsat/RAL L2 files, colocated with the L1C data.
  8. RALCLD (required RALFIL) is the name of an .orb format output file which will contain the RAL cloud information.

IASI L1C File Format

C80 Records
File header
!CMNT
FMT (=format id)
IGEOM RESLN [eg] (3=nadir, 0.25=resln)
INST_ID SAT_ID (=Instrument,satellite)
YYYYMMDD JDAY (=nominal date, day# since 1Jan2000)
ORBIT ORBSTA ORBEND (=Orbit#, Orbit Start HHMMSS, Orbit End HHMMSS)
NPIX (=No.pixels)
NBND (=No.bands)
WNOMIN(1) WNOMAX(1) NPTS(1) (=Wno1, Wno2, Npts)
... ... ... (=Wno1, Wno2, Npts)
WNOMIN(NBND) WNOMAX(NBND) NPTS(NBND) (=Wno1, Wno2, Npts)
NAVH NCLS (=No.AVHRR channels and max No.clusters)
AVH(1) AVH(2) ... AVH(NAVH) (=List of AVHRR Channels)
For each pixel ...
IPIX =Pix#
!yyyymmdd hhmmss millisec STP FOV ... [fixed text record]
YMD HMS MSC STP FOV LAT LON ZEN SZA CLD LND [single record]
For each band i=1, NBND ...
RAD(1,i) RAD(2,i) ... RAD(NPTS(i),i)
FieldFormatDescriptionRange/Notes
File Header
!CMNT A80 Comment record(s) (optional) Record starts with '!'
FMT F10.1 L1C file format version ≥3.2 accepted by MORSE
IGEOM I10 Viewing geometry 3=nadir for IASI
RESLN F10.4 Spectral sampling [cm-1] 0.25 for IASI
INST_ID A10 Instrument identification e.g. 'IASI-A'
SAT_ID A10 Satellite identification e.g. 'MetOp-A'
YYYYMMDD I10 Year, Month, Day of data
JDAY I10 Day# since 1 Jan 2000 (JDAY=0)
ORBIT I10 Orbit number since launch
ORBSTA I10 Orbit start time [HHMMSS]
ORBEND I10 Orbit end time [HHMMSS]
NPIX I10 No. of pixels or complete limb scans
NBND I10 No. of spectral bands
WNOMIN(i) F10.2 Lower Wno [cm-1] of Band i
WNOMAX(i) F10.2 Upper Wno [cm-1] of Band i
NPTS(i) I10 No. spectral points in Band i
NAVH I10 No. AVHRR channels included
NCLS I10 Max no. of AVHRR channel radiance clusters
AVH(j) A3 Identification of AVHRR channel j e.g. '3A 4 5', or blank if NAVH=0
For each pixel
IPIX I6 Pixel number 1:NPIX
YMD I9 Year, month, day, in YYYYMMDD format
HMS I6.6 Hours, minutes, seconds, in HHMMSS format
MSC I9 Milliseconds into day (0:86400000)
STP I4 IASI Mirror step# (1:30)
FOV I4 IASI Pixel/FOV# (1:4)
LAT F7.2 Latitude [deg N] (-90:90)
LON F8.2 Longitude [deg E] (-180:180)
ZEN F7.2 Satellite Zenith Angle [deg] (0:90)
SZA F7.2 Solar Zenith Angle [deg] (0:180)
CLD F7.1 Cloud fraction [%] (0:100)
LND F7.1 Land fraction [%] (0:100)
RAD F10.1 Radiance [nW/(cm2 sr cm-1)]

MIPAS_L1C

The IDL procedure mipas_l1c.pro reads a MIPAS L1B file and a list of microwindows, apodises the spectra and extracts the microwindows writing them as a
MIPAS L1C file. Typically, the procedure would be run interactively from an IDL session as
IDL> MIPAS_L1C, INPFIL, OUTFIL=OUTFIL, MWLIST=MWLIST

Arguments

ArgumentType I/O Description Notes
INPFIL STRING I Name of L1B input file
Optional
OUTFIL STRING O Name of L1C output file (input for MORSE) (1)
MWLIST STRING I Microwindow list file (2)
Notes
  1. OUTFIL: The default output filename is MIP_ooooo.l1c where ooooo is the Absolute Orbit Number.
  2. MWLIST: The list of required microwindows in .lst file format. If absent the program simply returns headers for each sweep (=spectrum) in the L1B file.

MIPAS L1C File Format

C80 Records
File Header
!CMNT
FMT (=format id)
IGEOM RESLN [eg] (3=nadir, 0.25=resln)
INST_ID SAT_ID (=Instrument,satellite)
YYYYMMDD JDAY (=nominal date, day# since 1Jan2000)
ORBIT ORBSTA ORBEND (=Orbit#, Orbit Start HHMMSS, Orbit End HHMMSS)
NSCN (=No.scans)
NSWP (=No.sweeps per scan, then nominal alts [km])
ALT(1) ALT(2) ...
... ALT(NSWP)
End of File Header
For each Scan 1... NSCN
       ISCN (=Scan#)
   For each Sweep 1... NSWP within Scan
!yyyymmdd hhmmss  millisec Scn Swp   Lat     Lon   LST     SZA   CldRad  CldIdx 
[fixed text record]
YMD   HMS   MSC   SCN   SWP   LAT   LON   LST   SZA   RCL   CIX
!NMW AltNom  AltSwp   RadCrv
[fixed text record]
NMIC   ALT(ISWP)   ZSWP   RCRV
        For each Microwindow IMIC=1, NMIC within Sweep
LAB(IMIC) NPT(IMIC) WN1(IMIC) WN2(IMIC)
RAD(1,IMIC) RAD(2,IMIC) ...
... RAD(NPT(IMIC),IMIC)
FieldFormatDescriptionRange/Notes
File Header
!CMNT A80 Comment record(s) (optional) Record starts with '!'
FMT F10.1 L1C file format version ≥3.2 accepted by MORSE
IGEOM I10 Viewing geometry 1=limb for MIPAS
RESLN F10.4 Spectral sampling [cm-1] 0.025 (FR) or 0.0625 (OR) for MIPAS
INST_ID A10 Instrument identification e.g. 'MIPAS'
SAT_ID A10 Satellite identification e.g. 'Envisat'
YYYYMMDD I10 Year, Month, Day of data
JDAY I10 Day# since 1 Jan 2000 (JDAY=0)
ORBIT I10 Orbit number since launch
ORBSTA I10 Orbit start time [HHMMSS]
ORBEND I10 Orbit end time [HHMMSS]
NSCN I10 No. of complete limb scans
NSWP I10 No. of sweeps per scan
ALT(i) F8.1 List of nominal sweep altitudes [km] MIPAS: Sweep#1 is highest alt
For each Scan 1 ... NSCN
ISCN I6 Scan number 1:NSCN
For each Sweep ISWP= 1 ... NSWP
YMD I9 Year, month, day, in YYYYMMDD format eg '20021231'
HMS I6.6 Hours, minutes, seconds, in HHMMSS format eg '235959'
SCN I4 Scan number within orbit 1:NSCN
SWP I4 Sweep# within scan 1:NSWP
LAT F7.2 Latitude [deg N] (-90:90)
LON F8.2 Longitude [deg E] (-180:180)
LST F7.3 Local Solar Time [hrs] (0:24)
SZA F7.2 Solar Zenith Angle [deg] (0:180)
RCL F8.1 Cloud Radiance
CIX F7.2 Cloud Index
NMIC I3 No. of microwindows for this sweep
ALT(ISWP) F8.1 Nominal altitude for this sweep [km] ALT(1:NSWP)
ZSWP F8.3 Actual altitude for this sweep [km]
RCRV F9.3 Earth radius of curvature [km]
For each Microwindow IMIC= 1 ... NMIC
LAB A8 Microwindow label eg 'H2O_0001'
NPT I No. of spectral points in Microwindow Usually ≤ 121 for MIPAS
WN1 D Lower Wavenumber limit [cm-1] of microwindow
WN2 D Upper Wavenumber limit [cm-1] of microwindow
RAD(k,j) R Radiance [nW/(cm2 sr cm-1)]

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