MORSE .l1c FILE

27APR24
Description
The MORSE retrieval can work with data from a variety of different instruments. However since each instrument has its own particular L1B file structure, a pre-processing stage, tailored to each L1B product, is required to convert the L1B files to a common format which can be read by MORSE: the L1C file, in plain text format.

Structure
The L1C file has a three-level nested structure, looping over Limb Scans/Pixels (top level), Sweeps (if limb scanning) and Microwindows.
Scan
A set of measurements used for the retrieval at a single location (either profile or pixel)
Sweep
All measurements within a scan acquired at a single time/viewing geometry. For limb-viewing retrievals this will correspond to the measurements at a particular tangent height, while for nadir-viewing a single spectrum.
Microwindow
A sweep measurement subdivided into separate spectral domains.

File Structure
File_Header_Section Defines NScn, NSwp, Resln
for iScn = 1, NScn Loop over Scans/Pixels
    Scan_Header_Record
    for iSwp = 1, NSwp Loop over Sweeps (1 for nadir-viewing)
        Sweep_Header_Section Defines NMic
        for iMic = 1, NMic Loop over Microwindows/Filters
            Microwindow_Data_Section
            or Filter_Data_Record

File Header Section
!CMNT Comment record(s) (optional)
Format_ID File format identifier
View_ID Resln Viewing geometry, spectral resolution
Instrument Satellite Instrument, Satellite ID
Nom_Date Julian_Day Nominal date, day# since 1Jan2000
Orbit Time_Start Time_End     Orbit#, and Start, End times
Limb-Viewing (View_ID=1,2)
NScn No. of limb scans or nadir-viewing pixels
NSwp Grd_Type No.sweeps/measurement altitudes per scan, Grid type
Nadir-Viewing (View_ID=3)
NPix No. of pixels
NBnd No. of bands (microwindows)
Wno_Min(1) Wno_Max(1) NPts(1) Band#1: limits and no. spectral points
Wno_Min(2) Wno_Max(2) NPts(2) Band#2: limits and no. spectral points
... ... ... Band#i: limits and no. spectral points
Wno_Min(NBnd) Wno_Max(NBnd) NPts(NBnd) Band#NBnd: limits and no. spectral points
NAVH NCLS (=No.AVHRR channels and max No.clusters)
AVH(1) AVH(2) ... AVH(NAVH) (=List of AVHRR Channels, or empty record if NAVH=0
Elevation-Viewing (View_ID=4,5)
NScn No. of limb scans or nadir-viewing pixels
NSwp Grd_Type No.sweeps/measurement altitudes per scan, Grid type
Grd(1) Grd(2) ... Measurement grid altitudes/angles (always top to bottom)
... Grd(NSwp)
Scan Header Record
iScn Scan#
Sweep Header Section
!CMNT Header text for next record
YMD   HMS   MSC   iScn   iSwp   Lat   Lon   LST   SZA   Cld_Rad   Cld_Idx   Single record
!CMNT Header text for next record
NMic   Grd(iSwp)   Alt_Adj   Rad_Crv   Single record
Microwindow Data Section
Mic_Lab   Mic_Npt   Mic_Min   Mic_Max   Mic_Noi   Single record
Rad(1)   Rad(2)   ...   As many records as required
...   Rad(Mic_Npt)
Filter Data Record
Flt_Lab   Alt_Rel   Rad_Flt   Flt_Noi   Mos_X   Mos_Y   Single record

Data Dictionary

Field Type Description Units Range
!CMNT String*80 Comment record first character is '!'
Alt_Adj Float Adjusted/Corrected altitude of sweep [1] km eg 58.4
Alt_Rel Float Altitude of meas. relative to boresight [2] km −15 : +15 expected
AVH(:) String*3 (NAVH) AVHRR channel, ∈ { '1', '2', '3A', '3B', '4', '5' }
Cld_Idx Float Cloud Index [3] 0.0 if not set
Cld_Rad Float Cloud Radiance [3] 0.0 if not set
Grd_Type String*3 Measurement Grid Type 'HGT' or 'GEO'
Flt_Lab String*8 Label of spectral filter channel eg 'HSDI_06'
Flt_Noi Float Filter channel noise estimate [4] eg 0.001
Format_ID Float L1C File Format identifier [5] ≥ 3.2
Grd(:) Float (NSwp) Nominal tangent points of measurement boresight km 0 – 100 expected
Grd_Type String Vertical coordinate for measurements (optional) ∈ { HGT, ELE, GEO }
HMS Long Time of measurement in UT hhmmss eg 120001
Instrument String*10 Instrument name (left justified) eg 'IASI-A'
iScn Integer Scan counter within file [6] 1 : Nscn (1 expected)
iSwp Integer Sweep# of measurement 1 : NSwp
Julian_Day Long Nom_Date as Day# since 1 Jan 2000 (=0) eg 8401 (1st Jan 2023)
Lat Float Latitude of measurement deg N −90 : +90
Lon Float Longitude of measurement deg E −180 : +180
LST Float Local solar time hr 0.0 (not set)
Mic_Lab String Label identifying HIROS microwindow eg 'HIROS_A'
Mic_Min Double Microwindow lower wavenumber limit cm-1 eg 1135.20
Mic_Max Double Microwindow upper wavenumber limit cm-1 eg 1136.20
Mic_Noi Float Microwindow transmittance noise estimate dimensionless [4] eg 0.01
Mic_Npt Integer Number of spectral points for microwindow eg 1001
Mos_X Integer x-index of mosaic containing measurement [7] eg 1
Mos_Y Integer y-index of mosaic containing measurement [7] eg 1
MSC Long Time of measurement in UT ms eg 43201000
NAVH Int No. AVHRR channels included 0 : 5
NBnd Integer No. spectral bands (microwindows) > 0
NCLS Integer Max no. of AVHRR channel radiance clusters 7 expected
NMic Integer No. Microwindows for sweep or No. filter measurements for image eg 3
NPix Integer No. pixels (profile locations) in file > 0
Nom_Date Long Nominal observation date yyyymmdd eg 20230101
NScn Integer No. vertical scans/pixels within file [6] ≥ 1 expected
NSwp Integer No. spectral sweeps/measurement altitudes per scan (1 for nadir-viewing) > 0
Orbit Long Satellite orbit number since launch > 0
Rad_Crv Double Earth Radius of Curvature in line-of-sight plane km 6300 – 6400 expected
Resln Float Spectral resolution[10] cm-1 ≥ 0
Satellite String*10 Satellite name (left justified) eg 'MetOp-A'
SZA Float Solar Zenith Angle of measurement deg 90.0 expected
Time_End Long End of measurement UT hhmmss eg 120000
Time_Start Long Start of measurement UT hhmmss eg 134059
Tra Float(Mic_Npt) Microwindow transmittance spectrum dimensionless [8] eg 0.999955
Tra_Flt Float Filter transmittance measurement dimensionless [8] eg 0.998021
View_ID Integer Viewing geometry[9] 1 : 5
YMD Long Date of measurement yyyymmdd eg 20230101

Notes

  1. Alt_Adj is the actual sweep altitude determined within the L1 processing (this parameter allows for instruments which make multiple limb scans at a nominal set of tangent heights, eg MIPAS).

  2. For HSDI filters Alt_Rel is added to Alt_Adj to obtain the geometric tangent altitude of the filter measurement. For a given filter within a given mosaic (ie Flt_Lab, Mos_X, Mos_Y) this number is expected to be constant.

  3. Cld_Idx and Cld_Rad are only defined for MIPAS and represent cloud-contamination tests.

  4. Flt_Noi, Mic_Noi noise estimates are expressed in same units as Rad.

  5. Format_ID: the first non-comment field is the format identifier which makes it possible for the same software to handle different versions of the L1C file structure.

  6. iScn, NScn: Scans/pixels correspond to the number of MORSE retrieval profile locations.

  7. Mos_X, Mos_Y: Mosaics within the full HSDI detector array are numbered from bottom (y=1) left (x=1).

  8. Tra, Tra_Flt transmittance measurements are dimensionless nominally in the range 0–1 although may lie outside this range once noise is added.

  9. 1=limb emission, 2=limb solar occultation, 3=nadir, 4=ground-based emission, 5=ground-based transmission

  10. A value 0 indicates spectral filter measurements rather than spectrally resolved measurements

Document Changes

05OCT22 Original

Examples: hsdi.l1c, hiros.l1c