MORSE .l1c FILE

04DEC25
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 format which can be read by MORSE: the L1C file, in plain text format. Even so, there are small differences in structure depending on the particular instrument.

Structure
The L1C file has a three-level nested structure, looping over Limb Scans/Pixels (top level), Sweeps (if limb scanning) and Microwindows.
Limb Scan/Pixel
For limb-scanning instruments, a sequence of measurements at different times/locations used for the retrieval at a single location. For nadir-viewing instruments just the single spectrum targeting the surface at a particular location.
Sweep
For limb-scanning, a spectrum acquired at a single time/viewing geometry. For nadir-viewing just a single spectrum, although in principle multiple spectra e.g. viewing at different angles could also be specified.
Microwindow
A sub-set of the complete spectrum.

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
Common File Header
!CMNT Comment record(s) (optional)
FORMAT_ID File format identifier
VIEW_ID RESLN Viewing geometry, spectral resolution
INSTRUMENT SATELLITE Instrument, Satellite ID or Location
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
NSWP GRD_TYPE No.sweeps/measurement altitudes per scan, Grid type
GRD(1) GRD(2) ... Measurement tangent altitudes (always top to bottom)
... GRD(NSWP)
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 elevation scans
NSWP No.sweeps per scan
Scan Header Record
ISCN Scan/Pixel#
Sweep Header Section
Limb-Viewing (VIEW_ID=1,2)
!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
Nadir-Viewing (VIEW_ID=3)
!CMNT Header text for next record
YMD   HMS   MSC   ISTP   IFOV   LAT   LON   ZEN   SZA   CLD_PCT   LND_PCT   Single record
Microwindow Data Section
MIC_LAB   MIC_NPY   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 C80 Comment record (starts with '!')
ALT_ADJ R Adjusted/Corrected altitude of sweep [1] km (0,100) expected
ALT_REL R Altitude of meas. relative to boresight [2] km (−15,+15) expected
AVH(NAVH) C3 AVHRR channel ∈ { '1', '2', '3A', '3B', '4', '5' }
CLD_IDX R Cloud Index (0.0 if not set) [3]
CLD_PCT R Cloud Fraction % [0,100]
CLD_RAD R Cloud Radiance (0.0 if not set) [3] ≥0
FLT_LAB C8 Label of spectral filter channel, eg 'HSDI_06'
FLT_NOI R Filter channel noise estimate r.u. > 0
FORMAT_ID R L1C File Format identifier [5] ≥ 3.2
GRD(NSWP) R Nominal tangent points of measurement boresight km 0–100 expected
GRD_TYPE C3 Vertical coordinate for limb-viewing measurements ∈ { HGT, ELE, GEO }
HMS I Time of measurement in UT hhmmss 0:235959
IFOV I Field-of-View counter 1:4 (IASI)
INSTRUMENT <C10 Instrument name eg 'IASI-A'
ISCN I Scan counter within file [6] 1 : NSCN
ISTP I Step counter across swath 1:30 (IASI)
ISWP I Sweep# of measurement 1 : NSWP
JULIAN_DAY I NOM_DATE as Day# since 1 Jan 2000 (=0), eg 8401 (1st Jan 2023)
LAT R Latitude of measurement deg N [−90, +90]
LND_PCT R Land Fraction (as opposed to sea) % [0,100]
LON R Longitude of measurement deg E [−180, +180]
LST R Local solar time (0 if not set) hr [0,24)
MIC_LAB <C8 Label identifying microwindow, eg 'HIROS_A '
MIC_MIN D Microwindow lower wavenumber limit cm-1 (0, MIC_MAX]
MIC_MAX D Microwindow upper wavenumber limit cm-1 [MIC_MIN, ∞]
MIC_NOI R Microwindow average noise, or 0.0 r.u. [4]
MIC_NPT I Number of spectral points for microwindow ≥ 1
MOS_X I x-index of mosaic containing measurement [7] ≥ 1
MOS_Y I y-index of mosaic containing measurement [7] ≥ 1
MSC I Time of measurement in UT ms [0,86400000)
NAVH I No. AVHRR channels included 0:5
NBND I No. spectral bands (nadir-viewing) > 0
NCLS I Max no. of AVHRR channel radiance clusters 7 expected
NMIC I No. Microwindows for sweep or No. filter measurements for image ≥ 0
NOM_DATE I Nominal observation date, eg 20230101 yyyymmdd ≥ 20000101
NPIX I No. pixels (profile locations) in file > 0
NPTS(NBND) I No. Spectral points in band (nadir-viewing) > 0
NSCN I No. limb scans (profile locations) in file [6] ≥ 1 expected
NSWP I No. spectral sweeps/measurement altitudes per scan > 0
ORBIT I Satellite orbit number (or equiv.) since launch > 0
RAD(MIC_NPT) R Spectral radiance or transmittance r.u.
RAD_CRV R Earth Radius of Curvature in line-of-sight plane km ~6400 expected
RAD_FLT R Filter radiance/transmittance measurement r.u. [8]
RESLN R Spectral sampling[10] cm-1 ≥ 0
SATELLITE <C10 Satellite name, eg 'MetOp-A   '
SZA R Solar Zenith Angle of measurement (<90 ≡ daytime) deg [0,180)
TIME_END I End of measurement UT hhmmss 000000:235959
TIME_START I Start of measurement UT hhmmss 000000:235959
Tra Float(Mic_Npt) Microwindow transmittance spectrum dimensionless [8] eg 0.999955
VIEW_ID I Viewing geometry[9] 1 : 5
WNO_MAX(NBND) D Upper Wavenumber of band(s) cm-1 > WNO_MIN
WNO_MIN(NBND) D Lower Wavenumber of band(s) cm-1 0 ≤ : < WNO_MAX
YMD Long Date of measurement yyyymmdd eg 20230101
ZEN R Satellite zenith angle deg [0,90]

Notes

  1. ALT_ADJ: actual sweep altitude determined within the L1 processing (as opposed to nominal tangent altitude in GRD)

  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