IASI read_l2_v6 IDL Program
IASI read_l2_v6 IDL Program |
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The procedure is run from the IDL command line and typically run twice, the first to extract a structure containing location and flags for all pixels in the file, and the second to extract profile data for selected locations.
A L2 file covers one orbit of data, typically 770 scan lines with 120 pixels
(or FOVs) per scan line, so about 90 000 pixels in total.
The first call (without L2DAT argument)
extracts the location and flag data for all pixels in the file.
The second line selects the subset of locations for which there is a good OEM
retrieval (see p76, Table 37 of
EUM/OPS-EPS/MAN/04/0033).
Further selection, eg within
particular lat/lon limits, can of course also be applied inside the WHERE ( )
The next call (with L2DAT argument)
extracts the L2 data at the selected locations.
However, if being run as part of a larger suite of processing, it may be
more convenient to have the procedure return control in such situations without
stopping. For this, use the FAIL and/or ERRMSG keywords.
For example:
Notes
Notes
Syntax
IDL> READ_L2_V6, L2FIL, LOC, L2DAT, /FORLI,
GRD=GRD, FAIL=FAIL, ERRMSG=ERRMSG
Argument Type I/O Description
L2FIL
STRING I
Name of IASI L2 file to be read
LOC
STRUCT(*) I/O
Location data and flags for each pixel
(I if L2DAT argument is present, O if absent)
[Format]
L2DAT
STRUCT(*) O
Level 2 data for selected pixels
[Format]
FORLI
FLAG I
(Optional) 1=include FORLI products, 0=exclude
[see L2DAT format]
GRD
STRUCT O
(Optional) Profile,spectral grids for L2 products
[Format]
FAIL
FLAG O
(Optional) 0=normal, 1=fatal error occurred
[see Error Handling]
ERRMSG
STRING O
(Optional) Text describing fatal error, ' ' (empty string)=normal
[see Error Handling]
Usage
For example:
IDL> READ_L2_V6, L2FIL, LOC
IDL> IDX = WHERE ( LOC.FLG_ITCONV EQ 5 )
IDL> READ_L2_V6, L2FIL, LOC[IDX], L2DAT
Error Handling
If the code detects an unexpected record size or
file structure it stops, with a message printed to the terminal.
IDL> READ_L2_V6, L2FIL, LOC, FAIL=FAIL, ERRMSG=ERRMSG
IDL> IF FAIL THEN PRINT, ERRMSG
LOC Structure
When the procedure is called with just
two formal arguments (ie without L2DAT)
the structure array
LOC is created, with dimension equal to the number of pixels in the
files (typically around 90 000 elements). This contains the location, time
and flags for each pixel.
Variable Type Description Notes
LOC.LIN INT Scan line# (1:770, approx)
(1)
LOC.FOV INT Field of View# (1:120)
(1)
LOC.DAY UINT Day# since 1 Jan 2000
(=Day#0) - value for scan line
(2)
LOC.MSC ULONG Milliseconds into
day (0:86400000) - value for scan line
(2)
LOC.LAT FLOAT Latitude (-90:90)
LOC.LON FLOAT Longitude (-180:180)
LOC.ZEN FLOAT Zenith angle at
surface (0:59, approx)
LOC.SZA FLOAT Solar Zenith Angle
(0:180, ≤90=daytime)
LOC.CLD FLOAT Percentage cloud
cover (0:100)
(3)
LOC.FLG_xxx BYTE or UINT
L2 Flags (see
EUM/OPS-EPS/MAN/04/0033
for list and definitions)
If called with the FORLI argument set,
the following are also included
CO_QFLAG BYTE CO Retrieval Quality
(4)
HNO3_QFLAG BYTE HNO3 Retrieval Quality
(4)
O3_QFLAG BYTE O3 Retrieval Quality
(4)
SO2_QFLAG BYTE SO2 Retrieval Quality
(5)
GRD Structure
When the procedure is called with the GRD argument present, the
GRD structure is created, containing levels (mostly pressures) on which
the L2 products are defined, also the spectral points at which the surface
emissivity is defined. The information is taken from the single GIADR
(=Global Internal Auxiliary Data Record)
in each L2 file (see Table 8.4, p59 of
EUM/OPS-EPS/MAN/04/0033),
converted to physical units. The GRD structure is only expected to
change with new data versions.
L2DAT Structure
If a third argument L2DAT is present in the call, this is interpreted
as the instruction to return the L2DAT structure containing the
L2 profile information at the locations LOC.LIN,LOC.FOV specified
in the second argument (i.e. along-track and across-track coordinates).
The data in the .nat file are from the Measurement Data Records (MDR),
described in Section 8.5, p61–68 of
EUM/OPS-EPS/MAN/04/0033.
The extracted data structure is as follows:
Notes