NOAA GOES-R Series Advanced Baseline Imager (ABI) Level 1b Radiances
The data are available from NOAA-NCEI
The convert_goes_ABI_L1b program converts ABI Level 1b Radiances in
netCDF format to a DART observation sequence file with
GOES_16_ABI_RADIANCE
observations (there is a namelist option to
select other GOES satellites, which will have the appropriate
observation type).
The Advanced Baseline Imager (ABI) instrument samples the radiance of the Earth in sixteen spectral bands using several arrays of detectors in the instrument’s focal plane. Single reflective band ABI Level 1b Radiance Products (channels 1 - 6 with approximate center wavelengths 0.47, 0.64, 0.865, 1.378, 1.61, 2.25 microns, respectively) are digital maps of outgoing radiance values at the top of the atmosphere for visible and near-infrared (IR) bands. Single emissive band ABI L1b Radiance Products (channels 7 - 16 with approximate center wavelengths 3.9, 6.185, 6.95, 7.34, 8.5, 9.61, 10.35, 11.2, 12.3, 13.3 microns, respectively) are digital maps of outgoing radiance values at the top of the atmosphere for IR bands. Detector samples are compressed, packetized and down-linked to the ground station as Level 0 data for conversion to calibrated, geo-located pixels (Level 1b Radiance data). The detector samples are decompressed, radiometrically corrected, navigated and resampled onto an invariant output grid, referred to as the ABI fixed grid.
Cite as: GOES-R Calibration Working Group and GOES-R Series Program, (2017): NOAA GOES-R Series Advanced Baseline Imager (ABI) Level 1b Radiances. [indicate subset used]. NOAA National Centers for Environmental Information. doi:10.7289/V5BV7DSR. [access date].
Specifying a vertical location
Top of the atmosphere radiance observations are sensitive to the
atmospheric constituents (e.g. water vapor) that reside in the vertical
profile of the atmosphere. Given this is an integrated quantity and does
not depend on a single vertical location, it may be appropriate to leave
the vertical location undefined (i.e. VERTISUNDEF) within the obs_seq.out
file, by setting the vloc_pres_hPa = -1
(See namelist options below). This approach,
however, limits the application of vertical localization during the assimilation step.
Alternatively, for some applications it may be appropriate to assign
a vertical location to the radiance observation, by setting the vloc_pres_hPa
to a vertical pressure level (hPa). This is an ongoing area
of observation-space localization research, and is the standard
workaround pioneered by Lili Lei and Jeff Whittaker.
Radiance versus Brightness Temperature
This converter assigns the observation type as GOES[16-19]_ABI_RADIANCE
.
The default setup in DART is that this radiance observation type is assigned
the quantity QTY_RADIANCE
. Radiance observations are commonly expressed
in spectrally resolved units (mW/cm/m^2/sr).
Alternatively, radiances can also be expressed as brightness temperatures
(units: Kelvin) and the DART code also supports observation quantities of
QTY_BRIGHTNESS_TEMPERATURE
. Both the spectral and temperature units
quantify the same physical properties of the atmosphere
(emitted and reflected radiation), however, in some applications it may
be advantageous to use brightness temperatures given their Gaussian
distribution. This is an ongoing area of research.
An overview of the namelist options
A description of the most important namelist options. Note that supplying an observation error value is mandatory. This is not the full list of namelist variables.
Variable |
Default |
Description |
---|---|---|
x_thin |
0 |
Skip this many observations per X scan |
y_thin |
0 |
Skip this many observations per Y scan |
goes_num |
16 |
GOES Satellite number |
reject_dqf_1 |
.true. |
Bad scan rejection critera. If .true. and DQF /= 0, the scan is rejected. If .false. any DQF > 1 rejects the scan. |
verbose |
.false. |
Run-time output verbosity |
obs_err |
MISSING_R8 |
The observation error standard deviation in units of radiance. IMPORTANT: the user must supply a value other than MISSING_R8. Be aware that the observation sequence files convert this to a variance. |
vloc_pres_hPa |
-1.0 |
If a positive value, the vertical location of the observation (hPa) is assigned with a vertical coordinate of VERTISPRESSURE. If negative value there is no vertical location and the coordinate is VERTISUNDEFINED. |
Radiance metadata supplied to obs_seq.out file
This converter is designed to supply metadata to the radiative transfer model (RTTOV) MODULE obs_def_rttov_mod that supports the calculation of the expected radiance observation during the assimilation step. Below is a description of this metadata information.
The integer values that describe the platform/satellite/sensor/channel combination for the GOES satellite are required by the RTTOV radiance model to assign the appropriate coefficent file during the radiance calculation. For more details refer to the RTTOV user guide.
Variable |
Value |
Description |
---|---|---|
sat az/el |
Supplied by data file |
GOES satellite azimuth and elevation angle |
sun az/el |
-888888 |
Sun azimuth and elevation angle. The default is for missing values. For IR channels reflected solar has no impact. For NIR/ VIS/UV providing sun az/el may be desirable but not required by RTTOV. |
platform |
4 |
Platform number supplied by converter code. |
sat_id |
16 |
Satellite ID number supplied by converter code. |
instrument |
44 |
Sensor number supplied by converter code |
channel |
Supplied by data file |
The wavelength channel (1-16) assigned from band_id variable in data file. |