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.