The LNO dataset has been reprocessed to add a radiance factor to all files and to improve the spectral calibration.
At the moment this dataset is in testing phase, and therefore is hosted on the NOMAD Science FTP in the directory /Data/hdf5_level_1p0a_LNO_Radiance_Factor (for those at BIRA, the files can also be found in the TRACE-GAS-ORBITER/NOMAD/test/iant/hdf5/hdf5_level_1p0a/ directory).
The LNO dayside nadir files now have two observation types, "DP" and "DF", which stand for "dayside nadir pass" and "dayside nadir fail". For example:
"Pass" indicates that both the diffraction order contains solar lines (to fit the solar reference spectra) and the nadir data contains solar and/or atmospheric absorption lines of sufficient depth that the pipeline was able to detect them and correctly shift both the solar and nadir spectral calibrations to match the lines. These files contain the best calibration.
"Fail" indicates that either:
- the diffraction order does not contain sufficiently deep solar lines to detect and correct the solar reference calibration
- the nadir data in the file does not contain any solar and/or atmospheric absorption lines of sufficient depth to detect and correct the solar reference calibration
- the nadir data in the file is too noisy to fit any solar or molecular lines.
In these cases, the spectral calibration has been estimated from the temperature of the LNO channel rather than a fit to absorption lines.
A fail does not necessarily mean that the data is not correct, however more care should be taken when interpreting the data - the spectral calibration is likely to be less accurate and there may be residuals in the data where solar lines have not be correctly divided out during the radiance factor calculation.
The thumbnails gallery (see ftp directory: /Data/hdf5_level_1p0a_LNO_Radiance_Factor/thumbnails/lno_1p0a_radiance_factor) contains a png for every observation, giving more information about the reason for the fail and details about the quality of the fit and the spectra in the file.
Below is a description of the new or important datasets in the file:
|Geometry/MeanIncidenceAngle||Mean incidence angle (1 value per spectra). It is the mean of the Point0 - Point5 IncidenceAngle values for that spectrum.|
|Science/YRadianceFactor||Spectra calibrated in radiance factor, where radiance factor = normalised nadir counts / normalised solar counts / solar-to-nadir scaling factor / cosine(MeanIncidenceAngle)|
|Criteria/LineFit/NumberOfLinesFit||Number of molecular/solar lines in the nadir data that were successfully fit|
|Criteria/LineFit/ChiSqError||A number indicating the quality of the solar/molecular line fit (higher means the fit was better)||Rename dataset - confusing|
|Criteria/LineFit/Error||0=fit failed, 1=fit passed|
|Science/YRadiance||The "Y" dataset from previous files. This is the radiance calculated from laboratory blackbody measurements, which uses the AOTF and blaze functions to calculate the full radiance hitting each pixel to derive the counts-to-radiance conversion. This should be used with caution, because 1) it relies on having correct AOTF and blaze functions; and 2) because the blackbody data used for the calibration is not reliable at high diffraction orders (as the planck function decreases and so the signal becomes very small).|
|Science/YRadianceSimple||The "YAtWavenumber" dataset from previous files. This is the radiance calibrated from laboratory blackbody measurements without using the AOTF or blaze functions. The counts to radiance conversion is derived from a simple planck function at the temperature of the blackbody and wavenumber of the pixel. This calibration can also be unreliable for high diffraction orders.|
|Science/YRadianceError||Error in the YRadiance dataset, taken from a fit to the continuum in the first 50 pixels|
|Science/SNRRadiance||Radiance SNR, i.e. YRadiance/YRadianceError|
|Science/YUnmodified||Raw counts unmodified from the level 0.3A HDF5 file|
|Science/YNormalisedCounts||Raw nadir counts, normalised to counts per pixel per second|
|Channel/MeasurementTemperature||Mean LNO baseplate temperature during the observation, taken from the TGO temperature readouts|
|Temperature/TemperatureDateTime||Datetimes for the temperature measurements in this dataset group. Temperatures start 10 minutes before the observation begins and end ten minutes after|
|Temperature/NominalSO||Temperature of the SO channel as recorded by TGO|
|Temperature/NominalLNO||Temperature of the LNO channel as recorded by TGO|
|Temperature/NominalUVIS||Temperature of the UVIS channel as recorded by TGO|
|Temperature/RedundantSO||Temperature of the SO channel (redundant sensor) as recorded by TGO|
|Temperature/RedundantLNO||Temperature of the LNO channel (redundant sensor) as recorded by TGO|
UVIS (and SO) grazing occultations have recently been added to the ftp in the hdf5_level_1p0a directory. Each grazing occultation is split into two separate files, one for the ingress (from the top of atmosphere up to the minimum tangent altitude) and one for the egress (up to the top of atmosphere). Hence two filenames, GI and GE respectively are required, for example: