Create Harp compliant qdoas output.

Layout of qdoas file

A qdoas file consist typically out of a main group with variables such as geolocations, time, … . The subgroup contains the results of a doas retrieval. Note that the name of main and subgroup can be freely chosen in qdoas.

Below in picture Fig. 1 a typical qdoas layout is shown.

hdfview of typical qdoas layout — Fig. 1 qdoas view

Qdoas to Harp mapping

A first application is to use the HARP functionalities on a qdoas output file. Therefore we perform some simplifications:

We split the subgroup into separate files and copy the output in another directory with a filename that gets the suffix of the original qdoas file.
geolocations are kept in every output file. A harp variable is created according to the conventions specified in http://stcorp.github.io/harp/doc/html/conventions/variable_names.html.
One Slant column of interest is chosen. (see qd2hp for how this is done in practice). Currently only one slant column is kept, because the retrieval focuses in most cases on one single absorber. Also, since the calculation of the AMF depends on the absorber, we choose to process AMF and VCD only for one slant column present in each output file. Note that easily multiple output files can be generated which differ in the absorber that is chosen.

Mapping of qdoas names

We list the cases where a general mapping can be done from qdoas to harp variables.

Table 1 Mapping of variable names between qdoas and harp names.
original name	harp name	unit attribute	qdoas group
SlCol(<absorber>)	<absorber>_column_number_density	molecules cm-2	qdoas subgroup
SlErr(<absorber>)	<absorber>_column_number_density_uncertainty	molecules cm-2	qdoas subgroup
Latitude	latitude	degree_north	qdoas main group
Longitude	Longitude	degree_east	qdoas main group
Pixel corner latitudes	latitude_bounds	degree_north	qdoas main group
Pixel corner longitudes	longitude_bounds	degree_east	qdoas main group
LoS Azimuth	sensor_azimuth_angle	units=degree	qdoas main group
LoS ZA	sensor_zenith_angle	degree	qdoas main group
SZA	solar_zenith_angle	degree	qdoas main group
Solar Azimuth Angle	solar_azimuth_angle	degree	qdoas main group
Date & time (YYYYMMDDhhmmss)	datetime_start	seconds since 2010-01-01	qdoas main group

SlCol(<absorber>), SlErr(<absorber>) is the main retrieved slant column of interest. Other slant columns from (pseudo-) absorbers are use in the fitting procedure, but are excluded in the conversion to a qdoas harp format.

How the mapping is might depend on the type of instrument. Qdoas2harp takes this into account and works for qdoas output from GOME-2, OMI and tropomi sensors.

Mapping for OMI.

For OMI an aux. file is needed to include latitude, longitude bounds variables.

In Fig. 2 an example is given of an qdoas outputfile after conversion. Note the limited set variables: only geolocations and a slant column of one species with error.

_images/fig2.png — Fig. 2 hdfview of a converted qdoas ouput file from OMI.

Based on the main attributes: sensor, L1_file, L1_spectral_band the corresponding L2 OMPIXCOR can be found, from which latitude_bounds and longitude_bounds can be constructed. Note that the filepath to the corresponding OMPIXCOR file needs to be provided. (see Command line tools)

Mapping for GOME2A,B and C:

For the latitude, longitude bounds: the corners ABCD are reordered as BDCA.