# S5P_L2_CH4

## Variables

The table below lists the variables that are present in the HARP product that results from an ingestion of `S5P_L2_CH4` data.

field name | type | dimensions | unit | description
--- | --- | --- | --- | ---
scan_subindex | int16 | {time} |  | pixel index (0-based) within the scanline
datetime_start | double | {time} | [seconds since 2010-01-01] | start time of the measurement
datetime_length | double |  | [s] | duration of the measurement
orbit_index | int32 |  |  | absolute orbit number
validity | int32 | {time} |  | processing quality flag
latitude | float | {time} | [degree_north] | latitude of the ground pixel center (WGS84)
longitude | float | {time} | [degree_east] | longitude of the ground pixel center (WGS84)
latitude_bounds | float | {time, 4} | [degree_north] | latitudes of the ground pixel corners (WGS84)
longitude_bounds | float | {time, 4} | [degree_east] | longitudes of the ground pixel corners (WGS84)
sensor_latitude | float | {time} | [degree_north] | latitude of the geodetic sub-satellite point (WGS84)
sensor_longitude | float | {time} | [degree_east] | longitude of the goedetic sub-satellite point (WGS84)
sensor_altitude | float | {time} | [m] | altitude of the satellite with respect to the geodetic sub-satellite point (WGS84)
solar_zenith_angle | float | {time} | [degree] | zenith angle of the Sun at the ground pixel location (WGS84); angle measured away from the vertical
solar_azimuth_angle | float | {time} | [degree] | azimuth angle of the Sun at the ground pixel location (WGS84); angle measured East-of-North
sensor_zenith_angle | float | {time} | [degree] | zenith angle of the satellite at the ground pixel location (WGS84); angle measured away from the vertical
sensor_azimuth_angle | float | {time} | [degree] | azimuth angle of the satellite at the ground pixel location (WGS84); angle measured East-of-North
altitude_bounds | float | {time, vertical, 2} | [m] | altitude bounds per profile layer
pressure_bounds | float | {time, vertical, 2} | [Pa] | pressure bounds per profile layer
surface_altitude | float | {time} | [m] | surface altitude
surface_altitude_uncertainty | float | {time} | [m] | surface altitude precision
surface_pressure | float | {time} | [Pa] | surface pressure
surface_meridional_wind_velocity | float | {time} | [m/s] | northward wind
surface_zonal_wind_velocity | float | {time} | [m/s] | eastward wind
land_fraction | float | {time} | [] | land fraction
CH4_column_volume_mixing_ratio_dry_air | float | {time} | [ppbv] | column averaged dry air mixing ratio of methane
CH4_column_volume_mixing_ratio_dry_air_uncertainty | float | {time} | [ppbv] | uncertainty of the column averaged dry air mixing ratio of methane (1 sigma error)
CH4_column_volume_mixing_ratio_dry_air_validity | int8 | {time} |  | continuous quality descriptor, varying between 0 (no data) and 100 (full quality data)
CH4_column_number_density_avk | float | {time, vertical} | [] | column averaging kernel for methane retrieval
CH4_column_number_density_apriori | float | {time, vertical} | [mol/m2] | a-priori column number density profile of methane
dry_air_column_number_density | float | {time, vertical} | [mol/m2] | column number density profile of dry air
H2O_column_number_density | float | {time} | [mol/m^2] | H2O total column density
H2O_column_number_density_uncertainty | float | {time} | [mol/m^2] | uncertainty of the H2O column density (standard error)
cloud_fraction | float | {time} | [] | cloud fraction from VIIRS data for the instantaneous field of view
aerosol_height | float | {time} | [m] | aerosol height parameter in the CH4 retrieval
aerosol_optical_depth | float | {time} | [] | aerosol optical thicknesss
surface_albedo | float | {time} | [] | surface albedo
surface_albedo_uncertainty | float | {time} | [] | precision of the surface albedo
snow_ice_type | int8 | {time} |  | surface snow/ice type; enumeration values: snow_free_land (0), sea_ice (1), permanent_ice (2), snow (3), ocean (4)
sea_ice_fraction | float | {time} | [] | sea-ice concentration (as a fraction)
index | int32 | {time} |  | zero-based index of the sample within the source product

## Ingestion options

The table below lists the available ingestion options for `S5P_L2_CH4` products.

option name | legal values | description
--- | --- | ---
ch4 | bias_corrected, corrected | whether to ingest the ‘normal’ CH4 column vmr (default) or the bias corrected CH4 column vmr (ch4=bias_corrected), or the bias corrected and destriping corrected CH4 column vmr (ch4=corrected)
band | NIR | whether to retrieve aerosol/cloud/surface properties of the TROPOMI SWIR band (default) or the NIR band (band=NIR)

## Mapping description

The table below details where and how each variable was retrieved from the input product.

field name | mapping description
--- | ---
scan_subindex | description | the scanline and pixel dimensions are collapsed into a temporal dimension; the index of the pixel within the scanline is computed as the index on the temporal dimension modulo the number of scanlines
datetime_start | path | /PRODUCT/time, /PRODUCT/delta_time[]
description | time converted from milliseconds since a reference time (given as seconds since 2010-01-01) to seconds since 2010-01-01 (using 86400 seconds per day); the time associated with a scanline is repeated for each pixel in the scanline
datetime_length | path | /@time_coverage_resolution
description | the measurement length is parsed assuming the ISO 8601 ‘PT%(interval_seconds)fS’ format
orbit_index | path | /@orbit
validity | path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/processing_quality_flags[]
description | the uint32 data is cast to int32
latitude | path | /PRODUCT/latitude[]
longitude | path | /PRODUCT/longitude[]
latitude_bounds | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/latitude_bounds[]
longitude_bounds | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/longitude_bounds[]
sensor_latitude | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/satellite_latitude[]
description | the satellite latitude associated with a scanline is repeated for each pixel in the scanline
sensor_longitude | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/satellite_longitude[]
description | the satellite longitude associated with a scanline is repeated for each pixel in the scanline
sensor_altitude | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/satellite_altitude[]
description | the satellite altitude associated with a scanline is repeated for each pixel in the scanline
solar_zenith_angle | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/solar_zenith_angle[]
solar_azimuth_angle | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/solar_azimuth_angle[]
sensor_zenith_angle | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/viewing_zenith_angle[]
sensor_azimuth_angle | path | /PRODUCT/SUPPORT_DATA/GEOLOCATIONS/viewing_azimuth_angle[]
altitude_bounds | condition | processor version >= 01.00.00
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/altitude_levels[]
description | derived from height per level (layer boundary) by repeating the inner levels; the upper bound of layer k is equal to the lower bound of layer k+1; the vertical grid is inverted to make it ascending
condition | processor version < 01.00.00
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/height_levels[]
description | derived from height per level (layer boundary) by repeating the inner levels; the upper bound of layer k is equal to the lower bound of layer k+1; the vertical grid is inverted to make it ascending
pressure_bounds | path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/surface_pressure[],/PRODUCT/SUPPORT_DATA/INPUT_DATA/pressure_interval[]

description

derived from surface pressure and pressure difference between retrieval levels (the pressure grid is equidistant between the surface pressure and a fixed top pressure); given a zero-based layer index k, the pressure bounds for layer k are derived as: (surface_pressure - k * pressure_interval, surface_pressure - (k + 1) * pressure_interval); the vertical grid is inverted to make it ascending

surface_altitude | path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/surface_altitude[]
surface_altitude_uncertainty | path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/surface_altitude_precision[]
surface_pressure | path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/surface_pressure[]
surface_meridional_wind_velocity | available | optional
condition | processor version >= 01.03.00
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/northward_wind[]
surface_zonal_wind_velocity | available | optional
condition | processor version >= 01.03.00
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/eastward_wind[]
land_fraction | available | optional
condition | processor version >= 02.09.00
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/land_fraction[]
CH4_column_volume_mixing_ratio_dry_air | condition | ch4 unset
path | /PRODUCT/methane_mixing_ratio[]
condition | ch4=bias_corrected
path | /PRODUCT/methane_mixing_ratio_bias_corrected[]
condition | ch4=corrected and processor version >= 02.07.00
path | /PRODUCT/methane_mixing_ratio_bias_corrected_destriped[]
CH4_column_volume_mixing_ratio_dry_air_uncertainty | path | /PRODUCT/methane_mixing_ratio_precision[]
CH4_column_volume_mixing_ratio_dry_air_validity | path | /PRODUCT/qa_value
CH4_column_number_density_avk | path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/column_averaging_kernel[]
description | the vertical grid is inverted to make it ascending
CH4_column_number_density_apriori | path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/methane_profile_apriori[]
description | the vertical grid is inverted to make it ascending
dry_air_column_number_density | path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/dry_air_subcolumns[]
description | the vertical grid is inverted to make it ascending
H2O_column_number_density | path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/water_total_column[]
H2O_column_number_density_uncertainty | path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/water_total_column_precision[]
cloud_fraction | condition | band=NIR
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/cloud_fraction_VIIRS_NIR_IFOV[]
condition | band unset
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/cloud_fraction_VIIRS_SWIR_IFOV[]
aerosol_height | condition | processor version >= 01.00.00
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/aerosol_mid_altitude[]
condition | processor version < 01.00.00
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/aerosol_mid_height[]
aerosol_optical_depth | condition | band=NIR
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/aerosol_optical_thickness_NIR[]
condition | band unset
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/aerosol_optical_thickness_SWIR[]
surface_albedo | condition | band=NIR
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/surface_albedo_NIR[]
condition | band unset
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/surface_albedo_SWIR[]
surface_albedo_uncertainty | condition | band=NIR
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/surface_albedo_NIR_precision[]
condition | band unset
path | /PRODUCT/SUPPORT_DATA/DETAILED_RESULTS/surface_albedo_SWIR_precision[]
snow_ice_type | available | optional
condition | processor version >= 02.07.00
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/snow_ice_flag[]
description | 0: snow_free_land (0), 1-100: sea_ice (1), 101: permanent_ice (2), 103: snow (3), 255: ocean (4), other values map to -1
sea_ice_fraction | available | optional
condition | processor version >= 02.07.00
path | /PRODUCT/SUPPORT_DATA/INPUT_DATA/snow_ice_flag[]
description | if 1 <= snow_ice_flag <= 100 then snow_ice_flag/100.0 else 0.0