# OMI_L2_OMSO2

## Variables

The table below lists the variables that are present in the HARP product that results from an ingestion of OMI_L2_OMSO2 data.

field name

type

dimensions

unit

description

datetime

double

{time}

[seconds since 2000-01-01]

time of the measurement

longitude

double

{time}

[degree_east]

longitude of the ground pixel center (WGS84)

latitude

double

{time}

[degree_north]

latitude of the ground pixel center (WGS84)

longitude_bounds

double

{time, 4}

[degree_east]

longitudes of the ground pixel corners (WGS84)

latitude_bounds

double

{time, 4}

[degree_north]

latitudes of the ground pixel corners (WGS84)

solar_zenith_angle

double

{time}

[degree]

solar zenith angle at WGS84 ellipsoid for center co-ordinate of the ground pixel

solar_azimuth_angle

double

{time}

[degree]

solar azimuth angle at WGS84 ellipsoid for center co-ordinate of the ground pixel, defined East-of-North

viewing_zenith_angle

double

{time}

[degree]

viewing zenith angle at WGS84 ellipsoid for center co-ordinate of the ground pixel

viewing_azimuth_angle

double

{time}

[degree]

viewing azimuth angle at WGS84 ellipsoid for center co-ordinate of the ground pixel, defined East-of-North

SO2_column_number_density

double

{time}

[DU]

SO2 vertical column density

cloud_fraction

double

{time}

[]

effective cloud fraction

cloud_pressure

double

{time}

[hPa]

effective cloud pressure

cloud_top_pressure

double

{time}

[hPa]

cloud top pressure

index

int32

{time}

zero-based index of the sample within the source product

## Ingestion options

The table below lists the available ingestion options for OMI_L2_OMSO2 products.

option name

legal values

description

so2_column_variant

pbl, 5km, 15km, trl, trm, stl

for V2 products: anthropogenic SO2 pollution at the planet boundary layer (so2_column_variant=pbl, default), showing passive degassing at 5km altitude (so2_column_variant=5km), or showing explosive eruptions at 15km (so2_column_variant=15km); for V3 products: planet boundary layer - 0.9km (so2_column_variant=pbl, default), lower troposphere - 2.5km (so2_column_variant=trl), middle troposphere - 7.5km (so2_column_variant=trm), or upper tropospheric and stratospheric - 17km (so2_column_variant=stl)

## Mapping description

The shape and size of each ground pixel is not included in the product. HARP therefore provides its own approximation which is based on interpolation of the available center coordinates for each of the ground pixels. Each corner coordinate is determined by its four surrounding center coordinates. The corner coordinate is exactly at the intersection of the cross that can be made with these four points (each line of the cross is the great-circle distance from one center coordinate to the other). In situations where a corner coordinate is not surrounded by four center coordinates (i.e. at the boundaries) virtual center coordinates are created by means of extrapolation. The virtual center coordinate is placed such that the distance to its nearest real center coordinate equals the distance between that nearest real center coordinate and the next center coordinate going further inwards. In mathematical notation: when c(i,m+1) is the virtual center coordinate and c(i,m) and c(i,m-1) are real center coordinates, then ||c(i,m+1) - c(i,m)|| = ||c(i,m) - c(i,m-1)|| and all three coordinates should lie on the same great circle. The four virtual coordinates that lie in the utmost corners of the boundaries are calculated by extrapolating in a diagonal direction (e.g. c(n+1,m+1) is calculated from c(n,m) and c(n-1,m-1)).

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

field name

mapping description

datetime

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Geolocation_Fields/Time[]

description

the time of the measurement converted from TAI93 to seconds since 2000-01-01T00:00:00

longitude

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Geolocation_Fields/Longitude[]

latitude

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Geolocation_Fields/Latitude[]

longitude_bounds

description

interpolated from the available center coordinates for each of the ground pixels

latitude_bounds

description

interpolated from the available center coordinates for each of the ground pixels

solar_zenith_angle

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Geolocation_Fields/SolarZenithAngle[]

solar_azimuth_angle

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Geolocation_Fields/SolarAzimuthAngle[]

viewing_zenith_angle

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Geolocation_Fields/ViewingZenithAngle[]

viewing_azimuth_angle

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Geolocation_Fields/ViewingAzimuthAngle[]

SO2_column_number_density

condition

so2_column_variant=pbl or so2_column_variant unset and V2 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/SO2ColumnAmountPBL[]

condition

so2_column_variant=5km and V2 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/SO2ColumnAmount05KM[]

condition

so2_column_variant=15km and V2 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/SO2ColumnAmount15KM[]

condition

so2_column_variant=pbl or so2_column_variant unset and V3 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/ColumnAmountSO2_PBL[]

condition

so2_column_variant=trl and V3 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/ColumnAmountSO2_TRL[]

condition

so2_column_variant=trm and V3 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/ColumnAmountSO2_TRM[]

condition

so2_column_variant=stl and V3 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/ColumnAmountSO2_STL[]

cloud_fraction

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/CloudFraction[]

cloud_pressure

available

optional

condition

V3 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/CloudPressure[]

cloud_top_pressure

available

optional

condition

V2 product

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_SO2/Data_Fields/CloudTopPressure[]