# OMI_L2_OMHCHO

## Variables

The table below lists the variables that are present in the HARP product that results from an ingestion of OMI_L2_OMHCHO 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)

HCHO_column_number_density

double

{time}

[molec/cm^2]

HCHO vertical column density

HCHO_column_number_density_uncertainty

double

{time}

[molec/cm^2]

uncertainty of the HCHO vertical column density

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_OMHCHO products.

option name

legal values

description

destriped

true

ingest column densities without destriping correction (default) or with destriping correction (destriped=true)

## 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_HCHO/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_HCHO/Geolocation_Fields/Longitude[]

latitude

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_HCHO/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

HCHO_column_number_density

condition

destriped unset

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_HCHO/Data_Fields/ColumnAmount[]

condition

destriped=true

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_HCHO/Data_Fields/ColumnAmountDestriped[]

HCHO_column_number_density_uncertainty

available

optional

condition

destriped unset

path

/HDFEOS/SWATHS/OMI_Total_Column_Amount_HCHO/Data_Fields/ColumnUncertainty[]