OMI_L2_OMHCHO — HARP 1.20 documentation

# 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)
sensor_altitude | double | {time} | [m] | altitude of Aura spacecraft
surface_altitude | double | {time} | [m] | terrain height
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
sensor_altitude | path | /HDFEOS/SWATHS/OMI_Total_Column_Amount_HCHO/Geolocation_Fields/SpacecraftAltitude[]
surface_altitude | path | /HDFEOS/SWATHS/OMI_Total_Column_Amount_HCHO/Geolocation_Fields/TerrainHeight[]
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[]