Sentinel-5P OFFL O3: Offline Ozone

OFFL/L3_O3

This dataset provides offline high-resolution imagery of total column ozone concentrations. See also COPERNICUS/S5P/OFFL/L3_O3_TCL for the tropospheric column data.

In the stratosphere, the ozone layer shields the biosphere from dangerous solar ultraviolet radiation. In the troposphere, it acts as an efficient cleansing agent, but at high concentration it also becomes harmful to the health of humans, animals, and vegetation. Ozone is also an important greenhouse-gas contributor to ongoing climate change. Since the discovery of the Antarctic ozone hole in the 1980s and the subsequent Montreal Protocol regulating the production of chlorine-containing ozone-depleting substances, ozone has been routinely monitored from the ground and from space.

For this product, there are two algorithms that deliver total ozone: GDP for the near real-time and GODFIT for the offline products. GDP is currently being used for generating the operational total ozone products from GOME, SCIAMACHY and GOME-2; while GODFIT is being used in the ESA CCI and the Copernicus C3S projects. More information. Product user manual

OFFL L3 Product

To make our OFFL L3 products, we find areas within the product's bounding box with data using a command like this:

harpconvert --format hdf5 --hdf5-compression 9
-a 'O3_column_number_density_validity>50;derive(datetime_stop {time})'
S5P_OFFL_L2__O3_____20181005T225147_20181006T003317_05073_01_010102_20181012T001415.nc
grid_info.h5

We then merge all the data into one large mosaic (area-averaging values for pixels that may have different values for different times). From the mosaic, we create a set of tiles containing orthorectified raster data.

The qa value is adjusted before running harpconvert to satisfy all of the following criteria:

• ozone_total_vertical_column in [0, 0.45]
• ozone_effective_temperature in [180, 260]
• ring_scale_factor in [0, 0.15]
• effective_albedo in [-0.5, 1.5]

Example harpconvert invocation for one tile: harpconvert --format hdf5 --hdf5-compression 9 -a 'O3_column_number_density_validity>50;derive(datetime_stop {time}); bin_spatial(2001, 50.000000, 0.01, 2001, -120.000000, 0.01); keep(O3_column_number_density,O3_effective_temperature,cloud_fraction, sensor_altitude,sensor_azimuth_angle, sensor_zenith_angle, solar_azimuth_angle,solar_zenith_angle)' S5P_OFFL_L2__O3_____20181005T225147_20181006T003317_05073_01_010102_20181012T001415.nc output.h5

Sentinel-5 Precursor

Sentinel-5 Precursor is a satellite launched on 13 October 2017 by the European Space Agency to monitor air pollution. The onboard sensor is frequently referred to as Tropomi (TROPOspheric Monitoring Instrument).

All of the S5P datasets, except CH₄, have two versions: Near Real-Time (NRTI) and Offline (OFFL). CH₄ is available as OFFL only. The NRTI assets cover a smaller area than the OFFL assets, but appear more quickly after acquisition. The OFFL assets contain data from a single orbit (which, due to half the earth being dark, contains data only for a single hemisphere).

Because of noise on the data, negative vertical column values are often observed in particular over clean regions or for low SO2 emissions. It is recommended not to filter these values except for outliers, i.e. for vertical columns lower than -0.001 mol/m^2.

The original Sentinel 5P Level 2 (L2) data is binned by time, not by latitude/longitude. To make it possible to ingest the data into Earth Engine, each Sentinel 5P L2 product is converted to L3, keeping a single grid per orbit (that is, no aggregation across products is performed).

Source products spanning the antimeridian are ingested as two Earth Engine assets, with suffixes _1 and _2.

The conversion to L3 is done by the harpconvert tool using the bin_spatial operation. The source data is filtered to remove pixels with QA values less than:

• 80% for AER_AI
• 75% for the tropospheric_NO2_column_number_density band of NO2
• 50% for all other datasets except for O3 and SO2

The O3_TCL product is ingested directly (without running harpconvert).