- Dataset Availability
- 2018-07-04T13:34:21Z–2024-12-17T18:34:38Z
- Dataset Provider
- European Union/ESA/Copernicus
- Earth Engine Snippet
-
ee.ImageCollection("COPERNICUS/S5P/OFFL/L3_AER_AI")
- Revisit Interval
- 2 Days
- Tags
Description
OFFL/L3_AER_AI
This dataset provides offline high-resolution imagery of the UV Aerosol Index (UVAI), also called the Absorbing Aerosol Index (AAI).
The AAI is based on wavelength-dependent changes in Rayleigh scattering in the UV spectral range for a pair of wavelengths. The difference between observed and modelled reflectance results in the AAI. When the AAI is positive, it indicates the presence of UV-absorbing aerosols like dust and smoke. It is useful for tracking the evolution of episodic aerosol plumes from dust outbreaks, volcanic ash, and biomass burning.
The wavelengths used have very low ozone absorption, so unlike aerosol optical thickness measurements, AAI can be calculated in the presence of clouds. Daily global coverage is therefore possible.
For this L3 AER_AI product, the absorbing_aerosol_index is calculated with a pair of measurements at the 354 nm and 388 nm wavelengths. The COPERNICUS/S5P/OFFL/L3_SO2 product has the absorbing_aerosol_index calculated using the 340 nm and 380 nm wavelengths.
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 'absorbing_aerosol_index_validity>50;derive(datetime_stop {time})'
S5P_OFFL_L2__AER_AI_20181030T213916_20181030T232046_05427_01_010200_20181105T210529.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.
Example harpconvert invocation for one tile:
harpconvert --format hdf5 --hdf5-compression 9
-a 'absorbing_aerosol_index_validity>50;derive(datetime_stop {time});
bin_spatial(2001, 50.000000, 0.01, 2001, -120.000000, 0.01);
keep(absorbing_aerosol_index,sensor_altitude,sensor_azimuth_angle,
sensor_zenith_angle,solar_azimuth_angle,solar_zenith_angle)'
S5P_OFFL_L2__AER_AI_20181030T213916_20181030T232046_05427_01_010200_20181105T210529.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).
Bands
Resolution
1113.2 meters
Bands
| Name | Units | Min | Max | Description |
|---|---|---|---|---|
absorbing_aerosol_index |
-21* | 39* | A measure of the prevalence of aerosols in the atmosphere. The UVAI index is based on spectral contrast in the ultraviolet (UV) spectral range for a given wavelength pair, where the difference between observed and modeled reflectance results in a residual value. When this residual is positive it indicates the presence of UV-absorbing aerosols, like dust and smoke, and is often referred to as the Absorbing Aerosol Index (AAI). Clouds yield near-zero residual values and strongly negative residual values can be indicative of the presence of non-absorbing aerosols including sulfate aerosols. Unlike satellite-based aerosol optical thickness measurements, AAI can also be calculated in the presence of clouds so that daily, global coverage is possible. This is ideal for tracking the evolution of episodic aerosol plumes consisting of desert dust, ash from volcanic eruptions, and smoke from biomass burning. See further details in the ATBD. |
|
sensor_altitude |
m | 828543* | 856078* | Altitude of the satellite with respect to the geodetic sub-satellite point (WGS84). |
sensor_azimuth_angle |
deg | -180* | 180* | Azimuth angle of the satellite at the ground pixel location (WGS84); angle measured East-of-North. |
sensor_zenith_angle |
deg | 0.098* | 66.87* | Zenith angle of the satellite at the ground pixel location (WGS84); angle measured away from the vertical. |
solar_azimuth_angle |
deg | -180* | 180* | Azimuth angle of the Sun at the ground pixel location (WGS84); angle measured East-of-North. |
solar_zenith_angle |
deg | 8* | 88* | Zenith angle of the satellite at the ground pixel location (WGS84); angle measured away from the vertical. |
Image Properties
Image Properties
| Name | Type | Description |
|---|---|---|
| ALGORITHM_VERSION | STRING | The algorithm version used in L2 processing. It is separate from the processor (framework) version, to accommodate different release schedules for different products. |
| BUILD_DATE | STRING | The date, expressed as milliseconds since 1 Jan 1970, when the software used to perform L2 processing was built. |
| HARP_VERSION | INT | The version of the HARP tool used to grid the L2 data into an L3 product. |
| INSTITUTION | STRING | The institution where data processing from L1 to L2 was performed. |
| L3_PROCESSING_TIME | INT | The date, expressed as milliseconds since 1 Jan 1970, when Google processed the L2 data into L3 using harpconvert. |
| LAT_MAX | DOUBLE | The maximum latitude of the asset (degrees). |
| LAT_MIN | DOUBLE | The minimum latitude of the asset (degrees). |
| LON_MAX | DOUBLE | The maximum longitude of the asset (degrees). |
| LON_MIN | DOUBLE | The minimum longitude of the asset (degrees). |
| ORBIT | INT | The orbit number of the satellite when the data was acquired. |
| PLATFORM | STRING | Name of the platform which acquired the data. |
| PROCESSING_STATUS | STRING | The processing status of the product on a global level, mainly based on the availability of auxiliary input data. Possible values are "Nominal" and "Degraded". |
| PROCESSOR_VERSION | STRING | The version of the software used for L2 processing, as a string of the form "major.minor.patch". |
| PRODUCT_ID | STRING | Id of the L2 product used to generate this asset. |
| PRODUCT_QUALITY | STRING | Indicator that specifies whether the product quality is degraded or not. Allowed values are "Degraded" and "Nominal". |
| SENSOR | STRING | Name of the sensor which acquired the data. |
| SPATIAL_RESOLUTION | STRING | Spatial resolution at nadir. For most products this is |
| TIME_REFERENCE_DAYS_SINCE_1950 | INT | Days from 1 Jan 1950 to when the data was acquired. |
| TIME_REFERENCE_JULIAN_DAY | DOUBLE | The Julian day number when the data was acquired. |
| TRACKING_ID | STRING | UUID for the L2 product file. |
Terms of Use
Terms of Use
The use of Sentinel data is governed by the Copernicus Sentinel Data Terms and Conditions.
Explore with Earth Engine
Code Editor (JavaScript)
var collection = ee.ImageCollection('COPERNICUS/S5P/OFFL/L3_AER_AI') .select('absorbing_aerosol_index') .filterDate('2019-06-01', '2019-06-06'); var band_viz = { min: -1, max: 2.0, palette: ['black', 'blue', 'purple', 'cyan', 'green', 'yellow', 'red'] }; Map.addLayer(collection.mean(), band_viz, 'S5P Aerosol'); Map.setCenter(-118.82, 36.1, 5);