Sentinel-5P OFFL CH4: Offline Methane

COPERNICUS/S5P/OFFL/L3_CH4
Dataset Availability
2019-02-08T08:13:16 - Present
Dataset Provider
Earth Engine Snippet
ee.ImageCollection("COPERNICUS/S5P/OFFL/L3_CH4")
Tags
tropomi ch4 methane climate eu esa copernicus sentinel s5p sron knmi

Description

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).

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 any values with QA values of less than 50.

OFFL/L3_CH4

This dataset provides offline high-resolution imagery of methane concentrations.

Methane (CH4) is, after carbon dioxide (CO2), the most important contributor to the anthropogenically enhanced greenhouse effect. Roughly three-quarters of methane emissions are anthropogenic and as such it is important to continue the record of satellite based measurements. TROPOMI aims at providing CH4 column concentrations with high sensitivity to the Earth’s surface, good spatiotemporal coverage, and sufficient accuracy to facilitate inverse modeling of sources and sinks. TROPOMI uses absorption information from the Oxygen-A Band (760nm) and the SWIR spectral range to monitor CH4 abundances in the Earth's atmosphere. [More information]

Currently, the following data quality issues are known, are not covered by the quality flags, and should be kept in mind when looking at the methane product and also at preliminary validation results. For more details, see the MPC VDAF website.

Filtering on qa_value < 0.5 does not remove all pixels considered bad. Some pixels with too low methane concentrations are still present:

  • Single TROPOMI overpasses show stripes of erroneous CH4 values in the flight direction.

  • Not all pixels above inland water are filtered.

  • Uncertainties for the XCH4 is only based on the single sounding precision due to measurement noise. For applications requiring an overall uncertainty estimate, we propose to multiply the provided error by a factor 2, which reflects the scatter of single sounding errors in the TCCON validation.

  • The current data release only provides XCH4 over land. Glint ocean observations will be added in the next data release.

OFFL L3 Product

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

harpconvert --format hdf5 --hdf5-compression 9
-a 'CH4_column_volume_mixing_ratio_dry_air_validity>50;derive(datetime_stop {time})'
S5P_OFFL_L2__CH4____20190223T202409_20190223T220540_07072_01_010202_20190301T221106.nc
grid_info.h5

We then merge all the data into one large mosaic (taking only one value 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 'CH4_column_volume_mixing_ratio_dry_air_validity>50; derive(datetime_stop {time}); bin_spatial(2001, 50.000000, 0.01, 2001, -120.000000, 0.01); keep(CH4_column_volume_mixing_ratio_dry_air, aerosol_height, aerosol_optical_depth, sensor_azimuth_angle, sensor_zenith_angle, solar_azimuth_angle, solar_zenith_angle)' S5P_OFFL_L2__CH4____20190223T202409_20190223T220540_07072_01_010202_20190301T221106.nc output.h5

Bands

Resolution
0.01 arc degrees

Bands

Name Units Description
CH4_column_volume_mixing_ratio_dry_air ppmV

column averaged dry air mixing ratio of methane

aerosol_height m

aerosol height parameter in the CH4 retrieval

aerosol_optical_depth

aerosol optical thickness in the SWIR band

Image Properties

Image Properties

Name Type Description
ALGORITHM_VERSION STRING

The algorithm version used in L2 processing. It's 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 3.5x7km2, except for L2__O3__PR, which uses 28x21km2, and L2__CO____ and L2__CH4___, which both use 7x7km2. This attribute originates from the CCI standard.

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 in Earth Engine

var collection = ee.ImageCollection('COPERNICUS/S5P/OFFL/L3_CH4')
  .select('CH4_column_volume_mixing_ratio_dry_air')
  .filterDate('2019-04-10', '2019-04-11');

var val_max = 1750;
var val_min = 1900;
var band_viz = {
  min: val_min,
  max: val_max,
  opacity: 1.0,
  palette: ["black", "blue", "purple", "cyan", "green", "yellow", "red"]
};

Map.addLayer(ee.Image(0).byte(), {}, "black background");
Map.addLayer(collection.mean(), band_viz, 'methane');
Map.setCenter(0.0, 0.0, 2);