SO₂ data and alert service

Introduction

Slant column density vs. vertical column density

Geographic regions

Data presentation and delivery

Solar Zenith Angle

What is the Dobson Unit?

Slant column retrieval

Background correction

Reference spectrum

Cloud cover fraction

Near-real time service

Criteria for exceptional SO2 concentrations

Air-mass factor using look-up tables

Air-mass factor using a chemistry transport model

SO2 column from OMI

Time period of available data

Data format specification

Data and Service version history

Validation of the data products

South Atlantic Anomaly

Downloading data & image files

Documentation

References

Acronyms

Acknowledgments

Near-real time SO2 data service

Based on the SCIAMACHY data, the system also sends notifications (or: alerts) of exceptional SO2 concentrations by email to users who have subscribed to that service; see this page for an introduction and description of what is provided by the alert service.

This NRT service provides data and images to the website. For this service, only data files and images with the data on satellite orbit coordinates are provided. The software processes incoming SCIAMACHY level-1 files in NRT. On a given day, the processing will involve only measurements of that day and the day before: processing older data is not very useful for the notification system.

By far most SCIAMACHY orbits are processed within about 5 hours after observation. But a few orbit from the beginning of the day (in terms of UTC) often arrive later than orbit from the middle or end of that day -- this is due to the late delivery of the data by the ground data network.

Images in the near-real time service

In the NRT service, things are a little different. Since the main goal of the NRT service is to give information on the location of SO2 peak values possibly related to volcanic eruptions or anthropogenic activities, it is not necessary that the values are exact. To at least have an idea of where SO2 peaks are related and a rough estimate of the total column of SO2 in the absence of cloud information, the VCD is calculated assuming clear-sky conditions, i.e. the absence of any clouds.

For OMI data there is no real SCD available, as the SO2 concentration is derived in a different way. Therefore only images of the VCD and CCF are available.

Process monitoring

Processing of OMI data is done by NASA/NOAA and the level-2 data is delivered in NRT to KNMI, where the plotting is done in NRT.

Graph showing how many SCIAMACHY orbit files are available as function of the hours after the end of the measurements along that orbit. The blue curve gives the time it took ESA to process the raw data and prepare the level-1b spectrum files. Once the these files are made, they are made available to, among others, KNMI. From KNMI they are pushed to BIRA-IASB, where they are picked up and calibrated (to form level-1c files) for the retrieval of trace gases, such as NO2, SO2 and BrO. The red curve shows the time to took for that step to be finished.