New approaches to merging multi-sensor satellite measurements of volcanic SO2 emissions

Abstract:

As part of the NASA MEaSUREs program, we are developing a unique long-term database of volcanic sulfur dioxide (SO₂) emissions for use by the scientific community, using observations from multiple satellite instruments collected since 1978. Challenges to creating such a database include assessing data continuity between multiple satellite missions and SO₂ retrieval algorithms and estimating measurement uncertainties. Here, we describe the approaches that we are using to merge multi-decadal SO₂ measurements from the ultraviolet (UV) Total Ozone Mapping Spectrometer (TOMS), Ozone Monitoring Instrument (OMI) and Ozone Monitoring and Profiler Suite (OMPS) sensors. A particular challenge has involved accounting for the OMI row anomaly (ORA), a data gap in OMI measurements since 2008 that partially or wholly obscures some volcanic eruption clouds, whilst still profiting from the high OMI spatial resolution and data quality, and prior OMI SO₂ validation. We present a new method to substitute missing SO₂ information in the ORA with near-coincident SO₂ data from OMPS, providing improved estimates of eruptive volcanic SO₂ emissions. The technique can also be used to assess consistency between different satellite instruments and SO₂ retrieval algorithms, investigate the impact of variable sensor spatial resolution, and estimate measurement uncertainties. It is particularly effective for larger eruptions producing extensive SO₂ clouds where the ORA obscures the volcanic plume in multiple contiguous orbits. Application of the technique is demonstrated using recent volcanic eruptions including the 2015 eruption of Calbuco, Chile. We also provide an update on the status of the multi-satellite long-term volcanic SO₂ database (MSVOLSO2L4).