Abstract
Determining the height of a volcanic SO2 cloud after a volcanic eruption
is a challenging task in UV satellite retrievals. The height is
nevertheless the most important yet uncertain parameter required to
forecast the movement of the volcanic cloud and to determine the total
SO2 column and ejected SO2 mass, especially for local authorities and
aviation safety applications. Retrieval algorithms developed so far use
direct fitting and optimal estimation techniques to determine the height
information, which is hidden in the spectral signature. They are
computationally very expensive and time consuming and therefore are not
practical in near-real time operational retrievals, especially for
current and future satellite UV instruments with high resolution and
related high data amount. We have therefore developed the ‘Full-Physics
Inverse Learning Machine’ (FP_ILM) retrieval algorithm that combines
principle component analysis and neural network , which performs an
extremely fast (3 ms per TROPOMI pixel) yet accurate (<2km
average accuracy) SO2 LH retrieval based on UV satellite measurements.
The algorithm was first applied to GOME-2 and introduced by Efremenko et
al. (2017) . Hedelt et al. (2019) further improved the algorithm and
applied it to Sentinel-5p/TROPOMI data. The algorithm was optimized and
validated in the framework of ESA’s Sentinel-5p Innovations project
(S5P+I) and is already performing SO2 LH retrievals in a
semi-operational near-real time environment. Recently, Fedkin et al.
(2021) applied the FP_ILM algorithm to OMI and OMPS data. Application
to future UV LEO (Sentinel-5) and GEO (Sentinel-4, GEMS, TEMPO)
satellite missions will follow. We present here SO2 LH results based on
GOME-2, OMI/OMPS, and TROPOMI measurements of the Raikoke (Kuril
Islands) volcanic eruption in June-July 2019 and La Soufriere St.
Vincent volcanic eruption in April 2021 and make intercomparisons
between the UV sensors as well as other (IR) independent measurements.