Global Monitoring of Volcanic SO2 Degassing Using Sentinel-5 Precursor Tropomi

We present here the TROPOMI SO 2 product, which is publicly available since April 2018. We describe the capabilities and limitations of the product for the monitoring of volcanic SO 2 degassing. With several examples, we illustrate the benefit of a small satellite pixel of 3.5 x 5.5 km 2 . Owing to its improved detection limit, the data can be used to generate time series of SO 2 mass over number of volcanoes, with a large range of SO 2 emissions. We use Nyiragongo as a show case and correlate the SO 2 mass data with lava lake level estimates and local measurements of the seismicity. This paper also presents on-going developments to further improve the performance of the product for weak SO 2 loadings using a new algorithm, COBRA

Identification of subsiding areas undergoing significant magmatic carbon dioxide degassing, along the northern shore of Lake Kivu, East African Rift

We processed InSAR time series of ENVISAT ASAR descending and ascending datasets and identified two new deforming areas on the northern shore of Lake Kivu, characterized by steady ground subsidence of up to ~1 cm/year over a time period of about seven years (December 2002/January 2003–March 2010). Two distinct areas can be identified: one centered on the Rumoka volcanic cone, which built up during the 1912 eruption of Nyamulagira volcano, and a broader one centered on the Bulengo area on the northern shoreline of Lake Kivu. Both areas include high density of diffuse magmatic degassing areas (“mazuku”), which are topographic depressions in which substantial amount of carbon dioxide accumulates. The steady deflation of at least two fluid reservoirs is consistent with geodetic data but the presence of weak, porous layers, possibly connected with hydrothermal and hydrogeological processes in aquifers and Lake Kivu, could also account for the observed subsidence. The subsidence could be due to pore pressure decrease in porous layers, which may also serve as preferential pathways for escaping gases percolating from the aquifers and Lake Kivu

Seasonal tropospheric influence on SAR interferograms near the ITCZ - The case of Fogo Volcano and Mount Cameroon

The potential of differential SAR interferometry (DInSAR) to measure volcanic ground deformation is widely recognized, despite several limitations still hindering its use in operational volcano monitoring, one of the most critical being water vapor change in the troposphere. In this paper we investigate tropospheric influence on SAR interferograms for two African active volcanoes strongly affected by the oscillation of the Inter-tropical convergence zone (ITCZ). Fogo Island (40,000 inhabitants), located in the southwestern part of the Cape Verde archipelago, is a 30-km-wide active volcano that last erupted in 1995. Mount Cameroon, with approximately 300,000 people living in its immediate surroundings, is the most active volcanic center of the 1600 km-long Cameroon volcanic line, counting seven eruptions over the last century. We analyze 72 SLC ASAR images of Fogo, acquired by ENVISAT from June 2005 to December 2007, and 14 SLC ASAR images of Mount Cameroon, acquired from July 2004 to January 2008. A total of 274 two-pass interferograms, computed from the SLC images, were used for fringe counting and least-squares data adjustment, allowing the estimation of a relative phase delay for each image. We then compare the InSAR-retrieved phase delays with two independent calculations of precipitable water vapor (PWV) in the troposphere, using MODIS and GPS, and observe that all time-series, for both regions under study, match up the ITCZ seasonal oscillation. We conclude that most (if not all) of the phase delays observed are due to water vapor change in the troposphere

L-band and C-band InSAR studies of African volcanic areas

Radar interferometry has proven to be a very suitable, low-cost and accurate tool to measure surface displacements. We investigate several data fusion or time-series analysis strategies which aim to mitigate C-band InSAR restrictions for volcano deformation monitoring applications. The focus is on active African volcanic areas. Firstly, data fusion of C-band ENVISAT/ASAR and L-band ALOS/PALSAR sensors helps the determination of a rifting event sequence that took place in summer 2007 in Lake Natron area. The second strategy investigated is a new Wavelet Based InSAR time series applied on ERS-2 data covering the Nyiragongo-Nyamulagira area. It allows new ground displacements identifications outside the local rift valley. Lastly, PALSAR Quad-Pol POLInSAR applicability is explored for La Palma Island.Peer reviewe

L-band and C-band InSAR studies of African volcanic areas

Radar interferometry has proven to be a very suitable, low-cost and accurate tool to measure surface displacements. We investigate several data fusion or time-series analysis strategies which aim to mitigate C-band InSAR restrictions for volcano deformation monitoring applications. The focus is on active African volcanic areas. Firstly, data fusion of C-band ENVISAT/ASAR and L-band ALOS/PALSAR sensors helps the determination of a rifting event sequence that took place in summer 2007 in Lake Natron area. The second strategy investigated is a new Wavelet Based InSAR time series applied on ERS-2 data covering the Nyiragongo-Nyamulagira area. It allows new ground displacements identifications outside the local rift valley. Lastly, PALSAR Quad-Pol POLInSAR applicability is explored for La Palma Island.Peer reviewe