Malte Westerhaus

TanDEM-X Time Series Analysis Reveals Lava Flow Volume and Effusion Rates of the 2012–2013 Tolbachik, Kamchatka Fissure Eruption

Assessing eruption volumes is one of the major challenges in volcano research but provides valuable insights into the dynamics of an eruption and the associated hazard. One way to estimate this important parameter is the generation and differencing of digital elevation models (DEMs) acquired before, during, and after an eruption. The satellite mission TanDEM-X enables generation of time series of DEMs using synthetic aperture radar satellite imagery. We use these data to study the 2012–2013 eruption of Tolbachik in Kamchatka. We developed a processing scheme for generation of 18 DEMs from TanDEM-X imagery that relies on the generation of a preeruption DEM which is used to process the syneruption and posteruption data pairs. Differencing each DEM with the preeruption DEM enables mapping the lava flows and measuring lava flow volume over time and to estimate lava extrusion rates. We find a final lava flow volume of 0.53 km3 covering an area of 36 km2 by the end of the eruption. An uncertainty analysis is performed while analyzing the DEM differences in areas where no topographic change is expected, leading to an error of ±0.01 km3 for the final lava flow volume. The lava effusion was with 247.92 m3/s very high in the first days of the eruption and rapidly decayed toward its end. While many basaltic eruptions follow an exponentially decaying flow model, the extrusion rates at Tolbachik are more compatible with a 1/t model. This special characteristic might be useful to gain further insight into the eruption process at Tolbachik.

Analysis of atmospheric signals in spaceborne InSAR - toward water vapor mapping based on multiple sources

The dominant error source for short wavelength spaceborne radar signals is due to water vapor present in the neutral atmosphere (neutrosphere). This distortion signal is characterized by high variations in time and space, and can be exploited as a valuable source for quantifying the water vapor content of the Earths atmosphere. Available water vapor measurements provided by Envisat Medium Resolution Imaging Spectrometer (MERIS) and simulations from numerical weather prediction models are still limited in observing rapid fluctuations of water vapor. Therefore, we are investigating Interferometric Synthetic Aperture Radar (InSAR) for water vapor mapping. In this paper, water vapor maps derived from Persistent Scatterer InSAR (PSI), MERIS, and the Weather Research and Forecasting (WRF) model are presented with comparative analyses.

On the Use of Bistatic TanDEM-X Images to Quantify Volumetric Changes of Active Lava Domes

TanDEM-X is a recent SAR mission, consisting of two almost identical spacecraft flying in close formation. The small distance between the two radar satellites allows two images to be acquired at the same time (bistatic images), strongly reducing the influence of temporal decorrelation, which is one of the major sources of error in repeat-pass interferometric analyses. For the first time, we successfully apply TanDEM-X data to observe topographic changes at active volcanoes by using the image pairs to generate high-resolution digital surface models (DSMs) for each transit of the satellites. Taking the difference between two bistatic DSMs allows us to assess substantial topographic changes and/or sudden ground displacements above the 1 m level. As the first test case, we used bistatic TanDEM-X data to assess topographic change due to the major Merapi 2010 eruption. The preliminary estimated volumetric loss of 19 � 10 6 m 3 is reasonable; however, strong phase noise due to geometrical decorrelation and resulting unwrapping errors affect the result. To demonstrate that much smaller topographic changes are observable with TanDEM-X, we further analyzed data acquired before and after a small explosion at Volcan de Colima in June 2011. The estimated volume loss of 2 � 10 5 m 3 fits well to ground truth data.

Integration of InSAR and GNSS Observations for the Determination of Atmospheric Water Vapour

High spatially and temporally variable atmospheric water vapour causes an unknown delay in microwave signals transmitted by space-borne sensors. This delay is considered as a major limitation in Interferometric Synthetic Aperture Radar (InSAR) applications as well as high-precision applications of Global Navigation Satellite Systems (GNSS). On the other hand, the delay could be quantified to derive atmospheric parameters such as water vapour. Temporal variability of water vapour is well estimated from ongoing GNSS measurements, while InSAR provides information about the spatial variations of water vapour. This project aims at assimilating InSAR phase observations and spatially-sparse GNSS measurements for the determination of atmospheric water vapour. In this contribution GNSS-based water vapour calculations and assessment of different strategies are presented. Work in progress is also reported including some preliminary results.

An Inventory of Surface Movements in the Upper Rhine Graben Area, Southwest Germany, from SAR-Interferometry, GNSS and Precise Levelling

Recent surface movements in the Upper Rhine Graben (URG) area are investigated with geodetic techniques. Line of sight (LOS) displacement rates from SAR interferometry (InSAR), horizontal and vertical rates from coordinate time series of permanent GNSS sites and vertical rates from precise levelling measurements are estimated with high accuracy. We show that the data sets are capable of providing detailed insight into the current movements in the URG area, which is required for a better understanding of geodynamic processes as well as for a reasonable exploitation of geopotentials in the URG. This paper focusses on a comparison of results from InSAR and levelling on a regional and on a local scale. A case study highlights temporal differences in the deformation characteristics of an oil extraction area detected from ERS-1/2 and Envisat data as well as from levelling measurements in multiple epochs. In order to benefit from the advantages of each technique, our work aims on a proper combination to consistently link the different observation methods in a rigorous multi-technique approach.