Glacier motion estimation using SAR offset-tracking procedures

Two image-to-image patch offset techniques for estimating feature motion between satellite synthetic aperture radar (SAR) images are discussed. Intensity tracking, based on patch intensity cross-correlation optimization, and coherence tracking, based on patch coherence optimization, are used to estimate the movement of glacier surfaces between two SAR images in both slant-range and azimuth direction. The accuracy and application range of the two methods are examined in the case of the surge of Monacobreen in Northern Svalbard between 1992 and 1996. Offset-tracking procedures of SAR images are an alternative to differential SAR interferometry for the estimation of glacier motion when differential SAR interferometry is limited by loss of coherence, i.e., in the case of rapid and incoherent flow and of large acquisition time intervals between the two SAR images. In addition, an offset-tracking procedure in the azimuth direction may be combined with differential SAR interferometry in the slant-range direction in order to retrieve a two-dimensional displacement map when SAR data of only one orbit configuration are available

The April 3, 2010 earthquake along the Pernicana fault (Mt. Etna - Italy): analysis of satellite and in situ ground deformation data integrated by the SISTEM approach

Etna is worldwide known as one of the most studied and monitored active volcanoes. Flank instability along the eastern and southern portion of Mt. Etna has been observed and measured thanks to geodetic networks and InSAR data analysis. The spreading area is bordered to the north by the east-west Pernicana Fault System (PFS) which dynamic is often linked with the eruptive activity, as recently observed during the 2002-2003 eruption. A seismic sequence occurred since April 2-3, 2010, along the PFS with two very shallow (a few hundred meters) mainshocks of magnitude 3.6 and 3.5. Explosions and ash emissions at the summit craters followed this swarm and culminated some days later (April 7-8). Just after the earthquake, specific GPS surveys were carried out aimed at monitoring the eastern part of the Pernicana fault, and the leveling route on the northeastern flank of the volcano was also surveyed. Trying to investigate the deformation occurred along the PFS during the events of April 3rd 2010, we performed a DInSAR (Differential Interferometric Synthetic Aperture Radar) analysis of ascending and descending Envisat, and of ascending ALOS-PALSAR images encompassing the date of the earthquake. The Envisat interferograms show very intense but local deformation on the Envisat ascending data and a low signal for the descending geometry, close to the Pernicana fault trace. This is probably due to the oblique normal/leftlateral kinematics of the PFS (as deduced also by GPS and leveling data), indeed both vertical (lowering) and horizontal (eastwards) components of motion produce a strong stretching of the LOS (Line Of Sight) distance for ascending geometry, while the two components act in opposite ways for the descending geometry, resulting in lower LOS distance variations compared to the ascending data set. We analyzed also the ALOS pair referring to 21/02/2010 – 08/04/2010 time and acquired along the ascending track number 638. The ALOS interferogram clearly show three fringes corresponding to roughly 35 cm of LOS displacement. The preliminary modeling of the interferograms agree with the seismic information (very shallow faulting, seismic moment) and show that the medium behave elastically. In order to investigate the ground deformation pattern associated with this event, an application of the novel SISTEM (Simultaneous and Integrated Strain Tensor Estimation from geodetic and satellite deformation Measurements) approach is presented here. To achieve higher accuracy and get better constraint of the 3D components of the displacements, we improved the standard formulation of SISTEM approach, based on the GPS and a single DInSAR sensor, in order to take into account all the available dataset (GPS, leveling, ascending and descending ENVISAT C-Band interferograms and the ALOS L-Band data). The 3D displacement maps obtained using the SISTEM approach well show the kinematics of the PFS, and are able to reconstruct also the ground deformation affecting the whole investigated area, defining the movements of the north-eastern flank of the volcano. These results, which provide an accurate spatial characterization of ground deformation, are hence promising for future studies aimed at improving the knowledge about the kinematics of the active faults of Mt. Etna

SAFER Response to Eyjafjallajökull and Merapi Volcanic Eruptions. In: ‘Let's embrace space’ Space Research achievements under the 7th Framework Programme, Edit by European Commission, DG Enterprise and Industry

After PREVIEW FP6 Project’s conclusion, the WP30210 within FP7 GMES SAFER (Services and Applications For Emergency Response) Project has the main objective to refine and consolidate the Earthquake & Volcanoes (E&V) services that were just tested in previous activities and to provide operative services to Users, the Civil Protection Authorities. Here we mainly report objectives and results for the specific tasks related to Eruptive volcanic parameters (WP30211). Four specific products related to the volcanic events which will contribute to the monitoring of the phenomena and mitigation of the eruption effects are expected within the end of the Project. They mainly concern: SAR displacement, high temperature events (HTE), Ash detection, SO2 concentration and flux, and Ash dispersion models. In particular, here we mostly focus on the activity performed in the occasion of FP7 GMES SAFER activation during two major volcanic eruptions occurred in 2010. The first activation was for the Eyjafjallajökull eruption occurred in Iceland between April and May 2010, and the second one was solicited in the occasion of the eruption of Mount Merapi (Indonesia) in October-November 2010. Here we present the results of both remote sensing and modeling activities performed during these two events.Published212-222ope

Lower edge of locked Main Himalayan Thrust unzipped by the 2015 Gorkha earthquake

Large earthquakes are thought to release strain on previously locked faults. However, the details of how earthquakes are initiated, grow and terminate in relation to pre-seismically locked and creeping patches is unclear ^1-4. The 2015 Mw 7.8 Gorkha, Nepal earthquake occurred close to Kathmandu in a region where the prior pattern of fault locking is well documented ^5. Here we analyze this event using seismological records measured at teleseismic distances and Synthetic Aperture Radar imagery. We show that the earthquake originated northwest of Kathmandu within a cluster of background seismicity that fringes the bottom of the locked portion of the Main Himalayan Thrust fault (MHT). The rupture propagated eastwards for about 140 km, unzipping the lower edge of the locked portion of the fault. High-frequency seismic waves radiated continuously as the slip pulse propagated at about 2.8 km s-1 along this zone of presumably high and heterogeneous pre-¬seismic stress at the seismic-aseismic transition. Eastward unzipping of the fault resumed during the Mw 7.3 aftershock on May 12. The transfer of stress to neighbouring regions during the Gorkha earthquake should facilitate future rupture of the areas of the MHT adjacent and up-dip of the Gorkha earthquake rupture.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/ngeo251

A Macroecological Analysis of SERA Derived Forest Heights and Implications for Forest Volume Remote Sensing

Individual trees have been shown to exhibit strong relationships between DBH, height and volume. Often such studies are cited as justification for forest volume or standing biomass estimation through remote sensing. With resolution of common satellite remote sensing systems generally too low to resolve individuals, and a need for larger coverage, these systems rely on descriptive heights, which account for tree collections in forests. For remote sensing and allometric applications, this height is not entirely understood in terms of its location. Here, a forest growth model (SERA) analyzes forest canopy height relationships with forest wood volume. Maximum height, mean, H100, and Lorey's height are examined for variability under plant number density, resource and species. Our findings, shown to be allometrically consistent with empirical measurements for forested communities world-wide, are analyzed for implications to forest remote sensing techniques such as LiDAR and RADAR. Traditional forestry measures of maximum height, and to a lesser extent H100 and Lorey's, exhibit little consistent correlation with forest volume across modeled conditions. The implication is that using forest height to infer volume or biomass from remote sensing requires species and community behavioral information to infer accurate estimates using height alone. SERA predicts mean height to provide the most consistent relationship with volume of the height classifications studied and overall across forest variations. This prediction agrees with empirical data collected from conifer and angiosperm forests with plant densities ranging between 102–106 plants/hectare and heights 6–49 m. Height classifications investigated are potentially linked to radar scattering centers with implications for allometry. These findings may be used to advance forest biomass estimation accuracy through remote sensing. Furthermore, Lorey's height with its specific relationship to remote sensing physics is recommended as a more universal indicator of volume when using remote sensing than achieved using either maximum height or H100

Global Soil Moisture Patterns Observed by Space Borne Microwave Radiometers and Scatterometers

Within the scope of the upcoming launch of a new water related satellite mission (SMOS) a global evaluation study was performed on two available global soil moisture products. ERS scatterometer surface wetness data was compared to AMSR-E soil moisture data. This study pointed out a strong similarity between both products in sparse to moderate vegetated regions with an average correlation coefficient of 0.83. Low correlations were found in densely vegetated areas and deserts. The low values in the vegetated regions can be explained by the limited soil moisture retrieval capabilities over dense vegetation covers. Soil emission is attenuated by the canopy and tends to saturate the microwave signal with increasing vegetation density, resulting in a decreased sensor sensitivity to soil moisture variations. It is expected that the new low frequency satellite mission (SMOS) will obtain soil moisture products with a higher quality in these regions. The low correlations in the desert regions are likely due to volume scattering or to the dielectric dynamics within the soil. The volume scattering in dry soils causes a higher backscatter under very dry conditions than under conditions when the sub-surface soil layers are somewhat wet. In addition, at low moisture levels the dielectric constant has a reduced sensitivity in response to changes in the soil moisture content. At a global scale the spatial correspondence of both products is high and both products clearly distinguish similar regions with high seasonal and inter annual variations. Based on the global analyses we concluded that the quality of both products was comparable and in the sparse to moderate vegetated regions both products may be beneficial for large scale validation of SMOS soil moisture. Some limitations of the studied products are different, pointing to significant potential for combining both products into one superior soil moisture data set. © The Author(s) 2008

Signatures of ERS-Envisat Interferometric SAR Coherence and Phase of Short Vegetation: An Analysis in the Case of Maize Fields

Interferometric observations between the European Remote Sensing, ERS-2, synthetic aperture radar (SAR) and the Envisat Advanced SAR (ASAR) are unique since they are characterized by a short repeat-pass interval (28 min) and a perpendicular baseline of approximately 2 km. In vegetated areas, this configuration should preserve from strong temporal decorrelation and enhance the sensitivity of coherence and SAR interferometric (InSAR) phase to volumes with small heights. This assumption could be tested with the data acquired during the dedicated ERS-Envisat Tandem mission on October 15, 2007, over the Seeland region, Switzerland. Five maize fields and one sunflower field presented lower coherence and offsets of the interferometric phase, i.e. height, with respect to neighboring bare fields. To gain understanding on the interferometric signatures, the interferometric water cloud model was used to simulate coherence and InSAR height for the maize fields. Both the coherence and the InSAR height present clear dependence upon vegetation height and exhibit strong consistency. Simulations showed that the modeled coherence and InSAR height are most sensitive to the two-way attenuation and the temporal coherence of the vegetation. The best correspondence between the observed and modeled InSAR parameters was obtained with two-way attenuation values between 2 and 4 dB/m (corresponding to an extinction between 1 and 2 dB/m) and high temporal coherence of the vegetation (above 0.6), with this being due to the very stable conditions of the weather during the 28-min interval between image acquisitions

Forest stem volume estimation using C-band interferometric SAR coherence data of the ERS-1 mission 3-days repeat-interval phase

Interferometric synthetic aperture radar (InSAR) coherence datasets from the 3-days phase of the European Remote Sensing Satellite (ERS-1) mission during the winter months of 1992 have been analyzed to assess the capability to retrieve forest stem volume in boreal forests. For three test sites in Sweden and Finland, coherence decreased for increasing repeat-pass interval from 3- to 12-days due to increasing temporal decorrelation. Overall strong decorrelation was observed for images acquired under unfrozen conditions or thawing conditions. Coherence was best preserved under stable frozen conditions and, in addition, short perpendicular component of the interferometric baseline (i.e., <300 m). Stem volume was estimated with the Interferometric Water Cloud Model (IWCM) and multi-temporal combination of single-image estimates. For the test site of Tuusula, Finland, data from eight 3-days image pairs yielded a relative RMSE of 28.2% for stem volumes ranging between 3 and 482 m3/ha. For the 6-days repeat-pass interval, the relative RMSE was only slightly worse (32.4%). For longer repeat-pass intervals, the relative RMSE was above 50%. This study suggests that C-band short-term coherence has potential to support retrieval of forest biomass but the prospects of Sentinel-1 coherence to estimate biomass appear to be limited to the 6-days coherence in areas characterized by stable frozen, or likewise stable dry, conditions