Giovanni Macaluso

Monitoring of an Alpine Glacier by Means of Ground-Based SAR Interferometry

Spaceborne differential synthetic aperture radar (SAR) interferometry has been proven to be a powerful tool in monitoring environmental phenomena and, in particular, in observing glaciers and retrieving information about their surface topography and dynamics. In the last decade, the use of this technique has been successfully extended from space to ground-based observations as a tool for monitoring, on a smaller scale, single landslides, unstable slopes, and more recently, areas covered by snow but not yet glaciers. In this letter, the results of an experimental activity carried out to evaluate the potential of ground-based microwave interferometry to estimate the velocity of an unstable area belonging to a glacier is reported. This experiment demonstrated the possibility of remotely monitoring surface displacements of the monitored glacier up to a distance of about 3 km even if, due to the lack of ground truths on the observed area, the data interpretation must be carefully worked out.

Using a Ground-Based SAR Interferometer and a Terrestrial Laser Scanner to Monitor a Snow-Covered Slope: Results From an Experimental Data Collection in Tyrol (Austria)

In this paper, we report on an experimental activity aimed at investigating the potential of two terrestrial remote-sensing techniques, namely, ground-based SAR (GB SAR) interferometry and terrestrial laser scanning, in order to retrieve snow-depth (SD) measurements in mountainous regions. Terrestrial laser scanning is a more consolidated technique based on the measurement of the optical (near infrared) reflectivity, and it is affected by the surface of the snow layer: a temporal data sequence allows us to estimate the absolute SD variation. Recent use of SAR interferometry to evaluate snow-mass characteristics is based on relating the measured interferometric phase shift to a change in the snow mass. Interferometric GB SAR measurements and terrestrial laser scanner scans were collected together with pointwise conventional measurements of physical snow parameters during the winters of 2005/2006 and 2006/2007. The experiment was carried out in the Wattener Lizum, a high Alpine area at about 2000-m elevation north of the main ridge of the Austrian Alps in Tyrol. Notwithstanding the difficulty of providing both lengthy data record in dry snow conditions and detailed knowledge of the observed snow characteristics, the obtained results confirmed the presence of a clearly measurable interferometric phase variation in relation to the growing height of the snow layer. A comparison of the SD maps obtained through the two techniques shows differences partly due to the different nature of the two observations.

Analysis of Ground-Based SAR Data With Diverse Temporal Baselines

In this paper, the algorithms developed for satellite synthetic aperture radar (SAR) interferometry were adapted to the ground-based SAR (GB-SAR) configuration and used for detecting the displacements of an alpine landslide which have occurred over many years. Indeed GB-SAR interferometry is based on the same principles as satellite SAR techniques but benefits from the GB-SARs versatility and capability of gathering many images per day. In monitoring applications of landslides moving only few centimeters per year, as the case here reported, the GB-SAR sensor is installed at repeated intervals several months apart over the observation period. Although the revisiting time is very similar to the satellite one, for each survey, lasting two or three days, more than ten images are available. They are analyzed separately and in combination with images from other surveys for coherent pixel selection. Interferograms are formed by cross-combining images from different surveys. Finally, the evolution of the deformation across the surveys is retrieved in a least square sense without any assumptions on its regularity. The used GB-SAR technique is described in detail in this paper, and the results obtained with regard to a landslide in the Italian Alps that has been monitored over a period of about three years are discussed.

DEM by Ground-Based SAR Interferometry

In this letter, a ground-based synthetic aperture radar (SAR) interferometer was used to generate digital elevation maps (DEMs) of the illuminated area. With respect to other ground-based data processing techniques, here, the effect of the propagation through the atmosphere is considered. An algorithm similar to multipass satellite SAR techniques was developed in accordance with the phase model used in the ground-based interferometry. Many images taken from different viewing angles were collected and combined to form different interferograms at a test site in Austria. Results from this technique have been compared with an existing geographic model of the test area.

Advances in ground‐based microwave interferometry for landslide survey: a case study

In the past few years differential synthetic aperture radar (SAR) interferometry (DInSAR) from ground‐based installations has provided multi‐temporal surface deformation maps of landslides. Experimental data have demonstrated its effectiveness for remote monitoring of terrain slopes and as an early‐warning system to assess the risk of rapid landslides. Following a brief description of the principles of operation of SAR interferometry, the use of a portable ground‐based radar to survey the large active landslide of Tessina, near Belluno in north‐eastern Italy, is described. This landslide was monitored for the first time in 2000. The current experimental study, carried out with a different instrumental configuration, confirms the effectiveness of this technique for estimating the evolution of landslide movements.

Propagation of Large Bandwidth Microwave Signals in Water

Large bandwidth microwave signals propagating in dispersive media can result in pulses decaying according to a non-exponential law. In particular, large bandwidth signals in the microwave band, propagating in media that can be described by the Debye model (for example fresh water), decays as the square root of the inverse of the propagation distance, instead of exponentially. Although it is a direct consequence of well-known theory of propagation in dispersive media, this result is a bit surprising and its experimental evidence has required a careful set-up.

An ultra-wideband high-dynamic range GPR for detecting buried people after collapse of buildings

An ultra wide band high dynamic range GPR radar - has been tested for buried victims detection. After a building collapse, for example due to an earthquake, the priority of search and rescue teams is to localize people trapped under debris. Several tools are available to help the detection of buried humans, such as micro-cameras, high sensitivity microphones, and so on. Many of these tools present some limitations such as low penetration depth and high susceptibility to external noises. In this paper the authors test the use of an Enhanced Ultra Wide Band (UWB), Continuous Wave Stepped Frequency (CW-SF) Ground penetrating radar as rescue equipment. The radar has been experimented both in controlled environment, and in a real test site, at the Fire-fighters Station of Pisa, Italy.

Long term landslide monitoring by ground-based synthetic aperture radar interferometer

A ground‐based synthetic aperture radar (GB SAR) interferometer was employed to detect small terrain movements which occurred over long periods of time on a landslide hazard zone in the Citrin Valley in northern Italy. Three measurement campaigns were carried out from September 2003 to September 2004. The radar instrumentation was carefully re‐installed at each campaign on the same observation point in order to avoid geometric decorrelation. Because of the global loss of coherence due to the long temporal separation between the observations, the retrieved displacements are limited to a number of very coherent points throughout the surveyed scenario. Radar data are locally compared with data provided by a global positioning system (GPS) network installed on the area interested by the landslide. Digital elevation model, photographic images, interferometric and GPS data are integrated within GIS environment providing a very effective geophysical knowledge tool.

Ground-based Radar Interferometry for Monitoring Unstable Slopes

A ground-based coherent radar instrumentation acquires a time series of radar images. The complex product, pixel by pixel, of a pair of holographic radar images, taken at different moments, gives an interferogram whose phase is related to pixel distance from the sensor. When terrain displacements occur in the time elapsed between two image acquisitions, the phase of the corresponding pixel will vary accordingly. Ground-based radar interferometry is a powerful technique for monitoring terrain deformation on unstable slopes. In this paper the technique is briefly described with reference to some recent experimental cases, reviewing in its potentials and limits. In spite of its indubitable advantages, a number of potential error sources have been recognized: instrumentation instability, repeatability of the measurements after removal and further reinstallation of the instrumentation, atmospheric path delay changes, temporal decorrelation of the scenario, and phase wrapping. All these limits can be overcome by suitable solutions (atmospheric corrections, coherent points analysis, phase unwrapping techniques) that will be discussed in this paper.

A reconfigurable stepped frequency GPR (GPR-R)

Ground Penetrating Radars are a unique and well known tool for soil investigation.