Prabu Dheenathayalan

Pipe failure predictions in drinking water systems using satellite observations

Soil deformation is believed to play a crucial role in the onset of failures in the underground infrastructure. This article describes a method to generate a replacement-prioritisation map for underground drinking water pipe networks using ground movement data. A segment of the distribution network of a Dutch drinking water company was selected as the study area. Failure registration data comprising 868 failures registered over 40 months and geographical network data were obtained from the water utility. Ground movement was estimated using radar satellite data. Two types of analyses were performed: cell and pixel based. For the cell-based analysis, asbestos cement (AC) pipes exhibited the highest failure rates. Older AC pipes were also shown to fail more often, whereas failure rates for PVC were the lowest. For the pixel-based analysis, ground movement was demonstrated to play a role in the failure of all materials combined. Therefore, a replacement-prioritisation map for AC was generated which combined ground movement data and pipe-age data. This method can be a beneficial resource for network managers for maintenance and continuous monitoring.

Radar target type classification and validation

The main challenge in analyzing the results of persistent scatterer techniques is to associate each coherent radar reflection to a real-world object, referred to as target type classification. In recent years different methods to perform target type classification were studied. In this paper we propose a height-based target type classification method to discriminate radar reflections emanating from the ground and above-ground objects. Data acquired from multiple spaceborne satellites such as ERS, Envisat, and TerraSAR-X covering Amsterdam, the Netherlands spanning over two decades from 1992 to 2012 are processed. The target classification results are validated with highly precise elevation data obtained from an independent airborne laser altimetry technique. In this paper we demonstrate that our target type classification method is accurate and thereby the generated DEM of the ground is of nearly sub-metric accuracy in case of ERS and Envisat, and TerraSAR-X.

Small Reflectors for Ground Motion Monitoring With InSAR

In recent years, synthetic aperture radar interferometry has become a recognized geodetic tool for observing ground motion. For monitoring areas with low density of coherent targets, artificial corner reflectors (CRs) are usually introduced. The required size of a reflector depends on radar wavelength and resolution and on the required deformation accuracy. CRs have been traditionally used to provide a high signal-to-clutter ratio (SCR). However, large dimensions can make the reflector bulky, difficult to install and maintain. Furthermore, if a large number of reflectors are needed for long infrastructure, such as vegetation-covered dikes, the total price of the reflectors can become unaffordable. On the other hand, small reflectors have the advantage of easy installation and low cost. In this paper, we design and study the use of small reflectors with low SCR for ground motion monitoring. In addition, we propose a new closed-form expression to estimate the interferometric phase precision of resolution cells containing a (strong or weak) point target and a clutter. Through experiments, we demonstrate that the small reflectors can also deliver displacement estimates with an accuracy of a few millimeters. To achieve this, we apply a filtering method for reducing clutter noise.