A COMPREHENSIVE ANALYSIS OF THE CAPABILITES AND LIMITATIONS OF PSI

Transcription

1 A COMPREHENSIVE ANALYSIS OF THE CAPABILITES AND LIMITATIONS OF PSI Rachel Holley, InSAR Surveying Consultant InSAR Surveying Team Fugro NPA Satellite Mapping

2 Introduction Look at the capabilities and limitations of PSI when applied to two different Terrafirma sites: Riga in Latvia and Stockholm in Sweden The outcomes have been very different and provide a useful insight into both the capabilities and the limitations of the technique.

3 Riga, Latvia

4 Riga

5 Information Processing area Riga is built mainly on weak sediments, high in organic particles. Part of the city also has a problem with karsts of dolomites and the gypsum layers. During the Soviet regime, Riga was a big industrial centre. The groundwater table dropped by 12 meters, due to extensive production systems (big consumption of energy and water). Now, the level of groundwater is increasing. During the construction of buildings in several places it has proved necessary to use wooden pillars in the foundations. Cracks in old buildings are a common consequence of the geological setting and groundwater changes. Sourced from LEGMA

6 PSI result Date range: 8 August 1992 to 24 October 2000 Data used: ERS-1 & 2 Number of images used: 53 (started with 63) PS density: 70 PS/km 2 Average annual motion rate (whole processing area) = mm/year, std dev = 1.7 Minimum motion rate: mm/year, maximum motion rate: 25.4 mm/year 87% of points are classed as stable, 10% of points are classified as subsiding, 3% PS points are classified as uplift

7 Capabilities of PSI 1. Monitoring urban areas to determine the general ground and structure movement trends 2. Assessment of the stability of single buildings i.e. architectural monuments 3. Monitoring of regions susceptible to regular flooding 4. Monitoring of landslides associated with slope instability 5. Monitoring of local surface movements 6. Monitoring industrial infrastrucuture i.e.hydroelectric power plants 7. Monitoring coastal zones for geohazard protection

8 Limitations of PSI 1. Data Archive 2. Geocoding 3. Artificial reflectors 4. Visualisation of PSI result The Terrafirma product has helped us to identify unknown ground deformations and estimate where special building controls and fieldwork are necessary LEGMA

9 Stockholm, Sweden

10 Stockholm

11 Information Processing area It is known that settlements of great magnitude have been on-going in this area since the 1960s as a result of land development. Settlement has been accelerated by water drainage for construction purposes. The settlement rates were accelerated in isolated areas by temporary dewatering associated with the recent tunnel construction.

12 PSI result Date range: 23 August 1992 to 8 November 2000 Data used: ERS-1 & 2 Number of images used: 45 (started with 49) PS density: 96 PS/km 2 Average annual motion rate (whole processing area) = 0.28 mm/year, std dev = 1.3 Minimum motion rate: mm/year, maximum motion rate: 17.9 mm/year 88% of points are classed as stable, 6% of points are classified as subsiding, 6% PS points are classified as uplift

13 Limitations of PSI 1. Lack of PS in specific areas of interest 2. PS were structures and not of the ground where there is known settlement 3. PSI result was not representative of known ground settlements 4. Artificial Reflectors

14 Capabilities of PSI 1. Monitoring Structural Stability 2. Identifying areas of on-going ground surface settlements and determine rates of motion for consideration in construction projects Reviewing the results and gaining a fuller understanding of the methods from the first hand experience will allow us to better evaluate where our company may be able to apply the methods in future. Based on the evaluation of these results we have already proposed to use this system for another ongoing project in Southern Europe where the conditions are more likely to result in a useful data set. Value statement

15 Conclusion Like any surveying technique, PSI has its capabilities and limitations. There is a trade-off between what motion is trying to be measured and the success of processing in capturing this. Different sites, will incure slightly different capabilities and limitations (particularly limitations) of the technique which need to be considered Some key limitations of the technique are: Low PS density Data archive The location of PS (on structures rather than the ground) Overall, PSI is a very powerful tool, with many capabilities including: A wide area can be studied Cost effective Key regions of motion can be identified to focus further investigation.