South Africa - Geo-harzards response using SAR interferometry

Geo-harzards response using SAR interferometry
Using SAR data to detect , monitor and respond to geo hazard affecting electrical Infrastructure caused by underground heating and dolomitic land
ISO/TC211 standards used ISO 19115-2, Geographic information — Metadata — Part 2: Extensions for acquisition and processing ISO 19159-3, Geographic information — Calibration and validation of remote sensing imagery sensors and data — Part 3: SAR/InSAR
Purpose To detect , monitor and respond to two main geohazards that occur within the Mpumalanga highveld, Gauteng and North West provinces of South Africa and affect electrical Infrastructure. Often, these geohazards occur quickly without warning and cause extensive damage to Infrastructure and property. This then increases the need for a long-term monitoring solution. Here, we looked at subsidence caused by dolomite and coal seams using mainly Geological data, thermal imagery and Synthetic Aperture radar data to analyze , model and respond to such events. A risk-based methodology is then used to determine the actions to be taken after identification of the hazard.		Detecting and monitoring areas that are vulnerable to subsidence and sinkholes due to dolomitic rock.
		Detecting and monitoring areas with underground burning to due to coal seams.
		Use Geographic Information Systems and Science (GISc) to analyze and model vulnerable areas.
		To model the land instability, various spatial datasets such as Synthetic Aperture Radar, Optical Imagery and geological data were used.
		A risk-based assessment methodology was used determine appropriate action to be taken following the identification of potential hazards.

Study Area: South Africa

Presence of carbonate rocks in the Highveld causes karst topography – leading to subsidence
Presence of coal seams in the Highveld causes spontaneous coal combustion– leading to subsidence

Processing Methodologies

SAR Interferometric Processing

Surface Temperature Retrieval

SAR deformation Mapping Results


Thermal Mapping Results


Risk Assessment in context
In this example; Line 1 and Line 2 are Transmission Power Lines that share a servitude where 80% of the structures are on areas prone to sinkholes.
These two lines connect substation A and substation B and further to this, there is no other source of supply coming into substation B only loads (customers) totaling 118MW are connected. In this example, sinkholes have formed.
	Risk rating of II (High Risk) For a high rated risk, risk treatment should be identified and deployed. Risk treatment approach is, Continual monitoring of the subsidence formation (via visual inspections and GISc). Conduct a detailed geotechnical analysis. Options to rehabilitate and/or re-route the powerline are currently being considered.
Consequence 3 - The consequence to operations is high because there will be a total loss of supply to Substation B (loss of 118MW).	Likelihod C - Due to the proximity of the sinkhole to the tower foundation (<10m). The probability of failure is high.

Country

South Africa

Organization

Contact person

Tshisikhawe Mphaphuli

Thandi Petunia Msibe

March 2024