Power is required by households and businesses for heat, light, cooking and communicating. The availability of power in a region may therefore affect issues of security and health, as well as the restoration of most sources of livelihood.
Method
As with most image analysis, the spatial resolution strongly determines what features may be identified and delineated. Satellite imagery with a resolution of at least 1.0 m is capable of displaying power facilities, such as power stations, transformers and substations. Imagery with a resolution of 50 cm is capable of showing the presence of local power supply, such as solar panels and wind turbines, while smaller features, such as utility poles and cables, require a spatial resolution of at least 25 cm to be visible. It might be assumed that collapsed power lines or pylons signify the temporary loss of power in a region while re-erected poles signify the restoration of power. Figure 5.52 shows the presence of shadows and cables in 15 cm aerial imagery of Haiti that indicate the presence of utility poles and power lines.
Figure 5.52 Power supply in Port-au-Prince after the 2010 Haiti earthquake
Night-time light datasets may also be used to monitor the removal and reinstallation of power by measuring radiance intensity and duration. Night-time lights have previously been used on a national scale to monitor a number of processes, including economic activity and CO2 emissions59 and provision of electricity.60 At the present time though, the only civilian night- time light data is available at a resolution of 0.5-2.7km. The data is acquired by the
Operational Linescan System (OLS) on-board a series of satellites belonging to the US Air Force Defense Meteorological Satellite Program (DMSP).
Case studies
In the Thailand and Pakistan studies, a time-series of DMSP-OLS annual night-light composite images from 2000 to 2009 were acquired from NOAA’s National Geophysical Data Center. To create these composite products, cloud-free single orbits were collected for each calendar year, then rectified and aggregated to generate stable light mosaics. The images therefore contain average night-time light values on a relative scale for each year. The results in Ban Nam Khem for the years 2002, 2004, 2006 and 2008 are presented in Figure 5.53.
Figure 5.53 Annual composite night-time light data over Ban Nam Khem before and after the 2004 tsunami. Image and data processing by NOAA's National Geophysical Data Center. DMSP data collected by US Air Force Weather Agency.
The average night-light values in Ban Nam Khem increased after the tsunami peaking during the reconstruction process in 2006. They then dropped slightly but remained higher than they were before the disaster. Meanwhile, data from Chella Bandi show less variability in night-time light values after the 2005 earthquake. It is possible that this is due to pixel saturation caused by the bright lights from the city of Muzaffarabad. The increased radiance intensity in Ban Nam Khem after the tsunami is likely to be due to increased human activity due to reconstruction and the presence of temporary camps during this period. The results show the potential for using night-time light data to monitor the return of power after a disaster. The DMSP-OLS satellites acquire global coverage every 24 hours, so changes in night-time lights over a much shorter period of time may also be monitored. Figure 5.54 shows a comparison of average night-time light values in Ban Nam Khem and Chella Bandi between 2004 and 2009.
Figure 5.54 Night-time lights in Ban Nam Khem and Chella Bandi normalised to pre-disaster condition
According to the key informants there were no significant problems associated with the reinstallation of power after the tsunami. Electricity supply was restored to some areas within 3-4 days although other areas had no electricity for a week. Power was also supplied to residents of temporary housing at no cost for the first year. The average installation date for the households in our survey was 16 months. The key informants also reported that the mains power was restored after 12 months on average. These observations match the date when a lot of the households had moved into government-supplied properties and also coincides with the peak in radiance observed in the night-time light composites. These structures all had electricity and transformers. Apparently temporary measures were adopted by some households that didn’t already have access to electricity, by extending electrical cables from the army-built houses. However, according to the household survey, the supply of power in Ban Nam Khem was not consistent for all households, with 16% complaining of power cuts and others complaining that the current was low and unstable.
Discussion
In Ban Nam Khem, optical imagery could not confidently be used to monitor the return of power to the village, unless it was assumed that power was supplied with transitional shelters and all new constructions. Annual night-time light composites appear to show an increase in human activity during the reconstruction process. Individual night-time light images therefore have the potential to show changes in the provision of power. Ground survey work was used independently to identify features that indicate the use of electricity such as TV aerials, and to identify issues related to the amount of lighting in a home.
Figure 5.55 Power supply features in Ban Nam Khem
The household survey and the key informant interviews also obtained a significant amount of useful information on the provision of power, including: the date when mains power was
may have affected households and/or their livelihoods and about price changes. Figure 5.55 shows power supply features in Ban Nam Khem and the amount of light in a typical army- built house. It was not possible to carry out a similar comprehensive analysis for Chella Bandi, due to the lack of access for field teams in the area.