Last summer, North Korea suffered a lot of human and material damage, including short-term, intensive rain in the Yalu River area, flooding and washing away riverside homes and farmland, and causing casualties. It was reported that not only the electric barbed wire installed along the Yalu River to prevent North Korean defections, but also power facilities such as telephone poles were damaged and lost due to heavy rain, and as the poor power situation worsened, difficulties in recovering from flood damage increased. Using nighttime illuminance images taken before and after heavy rain, we examined changes in light brightness values that occurred between July and August of last year through quantitative statistical analysis. Among the three cities and counties at the Yalu River estuary, Sinuiju City was found to have the largest decrease in nighttime power.
Using illuminance images taken by the JPSS meteorological satellite jointly operated by the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA), we examined trends in the increase and decrease in nighttime light at the Yalu River Estuary before and after heavy rain. The average images processed in July and the month after heavy rain in 2024 were compared and analyzed. The monthly average image is created by averaging the illuminance images taken for 1 month, that is, 30 days, and is posted on the night image public website along with daily shooting data (VIIRS Nighttime Light)provided in .
Monthly average illuminance images are produced on a monthly basis to remove data errors or noise and obtain high-quality images. For example, this is to remove all cloudy data and light from temporary fires such as forest fires or explosions and obtain permanent night light. The technical term for such data is ‘SNL (Stable Night Light)’. In the case of clouds, the ground light is obscured or weakly detected by the satellite sensor, and since forest fires do not occur all the time but occur temporarily, all errors and noise are removed, and the remainder is averaged to create a monthly representative image. There is a monthly average illuminance image obtained by processing data for one month, and an annual average illuminance image created from 365-day images per year is also provided. The average annual video is currently posted on the web portal from 2012 to 2023, and the 2024 data is expected to be released early this year. The pixel brightness value of the monthly average and annual average illuminance images is expressed as a 6-bit value from 0 (when there is no light) to a maximum of 63.
Annual and monthly average illuminance images can be useful in identifying nighttime light change trends in a specific area. For example, when looking at changes in illumination in the Ukraine war zone, you will see that night lights have decreased significantly since the outbreak of war. This may have been due to poor electricity supply due to the destruction or damage of major infrastructure facilities that supply power due to air raids and bombings, or because light was blocked from escaping due to facility lighting control.
In the case of the satellite image above, if you compare the average image of July, when there was heavy rain last summer at the mouth of the Yalu River, and the average image of August immediately after, you can detect a certain degree of decrease in light in the August image. Although the difference is not visually noticeable in satellite images, a clear difference can be identified if the brightness values are examined in detail through quantitative statistical analysis.
The change in brightness value of the Yalu River Estuary at night was examined in detail by dividing it into five stages. The monthly average images of July and August were analyzed using change detection techniques, and the Erdas Imagine 2022 version was used as a satellite image processing program. As an analysis technique, I applied the ‘Image Ratioing’ technique, which was evaluated as the most accurate in my old dissertation. If you look at the satellite image of the illumination change at the Yalu River Estuary above, you can see that nighttime lights have decreased significantly in the Sinuiju area. Pink and red colors, which indicate a decrease in the brightness of night lights, are widely observed in the Sinuiju area.
Jacob Bogle, an American private satellite expert, reported in a report by Radio Free Asia (RFA) last summer that heavy rains caused significant damage to power facilities, including electric barbed wire and utility poles, in the Yalu River area, resulting in loss and damage, resulting in a significant decrease in electricity supply in the area. It was evaluated that it appears to be Satellite images analyzing illuminance images also showed that red and pink colors with reduced nighttime light were widely spread throughout Sinuiju. It is assessed that the night-time power situation has worsened significantly as power facilities have been damaged. In the inland areas of North Pyongan Province, excluding the Yalu River, the night lights themselves are barely discernible and are believed to be immersed in a dark world.
Looking at the trend of increase and decrease in nighttime light area by city and county at the Yalu River Estuary, Sinuiju City (-18.6%) had the greatest power loss, followed by Yongcheon-gun (-5.3%) and Sindo-gun (-4.6%). Overall, it was analyzed that nighttime illumination decreased in an average of 10.7% of areas.
We looked at the changes in light brightness values across the three cities and counties using bar graphs. Although there are some places where the intensity of nighttime illumination has slightly increased, the heavy rain in July caused damage and loss of power facilities, and the overall nighttime power supply from July to August was greatly reduced, as shown in red and pink in the graph.
Looking at the table showing changes in nighttime light brightness values by three cities and counties, the maximum nighttime illuminance value in August decreased by 17.6% compared to July, and the average value decreased by 9%. The total of all brightness values decreased by about 10% overall, and Yongcheon-gun’s power reduction rate was found to be the largest at -12.8%. It is assessed that night-time power supply was relatively sluggish in the inland areas of Yongcheon-gun due to the focus on flood recovery in Sinuiju City and along the Yalu River.
As mentioned above, in relation to the heavy rain that occurred in North Korea last summer, the power loss situation at the mouth of the Yalu River was examined in detail from a different perspective using night-time illumination images. It has also been confirmed through the media that there was significant human and material damage in the Yalu River area. Although this study did not reveal anything particularly new, we hope that analysis using night-time illumination satellite data will be further developed along with in-depth research in the academic and security fields, and its use will increase.
Source: www.dailynk.com
