Comparing radar satellites. Use of Sentinel-1 leads to an increase in oil spill alerts in Norwegian waters
(2021) In Master Thesis in Geographical Information Science GISM01 20212Dept of Physical Geography and Ecosystem Science
- Abstract
- Radar’s ability to detect oil spills through clouds, fog, and darkness is a significant advantage. Oil spill alert services using radar satellites have been in use in Norway for more than 25 years. After introducing two radar satellites Sentinel-1A and 1B in 2015-2016, the number of oil spill alerts has increased by 250% in Norwegian waters. This increase does not track the slight decreasing trend in oil spills at sea detected by Norwegian remote sensing aircraft. It is also not consistent with the decreasing trends for both the number of oil spills and the yearly oil spill volume registered by international monitoring programs. One unconfirmed theory was that the new satellites could detect smaller-sized oil spills as they offered a... (More)
- Radar’s ability to detect oil spills through clouds, fog, and darkness is a significant advantage. Oil spill alert services using radar satellites have been in use in Norway for more than 25 years. After introducing two radar satellites Sentinel-1A and 1B in 2015-2016, the number of oil spill alerts has increased by 250% in Norwegian waters. This increase does not track the slight decreasing trend in oil spills at sea detected by Norwegian remote sensing aircraft. It is also not consistent with the decreasing trends for both the number of oil spills and the yearly oil spill volume registered by international monitoring programs. One unconfirmed theory was that the new satellites could detect smaller-sized oil spills as they offered a higher resolution radar.
Approximately 9400 satellite images from 2011-2018, with almost 3900 oil spill alerts, were analyzed to explain the increase in oil spill alerts. To estimate the additional mineral oil discharged into the sea after 2015, 25% of the oil spill alerts were analyzed by connecting oil spill alerts and sources, using historical ship tracks for Automatic Identification System (AIS) and oil and gas facility position data. Using In situ oil spill data from the offshore industy and having detailed information on the ships connected to the oil spills, substance discharged could be estimated. The result shows only a marginal increase in mineral oil (2.65%). Unknown substances not connected to any source, vegetable oils, and animal oils from ship activities mainly contribute to the increase. Hotspot analysis shows significant spatial clustering in oil spill alerts that overlap with offshore industry areas, fishing activities areas, and major shipping lanes.
To test the theory that the higher resolution radar sensor detects more minor-sized oil spills, a nonparametric test comparing Sentinel-1A/B to Radarsat-2 on oil slick size. The results show statistically significant differences in performance between Sentinel-1A/B and Radarsat-2 on small-size oil spills. A visual analysis by comparing radar images of Sentinel-1A and Radasrsat-2 on confirmed mineral oil slick shows how differently the two satellites detect small size oil slicks.
One challenge using radar for oil spill detections is “oil spill lookalikes” detections. The service provider uses likelihood settings for flagging an alert as mineral oil. The results show that confidence settings are inaccurate and therefore unsuitable for end-user operational applications without additional information. This thesis shows a need for further research regarding mineral oil and oil spill lookalikes. The thesis also concludes that service providers should further develop the use of ancillary source data to improve decision-making for end-users. (Less) - Popular Abstract
- Radar satellite sensors are designed to support different earth observation services, whereas oil spill services are one and have been used by Norway for more than 25 years. Radar’s ability to detect oil spills through clouds, fog, and darkness is a significant advantage. However, a challenge using radar for oil spill detections is “oil spill lookalikes” detections. Would new higher-resolution satellites make the task of sorting actual oil spills from “oil spills lookalikes,” or will it add to the challenge?
A trend shift occurred when the two Sentinel-1 satellites were implemented in the oil spill services in late 2015 and 2016. There was a significant increase in oil spill alerts of nearly 300% in Norwegian waters from 2015 to 2018.... (More) - Radar satellite sensors are designed to support different earth observation services, whereas oil spill services are one and have been used by Norway for more than 25 years. Radar’s ability to detect oil spills through clouds, fog, and darkness is a significant advantage. However, a challenge using radar for oil spill detections is “oil spill lookalikes” detections. Would new higher-resolution satellites make the task of sorting actual oil spills from “oil spills lookalikes,” or will it add to the challenge?
A trend shift occurred when the two Sentinel-1 satellites were implemented in the oil spill services in late 2015 and 2016. There was a significant increase in oil spill alerts of nearly 300% in Norwegian waters from 2015 to 2018. In 2018 Norway received an average of nearly four oil spill alerts per day. Also, The Norwegian Coastal Administration, responsible for following up on acute oil pollution, could not recognize the same trend comparing other sources of monitoring and information. One plausible theory was that the new satellites could detect smaller-sized oil spills as they offered higher resolution radar images. Another question raised was how many of these additional oil spill alerts are mineral oil, and where do they originate from? Moreover, by using higher-resolution satellites, is the oil spill service better in sorting mineral oil from mineral oil lookalikes?
More than 3500 oil spill alerts from more than 9000 satellite images over eight years within Norwegian waters have been used in this study. The results show that Sentinel-1 performs better than lower-resolution satellites on detecting small-sized oil slicks. Two years of ship movement data were also analyzed to see how many oil spill alerts related to shipping discharges. A significant increase in ship-related oil spill alerts was recorded after the implementation of Sentinel-1. However, most of the increase connects to ship-types allowed discharging animal or vegetable oils under certain conditions. The analysis actually shows a 29 percent decrease in mineral oil from ship-related spills after implementing Sentinel-1. On the other hand, oil spill alerts connected to the Norwegian offshore industry show a 36 percent increase. Still, in sum, there is only a marginal increase in mineral oil detected, where oil spill lookalikes, vegetable, and animal oils mainly contribute to the increase. The study also shows that when a service provider red flags oil spill alerts to be mineral oil, higher resolution sensors do not improve sorting the observations from “oil spill lookalikes.” One suggestion for improving the service is to implement more complementary source data in the analyses as much of the mineral oil “false alerts” was oil, but not mineral oil. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9068325
- author
- Njøten, Ove LU
- supervisor
- organization
- course
- GISM01 20212
- year
- 2021
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Geography, GIS, Satellite, Radar, Oil spill
- publication/series
- Master Thesis in Geographical Information Science
- report number
- 136
- language
- English
- id
- 9068325
- date added to LUP
- 2021-11-22 15:16:29
- date last changed
- 2021-11-22 15:16:29
@misc{9068325,
abstract = {{Radar’s ability to detect oil spills through clouds, fog, and darkness is a significant advantage. Oil spill alert services using radar satellites have been in use in Norway for more than 25 years. After introducing two radar satellites Sentinel-1A and 1B in 2015-2016, the number of oil spill alerts has increased by 250% in Norwegian waters. This increase does not track the slight decreasing trend in oil spills at sea detected by Norwegian remote sensing aircraft. It is also not consistent with the decreasing trends for both the number of oil spills and the yearly oil spill volume registered by international monitoring programs. One unconfirmed theory was that the new satellites could detect smaller-sized oil spills as they offered a higher resolution radar.
Approximately 9400 satellite images from 2011-2018, with almost 3900 oil spill alerts, were analyzed to explain the increase in oil spill alerts. To estimate the additional mineral oil discharged into the sea after 2015, 25% of the oil spill alerts were analyzed by connecting oil spill alerts and sources, using historical ship tracks for Automatic Identification System (AIS) and oil and gas facility position data. Using In situ oil spill data from the offshore industy and having detailed information on the ships connected to the oil spills, substance discharged could be estimated. The result shows only a marginal increase in mineral oil (2.65%). Unknown substances not connected to any source, vegetable oils, and animal oils from ship activities mainly contribute to the increase. Hotspot analysis shows significant spatial clustering in oil spill alerts that overlap with offshore industry areas, fishing activities areas, and major shipping lanes.
To test the theory that the higher resolution radar sensor detects more minor-sized oil spills, a nonparametric test comparing Sentinel-1A/B to Radarsat-2 on oil slick size. The results show statistically significant differences in performance between Sentinel-1A/B and Radarsat-2 on small-size oil spills. A visual analysis by comparing radar images of Sentinel-1A and Radasrsat-2 on confirmed mineral oil slick shows how differently the two satellites detect small size oil slicks.
One challenge using radar for oil spill detections is “oil spill lookalikes” detections. The service provider uses likelihood settings for flagging an alert as mineral oil. The results show that confidence settings are inaccurate and therefore unsuitable for end-user operational applications without additional information. This thesis shows a need for further research regarding mineral oil and oil spill lookalikes. The thesis also concludes that service providers should further develop the use of ancillary source data to improve decision-making for end-users.}},
author = {{Njøten, Ove}},
language = {{eng}},
note = {{Student Paper}},
series = {{Master Thesis in Geographical Information Science}},
title = {{Comparing radar satellites. Use of Sentinel-1 leads to an increase in oil spill alerts in Norwegian waters}},
year = {{2021}},
}