Satellite Imagery can be used effectively for several workflows - I have already written about Climate Monitoring & Land Monitoring before working on this post (April 2020). In this study, I have attempted Ship Detection using Remote Sensing in a) the Gulf of Kutch using Sentinel-1 SAR Satellite Imagery with the intention to see the extent of negative change in maritime activity due to the prevalent Coronavirus lockdown conditions and in b) the Suez Canal in the aftermath of the massive Ever Given container cargo vessel's stranding.
My aim through this professional blog is to demonstrate, using small and relatable studies, the scope and benefits of deploying Location Intelligence with the ultimate objective to monitor and improve Operations and Business Processes.
The two cases covered in this post can be accessed using the Section hyperlinks below:
SHIP DETECTION IN THE GULF OF KUTCH IN INDIA TO STUDY THE EXTENT OF REDUCED ECONOMIC ACTIVITY DUE TO CORONAVIRUS LOCKDOWN
The result of the Ship Detection study is depicted in the map below - More than 33% reduction in maritime activity has been observed in the Gulf of Kutch based on the count of Ships detected.
I have used Sentinel-1A GRD data for this study.
Much thanks to RUS Copernicus and Open Street Map for the invaluable training material
How is Object Detection possible from Satellite Imagery? And how accurate can it be?
The Imagery has been captured by Sentinel-1A satellite which has a Spatial Resolution of 5m by 20m. The parameter for objects to be detected was kept at a minimum of 30m in length. Reducing it further would increase the number of False Detections i.e. some objects would be classified as ships but would not be Ships in reality but other objects at sea.
The principle behind Object Detection from Aerial Imagery is how electromagnetic waves interact with Surface features on Earth. A ship appears brighter to the C-SAR instrument on-board the Sentinel-1 satellite as compared to Water in the vicinity, which is darker - refer the visual below. CFAR algorithm was one of the techniques used during the Processing workflow - the same methodology can be used to detect Icebergs in polar regions.
The extent of accuracy depends on Geological factors, characteristics of the Satellite instrument, methodology of processing the Imagery dataset, and even having local knowledge about the Area of Observation.
How to interpret these results?
A reduction in maritime activity was expected and ~37% seems plausible to me. Certain aspects to note, however, are-
a) Not all objects are Commercial Cargo vessels or Crude-carrying Vessels. Some 30m+ objects can also be Fishing Vessels, Port Security Vessels, Navy Vessels, Tourism Vessels, Pirate Vessels! or even false detections. However, one can safely assume that the Vessels clustered around Mundra Port and Kandla Port - major maritime hubs in this region - would be Commercial Cargo vessels - harbingers of trade. Also, with the Object Size of 30m that I have used as a parameter in this study, a lot of Shipping objects of the non-Commercial variety would be filtered out as well. Everything else set aside, the difference in Ship count between the two Imagery products - 148 - is a significant number.
b) Not all Shipping Objects detected are Active i.e. moving vessels. As you would notice, a fair number of Ships are clustered around the Kutch Coastline. Several of them could be docked, dysfunctional or undergoing maintenance.
c) The comparison has been done during two points in time, one year apart. Adding more observations i.e. performing a Multi-temporal analysis would have helped in drawing better inferences about maritime activity.
SHIP DETECTION IN THE SUEZ CANAL IN EGYPT TO STUDY THE MARITIME ACTIVITY PRE, DURING & POST THE EVER GIVEN SHIP STRANDING
The grounding of Ever Given - the Taiwanese Mega Container Vessel at the southern end of the Suez Canal in Egypt and the resulting blockage in Maritime Activity in this narrow but vital Shipping route which accounts for 12% of the world's trade, has sent economic shockwaves across the world, including in India. This unfortunate incident is an acute reminder of the interdependency involved in the globalized world we live in today and how it can trigger Supply Chain disruptions.
Drawing inspiration from a wonderful initiative from Google Earth - the 'Timelapse', here is my short Timelapse version of Maritime Activity in the Suez Canal over the last month, as detected using Sentinel-1 SAR (Radar) Imagery.
Video Case: Detecting Ships in the Suez Canal - Pre, During & Post the Ever Given Cargo Vessel stranding
What are some of the other applications of Object Detection on Water Bodies using Satellite Imagery?
Satellite Imagery, when combined with other tools, are used by Security management professionals to compare the reported records of Vessel whereabouts (mandatory for ships above a certain size) with the number of actual Vessels detected at sea derived from Satellite Imagery Analytics. This is done to spot the presence of and track 'Dark Ships' i.e. those that do not report their location and direction information - these may be participating in Smuggling / Illegal activities or could even pose a threat to National Security. Icebergs and Oil Spills can also be detected and monitored using Object Detection algorithms.
Refer my Remote Sensing work here - you'll are sure to find a few new use cases involving Object Detection every now and then.
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