A possibility to monitor the reclamation activities by remote sensing was discussed. The lights observed in the night time by Day Night Band (DNB) of Visible Infrared Imaging Radiometer Suite (VIIRS), ocean color observed in the day time by visible bands of VIIRS were the tools to monitor the surface activities, and the Automated Information System (AIS) was used to verify the types and number of vessels associated with the reclamation activities. The lights as the radiance from the surface were monitored by the object based analysis, where the object was defined as a radius of 5 km from the center of the Mischief Reef in the South China Sea (SCS). The time history of surface lights exhibited the increase of the radiance from January to May 2015 and the radiance was kept in the certain level to December 2016 with some variations. The ocean color, chlorophyll-a concentration as a proxy of sediments, showed an increase from February to June 2015 and returned to a low concentration in August 2015. According to the historical data of AIS, the number of dredgers has increased from February to August 2015 and the maximum number of dredgers was recorded in June 2015. The timing of increase of lights from surface, increase of chlorophyll-a concentration, and increase of number of vessels are consistent.
The South China Sea (SCS) is the second largest semi-enclosed sea in the world and hosts a large marine ecosystem with the terrestrial inputs from rivers [
of the SCS, along the coast of China, Vietnam, and the archipelagoes of Philippine, Malaysia and Indonesia. The SCS region is rich in both renewal fisheries resources, particularly pelagic resources, and hydrocarbon resources [
The Day Night Band (DNB) of Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi-National Partnership Program (S-NPP) provides a panchromatic image of the surface in the night, integrating from 500 to 900 nm [
Current ocean color sensors in space used for monitoring the biochemical properties of ocean water including Moderate Resolution Imaging Spectro-radiometer (MODIS) on Terra and Aqua are near the end of their lifetimes [
The regulation 19 of the Safety of Life at Sea (SOLAS) requires the automatic identification system (AIS) to be fitted aboard all ships of 300 gross tonnage and upwards engaged on international voyages, cargo ships of 500 gross tonnage and upwards not engaged on international voyages and all passenger ships irrespective of size [
DNB on VIIRS provided a new era to observe the lights from the surface in the night-time and in the real-time. The DNB is a good tool to monitor the anthropogenic activities on the remotely located ocean. As the reclamation activities on SCS were the significant concerns for countries facing to SCS, a possibility of remote sensing by DNB, as a change of light intensity from the surface, and by the chlorophyll-a concentration, as a proxy of sediment concentration associated with the dredging activities, were examined. Those two remotely monitored parameters were validated with the AIS data, which report the number of vessels with its name, type, and other related information.
VIIRS data were received at the receiving station located on the Miyakojima Island, Japan, which has a coverage to the central part of SCS. The received data were processed to level-0, 1, and 2 by the International Polar Orbiter Processing Package (IPOPP) provided by the Direct Readout Laboratory of NASA. DNB data were extracted from the Geolocation data for DNB and Sensor data record of VIIRS for DNB. DNB data were mapped over the region of interest using the HDF to TiFF function of IPOPP. Radiance of DNB from 0.0 to 100.0 nW∙cm−2∙sr−1 is recorded on the GeoTiFF data.
The series of GeoTiFF data of DNB are opened on ArcMAP for the scale variable objective analysis based on the size of anthropogenic activities on the coral reefs in the SCS, as the point based analysis didn’t work to detect the temporal change of activities. The Mischief Reef was selected to study the possibility of analyzing the temporal changes of activities within the coral reef and including waters around the reef. The object size of the Mischief Reef was defined as a radius of 5 km from the center of reef.
Chlorophyll-a concentration is also derived from the observation by the visible bands of VIIRS over SCS using the level-2 generation function of IPOPP, and the region of interest is projected into GeoTiFF data by IPOPP. The level-2 generation algorithm was extracted from the Ocean Biology Processing Group’s Sea-viewing Wide Field-of-View Sensor (SeaWiFS) Data Analysis System and produces VIIRS Ocean Color, chlorophyll-a concentration, from inputs of VIIRS Sensor Data Record products, the VIIRS Moderate Resolution Terrain Corrected Geolocation products and optional ancillaries [
The series of GeoTiFF data of chlorophyll-a concentration are opened on ArcMAP for the scale variable objective analysis as well as DNB analysis. The object size was determined as a radius of 5 km from the center of reef.
The historic data of AIS over SCS from December 2014 to August 2015 with an interval of 5 days were purchased. Each AIS data are opened on ArcMAP and the data included within the region of interest was clipped, which is defined within a diameter of 5 km from the center of the coral reef. The clipped data was transformed into the excel format with a function to convert from the table to excel so as to identify the Maritime Mobile Service Identity (MMSI), ship category, and gross tone.
Reef and Chlorophyll-a concentration in January 2015 (
The profile of the radiance observed by DNB indicates that dredging activities started from January 2015, but it is difficult to identify the timing when the dredging had terminated. In contrast, the profile of Chlorophyll-a concentration indicates that the dredging activities started from January 2015 and terminated by July judging from the decrease of suspended particles associated with the dredging activities and the clear water was returned in August 2015
tanker, fishing boat, passenger boat, and unknown. Each line is corresponding to one MMSI through the period from December 2014 to August 2015. One tug boat was recorded on December 16 and 21, 2014. On January 1st, 2015, one fishing boat, one passenger boat and unknown vessel were recorded within the Mischief Reef. In the Mischief Reef, the passenger boat was the first time and the last time recorded on AIS in this period. The number of vessels was very small from the middle of December 2014 to February 2015. The number of vessels recorded 5 and increased since February 25, 2015 including dredgers and others. The maximum number of vessels was recorded 21 on June 20, 2015. The period of high chlorophyll-a concentration was from March to June 2015 as indicated on
AIS exhibited the intermittent records for all most of vessels, some of them might be conducting frequent visits from and to the Mischief Reef or there was a possibility some of their AIS being turned off. From the middle of June 2015, two tankers visited and one fishing boat stayed in the Mischief Reef. Some of AIS records showed only MMSI but its name or types are unknown, but those unknown vessels might have a contribution to the reclamation activities.
The dredging and reclamation activities on SCS was monitored using the lights from the surface observed in the night time by DNB of VIIRS, ocean color observed in the day time by visible bands of VIIRS, and were validated by the types of vessels of AIS record. The lights as the radiance from the surface were monitored and the object based analysis was executed, where the object was defined as a radius of 5 km from the center of the Mischief Island. The time history of surface lights exhibited the increase of the radiance from January to May 2015 and the radiance was kept in the certain level to December 2015 with some variations. The dredging period was not identified only from the lights from the surface. The ocean color, chlorophyll-a concentration as a proxy of sediments, showed an increase from February to June 2015 and returned a clear water in August 2015, which could be corresponding to the dredging period. According to the historical data of AIS, the number of dredgers has increased from February to August 2015 and the maximum number of dredgers was recorded in June 2015. The timing of increase of lights from surface, increase of chlorophyll-a concentration, and increase of number of vessels were consistent among them. The dredging activities started in February 2015, while the first dredger was recorded on AIS. The termination of dredging activities could be estimated from the decrease of chlorophyll-a concentration from June to July 2015, while the number of dredgers decreased in July 2015. The AIS data exhibited the intermittent data distribution in time sequence which might be caused by the AIS equipment on board being turned off, but the AIS data supported the validation of remote sensing data. It was confirmed that AIS record are very useful for the validation of remote sensing data analysis.
DNB is able to detect the lights from the surface regardless the size of light source with the sufficient intensity within each pixel. The objective analysis made it possible to identify the temporal change of the light history associated with the anthropogenic activities over the coral reef, although it was difficult to monitor the temporal change by pixel base analysis due to moving vessels. The chlorophyll-a concentration as a proxy of sediments detected the temporal change of ocean color associated with the dredging activities. The combination of two different types of observations made it possible to confirm the dredging activities. Finally, it is possible to estimate that the dredging activities were conducted from February to June 2015, of which period was validated with AIS records. The reclamation activities might have continued to December 2016 judging from the surface lights over the Mischief Reef, which kept the certain level in radiance including lights from the associated supporting vessels and the land activities.
This research is partly supported by the Office of Naval Research Global of the USA with the grant number of N62909-15-1-2074.
The authors declare no conflicts of interest regarding the publication of this paper.
Asanuma, I., Hasegawa, D., Yamaguchi, T., Park, J.G. and Mackin, K.J. (2018) Island Activities Detected by VIIRS and Validation with AIS. Advances in Remote Sensing, 7, 171-182. https://doi.org/10.4236/ars.2018.73012