The Korea Institute of Ocean Science and Technology (KIOST) has announced that Cheollian-1, developed with Korea’s own technology and the world's first geostationary satellite for observing ocean color (GOCI^*), can provide more accurate satellite data for analyzing the concentration of phytoplankton in East Asian seas than either MODIS^* or VIIRS^*, which are NASA’s polar orbiting satellites for ocean color observation. The results of measurements by the First Geostationary Ocean Color Satellite (GOCI) have been published in an international academic journal^*.
* A payload onboard a satellite for observing marine phenomena, including red and green algae, by optically analyzing the color of the ocean
* MODIS/Aqua: NASA’s polar satellites for ocean-atmosphere-land observation (2002-present)
* VIIRS/NPP: NASA’s polar satellites for ocean-atmosphere-land observation (2011-present)
* Remote Sensing, Vol. 14, Iss. 1 (January-1, 2022),  (Article Title: Decadal Measurements of the First Geostationary Ocean Color Satellite (GOCI) Compared with MODIS and VIIRS Data)

Although phytoplankton is very small, it is spread across approximately 70% of the ocean’s surface, playing an important part in efforts to analyze climate change as a whole, as well as environmental changes in marine ecosystems. In addition, the Cheollian-1 observes the seas of East Asia (an area approximately 2,500 km × 2,500 km), including around the Korean Peninsula, which is one of the world’s regions most affected by climate change. The Yellow Sea and its marine environment have been especially impacted due to the rapid industrialization and high population densities of the nations around it.

Senior Researcher Park Myung-sook and her research team have observed the change in the value of chlorophyll-a concentration^*, which is used as basic calculation data in remote ocean color research, for over 10 years (June 2010 to March 2021) during which the Cheollian-1 mission operated. She compared the Cheollian-1 results to those from MODIS and VIIRS, finding that Cheollian-1 accurately analyzed seasonal changes in the four seasons over the 10-year period, while MODIS tended to overestimate chlorophyll-a concentrations in the spring when yellow dust occurs, and VIIRS did not show the spring plankton bloom* in spring very well over the same period.
* This is a photosynthetic pigment of phytoplankton produced from absorption of various nutrients and carbon dioxide from the ocean. It is used as an indicator of the status of marine ecosystems and global climate change.
* Phytoplankton occurs in larger quantities in spring than in winter, due to more favorable environmental conditions.

The better results from calculation using Cheollian-1 are possible because it is a geostationary satellite that can observe a specific sea area for one hour, 8 times a day, whereas MODIS and VIIRS can observe a specific sea area only once a day as they are designed to observe sea areas around the globe. Of particular note is that, while NASA has developed MODIS and other polar satellites to produce data on clear oceans, such as the Pacific and Atlantic, KIOST has developed a technology that can precisely analyze Korean oceans and their higher concentrations of fine dust and turbidity.
KIOST President Kim Woong-Seo said, “We are proud to have developed, using our own technology, the world's first geostationary ocean satellite, whose excellence has been proven to the world through the achievements from the satellite’s 10-year mission.” He added “KIOST will respond to current maritime issues including floating algae and red tides, and produce more accurate satellite data for scientific diagnosis of the impact of climate change on changes in the ocean.”
KIOST, the operating agency of Cheollian Satellite payloads, will continue to improve the accuracy of Cheollian-1 outputs, to be followed by the output from Cheollian-2B (GOCI-II)^*, launched in February 2020, and to develop technology to make ever-better use of such output in the future.
* Observation occurs 10 times a day, with a 13-band spectral resolution and a 250m spatial resolution. It produces 26 types of sea, air, and land data.