Ocean remote sensing satellites: Protecting the source of life on Earth

Ocean remote sensing satellite

Marine remote sensing satellites are specialized satellites used for detecting marine elements and the marine environment, serving fields such as marine biological resource development and utilization, marine pollution monitoring and prevention, coastal zone resource development, and marine scientific research. Marine elements include ocean color, ocean dynamics, and maritime targets.

Composition and Classification of Ocean Remote Sensing Satellites

Ocean remote sensing satellites generally consist of a platform and payloads, typically carrying optical and microwave remote sensing payloads. Optical payloads generally include sea color and temperature instruments, coastal zone imagers, etc., mainly used for sea color and temperature detection, and are characterized by narrow spectral bands, high signal-to-noise ratio, low polarization, and large field of view. Microwave payloads include scatterometers, radiometers, altimeters, synthetic aperture radar, etc. Altimeters have high accuracy in measuring sea surface altitude, while other payloads feature large field of view and all-weather operation. Synthetic aperture radar also features high spatial resolution.

Based on their functions, ocean remote sensing satellites typically include ocean color satellites, ocean dynamics satellites, and ocean target monitoring satellites.

Ocean color satelliteMultispectral remote sensors are used to acquire seawater signals, with visible and near-infrared light used to obtain ocean color information and infrared light used to obtain ocean temperature information. This technology can be used to detect seawater chlorophyll concentration, suspended sediment content, soluble organic matter content, ocean temperature, and water ice. It can also be used for marine environmental monitoring, marine fisheries resource development and utilization, marine pollution monitoring, marine environmental assessment, protection of maritime rights, and global environmental change research.

Ocean dynamic satelliteBy transmitting radar signals and measuring the echoes, sea surface height and backscattering coefficient are determined, and sea surface wind speed and direction are retrieved. Passive microwave technology is used to measure the microwave radiation temperature of the sea surface to obtain sea surface temperature, and wind speed is retrieved from this data. It is mainly used for detecting sea surface wind fields, temperature fields, sea surface height, wave fields, and current fields.

To obtain global ocean wind vector field and surface wind stress data, as well as global high-resolution ocean circulation, ocean geoid, gravity field and polar ice sheet data.

Ocean target monitoring satelliteMicrowave synthetic aperture radar is used to acquire high-resolution, all-weather marine target information for real-time monitoring of maritime targets and the marine environment. It can acquire information such as ocean wave field, sea surface wind speed field, storm surge flooding, internal waves, sea ice, and oil spills, providing services for marine surveillance and law enforcement, coastal zone surveys, marine resource surveys and development, marine environmental monitoring and protection, and safeguarding of maritime rights.

Development History of Marine Remote Sensing Satellites

As countries around the world have increasingly emphasized marine scientific research, marine remote sensing satellites have undergone three distinct development stages, which can be broadly categorized as follows:

1970-1978 – Exploration PhaseThe main purpose is to use manned spacecraft to carry out experiments and to use meteorological satellites and land satellites to explore the ocean.

1978-1985 – Experimental PhaseDuring this period, the United States launched an ocean satellite and a Yuyun-7 satellite, both of which carried a coastal zone color scanner. Both satellites were experimental research satellites.

1985-Present - Application Research and Business Use PhaseDuring this period, a large number of ocean satellites were successfully launched. Ocean remote sensing satellites detect marine environmental information by carrying various remote sensors, and can be divided into ocean color satellites, ocean dynamic satellites, and ocean topography satellites according to their functions.

In the past decade or so, ocean satellites specifically designed for ocean observation, as well as those with partial ocean information observation capabilities, have begun to develop towards higher spatial resolution, higher temporal resolution, higher spectral resolution, higher signal-to-noise ratio, and higher stability. As a result, the reliance on ocean satellites for marine environmental monitoring and military and civilian applications has been continuously increasing.

China's research on marine remote sensing satellites started relatively late, but has developed rapidly, achieving significant progress after years of development. Based on the functional classification and detection technology capabilities of marine remote sensing satellites, my country's marine satellites are planned and developed according to three series: ocean color, marine dynamic environment, and marine surveillance.

On May 15, 2002, my country successfully launched its first ocean color observation satellite, Haiyang-1A, achieving a breakthrough in my country's ocean satellite program and significantly improving the level of ocean color information extraction. In the following 20 years, my country launched several ocean satellites, including ocean color satellites, ocean dynamic environment satellites, ocean surveillance and monitoring satellites, and the Sino-French ocean satellite. These satellites are equipped with ultraviolet, visible, infrared, active and passive microwave remote sensing payloads, as well as related auxiliary payloads. They can quickly acquire information on sea surface wind fields, wave fields, sea surface height fields, sea surface temperature fields, ocean color elements, and environmental information of islands and coastal zones. They can also acquire information on changes in polar ice caps, sea ice, large rivers and lakes, terrestrial vegetation, and forest fires. These satellites have great application potential in areas such as marine and terrestrial natural resource and environmental monitoring, and natural disaster monitoring, providing technical support for my country's marine environmental protection, marine resource development, sea area use management, maritime rights protection, and polar and ocean management.

Ocean-1 series satellites

It is used for global ocean color element detection, sea surface temperature detection and coastal zone dynamic environmental monitoring. It is equipped with optical remote sensing payloads, mainly for ocean detection, but also for land and sea. The payloads have advantages such as multiple spatial resolutions, high signal-to-noise ratio, high dynamic range and wide swath. The effective payload configuration includes a water color and temperature scanner, a coastal zone imager, an ultraviolet imager, a calibration spectrometer and an automatic identification system for ships.

Ocean-2 series satellites

It is used for all-weather monitoring of various marine dynamic environmental parameters such as global sea surface wind field, significant wave height, sea surface height, and sea surface temperature. It directly provides near-real-time remote sensing observation data for early warning and forecasting of hazardous sea conditions, and provides support services for marine disaster prevention and mitigation, protection of maritime rights and interests, marine resource development, marine environmental protection, marine scientific research, and national defense construction. Its effective payload includes radar altimeter, microwave scatterometer, scanning microwave radiometer, and calibration radiometer.

Ocean-3 series satellites

Used for all-weather monitoring of global ocean and land information, the payload is synthetic aperture radar. It can improve its rapid response capability and expand its earth observation range through left and right attitude maneuvers. The acquired C-band multi-polarization synthetic aperture radar images can be used in multiple fields such as ocean, disaster reduction, water conservancy and meteorology. It is an important technical support for my country to implement marine development, conduct land environmental resource monitoring and emergency disaster prevention and mitigation.

Sino-French Ocean Satellite

The international collaborative scientific research satellite between China and France has the primary mission of acquiring information on global sea surface wave spectra, sea surface wind fields, and polar sea ice to further enhance scientific understanding of the changing patterns of the marine dynamic environment; improve the accuracy and timeliness of forecasts for hazardous sea conditions such as giant waves, tropical storms, and storm surges; and acquire data related to polar ice sheets to provide fundamental information for global climate change research. The satellite utilizes a scatterometer provided by China and a spectrometer provided by France. Both sides have established their own ground systems but share data, fully embodying the characteristics of joint consultation, joint construction, and shared benefits, as well as the five major development concepts of innovation, coordination, green development, openness, and sharing.

Ocean remote sensing satellite applications

Marine remote sensing is mainly used to investigate and monitor ocean circulation, nearshore currents, sea ice, ocean surface current fields, harbor water quality, nearshore engineering, reclamation, suspended sediment, shallow water topography, coastal surface chlorophyll concentration, and other marine hydrological, meteorological, biological, physical, and hydrodynamic aspects, as well as marine pollution and nearshore engineering. It has become a major monitoring method and information source for the ocean and coastal zones. Through the application of marine remote sensing data, we can carry out remote sensing observations of marine dynamics, ocean geoids, shallow water topography and depth, ocean color, marine pollution monitoring, and sea ice observation.

As the breadth and depth of marine satellite remote sensing applications continue to expand, marine remote sensing applications will usher in the era of big data. Marine satellite remote sensing data will become an important data support for the construction of a smart ocean, a digital ocean, a transparent ocean, a digital China, and a maritime power.

Development Trends of Marine Remote Sensing Satellites：Improve observation accuracy and spatiotemporal resolution

Satellite observation accuracy and spatiotemporal resolution are crucial indicators for evaluating satellite observation and application capabilities. With the increasing sophistication of marine research and application capabilities, higher demands are being placed on the accuracy and spatiotemporal resolution of marine satellite observations. Advances in marine remote sensing and data processing technologies will continuously drive improvements in these indicators to meet relevant application needs. For example, expanding the observation spectrum of remote sensors improves spatial resolution and detection sensitivity, enhancing the accuracy of product data. Expanding the observation swath and employing constellation technology can improve the temporal resolution of global marine remote sensing coverage to the hourly level, while high-orbit marine satellites can improve regional observation resolution to the minute level.

Quantitative remote sensing is the development trend of ocean satellites.

Quantitative applications are a key characteristic of marine satellite data applications. Remote sensing products generated from marine satellite data, such as chlorophyll, suspended sediment, sea surface temperature, sea surface height, sea surface wind field, and wave field, all fall under the category of quantitative inversion applications. Reliable and comprehensive calibration techniques and verification methods are crucial to ensuring high-quality marine satellite data products.

Therefore, internationally, ocean satellites have established calibration and verification fields specifically for the calibration of ocean remote sensing payloads and the verification of the authenticity of data products. Meanwhile, the on-board calibration units of remote sensing payloads are becoming increasingly sophisticated, external calibration technology is maturing, and calibration accuracy is continuously improving, ensuring that the quantitative applications of ocean satellites can meet the growing demand.

Application-oriented on-board data autonomous processing technology is continuously improving.

The high dynamism of the ocean and the sparseness of the objects served on the sea surface mean that these objects cannot receive service products through data center stations like they do on land. To achieve real-time ocean remote sensing data services, the direct reception of remote sensing data products processed by satellites by the objects on the sea surface will become an important development direction for ocean satellites.

Actively develop new types of marine remote sensing payloads

Currently, countries worldwide are actively developing marine remote sensing payload technology, leading to a continuous increase in observable elements and improved measurement accuracy by marine satellites. This has expanded the application areas of satellites and significantly enhanced their overall application capabilities. The emergence of new marine remote sensing payloads can greatly improve the observation capabilities of marine targets, fully adapting to future application needs.

Today, my country's marine satellite system has been basically completed, and marine satellite remote sensing has entered the era of big data. It is believed that with the rapid development of remote sensing technology and the continuous launch of spacecraft, marine satellite remote sensing will play a vital role in global climate change research, tropical oceans, polar oceans and sea ice, marine productivity and ecosystems, air-sea interaction, marine disaster forecasting, marine fisheries, and coastal zone management, while also gaining greater development space and achieving more significant application results.

Some content in this article is sourced from:

Artificial Intelligence and Deep Learning, China Aerospace Science Popularization Network, China Science Popularization Expo

Lin Mingsen, Zhang Youguang, Yuan Xinzhe: Development History and Future Prospects of Marine Remote Sensing Satellites

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