How does this satellite measure ocean salinity
2024-11-15
On November 14th, China's first ocean salinity detection satellite, developed by the Fifth Academy of China Aerospace Science and Technology Corporation, was successfully launched, marking an important step forward in the field of ocean dynamic environment observation and filling the gap in the ocean salinity detection capability of China's ocean dynamic satellite series. The reporter learned from the Fifth Academy that the marine dynamic environment includes various factors such as temperature, salinity, depth, wind, waves, and currents, among which measuring ocean salinity is a major challenge. In the past, China mainly obtained first-hand ocean salinity data through ocean research vessels or drifting buoys, with limited data coverage and observation continuity. At present, there is no large-scale continuous and stable high-precision ocean salinity detection data worldwide. After more than 10 years of dedicated efforts, the satellite development team of the General Department of the Fifth Academy of Remote Sensing Satellites has successively overcome key technologies such as high-precision and high stability L-band receivers, active passive joint electromagnetic compatibility, large-size high-precision antenna deployment, ocean salinity data preprocessing and inversion, and comprehensive aperture radiometer external calibration technology. This has enabled China to have an independent, controllable, high-precision, and highly continuous global ocean salinity data source. The researchers introduced that the use of satellite remote sensing methods to detect ocean salinity is mainly achieved by inverting the microwave radiation brightness temperature data of the sea surface obtained by satellites. However, the amplitude of brightness temperature changes is very small, and the detection is often affected by multiple factors. Therefore, high-precision ocean salinity detection from space has always been a world-class problem. Brightness temperature is a physical quantity that measures the intensity of microwave radiation on the sea surface, which varies with changes in ocean salinity and can be measured by receiving microwave radiation signals from the sea surface using a microwave radiometer. However, factors such as sea surface temperature, sea surface roughness, and human signal interference can all affect the accuracy of microwave radiometer measurements. In order to eliminate various interferences as much as possible, the researchers designed multiple remote sensing joint detection schemes and equipped the satellite with three types of remote sensing payloads: comprehensive aperture microwave radiometer, active and passive detectors, and spectrum monitoring instruments, which can synchronously measure various influencing factors of ocean salinity. This enables ocean salinity detection satellites to "observe, smell, and examine" the global ocean like traditional Chinese medicine, comprehensively obtaining the data required for ocean salinity detection. 'Wang' refers to the continuous observation of the global ocean by a satellite station from a 'space perspective'. Wen "is an important task of satellites, carrying several payloads for" listening "to microwave signals on the sea surface. The comprehensive aperture radiometer has selected the L-band, which is more sensitive to changes in sea surface brightness temperature, has longer wavelengths, and lower frequencies. Based on the principle of equivalent synthesis of large aperture antenna effects using small aperture antenna arrays, it listens to the "low voice" brightness temperature information of the sea surface; The passive detector in the active passive detector consists of three microwave radiometers in the L, C, and K bands, which respectively listen to the "low, medium, and high" parts of the sea surface. Among them, C-band and K-band signals can help achieve inversion of sea surface temperature data. The 'question' is completed by the spectrum monitor. Due to the fact that the L-band mainly used by satellites is also the working band for mobile communication, Beidou navigation, etc., the signals received by L-band microwave radiometers are often interfered by human activity signals. The spectrum monitor can not only listen to microwave signals on the sea surface and distinguish "timbre", but also identify location, as if asking "where the interference source is", and accurately lock in interference information to help researchers eliminate radio frequency interference. 'Cut' is the only active action of the satellite, which is completed by the active instrument of the active passive detector - the L-band microwave scatterometer. It detects the roughness of the sea surface by emitting microwave signals to the sea surface and measuring the backscattering coefficient of the signal when encountering sea waves, just like reaching out to "touch" the "skin condition" of the sea surface. Through the "observation, listening, questioning, and cutting" method, ocean salinity detection satellites obtain information such as sea surface brightness temperature, sea surface temperature, sea surface roughness, and radio frequency interference, and provide it to ground stations. Ground staff then process the data and deduce ocean salinity information. (New Society)
Edit：Yao jue Responsible editor：Xie Tunan
Source：Science and Technology Daily
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