Dr. En-chao Liu Profile

Dr. En-chao Liu

at Anhui-Ray Machine

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Publications (3)

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Proceedings Article | 12 December 2018 Paper

Development of automated observation radiometer for water-leaving radiance

Sheng-li Chen, Xin Li, En-chao Liu

Proceedings Volume 10850, 1085009 (2018) https://doi.org/10.1117/12.2504545

KEYWORDS: Radiometry, Calibration, Ocean optics, Satellites, Remote sensing, Spectroscopy, Optical design

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The water- leaving radiance (L_w) and remote sensing reflectance (R_rs)are not only the main apparent optic properties (AOPs) of water but also the basic parameters of ocean water color remote sensing. In order to realize the measurement of water- leaving radiance and remote sensing reflectance in the spectrum with the range from 300 nm to 900 nm, the high precision of the sea-surface radiance, the sky radiance and the sea-surface incident irradiance should be first obtained. The radiometer is composed of the measurement unit, control unit and tracking unit. The measurement unit is the core of the radiometer. Comparing with the previous tunnel radiometer, the measurement unit of the automatic observation radiometer is designed. In order to collect the spectral images of the incident slit into a plane, the radiometer uses flat-field concave grating for diffraction spectroscopy. And the linear array detector can detect the intensity signals of each spectrum simultaneously on the same plane. At the same time, in order to guarantee 10° field of view, the radiometer is equipped with the lens. It is also required to ensure the spectral observation principal plane make 135° with the principal plane so that it can avoid the influence of solar flares. In addition, the instrument shell adopts multi-layer coating treatment to avoid the erosion of the instrument structure parts by sea water and foggy sea atmosphere. After the spectrometer is installed, spectral calibration is done in the laboratory. The full width at half maximum of the radiometer is less than 4nm and the spectrum completely covers from 300nm to 900nm. The development of radiometer fills the gap of the automatic measurement of water- leaving radiance in China. It can inspect and correct satellite data and remote sensing products, and provide continuous and reliable on-site observation data for satellite remote sensing radiation calibration and product authenticity inspection.

Proceedings Article | 19 October 2016 Paper

Development of automated self-calibration spectra-radiometer

Xin Li, Li-na Xun, En-chao Liu, Yan-na Zhang, Wen-chao Zhai, Wei Wei, Quan Zhang, Gang-gang Qiu, Xiao-bing Zheng

Proceedings Volume 10155, 101553W (2016) https://doi.org/10.1117/12.2247557

KEYWORDS: Calibration, Spectral calibration, Reflectivity

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Test site vicarious calibration provides an absolute radiometric calibration for sensors. Surface reflectance is a critical parameter to be measured during a vicarious calibration field campaign. In order to realize long-term high precision observations of surface spectral reflectance in solar reflective bands, Automated Self-Calibration Spectra-Radiometer (ASCSR) was developed. ASCSR measures the global irradiance and the ground reflected radiance respectively with high spectral resolution from 400nm-2400 nm, the ratio of the two measurements is the surface reflectance. The degradation influences of instrument sensors and optical elements are removed by ratio-measurements and self-calibration. In the past two years ASCSR deployed in Dunhuang test site for continuous spectral reflectance measurements over 4 weeks. The measurements result of ASCSR is compared with traditional measurements which used SVC spectra-radiometer.

Proceedings Article | 19 October 2016 Paper

Measurements and analysis of solar direct irradiance-meter on Dunhuang radiometric calibration sites

En-chao Liu, Xin Li, Yan-na Zhang, Xiao-bing Zheng, Jing Yan

Proceedings Volume 10155, 101551M (2016) https://doi.org/10.1117/12.2246626

KEYWORDS: Atmospheric optics, Sensor calibration, Calibration, Atmospheric sensing, Sensors, Spectral calibration, Radio optics, Transmittance

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In order to realize the quantitative application of satellite remote sensing data and adapt to the demand of field calibration of hyper-spectral remote sensors, the solar direct spectral irradiance-meter was developed. According to the sampling principle of spectral irradiance, the irradiance-meter was designed with some technical improvements, the radiometric calibration based on system-level detector were adopted. Irradiance-meter took part in field calibration experiment on Dunhuang radiometric calibration sites and the correct data results were collected. The measurement results of spectral irradiance were consistent with simulated ground irradiance by MODTRAN model. The relative deviation of atmospheric optical depth(AOD) compared with solar radiometer CE318 was less than 4.84%. The whole day results of the irradiance observations and atmospheric transmission in the data applications were collected, the local atmosphere mode and the change of environment were reflected accurately, the input information of the atmospheric parameter were provided for the study of atmospheric properties and field calibration of remote sensors.

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