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On-orbit Calibrator’s First Show on FY-4 Satellite TEXT SIZE: A A A
Date:2017.02.22 Author:SI Xiaolong Clicks:

Last winter, China's new generation of geostationary meteorological satellite FY-4 was successfully launched in the Xichang Satellite Launch Center with Long March 3 B carrier rocket, in which scanning imaging radiometer (SIR) is one of four important loads. SIR is an important tool to catch the spectral radiometric information of the earth's surface and clouds to improve the accuracy of weather forecasts and climate observations. And the on-orbit calibrator developed by a joint team played its first show on satellite FY-4 to ensure the precision of SIR.

As for the precision of SIR, the credit definitely should go to the calibrator. If the “camera” of SIR on the meteorological satellite in vast space is sharp "lens" of insightful changes, the calibrator should be the "Lens cleaning cloth" to wipe the "lens" and keep the "lens" clear and bright.

The on-orbit calibrator was jointly developed by Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science (AIOFM) and Shanghai Institute of Technical physics (SITP). Now it is operated in the scheduled orbit.

It is amazing that this calibrator is the first one in China to achieve all-optical satellite calibration in the geostationary. It provides a high-precision radiation reference for satellite remote sensor to realize high-precision all-optical radiation calibration by the use of the solar diffuser with the ratio of radiation monitoring methods, i.e., by using the stable sun as the calibration light source, and the diffuser high-accurately BRDF-measured on ground, to obtain the alignment measurement of monitoring diffuser plate.

It is evident that during the satellite launch and on-orbit operation, the optical sensor system gradually attenuates and affects the quantitative accuracy of the remote sensor detection due to such factors as the vibration, the change of the ambient temperature, the environment of the electromagnetic radiation in space, and so on.

However, the satellite in-orbit lifetime is usually 5-8 years. How to ensure high accuracy of the satellite load during its lifetime? Scientists tried a variety of methods to calibrate the accuracy of the instrument in real-time.

Generally, most of the satellites launched in China adopt the method of ground substitute calibration, which needs to calculate the atmospheric radiation transmission and the signal passes through the atmosphere twice. The uncertainty of radiation calibration is generally 5% ~ 7%.

Differently, AIOFM and SITP equipped the FY-4 satellite multi-channel scanning imaging radiometer with a solar diffuser on-board calibrator based on the radiation, which provides real-time normalized on-orbit reflectance band radiation calibration for satellite load. The signal need not pass through the atmosphere. And the expected radiation calibration uncertainty of 3% to 5%, which provides a strong guarantee for the accuracy of the load, and do improve the accuracy of FY-4 satellite weather forecast.

                   

                    

                      

                         FY-4 schematic diagram (Image by Aerospace Science and Technology Group Eighth Research Institute) 

                                                                

                                                                          

FY-4 satellite launch (Image by Xinhua Internet)

 

 

 

 

 
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Email: aio@aiofm.ac.cn Tel: +86-0551-65591539 Fax: +86-0551-65591572