On February 28, RADI conducted a space-air-ground based on-orbit absolute radiation calibration test for the NanoSat named Spark, which was developed by the Microsatellite Innovation Institute under CAS, and was launched on December 22, 2016. Spark, consisting of two small satellites Spark-01 and Spark-02, with onboard hyperspectral sensors, has covered the whole China's territory, and will be committed to the “Spectral China” program.
An 11-member RADI research team was sent to China Remote Sensing Satellite Radiation Correction Field in Dunhuang to collect the water body spectral data in Yemawan, spectral data in the Dunhuang calibration field, the solar radiation data and atmospheric parameters in the area around the calibration field, and the spectral data of typical ground objects.
The calibration test was conducted to monitor and modify the radiation characteristics of Spark, and update its radiation calibration co-efficient. The test will help to facilitate the quantitative application of the “Spectral China” Program.
Absolute radiation calibration means to convert the digital values recorded by sensors into absolute radiance values by establishing the quantitative relationship between the original DN values of a remote sensor and the radiance.
Through this test for Spark carried out in Dunhuang field, RADI researchers have obtained the absolute radiation calibration coefficient of the onboard remote sensors by synchronically measuring the atmospheric reflectance and surface reflectance on the ground and calculating the radiance of the remote sensor at the entrance pupil through radiative transmission, before and after the satellite entered China’s territory.
The accurate radiation calibration, which bridges gaps of satellite remote sensing between image-based qualitative application and absolute-radiation-based quantitative application, makes the “Spectral China” Program come true.
In addition, a Shanghai satellite application team from the Microsatellite Innovation Institute has made a plan on the imaging time and satellite attitude according to the precise orbit forecast.
Spark-02 acquired the data from within the area of the Dunhuang calibration field on February 28, and its downlink data was received by the station in the early hours of March 1. In the near future, RADI calibration team will conduct an absolute calibration test for Spark-01.
RADI’s calibration team in the Dunhuang field.
Solar radiation intensity is measured through the automatic solar photometer to calculate aerosol optical depth and water vapor content.
Satellite-ground synchronous spectral measurement of Yemawan water body.
The ratio of solar diffusion to total radiation is obtained by measuring the total ratio of solar diffusion.
Spectral measurement of typical ground objects.