Radiometric Cross-Calibration of the Wide Field View Camera Onboard GaoFen-6 in Multispectral Bands

Abstract

GaoFen6 (GF-6), successfully launched on June 2, 2018, is the sixth satellite of the High-Definition Earth observation system (HDEOS). Although GF-6 is the first high-resolution satellite in China to achieve precise agricultural observation, it will be widely used in many other domains, such as land survey, natural resources management, emergency management, ecological environment and so on. The GF-6 was not equipped with an onboard calibration instrument, so on-orbit radiometric calibration is essential. This paper aimed at the on-orbit radiometric calibration of the wide field of view camera (WFV) onboard GF-6 (GF-6/WFV) in multispectral bands. Firstly, the radiometric capability of GF-6/WFV is evaluated compared with the Operational Land Imager (OLI) onboard Landsat-8, Multi Spectral Instrument (MSI) onboard Sentinel-2 and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra, which shows that GF-6/WFV has an obvious attenuation. Consequently, instead of vicarious calibration once a year, more frequent calibration is required to guarantee its radiometric consistency. The cross-calibration method based on the Badain Jaran Desert site using the bi-directional reflectance distribution function (BRDF) model calculated by Landsat-8/OLI and ZY-3/Three-Line Camera (TLC) data is subsequently applied to GF-6/WFV and much higher frequencies of calibration are achieved. Finally, the cross-calibration results are validated using the synchronized ground measurements at Dunhuang test site and the uncertainty of the proposed method is analyzed. The validation shows that the relative difference of cross-calibration is less than 5% and it is satisfied with the requirements of cross-calibration.

A Novel Radiometric Cross-Calibration of GF-6/WFV With MODIS at the Dunhuang Radiometric Calibration Site

“…(9). It should be noted that, currently, for the GF series satellite sensor data, the calibration coefficient offset caused by the dark current and other factors has been eliminated (0 for each band), so the calibration coefficient only includes the gain value [5,10,18]:…”

“…In addition to four popular bands (blue, green, red and NIR), the WFV on the GF-6 satellite senses four new bands that are crucial for vegetation remote sensing research, including one coastal band (400-450 nm), one yellow band (590-630 nm) and two red-edge bands (690-730 nm and 730-770 nm). The ground sample distance (GSD) and swath of WFV images are 16 m and 800 km, respectively [5,14]. WFV images are freely downloaded from the CRESDA (http://www.cresda.com/CN/).…”

“…WFV images are freely downloaded from the CRESDA (http://www.cresda.com/CN/). Unlike the GF-1/WFV sensor, which uses four WFV cameras to acquire images with an 800km swath, the GF-6/WFV sensor only uses one camera to meet this demand [5,9]. MODIS, aboard the polar Terra satellite launched on December 18, 1999, can provide near-daily global coverage data with 36 bands and a 2330-km swath [15].…”

“…For instance, taking Landsat-8/OLI (operational land imager), MODIS and Sentinel-2/MSI (multispectral instrument) as the radiometric references, Gao et al applied the cross-calibration method to GF-4/VNIR (visible and near-infrared) at the DRCS, Dalate site and Baotou site, and estimated the degradation of GF-4/VNIR [4]. Yang et al evaluated the radiometric capability of GF-6/WFV by using Landsat-8/OLI image and DEM (digital elevation model) established with ZY-3/TLC (three-line camera) to develop the bidirectional reflectance distribution function (BRDF) of the Badain Jaran Desert site and implemented the cross-calibration of GF-6/WFV with the support of MOD05 and time-series MODIS data and validated the cross-calibration results using synchronized ground measurements at the DRCS [5]. Gao et al carried out a radiometric cross-calibration of FY-3C (feng yun-3C)/VIRR (visible infrared radiometer) based on the Suomi-NPP (suomi national polar-Orbiting Partnership)/VIIRS (visible infrared imaging radiometer suite) at the DRCS [6].…”

“…However, it is difficult to find an available reference sensor with the same band setting as GF-6/WFV, especially for the four new bands. Consequently, Yang et al only obtained the cross-calibration coefficients of GF-6/WFV in the blue, green, red and near-infrared (NIR) bands [5]. Therefore, the best way to optimize the cross-calibration method to obtain all calibration coefficients of GF-6/WFV for all eight bands, even without enough valid reference bands, should be determined to achieve the quantitative applications of this type of sensor.…”