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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.

The coordinated development of urban energy-economy-environment (3E) systems is an inherent requirement for high-quality and sustainable development of cities. Circulation degree and sustainable development degree (SDD) are combined to the previous 3E system evaluation system to construct the integrated sustainable development evaluation model. This model realizes the accurate evaluation of different dimensions of 3E system. Jinan, the capital city of Shandong Province in eastern China, is selected for empirical analysis. Findings show that development degree, circulation degree, and SDD of the 3E system in Jinan are increasing basically, and temporal trend of development degree and SDD of 3E system is synchronized. This shows that 3E system in Jinan has been improved gradually during this period, and the development of 3E system is a key factor affecting its sustainability. In 2015-2017, circulation degree and SDD were superimposed and developed in parallel, indicating that Jinan has entered the primary stage of high-quality development. The obstacle degree model is introduced to explore the main factors that impede the sustainable development of 3E system in Jinan. This study revealed that the energy consumption structure, the proportion of new energy utilization, the development of tertiary industry, and water resources protection are the key issues that should be addressed in the sustainable development of 3E system in Jinan. The top-level design concerning these issues should be highlighted in the forthcoming 14th five-year plan period.

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