## 1 Introduction  
In recent years, with the gradual implementation of China's commercial space policy, several Chinese commercial remote sensing satellites have been launched by commercial companies. The Zhuhai-1 constellation from Orbita, Zhuhai, China is composed of 12 satellite missions, including eight hyperspectral satellites. The first four satellites were launched on 26 April 2018, and the remaining four satellites were launched on 19 September 2019. The Orbita Hyperspectral Sensor (OHS) on board each micro-nano satellite has similar electro-optics, with three complementary metal oxide semiconductor (CMOS) detectors designed with eight integration stages. To maintain reduced costs, none of the satellites are equipped with on-board calibrators (OBCs). Therefore, the combination of multiple CMOS detectors and multiple integration level settings makes the on-orbit radiometric calibration of the Zhuhai-1 micro-nano hyperspectral satellite constellation extremely complex and difficult. The sensor parameters are shown in Table 1.  
Zhuhai-1 constellation calibration and validation (Cal&Val) tasks are used to calibrate all of the CMOS detectors for all of the integration stages. In addition, it is essential to ensure that data from different OHSs in the whole Zhuhai-1 constellation are of high quality and consistency. Vicarious calibration [1] (VC) based on site campaigns is one of the current state-of-the-art radiometric calibration methods used for optical satellite sensors. Several calibration sites (e.g., Dunhuang, Baotou) are located in China and have been regularly used for the radiometric calibration of Chinese satellites. However, site campaigns are so expensive and labor-intensive that the frequent VC of all of the Zhuhai-1 OHSs is an impossible task. The radiometric calibration of similar satellite constellations, such as the SkySat constellation from Planet, is conducted using the Libya site without field measurements [2]. The bottom of atmosphere (BOA) data used to simulate TOA values are generated from Sentinel-2 BOA reflectance time series. Cross-calibration [3] is another important and widely used method that can be used for the radiometric calibration of most optical sensors. Usually, simultaneous or near-simultaneous observations from different satellite sensors are used to derive the calibration coefficients through band-by-band comparisons. As site measurement is not required, it can be used at high frequencies and is associated with low costs. For example, the Dove constellation is calibrated using cross-calibration with RapidEye, and it is validated using cross-calibration with Landsat and Sentinel, with lunar, and with RadCalNet site measurements. The choice of high-precision reference sensors is critical for cross-calibration [4]. Regarding hyperspectral sensors on board the Zhuhai-1 constellation, it is very difficult to match suitable reference bands for all of the calibrated bands. The radiometric calibration network [5,6] (RadCalNet) was initiated by the Working Group on Calibration and Validation (WGCV) of the Committee on Earth Observation Satellites (CEOS) in 2014. Moreover, the ground observation data of RadCalNet have been shown to be accurate and effective [7,8], and the data can be widely used in the radiometric calibration of satellite sensors such as visible light and near-infrared sensors [9, 10, 11]. The aim of RadCalNet is to provide a time-continuous, SI-traceable top-of-atmosphere (TOA) reflectance product to satellite operators, at a 10 nm spectral sampling interval, in the spectral range of 380 nm to 2500 nm. Currently, there are five sites involved in RadCalNet, which are located in the United States, France, Namibia, and China. Each site is equipped with automated ground instruments that are used to measure surface and atmospheric parameters for the simulation of TOA reflectance. The uncertainty associated with RadCalNet BOA reflectance, TOA reflectance, and atmosphere parameters is presented in the