# Geometric Processing and Accuracy Verification of Zhuhai-1 Hyperspectral Satellites
## 1 Introduction  
Orbita is deploying the \"Zhuhai-1\" remote sensing micro-nanostellite constellation, which will consist of 34 video, hyperspectral, radar, and infrared satellites distributed in different orbits [1]. The first batch of video satellites (OVS-1A, 1B) of the \"Zhuhai-1\" micro-nano constellation was launched successfully on 15 June 2017 and they have been in orbit for 1.5 years [2]. The second batch of satellites of the \"Zhuhai-1\" micro-nano constellation was successfully launched on 26 April 2018. The batch of satellites includes four Orbita hyperspectral satellites (OHS-A, OHS-B, OHS-C, and OHS-D) and one video satellite (OVS-2A), which have strong hyperspectral data acquisition abilities. A network of hyperspectral satellites has been realized in China for the first time [1]. Among them, four hyperspectral satellites have the same hardware configuration and operating status, and the cameras on each satellite are stitched together by three Complementary Metal Oxide Semiconductors (CMOS) sensors, with specific stitching on the focal surface, as shown in Figure 1.  
Figure 2 shows the spectrum structure for each CMOS sensor. Each piece of the CMOS contains 5056 \(\times\) 2968 pixels, and the imaging spectrum ranges from 400 to 1000 nm. In each CMOS sensor, the spectral average of 400-1000 nm is divided into 32 spectral segments through a filter, and each spectral segment occupies \(\leq\) 2968/32 = 92 rows on the sensor. Only eight rows are used for 8-level integral imaging. The hyperspectral satellite camera can acquire images with a 10-m resolution, 150-km width, and 32 spectrum segments. The single-start continuous sweeping work time is no less than 2 min and the one-track working time is no more than 8 min, with a global coverage ability within 5 days.  
The hyperspectral satellite platform is equipped with Global Navigation Satellite System (GNSS) receivers (supporting global positioning system (GPS) and Beidou) for measuring and downlinking the satellite position and speed. The satellite platform is equipped with three sensors and two sets of three-axis fiber optic gyroscopes. During the imaging stage, two sensors were used to observe the satellite attitude and the inertial attitude quaternion, processed by the sensor and gyro-Kalman filter, was transmitted to the ground station. The downlink frequency of the on-board GNSS and attitude data is 1 Hz. The main parameters of the four hyperspectral satellites are shown in Table 1.  
Figure 1: Schematic of the focal plane arrangement of the hyperspectral camera.  
Figure 2: Schematic of the CMOS sensor spectrum distribution.  
This paper presents the geometric processing methods involved in the production of Zhuhai-1 hyperspectral satellite basic products, including geometric calibration and basic product production algorithms. In the experiments, the OHS was geometrically calibrated and the spectral segment registration, single-view orientation, and regional adjustment accuracy of the basic products were evaluated. The results show that the geometric calibration accuracy of the Zhuhai-1 hyperspectral satellite is better than 0.5 pixels. The registration accuracy of the spectrum of the basic product is 0.3-0.5 pixels, the accuracy of the basic product image is better than 1.5 pixels, and the accuracy of the regional network adjustment is better than 1.2 pixels. The basic product has the ability to form large areas and can meet the application requirements.