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This paper aims to present the optical system of the Multispectral Camera MUX that is part of the payload for the CBERS 3 & 4 satellite (China Brazil Earth Resources Satellite). The CBERS program was created by Brazil and China for the development of Earth remote sensing satellites. The MUX camera is being developed by the Brazilian company OPTO ELETRÔNICA S.A. and consists of a multispectral camera with four spectral bands covering the wavelength range from blue to near infrared (from 450nm to 890nm) with a ground resolution of 20m and a ground swath width of 120 km. Besides MUX camera (optical system, signal processing electronics and mechanical frame), this company is also developing the Ground Support Equipment -GSE of this camera and is responsible for structural and environmental tests. At the moment, the project is in the Qualification Model (QM). During this phase of the development, the camera shall be submitted to several tests, including environmental, optical and structural tests with the objective of qualify the project and start the flight models manufacturing.

The purpose of this paper is to present the optical system developed for the Wide Field imaging Camera -WFI that will be integrated to the CBERS 3 and 4 satellites (China Brazil Earth resources Satellite). This camera will be used for remote sensing of the Earth and it is aimed to work at an altitude of 778 km. The optical system is designed for four spectral bands covering the range of wavelengths from blue to near infrared and its field of view is ±28.63º, which covers 866 km, with a ground resolution of 64 m at nadir. WFI has been developed through a consortium formed by Opto Electrônica S. A. and Equatorial Sistemas. In particular, we will present the optical analysis based on the Modulation Transfer Function (MTF) obtained during the Engineering Model phase (EM) and the optical tests performed to evaluate the requirements. Measurements of the optical system MTF have been performed using an interferometer at the wavelength of 632.8nm and global MTF tests (including the CCD and signal processing electronic) have been performed by using a collimator with a slit target. The obtained results showed that the performance of the optical system meets the requirements of project.

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Abstract-The first Brazilian remote sensing multispectral camera (MUX) is currently under development at Opto Eletrônica S.A. It consists of a four-spectral-band sensor covering a 450nm to 890nm wavelength range. This camera will provide images within a 20m ground resolution at nadir. The MUX camera is part of the payload of the upcoming Sino-Brazilian satellites CBERS 3&4 (China-Brazil Earth Resource Satellite). The preliminary alignment between the optical system and the CCD sensor, which is located at the focal plane assembly, was obtained in air condition, clean room environment. A collimator was used for the performance evaluation of the camera. The preliminary performance evaluation of the optical channel was registered by compensating the collimator focus position due to changes in the test environment, as an air-to-vacuum environment transition leads to a defocus process in this camera. Therefore, it is necessary to confirm that the alignment of the camera must always be attained ensuring that its best performance is reached for an orbital vacuum condition. For this reason and as a further step on the development process, the MUX camera Qualification Model was tested and evaluated inside a thermo-vacuum chamber and submitted to an as-orbit vacuum environment. In this study, the influence of temperature fields was neglected. This paper reports on the performance evaluation and discusses the results for this camera when operating within those mentioned test conditions. The overall optical tests and results show that the "in air" adjustment method was suitable to be performed, as a critical activity, to guarantee the equipment according to its design requirements.