Three-Year On-Orbit Radiometric Performance of the SDGSAT-1 Multispectral Imager (MSI)

This paper presents a comprehensive evaluation of the on-orbit radiometric performance of the Multi-spectral Imager (MSI) onboard the Sustainable Development Goals Science Satellite 1 (SDGSAT-1). Launched on November 5, 2021, SDGSAT-1 is the first scientific satellite dedicated to supporting the United Nations' 2030 Agenda for Sustainable Development. The study systematically assesses key radiometric performance parameters, including signal-to-noise ratio (SNR), radiometric resolution, uniformity, and absolute radiometric calibration accuracy. Results indicate that the B1-B3 bands exhibit good performance, with SNR exceeding 150 at high-reflectance sites (e.g., 309.5 for B1 over Gobi) and meeting requirements (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq$</tex-math></inline-formula>130 for B1, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq$</tex-math></inline-formula> 150 for B2-B7). However, B4-B7 bands show reduced SNR in low-reflectance regions (e.g., B5 SNR drops to 75.9 at LCFR Airport). Radiometric resolution remains stable for B1-B3 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\approx$</tex-math></inline-formula>1.0× 10<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-3}$</tex-math></inline-formula>), while B4-B7 display higher variability (up to 2.8× 10<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-3}$</tex-math></inline-formula>). Radiometric uniformity is better than 2% for B1-B4 but degrades to 4.3%–7.7% for B5-B7 due to detector response inconsistencies. Absolute calibration accuracy falls within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>7% for most bands, except B6 (7.2%<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>6.6%), meeting the design specifications. These findings indicate that SDGSAT-1 MSI has a relatively stable on-orbit status with its radiometric performance well met the requirement, except some saturation bands, i.e., B4, B5, and B7. Further efforts including enhanced calibration algorithms developing, cross radiometric calibration with payloads have good radiometric performance will be conducted. This paper provides critical insights into the operational characteristics of the MSI and offers a scientific basis for the long-term stability of satellite payloads and the reliability of data products, thereby supporting the achievement of global sustainable development goals.