Development of the Chinese Space-Based Radiometric Benchmark Mission LIBRA

Abstract

<jats:p>Climate observations and their applications require measurements with high stability and low uncertainty in order to detect and assess climate variability and trends. The difficulty with space-based observations is that it is generally not possible to trace them to standard calibration references when in orbit. In order to overcome this problem, it has been proposed to deploy space-based radiometric reference systems which intercalibrate measurements from multiple satellite platforms. Such reference systems have been strongly recommended by international expert teams. This paper describes the Chinese Space-based Radiometric Benchmark (CSRB) project which has been under development since 2014. The goal of CSRB is to launch a reference-type satellite named LIBRA in around 2025. We present the roadmap for CSRB as well as requirements and specifications for LIBRA. Key technologies of the system include miniature phase-change cells providing fixed-temperature points, a cryogenic absolute radiometer, and a spontaneous parametric down-conversion detector. LIBRA will offer measurements with SI traceability for the outgoing radiation from the Earth and the incoming radiation from the Sun with high spectral resolution. The system will be realized with four payloads, i.e., the Infrared Spectrometer (IRS), the Earth-Moon Imaging Spectrometer (EMIS), the Total Solar Irradiance (TSI), and the Solar spectral Irradiance Traceable to Quantum benchmark (SITQ). An on-orbit mode for radiometric calibration traceability and a balloon-based demonstration system for LIBRA are introduced as well in the last part of this paper. As a complementary project to the Climate Absolute Radiance and Refractivity Observatory (CLARREO) and the Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS), LIBRA is expected to join the Earth observation satellite constellation and intends to contribute to space-based climate studies via publicly available data.</jats:p>

Algorithm Stability and the Long-Term Geospace Data Record from TIMED/SABER

“…Lack of continuity and/or lack of measurement accuracy can render it nearly impossible to construct a long-term CDR or GDR with a scientifically (or economically) useful trend accuracy (e.g., Loeb, Wielicki et al, 2009). The tropospheric climate community is going to great lengths to achieve extremely high accuracy (and hence, extremely stable calibration) in the next generation of satellite-based climate missions with the Climate Absolute Radiance and Refractivity Observatory (CARREO) Pathfinder mission, the Traceable Radiometry Underpinning Terrestrial-and Helio-Studies (TRUTHS) mission, the LIBRA mission, and the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission (Shea, Fleming, et al, 2020;Fox, Kaiser-Weiss, et al, 2011;Zheng, Lu, et al, 2020;and Palchetti, Brindley, et al, 2020). These missions will enable construction of exceptionally accurate CDRs over decades.…”

Radiometric nonlinearity and the correction strategies for infrared hyperspectral benchmark sounder

“…There are several benchmark missions are under development by some space agencies including the Traceable Radiometry Underpinning Terrestrial-and Helio-Studies (TRUTHS) [3] developed in the European Space Agency (ESA), and the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission being underway in the National Aeronautics and Space Administration (NASA) [2]. In 2014, China start the Chinese Spaced-based Radiometric Benchmark (CSRB) project, with the ultimate goal of launching a flight unit of benchmark satellite named LIBRA [4].…”

“…Benefiting from three main advantages for Fourier transform spectrometers (FTS) including high throughput (Jacquinot advantage) [5], broad simultaneous spectral coverage (Fellgett advantage) [6], and intrinsic frequency calibration (Connes advantage) [7], the IR radiation measured by FTS approach is suited for the combined requirement of ultra-high accuracy and broad spectral coverage at a high resolution. Thus, the IR Spectrometer (IRS) selected by the LIBRA mission is a Fourier transform spectrometer, and the measurement requirements are listed in Table 1 [4]. In order to measure the IR radiances with ultra-high accuracy, the IRS should be well calibrated.…”

Characteristics of solar-irradiance spectra from measurements, modeling, and theoretical approach

“…In order to improve the accuracy of solar and terrestrial radiance and irradiance of absolute measurements, several agencies have initiated space radiometry traceability missions. European Space Agency (ESA) TRUTHS 6 , National Administration for Space and Aeronautics (NASA) CLARREO pathfinder 7 , and China Meteorological Administration (CMA) LIBRA 8 are a few examples of such missions. All these missions require a comprehensive analysis of the existing SSI records.…”