SI-Traceability and Measurement Uncertainty of the Atmospheric Infrared Sounder Version 5 Level 1B Radiances

Abstract

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on 4 May 2002. The AIRS is designed to measure atmospheric temperature and water vapor profiles and has demonstrated exceptional radiometric and spectral accuracy and stability in orbit. The International System of Units (SI)-traceability of the derived radiances is achieved by transferring the calibration from the Large Area Blackbody (LABB) with SI traceable temperature sensors, to the On-Board Calibrator (OBC) blackbody during preflight testing. The AIRS views the OBC blackbody and four full aperture space views every scan. A recent analysis of pre-flight and on-board data has improved our understanding of the measurement uncertainty of the Version 5 AIRS L1B radiance product. For temperatures greater than 260 K, the measurement uncertainty is better than 250 mK 1-sigma for most channels. SI-traceability and quantification of the radiometric measurement uncertainty is critical to reducing biases in reanalysis products and radiative transfer models (RTMs) that use AIRS data, as well as establishing the suitability of AIRS as a benchmark for radiances established in the early 2000s.Remote Sens. 2020, 12, 1338 2 of 25 measure surface temperature and emissivity, cloud top height, cloud liquid water and cloud fraction. The data from the IR sounders assimilated into Numerical Weather Prediction (NWP) models have demonstrated amongst the highest forecast improvement in NWP models of all data types. The data are regularly used in studies of processes affecting weather [7] and climate as well as the validation of weather and climate models [8]. The data are also used in applications including volcano alerts [9], drought prediction [10], and air quality and pollution transport [11]. The AIRS instrument has shown exceptional radiometric stability to date, making it a valuable tool for climate trending and model validation [12]. Remote Sens. 2019, 11, x FOR PEER REVIEW 2 of 25 models have demonstrated amongst the highest forecast improvement in NWP models of all data types. The data are regularly used in studies of processes affecting weather [7] and climate as well as the validation of weather and climate models [8]. The data are also used in applications including volcano alerts [9], drought prediction [10], and air quality and pollution transport [11]. The AIRS instrument has shown exceptional radiometric stability to date, making it a valuable tool for climate trending and model validation [12]. Remote Sens. 2020, 12, 1338 3 of 25The AIRS is a reference sensor in the Global Space-Based Intercalibration of Sensors (GSICS) [17,18]. AIRS is used operationally by the Japan Meteorological Agency (JMA) for comparison to Himawari 8/9 AHI JM [19], the Korean Meteorological Administration (KMA) for comparison to COMS [20], and NOAA for comparison to CrIS [21] and GOES [22], and EUMETSAT for comparison to IASI [23]. The results show that the AIRS compares with IASI and CrIS to better than 0.2 K (1-sigma) in most cases. The long record of AIRS, com...

The Atmospheric Infrared Sounder

“…Raw signals from the AIRS instrument are geolocated and converted to calibrated radiances using the OBC and space views and other types of calibration data including OBC emissivity and nonlinearity measured pre-flight and mirror polarized emission measured in-flight using the space views. The AIRS radiances have been shown to be accurate to better than 300mK (1σ) for scene temperatures greater than 260 K in most channels [9]. Radiances at the 1231 cm À1 window channel show excellent stability relative to independent sea surface temperature (SST) estimates, with a drift of less than 0.2-0.3 mK/decade, from 2002 to 2019 [10].…”

Comparison of the AIRS, IASI, and CrIS Infrared Sounders Using Simultaneous Nadir Overpasses: Novel Methods Applied to Data From 1 October 2019 to 1 October 2020

“…Much of the analysis done in this paper, due to the nature of the spatial collocation used, however, uses radiance measurements for scene temperatures between 210 and 260 K. At these colder temperatures, AIRS uncertainties depend much more on the detector module, but in general are less than 1 K 1σ for most channels (with exceptions primarily including SW channels). Readers are referred to Figure 8 of Pagano et al (2020) for more quantitative values.…”

“…AIRS uncertainty estimates from Pagano et al. (2020) are used in this paper for interpretation of the sounder radiance differences. It is important to note that the uncertainty estimates are for the Version 5 product but should have overall similar characteristics and magnitudes to the Version 6 products.…”

Technology Maturation Efforts for the Next Generation of Grating Spectrometer Hyperspectral Infrared Sounders

“…The AIRS has exceptional radiometric and spectral sensitivity and stability [19], [20] and has been operational from its launch in 2002 to the present without a serious failure. The radiometric stability is better than 2-3 mK/year [21] with accuracies better than 250 mK [22]. The AIRS performance has been well documented, and the instrument performance has not changed over the 20-year record, so we refer the reader to the literature [23].…”