Abstract
The hyperspectral infrared atmospheric sounder (HIRAS), the first Chinese hyperspectral infrared instrument, was launched in 2017 on board the fourth polar orbiter of the Feng Yun 3 series, FY-3D. The instrument is a Fourier transform spectrometer with 2275 channels covering three spectral bands (650–1136, 1210–1750, and 2155–2550 cm−1) with 0.625 cm−1 spectral resolution. The first data quality assessment of HIRAS observations at full and normal spectral resolutions is presented. Comparisons with short-range forecasts from the Met Office numerical weather prediction (NWP) global system have revealed biases (standard deviation) generally less than 2.6 K (2 K) in the spectral regions mostly unaffected by trace gases where the confidence in the NWP model is largest. Of particular concern, HIRAS detector 3 seems to suffer from sunlight contamination of its calibration towards the end of the descending node. This, together with an obstruction of the detector field of view by an element of the platform, results in accentuated bias and noise in the observations from this detector. At normal spectral resolution, a background departure double difference analysis has been conducted between HIRAS and the NOAA-20 crosstrack infrared sounder (CrIS). The results show that HIRAS and CrIS are in good agreement with a mean difference across the three bands of −0.05 K (±0.26 K at 1σ) and 75.2% of the channels within CrIS radiometric uncertainty, noting though that HIRAS is noisier than CrIS with, on average, a standard deviation 0.34 K larger.
Highlights
Hyperspectral infrared instruments such as the atmospheric infrared sounder (AIRS) and the crosstrack infrared sounder (CrIS) on board the U.S platforms Aqua, Suomi-National Polar-Orbiting Operational Environmental Satellite System Preparatory Project (SNPP), and NOAA-20, and the infrared atmospheric sounding interferometer (IASI) on board the European Metop platforms have been a fundamental part of the Earth observation system since the early 2000s [1,2,3]
We propose an assessment of the radiometric data quality of the new Chinese hyperspectral infrared atmospheric sounder (HIRAS) on board the FY-3D platform through a comparison with short-range forecasts from the Met Office numerical weather prediction (NWP) global system and a double comparison with NOAA-20 CrIS
The radiance simulator is a tool developed at the Met Office for the NWP satellite application facilities (NWP SAF) that enables the collocation in space and time of NWP model variables and their mapping in the observation spectral domain [27]; (2) HIRAS observations have been passively processed in an off-line version of the operational system
Summary
Hyperspectral infrared instruments such as the atmospheric infrared sounder (AIRS) and the crosstrack infrared sounder (CrIS) on board the U.S platforms Aqua, Suomi-National Polar-Orbiting Operational Environmental Satellite System Preparatory Project (SNPP), and NOAA-20, and the infrared atmospheric sounding interferometer (IASI) on board the European Metop platforms have been a fundamental part of the Earth observation system since the early 2000s [1,2,3]. We propose an assessment of the radiometric data quality of the new Chinese hyperspectral infrared atmospheric sounder (HIRAS) on board the FY-3D platform through a comparison with short-range forecasts from the Met Office NWP global system and a double comparison with NOAA-20 CrIS. A typical HIRAS cross-track scan takes about 10 seconds and consists of 33 interferometer sweeps composed of 29 Earth scenes, two deep space, and two internal calibration target
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