FengYun-3D HIRAS Overview and On-Orbit Performance

On 15 November, 2017, the FengYun 3D satellite was launched successfully into orbit. High spectral Infrared Atmospheric Sounder (HIRAS) is a new infrared sounding instrument which was carried onboard FY-3D to replace IRAS. HIRAS was designed and manufactured completely by Shanghai Institute of Technical Physics (SITP), Chinese Academy of Sciences (CAS) and it is a sign of a new age of vertical sounding system due to its distinct advantages of high spectral resolution, low radiometric noise and high spectral and radiometric accuracy. HIRAS is also a Fourier transform spectrometer (FTS) and is the third FTS for operational meteorological application that follows the Infrared Atmospheric Sounding Interferometer (IASI) onboard the European Metop-A/B satellite and the Cross-Track Infrared Sounder (CrIS) onboard the Suomi-NPP operational environmental satellite. HIRAS provides measurements of radiance spectra of 1370 channels in three spectral bands: the long wave IR (LWIR) band from 650 to 1136 cm^-1, middle wave IR (MWIR) band from 1210 to 1750 cm^-1, and short wave IR 2(SWIR) band from 2155 to 2550 cm^-1, with spectral resolution of 0.625cm^-1, 1.25cm^-1, 2.5cm^-1, respectively. HIRAS measurement scan sequence consists of 33 interferogram sweeps, including 29 Earth View (ES), 2 Deep Space (DS), 2 Internal Calibration Target (ICT) measurements. One complete scan sequence takes 10 seconds. View angle of each detector (Field of View, FOV) is 1.1° corresponding the nadir spatial resolution of 16 km (Fig 1). Detailed instrument characteristics and spectral band channels and sensitivity are listed in table 1~2.

After more than 3 month of preparation and out gassing, HIRAS infrared detectors was powered on and started to obtain its earth measurements from 1 March, 2018. Instrument telemetry parameters and raw measurements check, also instrument alignment and tuning work was finished on 20 April and HIRAS began the on-orbit test misson and provide valid observations. FY-3D satellite on orbit test work lasted 6 month from December, 2017 to June, 2018, HIRAS also completed on-orbit test in the end of June, 2018 and began generating L1 data operationally. HIRAS exhibited exciting and promising results from on orbit performance, correlated noise was well suppressed and less than the un-correlated noise after dynamic alignment of fixed mirror. The total NEdN meet the specification in requirement spectral region. The parameters related to Instrument Line Shape(ILS) were derived by minimizing the spectrum difference between the on-orbit measurements and Line-BY-Line (LBL) simulation of clear sky ocean observations. Spectral validation of comparing the measurement of HIRAS to that LBL calculation shows that the estimated absolute spectral calibration uncertainty is less than 5 ppm in all three bands. SNO observations between CrIS/IASI and HIRAS show that the estimated radiometric accuracy is better than 0.5K for LW, 0.7K for MW and 0.5K for SW in weak absorption spectral region respectively. HIRAS is a great improvement to Chinese satellite infrared atmospheric sounding system and is expected to serve broad communities in various applications related to NWP, atmospheric retrieval, cross calibration and climate research.