Search Results (3)

In this study, a novel method for retrieving atmospheric temperature profiles with tree-structured Parzen estimator (TPE) and multilayer perceptron (MLP) algorithms was proposed, using FY-4A/GIIRS (Geosynchronous Interferometric Infrared Sounder) and ERA5 data. Firstly, by adding solar altitude angle, satellite zenith angle, 2m temperature, and surface temperature to the input layer of MLP, there is an improvement in retrieval accuracy. Secondly, TPE is effective in optimizing the hyper-parameters of MLP, and a set of optimized hyper-parameters is obtained through iterative optimization. Thirdly, comparing the retrieved temperature profiles with ERA5 data, we found that retrieval accuracy is influenced by detector, signal-to-noise ratio, terrain, solar altitude angle, satellite zenith angle, and the horizontal temperature gradient. The mean biases of the two adjacent detectors show significant differences, and the retrieval accuracy of the center detectors is greater than that of the north and south sides. The retrieval accuracy is relatively poor in areas with high terrain and large satellite zenith angle. There is a monthly variation in the retrieval accuracy due to the horizontal temperature gradient and signal-to-noise ratio and a significant diurnal variation due to solar altitude angle and signal-to-noise ratio. Compared to in situ sounding data, the mean biases vary from −0.56 K to 0.60 K, and the standard deviations vary from 1.26 K to 2.17 K. The analysis of factors influencing retrieval accuracy provides important insights into improving the ability to retrieve atmospheric temperatures from geostationary hyperspectral IR sounder observations for near real-time (NRT) applications. Full article

Fengyun4A is the first geostationary satellite with payload of the infrared hyperspectral sounder. The geostationary platform-based instrument can provide observational 3-dimensional fields of temperature and humidity with high scanning frequencies and spatial resolutions. The IR instrument-observed temperature (T) and relative humidity (RH) profiles are closely related to the cloud states. Radiosonde observations are used to validate the Fengyun4A T and RH profiles under different cloud-type sky conditions. The cloud-type information comes from the Himawari-8 satellite which has substantial observing overlap with Fengyun4A over Asia. Taking the radiosonde observation as the reference, Fengyun4A T profile has uncertainty of 2.1 K under clear sky, and 3.7 K under cloudy sky. When cloudy sky is divided into cloud-type skies, the categories have disparities in temperature biases, varying from positive to negative. It is found that most of cloud-type categories have uncertainties of 2.5–3.0 K. The RH profiles have an uncertainty of 18% under clear sky and 21% under cloudy sky in absolute value. On average, the RH biases show neural but positively biased at the dry side and negatively biased at the wet side in the scatter plot. The International Satellite Cloud Climatology Project (ISCCP) cloud type can help to extend the quality flag of the Fengyun4A temperature profile. The impacts from cloud types on IR sounding profiles should be considered in product development or applications. Full article

This study presents a common recalibration method that has been applied to geostationary imagers’ infrared (IR) and water vapour (WV) channel measurements, referred to as the multi-sensor infrared channel calibration (MSICC) method. The method relies on data of the Infrared Atmospheric Sounding Interferometer (IASI), Atmospheric Infrared Sounder (AIRS), and High-Resolution Infrared Radiation Sounder (HIRS/2) on polar orbiting satellites. The geostationary imagers considered here are VISSR/JAMI/IMAGER on JMA’s GMS/MTSAT series and MVIRI/SEVIRI on EUMETSAT’s METEOSAT series. IASI hyperspectral measurements are used to determine spectral band adjustment factors (SBAF) that account for spectral differences between the geostationary and polar orbiting satellite measurements. A new approach to handle the spectral gaps of AIRS measurements using IASI spectra is developed and demonstrated. Our method of recalibration can be directly applied to the lowest level of geostationary measurements available, i.e., digital counts, to obtain recalibrated radiances. These radiances are compared against GSICS-corrected radiances and are validated against SEVIRI radiances, both during overlapping periods. Significant reduction in biases have been observed for both IR and WV channels, 4% and 10%, respectively compared to the operational radiances. Full article