Abstract
The Geostationary Environment Monitoring Spectrometer (GEMS) onboard the Geostationary Korean Multi-Purpose Satellite 2B was successfully launched in February 2020. GEMS is a hyperspectral spectrometer measuring solar irradiance and Earth radiance in the wavelength range of 300 to 500 nm. This paper introduces the spectral calibration algorithm for GEMS, which uses a nonlinear least-squares approach. Sensitivity tests for a series of unknown algorithm parameters such as spectral range for fitting, spectral response function (SRF), and reference spectrum were conducted using the synthetic GEMS spectrum prepared with the ground-measured GEMS SRF. The test results show that the required accuracy of 0.002 nm is achievable provided the SRF and the high-resolution reference spectrum are properly prepared. Such a satisfactory performance is possible mainly due to the inclusion of additional fitting parameters of spectral scales (shift, squeeze, and high order shifts) and SRF (width, shape and asymmetry). For the application to the actual GEMS data, in-orbit SRF is to be monitored using an analytic SRF function and the measured GEMS solar irradiance, while a reference spectrum is going to be selected during the instrument in-orbit test. The calibrated GEMS data is expected to be released by the end of 2020.
Highlights
The Geostationary Environment Monitoring Spectrometer (GEMS) is a hyperspectral spectrometer developed for Korea’s next-generation geostationary multi-purpose satellite program, the GK-2 program, which consists of two satellites, GK-2A and GK-2B
While the GK-2A satellite is dedicated to weather monitoring with a high-performing imaging instrument (16-channel imagers in the visible and infrared bands [1]), the GK-2B satellite is for ocean and environmental observation [2,3]
The operational level 1b (L1b) process for GEMS is prepared to provide a spectral accuracy of 0.02 nm, which is expected to be sufficient for many applications
Summary
The Geostationary Environment Monitoring Spectrometer (GEMS) is a hyperspectral spectrometer developed for Korea’s next-generation geostationary multi-purpose satellite program, the GK-2 program, which consists of two satellites, GK-2A and GK-2B. The OMPS program adopts two different fitting parameter bases: spectral shift including the FWHM of SRF. For example, an important source of wavelength uncertainty in a polar orbiter [16], is expected to be insignificant considering the scanning mechanism of GEMS (step and dwell) and the fixed, geostationary platform. As this type of iterative fitting method requires significant computational resources, SPECAL must be optimized and instrument-specific to meets its requirements while incurring reasonable numerical costs.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
