In-orbit optical performance assessment of Geostationary Ocean Color Imager
After Geostationary Ocean Color Imager (GOCI) was launched at June 27th, 2010, it is operated to observe the Korean peninsula on the geostationary orbit as one of the three main payloads in COMS satellite. Generally, the performance indicators are Ground Sample Distance (GSD), Modulation Transfer Function (MTF), and Signal to Noise Ratio (SNR) that verify the optical performance of payload. Most of all, the MTF performance is widely used since it is closely related to reliability and accuracy of observational target information in aspects of satellite image application. Especially, in case of ocean color sensor, for confirming the ability of GOCI to separate the slight difference of ocean color information, on-orbit MTF performance test and SNR assessment should be performed.
An In-Orbit Radiometric Calibration Method of the Geostationary Ocean Color Imager
The Geostationary Ocean Color Imager (GOCI) has been developed for the first time to provide multispectral data which is useful to detect, monitor, and predict short-term changes of coastal ocean environment around the Korean Peninsula from a geostationary platform. In this paper, an in-orbit solar calibration method for GOCI is introduced. Based on the radiometric model of GOCI, solar calibration method using onboard calibration devices has been constructed. A nonlinear radiometric model has been validated using test results obtained during ground tests. The gain parameters of the GOCI radiometric model will be continually updated by the in-orbit solar calibration. The GOCI is equipped with two onboard calibration devices: Solar Diffuser (SD) and Diffuser Aging Monitoring Device (DAMD). The SD, which is located in front of a pointing mirror covering full aperture of the GOCI, is used for calibrating end-to-end radiometric response. The DAMD, which covers partial aperture, detects a potential degradation of the SD.
Radiometric Sensitivity Comparisons of Multispectral Imaging Systems
Multispectral imaging systems provide much of the basic data used by the land and ocean civilian remote-sensing community. There are numerous multispectral imaging systems which have been and are being developed. A common way to compare the radiometric performance of these systems is to examine their noise-equivalent change in reflectance, NE Delta-rho. The NE Delta-rho of a system is the reflectance difference that is equal to the noise in the recorded signal. A comparison is made of the noise equivalent change in reflectance of seven different multispectral imaging systems (AVHRR, AVIRIS, ETM, HIRIS, MODIS-N, SPOT-1, HRV, and TM) for a set of three atmospheric conditions (continental aerosol with 23-km visibility, continental aerosol with 5-km visibility, and a Rayleigh atmosphere), five values of ground reflectance (0.01, 0.10, 0.25, 0.50, and 1.00), a nadir viewing angle, and a solar zenith angle of 45 deg.