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.
X-ray imaging using 100 µm thick Gas Electron Multipliers operating in Kr-CO2 mixtures
Krypton is known to have the best value of position resolution amongst the noble gases within the range 14 − 34 keV , which makes it a good candidate for imaging applications. Also, the choosing of 100μm thick Gas Electron Multipliers (GEM) over the standard GEM plates presents an undeniable advantage as the former is more robust to sparking while achieving similar multiplication coefficients. By taking these factors into account, higher charge gains and better values of position resolution can be achieved to produce cleaner imaging data in the energy range 14− 34 keV . A cascade of two non-standard GEM plates (twice the thickness of a standard GEM) fabricated at CERN was coupled to a 2D resistive readout with an active area of 10× 10 cm. This setup allows event energy and interaction position information to be recorded using only four channels, simplifying the electronic system and the image reconstruction process. This detection system was operated in krypton-based mixtures and irradiated by a Fe and a continuous X-ray source. Whenever possible, the results were compared to the ones achieved in a Ar-CO2 (70:30) mixture. Parameters such as the charge gain, energy resolution, image signal-to-noise ratio, position resolution and contrast response were measured under the described conditions. For krypton-based mixtures, the improvement in position resolution and in contrast response was recorded for radiation energies higher than 18 keV .
In-flight calibration of the EOS Multiangle Imaging Spectroradiometer (MISR)
12 The Multi-angle Imaging SpectroRadiometer (MISR) is one of five instruments on the EOS/Terra spacecraft. MISR consists of nine Earth-viewing cameras which continuously acquire global data sets in view perspectives from nadir to 70 degree(s). In order to maintain the radiometric calibration of the cameras, the instrument is equipped with an on-board calibrator. Spectralon panels, deployed at bi-monthly intervals, reflect sunlight into the cameras to be tested. This reflected light is measured by photodiode detectors which define the radiometric scale and allow the sensor calibration to be achieved. There exists six sets of four spectrally filtered photodiodes. For the first of the in- flight experiments the analysis was focused on validating the performance of the on-board calibrator components. As a result of these studies one blue-filtered, light-trapped detector was selected as the primary standard. All other on- board photodiodes have now been adjusted to be in agreement. This procedure has allowed improved band-to-band and camera- to-camera calibrations, in that all camera calibrations are traceable to a single standard. With these procedures in place MISR now plans to calibrate once every two months. New radiometric response coefficients will be delivered to the processing center following each experiment. This paper reports on these validation studies, and the post-launch radiometric response of the MISR cameras as determined during the first six months of on-orbit MISR calibration.