Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and
CH4, from space with a Fourier transform spectrometer and a push broom imager. The GOSAT was launched on January
23, 2009. The initial functional check-out phase was completed on April 10 to confirm the on-orbit performance. The
initial calibration and validation phase was completed on July 30 in the following 3 months to acquire observation data at
calibration and validation sites. The initial calibration was evaluated on accuracies of radiometry, geometry and
spectrometry by using acquired data. The results were reflected to the improvement of the Level 1 algorithm and the
products. The initial calibrated Level 1 products have been already released to the GOSAT research PIs in August.
Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and
CH4, from space. The GOSAT carries a Fourier transform spectrometer and a push broom imager. The development of
GOSAT satellite and sensors has almost finished after the characterization of sensor performance in laboratory. In orbit,
the observation data will be evaluated by onboard calibration data and implemented by ground processing system. Level
1 algorithm and processing system are developed by JAXA. The post-launch calibration items are planned and the
methods are developed before launching. We show the Level 1 processing and in-orbit calibration of GOSAT sensors.
KEYWORDS: Calibration, Sensors, Fourier transforms, Reflectivity, Short wave infrared radiation, Black bodies, MODIS, Signal to noise ratio, Lamps, Gases
Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and
CH4, from space. The GOSAT carries a Fourier transform spectrometer and a push broom imager. The GOSAT
development is going on in phase-C/D and characterized the sensor performance in laboratory. In orbit, the observation
data will be evaluated by onboard calibration data and implemented by ground processing system. The post-launch
calibration items are planned and the methods will be developed before the launch. The methods are investigated by
analyzing the current MODIS data, which has similar wavelength bands to GOSAT. In this paper, we show the
calibration plans of pre-flight test, onboard calibration, and post-launch vicarious calibration of GOSAT sensors.
The Global Imager (GLI) was launched on board the Advanced Earth Observing Satellite II (ADEOS-II) on December 14, 2002. We conducted vicarious calibration of the GLI ocean color channels in visible to near-infrared channels. For the calibration we used the normalized water-leaving radiance derived from the Marine Optical Buoy (MOBY), and the aerosol optical properties (aerosol optical depth, size distribution, and refractive index) released in the Aerosol Robotic Network (AERONET).
The following GLI characteristics are recognized from the calibration results. First, GLI underestimates the radiance in channels 1, 2, 4, and 5. Next, in near-infrared channels, it is suggested that GLI overestimates the radiance on the order of 15% in channels 18 and 19. Furthermore, the comparison of the result with other vicarious calibration results suggests the possibility that the GLI observed radiance has offset radiance versus the simulated radiance. The estimated offset is about 0.4 W/m2/um/sr in channel 19, which is considered appropriate by the adaptation test to the GLI standard atmospheric correction algorithm.
The Advanced Earth Observing Satellite-II (ADEOS-II) was launched on 14 December 2002, and its functions were checked until 2003 spring. The Global Imager (GLI) on board ADEOS-II has 36 channels (thirty 1-km resolution, six 250-m resolution) from ultraviolet to thermal infrared to facilitate understanding the global environmental changes in oceans, land and clouds with high accuracy. Ocean algorithms (e.g., ocean atmospheric correction and sea-surface temperature) need highly accurate sensor characterization coefficients because they retrieve sea-surface upward radiance precisely from the top of the atmosphere. The NASDA GLI calibration team includes members of sensor development, ground system integration, and science application groups. The team started investigating GLI characteristics and radio- and geo-correction processes in the initial verification period. In this paper, we will describe the initial results, radiometric accuracy, 12- or 48-detector dependency, scan-mirror surface, incident-angle dependency, and dynamic range related to oceanographic applications.
The GLI was launched on board the ADEOS-II on December 14, 2002. For the early phase evaluations of the observation radiances, the GLI calibration team carried out vicarious calibrations by using MOBY measurements. To achieve the calibrations, we used two methods, which utilize two near-infrared channels and the measurement of the aerosol optical thickness, to predict the aerosol optical properties. Applying these methods, we derived early GLI vicarious calibration factors for ocean-color channels.
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