Abstract
This principle focus of this study is the absolute radiometric calibrations of FORMOSAT-2 RSI imagery in orbit. There are two principal parts for achieving this calibration. The first is the assessment of the calibration site by examining atmospheric observations from ground stations and field measurements via ground-based radiometric instruments. After careful consideration based on the essential requirements for a suitable calibration site i.e., prevailing clear and clean atmosphere conditions over a wide, flat and near lambertian surface with high reflectance, the airport on Dongsha Island was considered to be an suitable site. The next phase is to design a scheme for the field campaign at the calibration site for radiometric calibration. Thus a synchronous experiment acquiring simultaneous measurements from the FORMOSAT-2 Remote Sensing Instrument (RSI) sensor and ground-based instruments was proposed and implemented for the period 16 to 19 September 2004. As a result, a set of reasonable radiometric coefficients for the absolute radiance calibration of the RSI was successfully constructed via the radiative transfer code associated with the synchronous measurements in this study.
Highlights
The FORMOSAT-2 satellite was launched successfully on 21 May 2004
The FORMOSAT-2 satellite orbits the earth at exactly 14 revolutions a day, Remote Sensing Instrument (RSI) observations can be applied to natural disaster evaluation, agriculture development, land-use and urban planning, environmental monitoring, and ocean surveillance around Taiwan and its neighboring waters
Where C is the output signal and corresponds to r* in Eq (1); R is the mean spectral radiance (W / m2 / sr / mm); K0 is absolute radiometric calibration factor, depending on the band; Gsel is the gain factor attached to the gain number; h is the inter-detector equalization coefficient; the gain value, K0Gsel h, is the conversion factor between digital counts and mean spectral radiance; C0 is the dark current for the detector; and N is the noise
Summary
The FORMOSAT-2 satellite was launched successfully on 21 May 2004. The FORMOSAT-2 satellite orbits the earth at exactly 14 revolutions a day, RSI observations can be applied to natural disaster evaluation, agriculture development, land-use and urban planning, environmental monitoring, and ocean surveillance around Taiwan and its neighboring waters. Before launching a satellite into space, it is very important to accurately calibrate radiometric parameters of the on-board sensor, such as response functions and radiometric conversion coefficients. It is essential not to neglect absolute radiance calibration. In the case of the FORMOSAT-2 RSI, ensuring reliability of radiometric observations is dependent upon the accuracy of absolute observing radiances. This study attempts to develop a viable procedure for retrieving relevant radiometric parameters for the RSI sensor in-orbit
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