Day-1 INSAT-3DR Vicarious Calibration Using Reflectance-Based Approach Over Great Rann of Kutch
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RESEARCH ARTICLE
Day-1 INSAT-3DR Vicarious Calibration Using Reflectance-Based Approach Over Great Rann of Kutch Piyushkumar N. Patel1 • K. N. Babu1 • R. P. Prajapati1 • Vikram Sitapara1 • A. K. Mathur1 Received: 14 July 2017 / Accepted: 13 November 2017 Ó Indian Society of Remote Sensing 2018
Abstract This study describes the post-launch calibration for visible (VIS) and shortwave infrared (SWIR) bands of Indian National Satellite System (INSAT)-3DR imager over Great Rann of Kutch (GROK) on Day-1 (15th September 2016), when the first time INSAT-3DR Imager camera was switched on. In order to account the characterization of errors and undetermined post-launch changes in sensor spectral response, this calibration activity was performed and extended for its monitoring to Day-56 (since the Day-1; 09th November 2016). A reflectance based technique is used in the present study. The surface reflectance and atmospheric variables were measured over the site as per solar and viewing geometry of the INSAT-3D scan. Top of atmosphere (TOA) spectral radiances were computed using 6SV (second simulation of the satellite signal in the solar spectrum) radiative transfer code with the in situ measurements as well as spectral response function of each channel. Preliminary results of the Day-1 vicarious calibration yield gain coefficients of 0.974 and 0.820 for VIS and SWIR channels respectively despite the inhomogeneity of the ground target caused by sufficient sub-surface soil moisture. In extension of the present study, the obtained gain coefficients were 1.001 and 0.9887 for VIS and SWIR, respectively, during Day-56 which indicates the performance of sensor is within the range of pre-launch laboratory calibration. Keywords INSAT-3DR Vicarious calibration Reflectance 6SV Radiative transfer model
Introduction The advancement and popularity of satellite data usage for societal benefits not only requires the development of new and complex satellites but also to improve the quality of satellite sensors and their data products. Therefore, it has become more essential to continually upgrade the ability to provide calibration of sensors. Generally, calibration procedure includes first radiometric calibration prior to the launch (Bruegge et al. 1998) and later the on-board calibration (Bruegge et al. 1993), but in the absence of onboard calibration facility, a post-launch vicarious calibration exercise provides an aid to compensate the degradation of the satellite sensor (Rao 2001). Vicarious calibration provides a method for calibration of satellite sensors using reference and precise measurements of spectral reflectance & Piyushkumar N. Patel [email protected] 1
Calibration and Validation Division, Space Applications Centre, ISRO, Ahmedabad, India
from the ground instruments over a terrestrial calibration site. This calibration coefficients can be incorporated for the accurate characterisation of the conversion of digital counts to radiance values. Vicarious calibration is a broadly adopted technique for continuous monito
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