Updating Absolute Radiometric Characteristics for KOMPSAT-3 and KOMPSAT-3A Multispectral Imaging Sensors Using Well-Characterized Pseudo-Invariant Tarps and Microtops II

Jong-Min Yeom,Seungtaek Jeong,Chul-Uong Choi,Jonghan Ko,Jisoo Hwang,Chang-Suk Lee

doi:10.3390/rs10050697

Abstract

Radiometric calibration of satellite imaging sensors should be performed periodically to account for the effect of sensor degradation in the space environment on image accuracy. In this study, we performed vicarious radiometric calibrations (relying on in situ data) of multispectral imaging sensors on the Korea multi-purpose satellite-3 and -3A (KOMPSAT-3 and -3A) to adjust the existing radiometric conversion coefficients according to time delay integration (TDI) adjustments and sensor degradation over time. The Second Simulation of a Satellite Signal in the Solar Spectrum (6S) radiative transfer model was used to obtain theoretical top of atmosphere radiances for both satellites. As input parameters for the 6S model, surface reflectance values of well-characterized pseudo-invariant tarps were measured using dual ASD FieldSpec® 3 hyperspectral radiometers, and atmospheric conditions were measured using Microtops II® Sunphotometer and Ozonometer. We updated the digital number (DN) of the radiance coefficients of the satellites; these had been used to calibrate the sensors during in-orbit test periods in 2013 and 2015. The coefficients of determination, R2, values between observed DNs of the sensors, and simulated radiances for the tarps were more than 0.999. The calibration errors were approximately 5.7% based on manifested error sources. We expect that the updated coefficients will be an important reference for KOMPSAT-3 and -3A users.

Highlights

Radiometric calibration of satellite sensors involves converting a measured digital number (DN) to physical units of radiance to provide reliable quantified scientific data
The detailed sensor specifications are slightly different, the multispectral bands of the Advanced Earth Image Sensor System (AEISS) and AEISS-A, mounted on KOMPSAT-3 and -3A, respectively, have the same spectral response functions (SRF) and practical spectral ranges as the bands affected by atmospheric constituents and the surface
We focused on updating the absolute radiometric calibration results of KOMPSAT-3 and KOMPSAT-3A according to time delay integration (TDI) adjustments and sensor degradation over time

Summary

Introduction

Radiometric calibration of satellite sensors involves converting a measured digital number (DN) to physical units of radiance (e.g., reflectance) to provide reliable quantified scientific data. The process can be classified into pre- and in-flight calibrations [1]. Pre-flight calibration is conducted using laboratory experiments of a well-known radiance source to determine the linear relationship between DN and radiance for each spectral band of the satellite sensor. The satellite imaging sensor of the launched satellite is well calibrated by the pre-flight process, the sensor responses to radiometric targets tend to change in orbit because of the differences between laboratory and space environments. In a previous report on sensor degradation of the advanced very high-resolution radiometer (AVHRR), band 1 (0.58–0.68 nm) and 2 (0.725–1.00 nm) responses decreased by 4.5% and 3.6%, respectively, in just one year [6]. The DN to radiance coefficient must be periodically updated to maintain the quality of satellite imagery [8,9]

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