Quantifying the Impact of Solar Spectra on the Inter-Calibration of Satellite Instruments

Rajendra Bhatt,David R Doelling,Arun Gopalan,Odele Coddington,Benjamin Scarino,Conor Haney

doi:10.3390/rs13081438

Abstract

In satellite-based remote sensing applications, the conversion of the sensor recorded top-of-atmosphere reflectance to radiance, or vice-versa, is carried out using a reference spectral solar irradiance (SSI) dataset. The choice of reference SSI spectrum has consistently changed over the past four decades with the increasing availability of more accurate SSI measurements with greater spectral coverage. Considerable differences (up to 15% at certain wavelengths) exist between the numerous SSI spectra that are currently being used in satellite ground processing systems. The aim of this study is to quantify the absolute differences between the most commonly used SSI datasets and investigate their impact in satellite inter-calibration and environmental retrievals. It was noted that if analogous SNPP and NOAA-20 VIIRS channel reflectances were perfectly inter-calibrated, the derived channel radiances can still differ by up to 3% due to the utilization of differing SSI datasets by the two VIIRS instruments. This paper also highlights a TSIS-1 SIM-based Hybrid Solar Reference Spectrum (HSRS) with an unprecedented absolute accuracy of 0.3% between 460 and 2365 nm, and recommends that the remote sensing community use it as a common reference SSI in satellite retrievals.

Highlights

IntroductionAccurate absolute measurements of the total and spectral irradiance from the Sun, especially between 200–2400 nm, are essential for comprehensive understanding of the
Accurate absolute measurements of the total and spectral irradiance from the Sun, especially between 200–2400 nm, are essential for comprehensive understanding of theEarth’s atmospheric chemistry and climate change [1,2]
This paper presents a detailed quantitative study of how the inter-calibration between two sensors is impacted by a difference in solar spectra used by the two instruments

Summary

Introduction

Accurate absolute measurements of the total and spectral irradiance from the Sun, especially between 200–2400 nm, are essential for comprehensive understanding of the. Earth’s atmospheric chemistry and climate change [1,2]. The conversion of satellite-measured radiances to reflectance values, or vice-versa, is performed using a reference spectral solar irradiance (SSI) dataset. With the increasing availability of improved SSI datasets, the choice of a reference SSI spectrum for satellite based remote sensing applications has constantly changed in the past four decades. SSI spectra were derived using ground-based or high-altitude aircraft/rocket measurements [3,4,5,6]. The associated uncertainty of these SSI datasets is considerably large, especially at shorter wavelengths, as the measurements were greatly influenced by the atmospheric absorptions

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