BRDF Estimations and Normalizations of Sentinel 2 Level 2 Data Using a Kalman-Filtering Approach and Comparisons with RadCalNet Measurements

Bertrand Saulquin

doi:10.3390/rs13173373

Abstract

BRDF estimation aims to characterize the anisotropic behaviour of the observed surface, which is directly related to the type of surface. BRDF theoretical models are then used in the normalization of the satellite-derived observations to virtually replace the sensor at the nadir. Such normalization reinforces the homogeneity within and between satellite-derived time series. Nevertheless, the inversion of the necessary BRDF parameters for the normalization requires the implementation of robust methods to account for the noise in the Level 2 surface reflectances caused by the atmospheric correction process. Here, we compare normalized reflectances obtained with a Kalman filtering approach with i/the classical weighted linear inversion and ii/a normalization performed using the coefficients of the NASA-MODIS BRDF MCD43A1 band 2 product. We show, using the RadCalNet nadir-view reflectances, that the Kalman filtering approach is a more suitable approach for the Sen2Cor level 2 and the selected sites. Using the proposed approach, daily global maps of land surface BRDF coefficients and the derived normalized Sentinel 2 reflectances would be extremely useful to the global and regional climate modelling communities and for the world’s cover monitoring.

Highlights

As part of the Copernicus program of the European Commission (EC), the EuropeanSpace Agency (ESA) has developed and currently operates the Sentinel-2 (S2) optical missions, currently designed as a constellation of two satellites to improve revisit and global coverage from 10 to 60 m resolution, depending on the spectral bands [1]
Level 2, many complex models are involved in the retrieval of from Top Of Atmosphere (TOA) to Bottom Of Atmosphere (BOA) signals [1]
We examine the Bidirectional Reflectance Distribution Function (BRDF) parameter estimations using two methods, a classical weighted linear inversion as implemented by NASA for the Moderate Resolution

Summary

Introduction

As part of the Copernicus program of the European Commission (EC), the EuropeanSpace Agency (ESA) has developed and currently operates the Sentinel-2 (S2) optical missions, currently designed as a constellation of two satellites to improve revisit and global coverage from 10 to 60 m resolution, depending on the spectral bands [1]. Level 2, many complex models are involved in the retrieval of from Top Of Atmosphere (TOA) to Bottom Of Atmosphere (BOA) signals [1]. The Level 2 BOA estimates [3] is a major topic when ensuring that the activities of the mission address the initial requirements. Such validation processes involve in-situ data or Fiducial Reference Measurements (FRM) [4] that represent “truths” to be targeted by the. The Mission Performance Centre (MPC), as part of the European Space Agency’s S2 ground segment, operationally carries out the routine S2 calibration and validation activities and investigates potential tracks for improvement, as explored in this paper

Methods

Results

Conclusion