Correction of sun glint effect on MIVIS data of the Sicily campaign in July 2000

E Zappitelli E Zappitelli,S Pignatti S Pignatti,R M Cavalli R M Cavalli

doi:10.4401/ag-3150

Abstract

To assess the suspended and dissolved matter in water in the visible and near infrared spectral regions it is necessary to estimate with adequate accuracy the water leaving radiance. Consequently radiance measured by a remote sensor has to be corrected from the atmospheric and the sea surface effects consisting in the path radiance and the sun and sky glitter radiance contributions. This paper describes the application of the sun glint correction scheme on to airborne hyperspectral MIVIS measurements acquired on the area of the Straits of Messina during the campaign in July 2000. In the Messina case study data have been corrected for the atmospheric effects and for the sun-glitter contribution evaluated following the method proposed by Cox and Munk (1954, 1956). Comparison between glitter contaminated and glitter free data has been made taking into account the radiance profiles relevant to selected scan lines and the spectra of different pixels belonging to the same scan line and located out and inside the sun glitter area. The results show that spectra after correction have the same profile as the contaminated ones, although, at this stage, free glint data have not yet been used in water constituent retrieval and consequently the reliability of such correction cannot be completely evaluated.

Highlights

The sea water color depends on the concentration of dissolved and suspended matter and on their scattering and absorption properties
The aim of this work is to apply the well known method proposed by Cox and Munk (1954, 1956) to MIVIS (Multispectral Infrared and Visible Imaging Spectrometer, Daedalus AA500) data acquired in the area of the Straits of Messina to evaluate if an acceptable sun glint correction could be possible
To correct MIVIS images for atmospheric effects and sun glint contribution, a procedure has been developed taking into account the sea wave slope Probability Density Function (PDF) and modeling the water surface as a large number of small facets reflecting the sunlight (Cox and Munk, 1954, 1956)

Summary

Introduction

The sea water color depends on the concentration of dissolved and suspended matter and on their scattering and absorption properties. Many remote sensing retrieval algorithms use the slope statistics of Cox and Munk to simulate the reflectance of the ocean surface while more recent slope measurements (like laser glitter, radar back scattering and microwave) have been used to define a small scale description of the sea surface roughness (Wenying et al, 2002). The MIVIS instrument is an airborne whisk broom scanner acquired by CNR (Italian National Research Council) in the framework of LARA (Airborne Laboratory for Environmental Studies) It is a simultaneous multispectral imaging system that operates in the range from visible to thermal-IR, with a high spectral resolution, 102 bands (table I), FoV (Field of View) and IFoV (Instantaneous Field of View) of 71.059° and 2.0 mrad, respectively

Sunlint correction methodology

The case study of Messina

In all the three runs the computed Cox and Munk sun

Conclusions