Correction of Sunglint Effects in High Spatial Resolution Hyperspectral Imagery Using SWIR or NIR Bands and Taking Account of Spectral Variation of Refractive Index of Water

Abstract

Passive high spatial resolution hyperspectral and multispectral imaging systems in the solar spectral region from aircraft and satellite platforms are being increasingly used for remote sensing of coastal waters and inland lakes. However, the remotely sensed data are often contaminated by the specular reflection of solar radiation at the air/water interface. Thus, the effects of sunglint need to be corrected. The purpose of sunglint correction is to remove the undesired specular reflected portion of radiance that does not carry any information about the water body and its bottom surface properties and to obtain the water-leaving radiance from the measured total radiance. In general, adequate treatment of the spectral variation of the sunglint effect with due consideration of the physics and the spectroscopy principles has not been done in previously reported hyperspectral sunglint removing techniques. In this study, a practical sunglint removing technique using either a shortwave infrared (SWIR) band or a near-infrared (NIR) band has been developed, where the liquid water absorption is sufficiently large, and the water-leaving radiance (in units of reflectance) is negligible. In the proposed method, proper consideration has been taken for the spectral Fresnel reflection in the wavelength range of 0.35–2.5 mm. Four cases of sunglint removal from hyperspectral imaging data acquired from two airborne imaging spectrometers have been presented.

An Improved Scheme for Correcting Remote Spectral Surface Reflectance Simultaneously for Terrestrial BRDF and Water‐Surface Sunglint in Coastal Environments

“…(2003) sunglint corrections. (e) Water detail with the FlexBRDF + Gao and Li (2021) sunglint corrections. Both glint corrections eliminate mosaic boundaries and reveal more detailed benthic structures.…”

“…In this study, we present the first simultaneous vegetation and sunglint BRDF correction workflow applicable for the land-water interface and demonstrate the significance of a multiple correction approach in generating continuous surface reflectance products that are useable at the watershed scale. We independently validate the FlexBRDF (Queally et al, 2022) correction algorithm and the Hochberg et al (2003) and Gao and Li (2021) sunglint correction algorithms for their applicability in heterogeneous coastal environments. All tested methods quantitatively improve data accuracy and produced more continuous regional data mosaics.…”

“…The sunglint correction follows: $$${\rho }_{c}(\lambda )=\rho (\lambda )-\left({\rho }_{\text{fresnel}}(\lambda )\ast \frac{\rho \left({\lambda }_{c}\right)}{{\rho }_{\text{fresnel}}\left({\lambda }_{c}\right)}\right)$$$ where $${\rho }_{\text{fresnel}}$$ is the modeled Fresnel reflectance. Gao and Li (2021) suggest a $${\lambda }_{c}$$ of 1650 nm for AVIRIS‐NG data. Existing sunglint correction methods often assume negligible water leaving reflectance in the NIR.…”

“…Our experiment tested two sunglint correction algorithms for their applicability in coastal environments. We chose the Hochberg et al (2003) and Gao and Li (2021) algorithms to include within our experiment because of 10.1029/2021JG006712 14 of 21 their ease of use and scalability when applied to a global hyperspectral data set. We explored the use of methods like Hedley et al (2005) which require the manual selection of optically similar water to calibrate the glint correction, but we found the application of supervised methods cumbersome when performing programmatic corrections over multiple flight lines, making them unsuitable without sufficient a priori knowledge.…”

“…Here, we provide the first workflow of its kind for in tandem terrestrial BRDF correction and water surface sunglint correction in coastal environments. We apply the FlexBRDF terrestrial BRDF correction algorithm (Queally et al, 2022) in tandem with the Hochberg et al (2003) and Gao and Li (2021) sunglint correction algorithms to produce continuous reflectance products across the land-water interface for three regions that cover a range of vegetation and water column compositions. This provides independent validation of the previous approaches, while demonstrating how they can be used together to provide nearly observer-independent reflectance data products for coastal environments including land and water surfaces.…”