Sun glint requirement for the remote detection of surface oil films

Abstract

Natural oil slicks in the western Gulf of Mexico are used to determine the sun glint threshold required for optical remote sensing of oil films. The threshold is determined using the same‐day image pairs collected by Moderate Resolution Imaging Spectroradiometer (MODIS) Terra (MODIST), MODIS Aqua (MODISA), and Visible Infrared Imaging Radiometer Suite (VIIRS) (N = 2297 images) over the same oil slick locations where at least one of the sensors captures the oil slicks. For each sensor, statistics of sun glint strengths, represented by the normalized glint reflectance (LGN, sr−1), when oil slicks can and cannot be observed are generated. The LGN threshold for oil film detections is determined to be 10−5–10−6 sr−1 for MODIST and MODISA, and 10−6–10−7 sr−1 for VIIRS. Below these thresholds, no oil films can be detected, while above these thresholds, oil films can always be detected except near the critical‐angle zone where oil slicks reverse their contrast against the background water.

Cloud and Sun‐glint statistics derived from GOES and MODIS observations over the Intra‐Americas Sea for GEO‐CAPE mission planning

“…Number of hourly observations during a day (2006–2010) with Sun‐glint reflectance ( L gn ) >10 −5 sr −1 . Under such Sun‐glint influence, surface oil slicks can always be observed due to surface wave damping [ Sun and Hu , ].…”

“…Note that the GOES-derived cloud statistics are based on 4 km resolution measurements, and cloud cover has been shown to be sensitive to spatial resolution. Although the average differences between 4 km and 1 km and between 1 km and 250 m are not large (about 10%), in certain months or regions the difference between can always be observed due to surface wave damping [Sun and Hu, 2016].…”

Using remote sensing to detect the polarized sunglint reflected from oil slicks beyond the critical angle

“…Due to the strong light absorption characteristic of clear water and crude oil at near‐infrared wavelengths [ Lammoglia and de Souza Filho , ; Wettle et al ., ], the backscattering radiance from oil or clear water was ignored in this study. Oil slicks are often observed in and around the sunglint region within various optical imagery of the sea surface [ Hu et al ., ; Jackson and Alpers , ; Lu et al ., ; Sun and Hu , ; Sun et al ., ]. When oil slicks or the seawater surface are illuminated by sunlight, the Fresnel reflection of the directly incident sunlight at the smooth surface can be described by Fresnel's law.…”

“…[], and Lu et al . []), including optical sensors [ Chust and Sagarminaga , ; Giammona et al ., ; Hu et al ., ; Lu et al ., ; Sugioka et al ., ; Sun and Hu , ; Sun et al ., ], synthetic aperture radar (SAR) [ Brekke and Solberg , ; Garcia‐Pineda et al ., ; Hodgins et al ., ; Keramitsoglou et al ., ; Zheng et al ., ], thermal sensors [ Asanuma et al ., ; Cai et al ., ; Cross , ; Innman et al ., ; Leifer et al ., ; Lu et al ., ; Salisbury et al ., ; Tseng and Chiu , ], and laser fluorescence [ Brown et al ., ; Brown and Fingas , ]. These different technologies possess unique characteristics, theoretical bases, related data processing techniques, and quantitative remote sensing models.…”

“…Following specific and careful refinements (especially the refractive index correction), the normalized sunglint reflectance ( L GN ) of oil slicks can be estimated accurately [ Lu et al ., ]. Different values of L GN required to detect oil slicks have been evaluated for different sensors [ Sun and Hu , a]. The modeled critical angle is often presented as the point at which the L GN of oil slicks and oil‐free seawater intersect, which is where the reversal in brightness occurs [ Jackson and Alpers , ; Lu et al ., ].…”