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

Abstract

Knowledge of cloud cover, frequency, and duration is not only important to study cloud dynamics, but also critical in determining when and where to take ocean measurements from geostationary orbits such as the Geostationary Coastal and Air Pollution Events (GEO‐CAPE) mission due to the challenges in achieving complete hemispheric coverage of coastal oceans, estuaries, and inland waters at hourly frequency. Using GOES hourly measurements at 4 km nadir resolution between 2006 and 2011, the number of cloud‐free hourly observations per day (Ncf) for solar zenith angle θo < 80° was estimated for each 0.1° location of the Intra‐Americas Sea. The number of Sun‐glint‐affected hourly observations per day (Nsg) was also calculated based on the planned GEO‐CAPE observation geometry and realistic wind speed. High‐latitude and equatorial oceans showed the lowest Ncf (<2.4) in all climatological months, and highest Ncf was observed in the Gulf of Mexico (GoM) and Caribbean (>4.5). Different regions showed differences in seasonality of cloud‐free conditions and also showed differences in the hour of a day at which the satellite observations would have the maximal cloud‐free and glint‐free probability (Tmax). Cloud cover from Moderate Resolution Imaging Spectroradiometer (MODIS) 1 km measurements are >10% higher than those from the MODIS 250 m measurements, supporting ocean color missions at subkilometer resolutions to enhance both spatial coverage and temporal frequency. These findings provide valuable information for GEO‐CAPE mission planning to maximize its science value through minimizing the impacts of clouds and Sun glint.

Sampling Uncertainties of Long-Term Remote-Sensing Suspended Sediments Monitoring over China’s Seas: Impacts of Cloud Coverage and Sediment Variations

“…Cloud coverage levels from the Terra/MODIS system were generally higher than afternoon observations from the Aqua/MODIS system, for each sub region as well as for the entire study area. The results are also consistent with previous studies on valid ocean observation rates from the Terra/Aqua MODIS systems [21]. These showed that there were more valid Aqua observations than Terra observations, due to lower cloud coverage in the afternoons.…”

“…As a result, it was found that each day, only 12%, on average, of the Aqua/MODIS ocean products were valid [10,19,20], and for some regions under persistent cloud coverage, monthly averaged valid observation could be less than one. High-latitude and equatorial oceans experienced the lowest levels of cloud-free period, with the valid number of observations being less than 2.4 per month [21]. Some research has been dedicated to improving temporal coverage for a single observation area by merging data from multiple satellite sources.…”

Computational approaches for sub-meter ocean color remote sensing

“…Tower-, ship-, or drone-based applications of small, lightweight imaging spectrometers in aquatic remote sensing have considerable promise to fill an operational niche between in situ sampling, aircraft-based studies, and satellite ocean color monitoring, by providing fine temporal and spatial resolution data with minimal operational constraints [Klemas, 2015]. Low-altitude platforms have an advantage over aircrafts and satellites because they can operate underneath cloud cover, an important consideration in typically cloudy and spatially dynamic ocean regions such as coastal waters Feng et al, 2017] and the marginal ice zone [Engelsen et al, 2002]. This study demonstrated that a currently available imaging spectrometer was able to recover WQPs from a fixed-platform on very fine spatial scales, on the order of centimeters, despite the low signal-to-noise ratio measurements from the imaging spectrometer and the complications arising from applying glint correction approaches to waters with fine-scale changes in their surface reflectance characteristics.…”

Assessment of the Number of Valid Observations and Diurnal Changes in Chl-a for GOCI: Highlights for Geostationary Ocean Color Missions

“…One of the most important tasks that must be performed before launching a new geostationary satellite is to determine the mission necessity, that is, determining what can be missed with low Earth orbit (LEO) instruments. The improved coverage of a geostationary mission can be indirectly inferred through statistics of cloud-free days using hourly cloud coverage observations from meteorological satellites (i.e., the GOES system) [ 19 ]. Indeed, more than one cloud-free observation is expected over the Intra-Americas Sea when geostationary satellite observations are available [ 19 ] given the mean daily cloud coverage of 72% for the global ocean [ 21 ].…”

“…The improved coverage of a geostationary mission can be indirectly inferred through statistics of cloud-free days using hourly cloud coverage observations from meteorological satellites (i.e., the GOES system) [ 19 ]. Indeed, more than one cloud-free observation is expected over the Intra-Americas Sea when geostationary satellite observations are available [ 19 ] given the mean daily cloud coverage of 72% for the global ocean [ 21 ]. However, such statistics are based on meteorological satellite data rather than real ocean color observations; hence, the extent to which the valid data coverage of ocean color retrievals can be improved through geostationary missions remains unknown.…”