Estimating the Transmittance of Visible Solar Radiation in the Upper Ocean Using Secchi Disk Observations

Abstract

Penetration of visible solar radiation (VSR) drives heating and phytoplankton photosynthesis in the upper water column; thus, it is always important to accurately describe the vertical distribution of VSR in the oceans. Before the invention and application of modern optical‐electronic instruments to measure the vertical profiles of VSR, the transmittance of VSR from surface to deeper ocean (TVSR) was commonly estimated based on water types and subsequently incorporated in dynamic ocean circulation models. However, the measurement of Secchi disk depth (ZSD) has been carried out since the 1860s and there are about a million of ZSD data available for the global oceans. Because ZSD represents a measure of water's transparency, here we present a scheme based on radiative transfer to accurately estimate TVSR with ZSD as the sole input. It is found that the median ratios between modeled and measured TVSR are ~0.8–1.0 for TVSR in a range of 1–100% for measurements made in coastal waters and oceanic gyres. However, this median ratio spans ~0.04–1.0 for the same measurements when the classical water‐type‐based model was applied. These results suggest a great advantage, and potentially significant impact, in incorporating the volumetric ZSD data to model the dynamic ocean–atmosphere systems in the past 100+ years.

Increasing Shortwave Penetration Through the Bottom of the Oceanic Mixed Layer in a Warmer Climate

“…Meanwhile, the quality of the observed temperature and salinity also exhibits large uncertainty, especially prior to the Argo era (Cheng et al., 2020), which further leads to the large uncertainty in Q pen due to the dominant influence from H m . As for the H p effect, surface chlorophyll exhibits a significant difference between satellite ocean color data and in situ data (Groom et al., 2019; Lee et al., 2019), which also leads to large uncertainty in Q pen estimation, especially in the shallow ML, such as in the eastern equatorial Pacific.…”

Tracking a Surrogate Hazardous Agent (Rhodamine Dye) in a Coastal Ocean Environment Using In Situ Measurements and Concentration Estimates Derived from Drone Images

“…Third, the red ratio does not incorporate a working knowledge of the vertical dye plume and/or any potential stratification beneath the sea surface (e.g., Lee et al [28] who looked into models of vertical profiles of Chlorophyll from remote sensing of ocean color). Future missions could incorporate sub-surface sampling of the dye using different types of dronebased water sampling devices (e.g., Castendyk et al [29]) coupled with multiple Secchi disk observations (e.g., Lee et al [30]) at the sampling locations, but these additional observations were beyond the scope of resources and capabilities available to the present study. Consequently, dye estimates based on red ratios derived from our drone images may in fact include some dye beneath the water surface.…”

Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

“…In other cases, the observer records the average depth when the disk disappears and reappears [12][13][14]. As for dimension, the Secchi disk is standardized at 30 cm diameter [9,[15][16][17][18]. Some different dimensions are used such as 10 [18], 20 [19][20][21][22], 25 [23,24], 40, and 45 cm [23,24].…”