Deriving Tidal Structure From Satellite Image Time Series

Emily C Geyman,Adam C Maloof

doi:10.1029/2019ea000958

Emily C Geyman, Adam C Maloof

Open Access

https://doi.org/10.1029/2019ea000958

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Abstract

AbstractIn shallow coastal regions, tides often control the water flux, which in turn directs sediment transport, nutrient delivery, and geochemical gradients. However, tides in shallow areas are spatially heterogeneous, making it challenging to constrain the geographic structure of tidal phase and amplitude without extensive networks of tide gauges. We present a simple remote sensing method for deriving tidal structure from satellite time series. Our method is based on two observations: (1) Tidally driven variations in water depth can be detected as changes in pixel intensity in optical satellite imagery, and (2) repeating passes by an orbiting satellite capture a region at different phases of the tidal cycle. By stacking multiple satellite acquisitions of a shallow bank, we can compute the relative tidal phase and amplitude for each pixel location, thereby resolving a detailed map of tidal propagation and attenuation. While our method requires a set of local water‐depth measurements to calibrate the color‐to‐depth relationship and compute tidal amplitude (in meters), our method can produce spatial estimates of tidal phase and relative amplitude without any site‐specific calibration data. As an illustration of the method, we use Landsat imagery to derive the spatial structure of tides on the Great Bahama Bank, estimating tidal phase and amplitude with mean absolute errors of 15 min and 0.15 m, respectively.

Highlights

The behavior of oceanic tides on shallow continental shelves—and the implications for topics as broad as the evolution of the Earth-Moon orbit (Coughenour et al, 2009; Hansen, 1982) and the global mixing of the ocean (Munk & Wunsch, 1998)—has occupied the minds of scientists for over a century (Jeffreys & Shaw, 1920; Taylor & Shaw, 1919)
The advent of satellite altimetry in the early 1990s revolutionized our understanding of global oceanic tides (Cartwright & Ray, 1990; Egbert & Ray, 2000; Tierney et al, 2000)
Model Validation To evaluate the accuracy of our tide model, we compare the predictions of tidal phase and amplitude to the measured values at each of our five gauges (Figure 1)

Summary

Introduction

The behavior of oceanic tides on shallow continental shelves—and the implications for topics as broad as the evolution of the Earth-Moon orbit (Coughenour et al, 2009; Hansen, 1982) and the global mixing of the ocean (Munk & Wunsch, 1998)—has occupied the minds of scientists for over a century (Jeffreys & Shaw, 1920; Taylor & Shaw, 1919). We choose the GBB as a proof-of-concept study because shallow water carbonate platforms represent the most important ancient archive of sea level, environmental, and ocean geochemical information, so studying modern analog settings such as the Bahamas is a key component of any translation of the rock record into paleoenvironmental interpretations (e.g., Broecker & Takahashi, 1966; Dyer et al, 2018; Geyman & Maloof, 2019b; Harris et al, 2015; Maloof & Grotzinger, 2012; Oehlert et al, 2012; Patterson & Walter, 1994; Swart et al, 2009) It has become clear in modern settings that tidal pumping of water and nutrients plays a critical role controlling the transport and chemistry of carbonate sediment, but global tide models still cannot resolve tidal dynamics on shallow platforms (Shum et al, 1997)

Data and Methods

Results

Discussion