Airborne Ocean Surface Current Measurements for Offshore Applications

Anderson, Steven P.; Zuckerman, Seth; Smirren, Jan van; Smith, Robert

doi:10.4043/25956-ms

Cited by 3 publications

(4 citation statements)

References 10 publications

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“…The measurement noise levels are shown in the right hand columns of Figures 23 and 24. The measurement noise values for ROCIS are between 0.05 m/s and 0.1 m/s and agree well with previous estimates of ROCIS performance [8]. On the 26th DopplerScatt collected data using a high-resolution mode and a low-resolution mode on the 25th.…”

Section: Surface Current Comparisonssupporting

confidence: 86%

“…We have presented the results of an experiment conducted on and around a Chevron platform instrumented site in the Gulf of Mexico that was near the edge of a loop current eddy, that compared two different methods for measuring ocean surface currents using remote sensing. The first method, implemented by the the Remote Ocean Current Imaging System (ROCIS) [8], utilizes Doppler shifts in the surface wave dispersion relation, which can be estimated by computing the space-time spectra of digital imagery. The second method, Doppler scatterometry [4], implemented by the NASA/JPL DopplerScatt instrument, measures the Doppler shift in the capillary phase velocity due to surface currents.…”

Section: Discussionmentioning

confidence: 99%

“…Note that classical Stewart and Lovejoy [14] result in this equation will not apply in the presence of wave breaking. ROCIS uses multiple surface wave wavelengths to form an average current estimate [8], and the effective depth of the estimated current is representative of the average current over the top few meters. Due to averaging over the collected data, one independent surface current measurement is obtained every 675 m [8].…”

Section: The Rocis Instrumentmentioning

confidence: 99%

“…The strong current fronts associated with Loop Current eddies provided an environment suitable for assessing the DopplerScatt surface current estimates in the presence of strong and weak currents, and in the presence of significant horizontal current shear, as well as different current measurement depth. As an independent measurement of the DopplerScatt surfaces currents, we used surface currents measured by the mature Remote Ocean Current Imaging System (ROCIS) [8], as well as near-surface ADCP measurements from a stationary buoy. The presence of independent ROCIS information also allowed for the validation of the corrections that must be applied to the DopplerScatt currents to remove gravity wave modulation effects.…”

Section: Introductionmentioning

confidence: 99%

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Ka-Band Doppler Scatterometry over a Loop Current Eddy

et al. 2020

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Doppler scatterometry is a promising new technique for the simultaneous measurement of ocean surface currents and winds. These measurements have been recommended by the recent US NRC Decadal Review for NASA as being priority variables for the coming decade of Earth observations. In addition, currents and winds are useful for many applications, including assessing the operating conditions for oil platforms or tracking the dispersal of plastic or oil by surface currents and winds. While promising, Doppler scatterometry is relatively new and understanding the measurement characteristics is an important area of research. To this end, Chevron sponsored the deployment of DopplerScatt, a NASA/JPL Ka-band Doppler scatterometer, over instrumented sites located at the edge of a Gulf of Mexico Loop Current Eddy (LCE). In addition to in situ measurements, coincident synoptic maps of surface currents were collected by the Areté ROCIS instrument, an optical current measurement system. Here we report on the results of this experiment for both surface currents and winds. Surface current comparisons show that the Ka-band Current Geophysical Model Function (CGMF) needs to include wind drift currents, which could not be estimated with prior data sets. Once the CGMF is updated, ROCIS and DopplerScatt show good agreement for surface current speeds, but, at times, direction differences on the order of 10° can occur. Remote sensing optical and radar data agree better among themselves than with ADCP currents measured at 5 m depth, showing that remote sensing is sensitive to the the currents in top 1 m of the ocean. The LCE data provided a unique opportunity to study the effects of surface currents and stability conditions on scatterometer winds. We show that, like Ku-band, Ka-band estimates of winds are related to neutral winds (and wind stress) and are referenced relative to the moving frame provided by the current. This is useful for the study of air-sea interactions, but must be accounted for when using scatterometer winds for weather prediction.

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Section: Surface Current Comparisonssupporting

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Section: The Rocis Instrumentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ka-Band Doppler Scatterometry over a Loop Current Eddy

et al. 2020

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Assessing the Variability in Intensity and Width of the Loop Current Eddy High Speed Band from Airborne Ocean Surface Current Measurements

Schiller

Smith

et al. 2017

Day 2 Tue, May 02, 2017

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The specific position and variability in width and intensity of the high speed band of currents associated with Loop Current Eddies (LCEs) is of significant interest to offshore operators in the Gulf of Mexico. This is particularly the case when undertaking drilling or offshore development operations and the activities may be located close to or inside the LCE. A study of the Remote Ocean Current Imaging System (ROCIS) data from May 2015 has been undertaken to provide further insight into the variability in intensity and width of the LCE high speed band. We defined the band to be limited by the 0.75 m/s (~1.5 knots) threshold, a typical limit for offshore operations in the Gulf of Mexico. Preliminary results show relevant spatial and temporal variability. The width of the high speed band ranged between ~40–100 km, depending on the state of the LCE, interactions with surrounding eddies and the geopgraphical location of the measurements. Peak speeds ranged from about 1m/s to 1.9 m/s. The shape of the speed profile across the band was also variable. Some cases presented a strong correlation with the Sea Surface Temperature (SST) front of the LCE, where speeds dropped significantly outside of the front. The identification of a few patterns of the high speed band was a promising result within the ongoing effort to derive expected relationships between LCE metrics such as high speed band witdth, intensity, LCE area and strength of the SST front.

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Development and Deployment of the Surface Current Imaging Nowcast System

Anderson

Zuckerman

Stear

et al. 2021

Day 2 Tue, August 17, 2021

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This paper describes the development and installation of an ocean surface current monitoring device called SCINS: Surface Current Imaging Nowcast System. We describe the process of designing and building the prototype system, installation on an offshore platform, implementation of real-time reporting, and results from one year of operations. SCINS utilizes passive long-wave infrared imaging of the ocean to derive surface currents. This is done using a time-series of images to observe the phase-speed of the ocean waves. Then, the Doppler shift of the observed waves due to the surface current is determined using a non-linear least squares fit. The primary components of SCINS are a long-wave infrared camera and a data acquisition computer. The camera is mounted several 10s of m above the water surface. The system collects imagery at 2 Hz for 5 minutes every 15 minutes, day and night, and calculates surface currents in real-time. In this paper, we describe the results from deploying SCINS on an offshore platform, Chevron's Big Foot TLP, in the Gulf of Mexico for one year of continuous data collections, including several tropical storm and hurricane events. Results are compared to environmental data to describe system performance as a function of wind, wave, and sea conditions. We describe the engineering challenges and lessons learned from designing and installing this new type of passive imaging system for offshore use. We conclude that SCINS is an effective method for measuring surface currents in the vicinity of offshore platforms, requiring very little maintenance and without the need to put any instrumentation in the water.

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Airborne Ocean Surface Current Measurements for Offshore Applications

Cited by 3 publications

References 10 publications

Ka-Band Doppler Scatterometry over a Loop Current Eddy

Ka-Band Doppler Scatterometry over a Loop Current Eddy

Assessing the Variability in Intensity and Width of the Loop Current Eddy High Speed Band from Airborne Ocean Surface Current Measurements

Development and Deployment of the Surface Current Imaging Nowcast System

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