Platform Harvest Research Articles

Estimated air emissions savings from partially removing and reefing the jacket of a large California oil and gas platform

This paper estimates the potential emission savings that could be achieved if the jacket of a large California oil and gas platform is partially removed and converted to an artificial reef rather than fully removed. The platform selected for study is Platform Harvest which is located on the federal Outer Continental Shelf (OCS) offshore Point Conception in Santa Barbara County, California. Platform Harvest, a large steel jacketed structure located in 675 feet of water, ceased production in 2015 and plans are now being developed for removing the structure. Under the partial removal option, the upper sections of the jacket would be removed to a depth of 85 feet below the ocean surface with the remainder left in-situ to serve as an artificial reef. The full removal option involves removing the entire jacket by cutting the jacket legs and piles off 15 feet below the seabed, cutting the jacket into sections for lifting by a heavy lift vessel, and transporting the jacket components on cargo barges to shore for recycling or disposal. The results of the study show the partial removal jacket option would result in a 10-fold reduction in emissions of nitrogen oxide, sulfur dioxide, green-house gases, and other criteria pollutants as compared to the full removal option.

Wideband Ocean Altimetry Using Ku-Band and K-Band Satellite Signals of Opportunity: Proof of Concept

A proof-of-concept experiment has demonstrated that wideband (400 MHz) signals of opportunity (SoOp) transmitted in K- and Ku-bands from geostationary satellites can be used for coastal altimetry. An essential finding from this experiment is that the full broadcast spectrum consisting of multiple digital channels can be processed as a single wideband signal source. An established error model for Global Navigation Satellite System interferometric altimetry was shown to accurately represent the sea surface height (SSH) retrievals when evaluated using the full bandwidth. This experiment was conducted over a 72-h period at Platform Harvest off the Pacific Coast. Colocated tide gauge and LiDAR measurements were used as in situ data. Two anomalies were observed in the experiment: 1) multiple peaks in the cross correlation waveform from one polarization of Ku-band frequency and 2) decrease in signal-to-noise ratio from loss of a data channel. When the instances of multiple peaks were eliminated and the equivalent bandwidth recomputed using only the active channels, SSH error from these cases agreed well with the model prediction. Application of SoOp wideband altimetry will, therefore, require a monitoring capability to identify changes in the transmission spectrum, total power, and waveform shape, for quality control and setting an appropriate observation error covariance. Measurement precision from a satellite receiver is predicted to be between 4 and 6 cm using the error model. SoOp altimetry with these signals may improve coastal measurements and increase the sampling and revisit rate through the use of a constellation of small satellites.

Precision of Ku-Band Reflected Signals of Opportunity Altimetry

This letter provides a proof-of-concept experiment and validation of an error model for bistatic altimetry using signals of opportunity (SoOps). Coastal sea surface height plays a prominent role in measuring the total water-level envelope directly and is one of the key quantities required by storm surge applications and services. Nadir satellite altimeters have a long history of mapping the variability of the earth’s open ocean. However, they exhibit problems operating in coastal areas due to the effects, such as land contamination, rapid variations due to tides, and atmospheric effects. One technique for filling this gap is bistatic altimetry using SoOp (e.g., digital communication signal reflections). In this letter, we investigate capabilities of this technique. Twenty three days of data were collected at platform harvest from a single channel of the Ku-Band direct broadcast satellite. The wind speed observed during the experiment was between 4 and 14 m/s and significant wave height was between 0.7 and 4 m as measured by buoy 46 218 located 8 km away. The standard deviation in the estimation of height was found to be 7.2 cm (the same as predicted from theory). Using a least-squares approach improved the precision reducing the standard deviation to 6.8 cm. It is shown that the error in the estimation of height can be reduced to 3.5 cm by utilizing the full bandwidth (all the channels) of the SoOp. Extrapolating these results, we predict a precision of 5.3 cm from a typical (e.g., Jason) orbit of 1380 km.

A proposed probabilistic seismic tsunami hazard analysis methodology

We expand on existing probabilistic tsunami hazard analysis (PTHA) approaches by presenting a methodology wherein the epistemic uncertainties associated with tsunami timing, generation, and propagation are separated from aleatory uncertainties. The contributions of epistemic and aleatory uncertainties to the overall uncertainty in tsunami hazard are evaluated through a two-level Monte Carlo analysis. The total epistemic uncertainty contribution defines the variance of the tsunami inundation hazard distribution. Through Bayesian inference, the available catalog of tsunami runup data is used to refine the hazard estimate, where the prior distribution is weighted by epistemic uncertainties. The general PTHA framework is further modified to include a hazard function accounting for peak water elevation, velocity, duration of inundation, and warning time. We carry out a formal sensitivity analysis of the tsunami generation and propagation on the feasible model parameter space using the multi-objective generalized sensitivity analysis algorithm. Parameters showing a significant influence on tsunami hazard include the tidal elevation, moment magnitude (M w), the Gutenberg–Richter (G–R) distribution β parameter, epicenter location, and the rake angle. Parameters showing minimal influence on tsunami hazard include the G–R maximum seismic moment magnitude (M max) parameter, strike angle, dip angle, seismic depth and Manning’s roughness. As a proof of concept, the methodology is applied to a case study of tsunami hazard posed to National Oceanic and Atmospheric Administration Station 9411406 (Oil Platform Harvest, CA, USA) by seismic sources along the Aleutian Islands, AK.

Application of the ICF Coherence Time Method for Ocean Remote Sensing Using Digital Communication Satellite Signals

This paper applies an ocean remote sensing method, first developed for reflected Global Navigation Satellite System (GNSS-R) signals, to reflected digital communication satellite signals. The fundamental observation is the time series of the Interferometric Complex Field (ICF) of the reflected signal. A relationship is derived between the coherence time of the ICF time series and the significant wave height (SWH) and mean wave period (MWP) of the ocean. Direct and reflected signals from the S-band satellite transmissions providing the commercial XM radio service were recorded at Platform Harvest over a 65-day period. In situ measurements from a nearby buoy were used to calibrate this measurement by determining coefficients of a semi-empirical model. SWH retrievals using this model on 1 min of reflected signal observations were found to have a standard deviation of 0.38 m over the range from 1 to 4.5 m. An error analysis was done to show that the primary contribution to this error was uncertainty in the relationship between MWP and SWH, and to quantify the retrieval error from different forward models.

Long term changes of altimeter range and geophysical corrections at altimetry calibration sites

Accurate sea level trend determination is fundamentally related to calibration of both the instrument as well as to investigate if there are linear trends in the set of standard geophysical and range corrections applied to the sea level observations. Long term changes in range corrections can leak into the observed sea level record and be interpreted as part of the sea level trend. Particularly if these exhibit anomalous trend close to the satellite calibration sites.Long term changes in the routinely applied TOPEX/Jason corrections as well as their changes in coastal regions are investigated at four altimetry calibration sites: Bass Strait, Corsica, Gavdos and platform Harvest. Furthermore, alternative corrections are tested to investigate if the use of a different set of corrections will lead to different local and regional sea level changes at those sites. The results show that no significant linear trends in the sum of range corrections are found for the calibrations sites both for local scales (within 50km around the selected site) and for regional scales (within 300km). However, the geophysical corrections accounting for atmospheric pressure loading and high frequency sea level variations (dynamic atmosphere correction) that is frequently applied to in situ gauge and the altimeter observations should be considered with care for calibration with in situ observations. Over the 18years (1993–2010), the dynamic atmosphere correction shows a regional trend close to 1mm/year at both Mediterranean sites (Corsica and Gavdos).

GPS monitoring of vertical seafloor motion at Platform Harvest

We describe results from two decades of monitoring vertical seafloor motion at the Harvest oil platform, NASA’s prime verification site for the TOPEX/Poseidon and Jason series of reference altimeter missions. Using continuous GPS observations, we refine estimates of the platform subsidence—due most likely to fluid withdrawal linked to oil production—and describe the impact on estimates of stability for the altimeter measurement systems. The cumulative seafloor subsidence over 20yrs is approximately 10cm, but the rate does not appear constant. The apparent non-linear nature of the vertical motion, coupled with long-period GPS errors, implies that the quality of the seafloor motion estimates is not uniform over the 20-yr period. For the Jason-1 era (2002–2009), competing estimates for the subsidence show agreement to better than 1mmyr−1. Longer durations of data are needed before the seafloor motion estimates for the Jason-2 era (2008–present) can approach this level of accuracy.

The Harvest Experiment: Monitoring Jason-1 and TOPEX/POSEIDON from a California Offshore PlatformSpecial Issue: Jason-1 Calibration/Validation

We present calibration results from Jason-1 (2001–) and TOPEX/POSEIDON (1992–) overflights of a California offshore oil platform (Harvest). Data from Harvest indicate that current Jason-1 sea-surface height (SSH) measurements are high by 138 ± 18 mm. Excepting the bias, the high accuracy of the Jason-1 measurements is in evidence from the overflights. In orbit for over 10 years, the T/P measurement system is well calibrated, and the SSH bias is statistically indistinguishable from zero. Also reviewed are over 10 years of geodetic results from the Harvest experiment.

Mapping the sea surface using a GPS buoy

On May 22 and 24, 1995, a buoy, designed to float with the water surface and equipped with a GPS antenna, was deployed off the California coast at 16 locations near the Texaco oil platform, Harvest. The purpose of this deployment was threefold:.(1) to demonstrate the ability of this style of buoy to calibrate the TOPEXIPOSEIDON (TIP) altimeter range measurement as it overflew the platform: (2) to demonstrate the ability of the buoy to map the ocean's surface over a 10‐km‐diameter circle surrounding platform Harvest; and (3) to demonstrate the ability of the buoy to measure the sea state accurately. During the 1.6‐h period surrounding the time of the TIP overflight, the buoy‐measured sea level never differed by more than 1.5 cm from the sea level measured by the National Oceanic and Atmospheric Administration (NOAA) acoustic tide gauge on the platform. The good agreement demonstrated the capability of this style of buoy to calibrate altimetric satellites. A paraboloid was fitted to sea level from 16 buoy locations surrounding the platform with a 2.5‐cm rms residual. On a 10‐km‐diameter circle centered on the platform, the paraboloid was within 2.4‐cm rms of the Ohio State University Mean Sea Surface (OSUMSS95). H u3 values calculated around the overflight times from the GPS buoy vertical positions had a mean difference of 2 cm and a standard deviation of 18 cm from values calculated from the University of Colorado (CU) pressure gauge system. At the time of the overflight, H u3 was near 2 m, while 3‐m seas were observed by the CU pressure system during measurements later in the day. This experiment demonstrates that a simple wave‐rider buoy design can give comparable accuracies to that of more complex GPS platforms such as the University of Colorado's spar buoy, but is much easier to deploy and capable of being used in more severe weather conditions. Thus, such a buoy and derivative designs have great potential for calibrating altimetric experiments, and for oceanographic and geodetic mapping experiments.

On the sea state dependence of sea level measurements at Platform Harvest

This paper investigates correlations between sea level measurements and H 1/3 at Texaco's Platform Harvest. In order to do so, a relationship is shown between the sample standard deviations of the 6‐min NOAA acoustic system measurements and H 1/3 as estimated from CU Paros depth sensors. A transfer function for the NOAA acoustic system is developed by comparison between spectra of 2‐s tsunami mode data with spectra from 1.1‐s pressure data. Part of this transfer function is caused by the decay in pressure effects due to waves between the surface and the orifice of the protective well. The rest is due to damping characteristics of the protective well itself. The transfer function helps show the limitations of using the sample standard deviations of the NOAA acoustic system as a measure of H 1/3 . Differences between sea level measurements show a distinct component related to H 1/3 . The effects related to H 1/3 low‐frequency differences in the measurements, and wave effects are separated using an iterative procedure. If H 1/3 ‐related effects are removed, then the sea level measurements agree to better than 1 cm rms for all three systems. The cause of the low‐frequency differences is not understood. An estimate of the H 1/3 dependence of each individual system is found by removing a 1‐year tidal prediction based on the NOAA acoustic system from sea level from each of the systems. It is assumed that real H 1/3 dependencies in sea level are small. The resulting residuals are iteratively separated as before. These results indicate that the greatest H 1/3 dependence is found in the NOAA Digibub system and the least in the NOAA acoustic system. It should be noted that the H 1/3 dependency found here occurs because of the harsh open ocean conditions at Platform Harvest and would not be expected to be observed under normal conditions in sheltered waters such as harbors, rivers, or lagoons.

CU sea level system at Platform Harvest

Calibration data for the TOPEX/Poseidon altimeter was collected at Texaco's Platform Harvest off the coast of southern California. The CU sea level system, containing two Paros depth sensors, was designed and installed at Platform Harvest to collect submerged pressure data. Corrections for instrument bias, water density, and atmospheric pressure were applied to each depth sensor and sea level obtained relative to an established benchmark on the platform. Estimates of H 1/3 were determined to characterize the sea state during the 2‐h period surrounding each overflight using classical theory. To test the validity of these assumptions, the ratio between spectra measurements from the upper and lower depth sensors was normalized by the expected theoretical ratio. The results differ from theory by ∼1% with a standard deviation of ∼2%. The weighted mean frequency as a function of H 1/3 was calculated during several overflight periods. Results indicate that the frequency content tends to be bimodal for H 1/3 valu...

Significant waveheight comparisons between TOPEX and Platform Harvest

Two sources of H1/3 estimates were available at Platform harvest; a NOAA buoy and CU depth sensor highrate data.

Platform Harvest sea level measurement comparisons

Three in situ water level measurement systems have been installed on Platform Harvest in support of the TOPEX/Poseidon Satellite Verification Experiment. Each of the systems have fundamentally different instrument configurations, which provides a unique simultaneous set of measurements in a deep water‐exposed near‐shore environment. Each of the sensor “zeros”; have also been referenced to the same datum as a requirement of the experiment; thus absolute differences can be analyzed. Straightforward, simple comparisons of the systems are presented for TOPEX/Poseidon cycles 2 through 30. The systems are shown to agree well both in the mean and in frequency content. Nontidal sea level residuals are shown to be highly correlated to atmospheric pressure.

Overview of the TOPEX/Poseidon Platform Harvest verification experiment

An overview is given of the in situ measurement system installed on Texaco's Platform Harvest for verification of the sea level measurement from the TOPEX/Poseidon satellite. The prelaunch error budget suggested that the total root mean square (RMS) error due to measurements made at this verification site would be less than 4 cm. The actual error budget for the verification site is within these original specifications. However, evaluation of the sea level data from three measurement systems at the platform has resulted in unexpectedly large differences between the systems. Comparison of the sea level measurements from the different tide gauge systems has led to a better understanding of the problems of measuring sea level in relatively deep ocean. As of May 1994, the Platform Harvest verification site has successfully supported 60 TOPEX/Poseidon overflights.

GPS measurements of the baseline between Quincy and Platform Harvest

As part of TOPEX altimeter verification, the Global Positioning System has been used to measure the baseline between the verification site at oil platform Harvest and a GPS antenna collocated with the satellite laser ranging site at Quincy, California.

NOAA/National Ocean Service Platform Harvest instrumentation

NOAA has installed two separate water level measurement systems and a suite of ancillary measurement sensors in support of the TOPEX/Poseidon Verification Experiment at Texaco Platform Harvest. The experimental measurement systems are modifications of NOAA's next‐generation water level measurement system (NGWLMS) that is being implemented into the National Water Level Observation Network of the United States. The primary system is configured with a downward looking acoustic water level sensor and the secondary system with a digital “bubbler”; pressure water level sensor (Digibub). The ancillary measurements being made are of barometric pressure, relative humidity, air temperature, water temperature, and water conductivity. Six‐minute interval measurements from each water level sensor and hourly measurements from each ancillary sensor are collected on independent remote terminal units on the platform. The data are transmitted every 3 h via GOES satellite to NOAA for processing in Silver Spring, Maryland. The installation of the measurement systems on the offshore oil platform has required a unique set of elevation corrections that are applied on an operational basis to the water level elevations. These include acoustic sound path air temperature differences for the acoustic data, and water density, nitrogen, and air column corrections to the Digibub data. NOAA field personnel have completed a platform survey in which elevation differences on the platform between the water level sensor “zeros”; and the GPS reference point were established.

Calibration of TOPEX/POSEIDON at Platform Harvest

We present estimates for the mean bias of the TOPEX/POSEIDON NASA altimeter (ALT) and the Centre National d'Etudes Spatiales altimeter (SSALT) using in situ data gathered at Platform Harvest during the first 36 cycles of the mission. Data for 21 overflights of the ALT and six overflights of the SSALT have been analyzed. The analysis includes an independent assessment of in situ measurements of sea level, the radial component of the orbit, wet tropospheric path delay, and ionospheric path delay. (The sign convention used in this paper is such that, to correct the geophysical data record values for sea level, add the bias algebraically. Unless otherwise stated, the uncertainty in a given parameter is depicted by ±σx, where σx is the sample standard deviation of x about the mean.) Tide gauges at Harvest provide estimates of sea level with an uncertainty of ±1.5 cm. The uncertainty in the radial component of the orbit is estimated to be ±1.3 cm. In situ measurements of tropospheric path delay at Harvest compare to within ±1.3 cm of the TOPEX/POSEIDON microwave radiometer, and in situ measurements of the ionospheric path delay compare to within −0.4±0.7 cm of the dual‐frequency ALT and 1.1±0.6 cm of Doppler orbitography and radiopositioning integrated by satellite. We obtain mean bias estimates of −14.5±2.9 cm for the ALT and +0.9±3.1 cm for the SSALT (where the uncertainties are based on the standard deviation of the estimated mean , which is derived from sample statistics and estimates for errors that cannot be observed). These results are consistent with independent estimates for the relative bias between the two altimeters. A linear regression applied to the complete set of data shows that there is a discernable secular trend in the time series for the ALT bias estimates. A preliminary analysis of data obtained through cycle 48 suggests that the apparent secular drift may be the result of a poorly sampled annual signal.

Calibration of the TOPEX altimeter using a GPS buoy

The use of a spar buoy equipped with a Global Positioning System (GPS) antenna to calibrate the height measurement of the TOPEX radar altimeter is described. In order to determine the height of the GPS antenna phase center above the ocean surface, the buoy was also equipped with instrumentation to measure the instantaneous location of the waterline, and tilt of the buoy from vertical. The experiment was conducted off the California coast near the Texaco offshore oil platform, Harvest, during cycle 34 of the TOPEX/POSEIDON observational period. GPS solutions were computed for the buoy position using two different software packages, K&RS and GIPSY‐OASIS II. These solutions were combined with estimates of the waterline location on the buoy to yield the height of the ocean surface. The ocean surface height in an absolute coordinate system combined with knowledge of the spacecraft height from tracking data provides a computed altimeter range measurement. By comparing this computed value to the actual altimeter measurement, the altimeter bias can be calibrated. The altimeter height bias obtained with the buoy using K&RS was −14.6±4 cm, while with GIPSY‐OASIS II it was −13.1±4 cm. These are 0.1 cm and 1.6 cm different from the −14.7±4 cm result obtained for this overflight with the tide gauge instruments located on Platform Harvest.

Using FMS Log to Aid in Structural Interpretation, Point Arguello, Offshore California: ABSTRACT

Formation Microscanner (FMS) images computed by Schlumberger from dual dipmeter's microresistivity curves have been used as an aid in mapping complex thrust structures at Platform Harvest, Point Arguello field, offshore California. The FMS images were analyzed and compared to the tadpole plots from seven deviated wells drilled into the fractured Monterey Formation. Intervals where the dipmeter data was highly scattered or unresolved on the tadpole plots were resolved by examining the FMS images. Tight folds where the bedding was to steep for resolution by a dipmeter could be identified through the examination of the FMS images. Additional structural details such as fold geometry, hinge area characteristics, and fault induced breccia zones could be identified, allowing detailed correlation and mapping of the Monterey Formation structure.