Round-trip Travel Time Research Articles

Range-resolved gas concentration measurements using tunable semiconductor lasers

A method for range-resolved gas sensing using path-integrated optical systems is presented. The method involves dividing an absorption path into several measurement segments and extracting the gas concentration in each segment from two path-integrated measurements. We implemented the method with tunable lasers (a 1389-nm VCSEL and a 10.9-μm pulsed quantum cascade laser) and a group of retro reflectors (RRs) distributed along absorption paths. Using a rotating mirror with the VCSEL configuration, we could scan a group of seven tape RRs spaced by 10 cm in ∼ 9 ms to extract an H2O concentration profile. Reduced H2O concentrations were recorded in the segments purged with dry air. Hollow corner cube RRs were used in the quantum cascade laser configuration at distances up to 1.1 km from the laser. Two RRs placed at 66 m and 125 m from the laser allowed us to determine H2O concentrations in both segments. The RRs returns were separated due to the different round trip travel time of the 200-ns laser pulse. Novel instruments for range-resolved remote sensing in the atmosphere can be developed for a variety of applications, including monitoring the fluxes of atmospheric pollutants and controlling air quality in populated areas.

Arterial Wave Refection Properties Are Associated With C-Reactive Protein And Exercise Capacity In Heart Transplant Recipients

Recent studies suggest that central artery augmentation index (AI), a composite measure of the amplitude and timing of the arterial reflected pressure wave, is positively associated with serum C-reactive protein (CRP) and inversely associated with exercise capacity in healthy adults. In heart transplant recipients (HTRs) during the first year after transplantation, elevated CRP is an independent predictor of cardiac vasculopathy and mortality, and exercise capacity remains 60-70% of age-matched healthy subjects. PURPOSE: To determine whether central artery wave refection properties are associated with CRP and exercise capacity in HTRs early after transplantation. METHODS: Two months after heart transplantation, 20 HTRs [age=54.4±2.3 yrs; sex=15M/5F; body mass index, BMI=26.2±0.7 kg/m2] reported to the laboratory after an 8 hour fast. Aortic pressure waveforms were synthesized using a validated generalized transfer function obtained from high-fidelity non-invasive pressure waveforms of the radial artery via applanation tonometry. Central AI was calculated as the ratio of aortic augmented pressure to aortic pulse pressure and was corrected for heart rate. The roundtrip travel time of the reflected wave to and from peripheral reflecting sites (ATp) was calculated as the time duration between the diastolic foot and the infection point of the aortic pressure wave. Fasting venous blood samples were obtained to determine serum lipids and plasma inflammatory proteins and a symptom-limited treadmill test with oxygen uptake (VO2) was performed to determine exercise capacity. RESULTS: AI and δTp were positively (r=0.68, p=0.001) and inversely (r=−0.62, p=0.003) associated with logCRP, respectively, but not with interleukin-6, tumor-necrosis factor-α, HDL, LDL, total cholesterol, age, blood pressure, or BMI. AI was also inversely associated (r=−0.54, p=0.016; r=−0.51, p=0.027) and δTp was positively associated (r=0.47, p=0.04; r=0.57, p=0.01) with peak VO2 and exercise test duration, respectively. Furthermore, CRP was inversely associated with exercise test duration (r=−0.65, p=0.003) and peak VO2 (r=−0.43, p=0.06). CONCLUSIONS: Increased arterial pressure wave refection is associated with elevated CRP and reduced exercise capacity in HTRs during the early post-transplantation period.

Effect of resistance training on arterial wave reflection and brachial artery reactivity in normotensive postmenopausal women

Large elastic artery stiffness increases with age and menopause is a mitigating factor in women. High-intensity resistance training (RT) increases arterial stiffness in young men and women. However, the effects of moderate intensity RT on central aortic pressure wave reflection in healthy postmenopausal women are unknown. Healthy sedentary normotensive postmenopausal women were randomly assigned to either 18 weeks (2 days/week) of RT (RES n = 13) or aerobic training (AER n = 10). Central aortic pressure wave reflection and brachial artery reactivity were assessed before and after training. Central aortic pressure wave reflection was evaluated by measuring aortic augmentation index (AI(a)) and round trip travel time (Deltat (p)) of the reflected arterial pressure wave using applanation tonometry. Brachial artery reactivity was assessed using brachial artery flow mediated dilation (FMD). Eighteen weeks of RT did not change AI(a) (28.9 +/- 1.9 vs. 28.5 +/- 1.9%; mean +/- S.E.M.) or Deltat (p) (140.6 +/- 2.4 vs. 141.2 +/- 2.1 ms). In contrast, the AER group showed a decrease in AI(a) from 28.8 +/- 2.1 to 25.1 +/- 1.4% (P < 0.05) and an increase in Deltat (p) from 137.3 +/- 2.5 to 144.6 +/- 2.9 ms (P < 0.05). Brachial FMD did not significantly change in either group following training. This prospective, randomized study demonstrated that moderate intensity whole body RT in previously sedentary, normotensive postmenopausal women does not alter central aortic pressure wave reflection.

Effects of Resistance Exercise Training on Arterial Function in Young, Healthy Men and Women

PURPOSE: There is evidence that resistance exercise (RT) can increase central arterial stiffness during high-intensity and high-volume training regimens. The purpose of this study was to determine whether RT, when performed in accordance with ACSM guidelines, has deleterious effects upon central arterial function in young, healthy men and women. METHODS: Previously untrained subjects were assigned either to a group that performed RT 3 days/week for 12 weeks (TRAIN; n=22; 19.8 ± 1.4 yrs) or to a control group that did not train (CONTR; n=12; 20.7 ± 2.9 yrs). Training consisted of 2 sets of 12 repetitions performed to volitional failure on 7 variable resistance machines. Resting aortic augmentation index normalized at 75 bpm (AIa), round trip travel time of aortic pressure waves (Dtp), and regional arterial pulse wave velocity (PWV) were measured non-invasively using applanation tonometry. Regional PWV (m/sec) between the carotid-radial (CRPWV), carotid-femoral (CFPWV), and femoral-dorsalis pedis (FDPWV) arteries were calculated by determining the delay between the appearance of the pressure waveform foot in each site with simultaneous ECG. AIa and Dtp were calculated from aortic pressure waveforms, which were synthesized using a generalized transfer function from high fidelity radial pressure waveforms calibrated from standard brachial artery sphygmomanometry in triplicate. RESULTS: AIa and Dtp were unchanged in TRAIN (from-1.6±14.1 to 1.2±10.5 %; from 157.4±28.3 to 155.5±12.8 msec) and CONTR (from-4.0±9.1 to-3.4±10.2 %; from 151.3±11.6 to 154.7±10.6 msec). CRPWV, CFPWV, and FDPWV were unchanged in TRAIN (from 8.4±1.1 to 8.0±1.0 m/s; from 6.2±0.6 to 6.3±0.8 m/s; from 9.4±1.5 to 9.6±1.4 m/s) and CONTR (from 8.2±0.7 to 8.0±0.6 m/s; from 7.0±0.7 to 6.9±0.8 m/s; from 8.3±1.1 to 8.1±1.1 m/s). TRAIN significantly (p=0.05) increased Chest Press (+37.5%) and Leg Extension (+41.9%) strength. CONTR values for Chest Press (+1.0%) and Leg Extension (+0.5%) strength did not change. CONCLUSION: RT had no adverse effects upon either amplitude and timing of aortic reflected pressure or regional arterial PWV in young, healthy men and women when training was performed consistent with ACSM guidelines.

Effect of Acute Cold Pressor Test on Amplitude and Timing of Central Pressure Wave Reflection in Young Healthy Adults

Physiological states of chronic elevated sympathetic nervous system (SNS) activity (e.g., aging, heart failure) are associated with increased central artery stiffness. However, the role of acute SNS activation on central arterial pressure wave reflection properties and arterial stiffness are unknown. PURPOSE: To investigate the effects of acute SNS activation on aortic pressure wave reflection properties and arterial stiffness in young, healthy adults. METHODS: Ten subjects (age 25.0±3.3 yrs; 7M/3F) performed a cold pressor test (CPT) via hand immersion in ice water (4°C) for 3 min. Aortic pressure waveforms were synthesized using a generalized transfer function from non-invasive radial pressure waveforms (calibrated from brachial sphygmomonometry) obtained via applanation tonometry on the contralateral arm before (PRE), immediate-post (IP), 90 sec-post, and 180 sec-post CPT. Aortic augmentation index (AIa), a measure of amplitude and timing of arterial wave reflection, and AT, the roundtrip travel time of the reflected wave to and from the periphery, were used as indices of arterial stiffness. One-way ANOVA w/repeated measures and pairwise comparisons w/Bonferonni correction were used for analysis. RESULTS: Blood pressure (BP) and hemodynamic variables (mean±SD) are displayed n the table below (*p<0.0167 vs. PRE):TableThe IP change in mean BP was significantly correlated to IP change in AIa (r=0.80, p=0.01), but not to the IP change in AT (r=−0.41, p=0.26). Furthermore, the magnitude of increase in systolic BP (28.0±15.4% vs. 20.4±13.4%, p=0.016) and pulse BP (25.7±26.5% vs. 11.4±17.2%, p=0.02) was greater in the aorta than in the brachial artery, respectively. CONCLUSIONS: Acute elevation in SNS activity via CPT results in a significant increase in AI due in part to increased mean arterial BP. However, the larger increase in systolic and pulse BP in the aorta than in the brachial artery suggests an increased amplitude and/or early return of the central arterial reflected wave from the periphery also contributes to increased arterial stiffness during acute SNS activation.

Internal Tides in the Southwestern Japan/East Sea

Abstract This paper investigates the internal tidal energy distribution in the southwestern Japan/East Sea using vertical round-trip travel time (τ) data from 23 pressure-sensor-equipped inverted echo sounders (PIES). The τ records are analyzed by bandpass filtering to separate time-dependent variability of the semidiurnal and diurnal bands. The semidiurnal internal tides exhibit a horizontal beam pattern of high energy, propagating into the open basin. They originate from a restricted portion of the shelf break where the Korea Strait enters the Ulleung Basin. The generation appears to occur at ∼200-m water depth near 35.5°–35.7°N and 130°–131°E, where the slope of bottom topography matches that of the wave characteristics, coinciding with the location where the semidiurnal barotropic cross-slope tidal currents are strongest. Maximum vertical displacement of the thermocline interpreted as a long-wave first baroclinic mode from the measured τ is about 25 m near the generation region. Annual and monthly variations of the propagation patterns and generation energy levels are observed, and these are closely associated with changes in the mesoscale circulation and stratification. Eastward (westward) refraction is observed when a warm (cold) eddy crosses the path of internal tide propagation. Moreover, when the generation region is invaded by cold eddies that spoil the match between shelf break and thermocline depth, the internal tidal energy level decreases by a factor of about 2. A simple geometric optics model is proposed to explain the observed horizontal refraction of the beam of semidiurnal internal tides in which stratification and current shear play essential roles. In contrast, diurnal internal tides are observed to be trapped along the continental slope region around 36°N.

A Multi-Index GEM Technique and Its Application to the Southwestern Japan/East Sea

Abstract This paper demonstrates a new gravest empirical mode (GEM) technique that constructs multi-index lookup tables of temperature (T) and specific volume anomalies (δ) using historical hydrocasts as a function of three indices: round-trip travel time (τ) from sea floor to the surface, sea surface temperature, and pressure. Moreover, the historical hydrocasts are separated into non-mixed-layer (NML) and mixed-layer (ML) groups, and a single GEM field is constructed for each group. This is called the MI-GEM technique. The appropriate dates for MI-GEM fields are determined by the monthly distribution of the number of NML and ML profiles in the historical hydrocasts, which are also well correlated with the strength of the winds during the 2 yr of observations. The T and δ profiles that are determined by this MI-GEM technique capture 92% and 88% of the T and δ variances in the depth range of 0–200 db. These values reduce by about one-third of the unexplained error variance of the residual GEM, which was recently developed and applied to the optimal interpolated τ data in the southwestern Japan/East Sea (JES) by Mitchell et al. Comparisons with the in situ CTD casts demonstrate that the MI-GEM technique almost always produces improved full water column profiles of T and δ. Whereas the residual GEM estimates had exhibited qualitatively erroneous features like T inversions in the near–surface layer and too thin or thick intermediate water layers in some regions, the MI-GEM estimates avoid those problems, which were inherent to the residual GEM technique in the southwestern JES.

Geolocation in ad hoc networks using DS-CDMA and generalized successive interference cancellation

Channel estimation and distributed positioning algorithms are presented for geolocation in a wireless ad hoc network. The network uses a direct-sequence code-division multiple-access-based handshaking protocol, in which nodes receive multiple acknowledgment packets in response to a request-to-send waveform. Round-trip travel time (RTT) and angle-of-arrival (AOA) measurements are obtained using the generalized successive interference cancellation/matching pursuits (GSIC/MP) algorithm. The performance of GSIC/MP is evaluated via simulation and comparison to the Crame/spl acute/r-Rao bound. Position estimates are initialized using linearized least-squares and updated by an extended Kalman filter-based algorithm that includes measurement validation for nonline-of-sight error mitigation. The method is generalized for distributed estimation in sparsely connected networks: at each node, position estimates from connected nodes are incorporated via a fusion algorithm and updated using locally processed RTT/AOA measurements. Finally, comprehensive ad hoc network simulations are presented including channel ray tracing, RTT/AOA estimation and validation, and distributed positioning.

Monitoring formation of high intensity focused ultrasound (HIFU) induced lesions using backscattered ultrasound

Backscattered radio frequency (RF) data collected in a series of in vitro experiments, in which HIFU lesions were created in bovine liver tissue, were analyzed using two signal processing approaches to visualize temporal evolution of lesion formation. Change in round-trip travel time provides information related to temperature change during and after therapy. Changes in the RF spectrum related to changes in scattering properties of the heated region were observed before visible changes appeared on B-mode images. Effect of increased attenuation in the necrosed tissue region was also observed. Results demonstrate potential for these two techniques in image-guided HIFU therapy.

Geometric derivation of expectation-maximization and generalized successive interference cancellation algorithms with applications to CDMA channel estimation

The expectation-maximization (EM) algorithm is well established as a computationally efficient method for separable signal parameter estimation. Here, a new geometric derivation and interpretation of the EM algorithm is given that facilitates the understanding of EM convergence properties. Geometric considerations lead to an alternative separable signal parameter estimator based on successive cancellation. The new generalized successive interference cancellation (GSIC) algorithm is then applied to multiuser delay and channel estimation for code-division multiple access (CDMA) radiolocation and communication. The radiolocation application uses a handshaking protocol in which multiple reference nodes transmit acknowledge (ACK) CDMA packets to a master node, which then computes round-trip travel times (RTTs). Simulation results comparing EM and GSIC are presented for the CDMA channel-estimation problem.

Combining Inverted Echo Sounder and Horizontal Electric Field Recorder Measurements to Obtain Absolute Velocity Profiles

Profiles of absolute velocity are difficult to obtain in the ocean, especially over long periods of time at the same location. This paper presents a method of estimating full water column absolute horizontal velocity profiles as a function of time by combining historical hydrography with the measurements from two separate instruments, the inverted echo sounder (IES) and the horizontal electric field recorder (HEFR). Hydrography is used to construct temperature, salinity, and specific volume anomaly characteristics as functions of the independent variables pressure and seafloor-to-sea-surface round-trip acoustic travel time (τ). Each IES measured τ is combined with these two-dimensional characteristics to estimate the profile of specific volume anomaly, which then is integrated vertically to obtain profiles of geopotential height anomaly (Δϕ). Profiles of Δϕ from adjacent IES sites are differenced to yield vertical profiles of relative geostrophic velocity. Horizontal electric fields arising from the vertically averaged horizontal water velocity provide the requisite referencing of the IES-derived relative velocities. Comparisons are presented between HEFR+IES absolute velocities in the Southern Ocean near 51°S, 143.5°E and absolute velocities determined via hydrography, acoustic Doppler current profiler, and current meter.

A deep-sea observatory experiment using acoustic extensometers: precise horizontal distance measurements across a mid-ocean ridge

In July 2000, an array of instruments called acoustic extensometers was deployed at the Cleft segment of the southern Juan de Fuca Ridge, a seafloor observatory site selected by the National Science Foundation RIDGE Program. These instruments are designed to precisely measure horizontal deformation across the axis of a mid-ocean ridge in order to detect and quantify seafloor spreading events. The instruments were deployed in semipermanent seafloor benchmarks in a linear array that is 1.2-km long and spans the floor of the axial valley. The instruments make daily measurements of distance to their neighbors in the array by recording the round trip travel time of 100-kHz acoustic pulses, and simultaneous temperature measurements are used to correct the ranges for sound speed variations. The instruments are expected to have lifetimes of at least five years. In addition, precise pressure measurements have been made at each benchmark with a remotely operated vehicle in order to monitor for vertical deformation across the array. Preliminary results show that the resolution of the acoustic measurements is /spl plusmn/1-2 cm and that no abrupt deformation events occurred during the first year.

Long-Distance Transport of Bulk Goods in the Pre-Hispanic American Southwest

The paper examines the limits of efficient foot transport of utilitarian goods and food in the pre-Hispanic American Southwest, basing this assessment on field studies of long-distance portage, both domestic and commercial, in the roadless hills of modern-day eastern Nepal. The paper predicts the effect of load weight on transport costs and energy profits and also examines the relationship between distance and round-trip travel time for portaging 50-kg loads over one-way distances ranging from 50 to 250 km. The Nepali evidence refutes Lightfoot's 50-km operational limit for an “effective redistribution network, based on foot transportation.” The extensive network of domestic and commercial portage operating today in eastern Nepal demonstrates clearly that foot transport of food staples and durable goods would have been feasible in the pre-Hispanic American Southwest on a regular basis over distances of at least 100 to 150 km and on an occasional basis over much longer distances.

Structure of the North Atlantic current in stream-coordinates and the circulation in the Newfoundland basin

Accurate knowledge of the absolute North Atlantic Current (NAC) transport has been limited in the past by the difficulty of obtaining absolute velocity measurements. For this study, historical hydrography was combined with time series of round trip travel time from inverted echo sounders, bottom pressure sensor measurements, and measured velocities from deep current meters, via a “Gravest Empirical Mode” technique, to yield time series of temperature and absolute velocity sections. These sections were used to determine the mean NAC stream-coordinates structure of temperature and absolute velocity for the period from August 1993 to February 1995. This structure is narrower and stronger than the corresponding Eulerian average, with peak speeds greater than 80 cm s −1 and bottom velocities exceeding 10 cm s −1 . The calculated mean NAC transport was 131±14 (×10 6 m 3 s −1 ); temporal variations resulted in a 41×10 6 m 3 s −1 standard deviation. The stream-coordinates estimate of mean absolute transport was found to be about 10% smaller than the corresponding Eulerian mean transport of 146×10 6 m 3 s −1 as a result of partially summing the north and south transports within the Mann Eddy, a large semi-permanent anticyclonic eddy normally located just offshore of the NAC. Most transport sections across the NAC in this region include the northward transport of the inshore side of the Mann Eddy because it is difficult to discriminate between the two flows. Historical estimates place the Mann Eddy absolute transport around 50–60×10 6 m 3 s −1 ; thus, the transport crossing this transect that can be identified with the NAC is about 90×10 6 m 3 s −1 . The barotropic component of the transport (defined as the bottom velocity multiplied by the water depth) is found to contribute at least 30% of the total absolute transport, depending on the choice of baroclinic reference level. Because a time series of transport measurements was made in this study, the accuracy of the mean transport estimate is better than previous estimates, which have all been based on snapshot measurements. From a combination of these measurements with other published measurements, a scheme for the overall circulation and transport in the Newfoundland Basin is suggested.

Ultrasonic measurement of the elastic constants of sodiump-nitrophenolate dihydrate single crystals

Sodium p-nitrophenolate dihydrate single crystals possess excellent nonlinear optical properties such that they can be used for optical second-harmonic generation. It belongs to the orthorhombic system with the space group Ima2. Slow evaporation or slow cooling techniques can be used to grow good optical quality single crystals from supersaturated solution. All the nine elastic constants of this crystal have been measured using an ultrasonic technique. Samples for measurements have been cut along desired crystallographic axes and the pulse echo overlap technique has been used to measure longitudinal and shear ultrasonic wave velocities along appropriate symmetry directions in the crystal. The McSkimin Delta t criterion has been applied to determine the round trip travel time accurately, from which the nine elastic constants have been evaluated. Temperature variation of selected elastic constants in a limited range have also been measured and reported.

Transmission beam pattern and echolocation signals of a harbor porpoise (Phocoena phocoena).

The transmission beam pattern of an echolocating harbor porpoise (Phocoena phocoena) was measured in both the vertical and horizontal planes. An array of seven Brüel and Kjaer 8103 hydrophones connected to an amplifier-line driver module was used to measure the beam patterns. The porpoise was trained to station in a hoop and echolocate a cylindrical target located at a range between 7 and 9 m while the array was located 2 m in front of the hoop. The 3-dB beamwidth in both the vertical and horizontal planes was the same at approximately 16 degrees and the beam was pointed toward the forward direction. The individual hydrophones in both the vertical and horizontal arrays measured signal waveforms that were similar throughout the 40-degree span of the array. The porpoise emitted signals with intervals that were 20 to 35 ms longer than the round trip travel time between the animal and the target. The average source level, peak frequency, and bandwidth were 157 dB, 128 kHz, and 16 kHz, respectively.

Laboratory tests of a time-domain reflectometry system for frazil ice detection

A prototype, electromagnetic-based frazil ice detection system (patent pending) has been developed and tested under simulated frazil ice accretion conditions in an environmentally controlled flume. The system employs a time-domain reflectometer (TDR) and specially designed transmission line sensor to monitor the accretion of frazil ice by measuring the propagation time along the sensor when it is submerged. Changes in the round-trip travel time of the TDR pulse result from a decrease in the localized bulk dielectric constant as frazil ice accretes and displaces water around the sensor. Two frazil detection sensor configurations were tested, a parallel transmission line probe and a semicylindrical mesh coaxial probe. During 2 h long experiments, the TDR clearly indicated a decreasing probe propagation time as frazil ice continued to accrete. This is indicative of the decreasing bulk dielectric constant of the frazil ice and water mix. Continuous real-time data from the TDR were recorded. From these data, an estimate of volumetric ice fraction was calculated using a simple linear dielectric mixing equation. Volumetric ice fractions estimates for both probe configurations were calculated to increase from approximately 0.02 to 0.18 during the test. The system shows promise for detection and measurement of frazil ice growth and accretion in freshwater bodies.Key words: frazil ice, trash rack, water intake, icing detection, time-domain reflectometry, TDR.

Central Place Models of Acorn and Mussel Processing

We use a central place foraging model of field resource processing to explore the archaeological implications of experimental and ethnographical observations pertaining to the collection and processing of black oak (Quercus kelloggii) and big mussel (Mytilus californianus). These data suggest oak field processing will generally be minimal and confined mainly to drying and that big mussel may be transported unprocessed or completely processed depending on round-trip travel time and mussel colony productivity. Archaeological data further demonstrate that the field processing of mussels is frequently at odds with central place model predictions, suggesting optimization of quantities other than calories and time.

Further evidence that the sound-speed algorithm of Del Grosso is more accurate than that of Chen and Millero

Estimates of the bottom depth of the ocean at 11 sites were determined by combining round-trip acoustic travel time measurements made by inverted echo sounders on the ocean bottom with sound-speed profiles determined from simultaneously measured temperature and salinity profiles. These depths were converted into pressures and were compared to independently measured bottom pressures to determine the accuracy of the algorithms used to calculate the sound-speed profile. The sound-speed algorithms tested were those derived by Del Grosso [J. Acoust. Soc. Am. 56, 1084–1091 (1974)] and by Chen and Millero [J. Acoust. Soc. Am. 62, 1129–1135 (1977)], as well as the corrected version of Chen and Millero’s algorithm recently published by Millero and Li [J. Acoust. Soc. Am. 95, 2757–2759 (1994)]. The results of this study agree with the results from recent acoustic tomography experiments which indicate that the algorithm of Del Grosso for the speed of sound in seawater is more accurate than the currently accepted standard algorithm of Chen and Millero. Del Grosso’s algorithm also produces more accurate results than those from the Millero and Li correction to the Chen and Millero algorithm.

Investigations of Temperature Effects on NOAA's Next Generation Water Level Measurement System

Abstract The National Oceanic and Atmospheric Administration collects tide and water-level data by using an acoustic tide gauge in its Next Generation Water Level Measurement System (NGWLMS). The elevation of the water is calculated from the round-trip travel time of an acoustic wave generated from a source mounted above the water. At some, sites, solar radiation on the tide well can set up a nonuniform temperature structure in the well. This temperature effect can modify the travel time of the sound pulse, thereby introducing an offset into the estimate of the water level and hence into the computation of datums, such as mean sea level, which is a significant global change index. This diurnal temperature effect was quantified by computing day and night datums for tide stations located at La Jolla, California, and Baltimore, Maryland. By employing the difference in these datums, a method of delineating and removing this temperature effect was developed. This analysis resulted in 1) a quantifiable method f...