Limited Set Of Observations Research Articles

Physics-informed neural network for volumetric sound field reconstruction of speech signals

Recent developments in acoustic signal processing have seen the integration of deep learning methodologies, alongside the continued prominence of classical wave expansion-based approaches, particularly in sound field reconstruction. Physics-informed neural networks (PINNs) have emerged as a novel framework, bridging the gap between data-driven and model-based techniques for addressing physical phenomena governed by partial differential equations. This paper introduces a PINN-based approach for the recovery of arbitrary volumetric acoustic fields. The network incorporates the wave equation to impose a regularization on signal reconstruction in the time domain. This methodology enables the network to learn the physical law of sound propagation and allows for the complete characterization of the sound field based on a limited set of observations. The proposed method’s efficacy is validated through experiments involving speech signals in a real-world environment, considering varying numbers of available measurements. Moreover, a comparative analysis is undertaken against state-of-the-art frequency domain and time domain reconstruction methods from existing literature, highlighting the increased accuracy across the various measurement configurations.

An observation-based, reduced-form model for oxidation in the remote marine troposphere

The hydroxyl radical (OH) fuels atmospheric chemical cycling as the main sink for methane and a driver of the formation and loss of many air pollutants, but direct OH observations are sparse. We develop and evaluate an observation-based proxy for short-term, spatial variations in OH (ProxyOH) in the remote marine troposphere using comprehensive measurements from the NASA Atmospheric Tomography (ATom) airborne campaign. ProxyOH is a reduced form of the OH steady-state equation representing the dominant OH production and loss pathways in the remote marine troposphere, according to box model simulations of OH constrained with ATom observations. ProxyOH comprises only eight variables that are generally observed by routine ground- or satellite-based instruments. ProxyOH scales linearly with in situ [OH] spatial variations along the ATom flight tracks (median r2 = 0.90, interquartile range = 0.80 to 0.94 across 2-km altitude by 20° latitudinal regions). We deconstruct spatial variations in ProxyOH as a first-order approximation of the sensitivity of OH variations to individual terms. Two terms modulate within-region ProxyOH variations-water vapor (H2O) and, to a lesser extent, nitric oxide (NO). This implies that a limited set of observations could offer an avenue for observation-based mapping of OH spatial variations over much of the remote marine troposphere. Both H2O and NO are expected to change with climate, while NO also varies strongly with human activities. We also illustrate the utility of ProxyOH as a process-based approach for evaluating intermodel differences in remote marine tropospheric OH.

Spatial reconstruction of sound fields using local and data-driven functions.

Sound field analysis methods make it possible to characterize and reconstruct a sound field from a limited set of observations. Classical approaches rely on the use of analytical basis functions to model the sound field throughout the observed domain. When the complexity of the sound field is high, for example, in a room at mid and high frequencies, propagating wave representations can be suboptimal due to model discrepancy. We examine the use of local representations to alleviate this model discrepancy and explore data-driven approaches to obtain suitable models. Specifically, local representations are used to reconstruct the sound field over a large spatial aperture in a room. The performance of local models is compared against conventional plane wave reconstructions and the use of data-driven local functions is examined. Dictionary learning and principal component analysis are used to obtain functions from extensive spatial measurements in an empty room. The results indicate that local partitioning models conform to fields of high spatial complexity. Dictionary learning generalizes across different rooms and frequencies-conferring potential for modelling complex sound fields based on their local and statistical properties.

Impacts of River Engineering on River Channel Behaviour: Implications for Managing Downstream Flood Risk

Although knowledge of sediment transport has improved over the last 25 years, our understanding of bedload transfer and sediment delivery is still based on a limited set of observations or on models that make assumptions on hydraulic and sediment transport processes. This study utilises repeat lidar survey data of the River Caldew above the City of Carlisle in the UK to investigate the balance of erosion and deposition associated with channel switching from an engineered and managed single thread channel to a naturalising incipient wandering system. Over the 11-year survey period (four bankfull flood events) around 271,000 m3 of sediment were delivered to the river and floodplain and 197,000 m3 eroded suggesting that storage rates of around 7000 m3/annum occurred. The balance of erosion and deposition is influenced by channelisation with very restricted overbank sedimentation and only limited local and transient in-channel bar deposition along the engineered reach (8000 m3 eroded). This contrasts with the activity of the naturalising reach downstream where a developing wandering channel system is acting to store coarse sediment in-stream as large bar complexes and the associated upstream aggrading plane bed reaches and overbank as splay deposits (87,000 m3 stored). Such behavior suggests that naturalisation of channelised systems upstream of flood vulnerable urban areas can have a significant impact on sediment induced flooding downstream. This conclusion must, however, be moderated in the light of the relatively small volumes of material needed to instigate local aggradation in over-capacity urban channels.

Near earth space object detection using parallax as multi-hypothesis test criterion.

The US Strategic Command (USSTRATCOM) operated Space Surveillance Network (SSN) is tasked with Space Situational Awareness (SSA) for the U.S. military. This system is made up of Electro-Optic sensors, such as the Ground-based Electro-Optical Deep Space Surveillance (GEODSS) and RADAR based sensors, such as the Space Fence Gaps. They remain in the tracking of Resident Space Objects (RSO's) in Geosynchronous Orbits (GEO), due to limitations of SST and GEODSS system implementation. This research explores a reliable, ground-based technique used to quickly determine an RSO's altitude from a single or limited set of observations. Implementation of such sensors into the SSN would mitigate GEO SSA performance gaps. The research entails a method used to distinguish between the point spread function (PSF) observed by a star and the PSF observed from an RSO by using Multi-Hypothesis Testing with parallax as a test criterion. Parallax is the effect that an observed object will appear to shift when viewed from different positions. This effect is explored by generating PSFs from telescope observations of space objects at different baselines. The research has shown the PSF of an RSO can be distinguished from that of a star using single, simultaneous observations from reference and parallax sensing telescopes. This report validates these techniques with both simulations and experimental data from the SST and Naval Observatory sensors.

Taking Time, Sharing Spaces: Adaptive Risk Governance Processes in Rural Japan

Rural and peri-urban communities in Japan, as well as in many other regions of the world, face risks of discrete event natural phenomena, including earthquakes, floods, and landslides. They also face persistent disruptive stress due to risks that remain active over long durations, such as the loss of community capacities due to an aging population. This article describes my observations of and subsequent reflections on adaptive risk governance and community resilience building processes in two areas of western and southern Japan—Chizu in Tottori Prefecture and towns near Kumamoto City in Kumamoto Prefecture. Four aspects of adaptive risk governance from this limited set of observations stood out: (1) the importance of establishing a durable, patient process, (2) initiated and facilitated by a trusted figure, in (3) a space or venue accessible and open to the community, and (4) augmented by boundary objects that facilitate role playing, iteration, and ownership by the community of solutions generated in these dialogues.

Photopolarimetric Sensitivity to Black Carbon Content of Wildfire Smoke: Results From the 2016 ImPACT‐PM Field Campaign

AbstractDetailed characterization of the aerosol content of wildfire smoke plumes is typically performed through in situ aircraft observations, which have limited temporal and spatial coverage. Extending such observations to regional or global scales requires new remote sensing approaches, such as retrievals that make use of spectropolarimetric, multiangle imaging. In this work measurements made during the Imaging Polarimetric Assessment and Characterization of Tropospheric Particulate Matter (ImPACT‐PM) field campaign in a smoke plume near the town of Lebec in Southern California by the Navy Center for Interdisciplinary Remotely Piloted Aircraft Studies Twin Otter aircraft on 8 July 2016 are used in conjunction with near‐coincident measurements from the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) on the National Aeronautics and Space Administration ER‐2 high‐altitude research aircraft to assess the sensitivity of spectropolarimetric measurements to the black carbon content of the plume. Tracking visible features in the smoke through the sequence of AirMSPI observations allowed the height of the plume to be estimated through geometric techniques. Then, by constraining the fractional amounts of the aerosol constituents with the in situ data, radiative closure was obtained through simulations performed with a polarimetric radiative transfer code, demonstrating the ability to constrain the black carbon mass fraction to approximately 5%, given the uncertainties in the AirMSPI measurements and the assumption of external mixing of aerosol components. The AirMSPI retrieval, made using a limited set of observations from the 470 nm polarimetric spectral band alone, was also generally consistent with operational retrievals of aerosol optical depth and surface reflectance made by the Multi‐Angle Implementation of Atmospheric Correction algorithm at 1 km resolution.

Evolution of the Solar Lyα Line Profile during the Solar Cycle

Abstract Recent studies of interstellar neutral (ISN) hydrogen observed by the Interstellar Boundary Explorer (IBEX) suggested that the present understanding of the radiation pressure acting on hydrogen atoms in the heliosphere should be revised. There is a significant discrepancy between theoretical predictions of the ISN H signal using the currently used model of the solar Lyα profile by Tarnopolski & Bzowski and the signal due to ISN H observed by IBEX-Lo. We developed a new model of evolution of the solar Lyα profile that takes into account all available observations of the full-disk solar Lyα profiles from SUMER/SOHO, provided by Lemaire et al., covering practically the entire 23rd solar cycle. The model has three components that reproduce different features of the profile. The main shape of the emission line that is produced in the chromosphere is modeled by the kappa function; the central reversal due to absorption in the transition region is modeled by the Gauss function; and the spectral background is represented by the linear function. The coefficients of all of those components are linear functions of the line-integrated full-disk Lyα irradiance, which is the only free parameter of the model. The new model features potentially important differences in comparison with the model by TB09, which was based on a limited set of observations. This change in the understanding of radiation pressure, especially during low solar activity, may significantly affect the interstellar H and D distributions in the inner heliosphere and their derivative populations.

Situations Saved by the Human Operator when Automation Failed

In many systems an increased level of automation implies an altered role for the human operator. Behind the introduction of new automation lies different automation philosophies which stretches from trying to use as much automation as possible to adding automation only as a support to human tasks in specific situations.The Swedish Radiation Safety Authority has assigned AF Infrastructure, Department of Risk Management to describe the current automation philosophies within the nuclear industry. The assignment also includes a survey of events in which human involvement was necessary in order to save situations in which the automation failed.Much of the knowledge of human-machine interaction in process systems is derived by learning from incidents. These incidents, however, only represent a limited set of observations of real life human-machine interactions when the human in most cases did not have a positive effect on the sequence of events. Cases when the human operator did have a positive effect on the sequence of events are typically not reported as they in most cases do not lead to incidents. Thus, much of the available information on human-machine interactions is biased towards cases of human errors, and does not give a true picture of real-life. It is the hypothesis of this paper that the role of the human operator as a vital safety function is more significant than normally concluded by studying incident reports which claim human error as a contributing cause to accidents.In this report two events are described in which human intervention was crucial for the successful outcome of the situation; Vandellos/Spain 1989 and Forsmark/Sweden 2006. These events show that the human operator is one of the most vital parts of the defence in depth at a power station, hence a strong focus should be given to looking after and maintaining the human abilities in order for her to be able to act safely in emergency situations.The events also show the potential improvement of the defence in depth by making the most of the unique human abilities of intuitive and creative thinking and acting without access to external sources of power or prearranged procedures.These abilities are, however, affected by the level of automation, e.g. a too high level of automation can lead to a lack in situation awareness whilst a too low level can lead to too high levels of mental workload for the operators. To avoid degradation in human abilities to safely intervene, changes in automation levels should always be preceded by an analysis of its long term effect on the human operators’ skills and capabilities.To gain more knowledge on the role of the human operator as a safety function in process systems, it is suggested that real-life human machine interaction is actively observed in order to also identify cases when human intervention prevents incidents at the very early stages of the sequence of events. These cases are normally impossible to retrieve from historical records, which mainly cover incident investigations of cases that lead to severe consequences.Many of the theories on automation philosophy used in this paper originate from the aviation industry, but it is shown that they are equally applicable within other sectors as well, i.e. the process industry.

PCO2 and CO2 exchange during high bora winds in the Northern Adriatic

Episodic high wind events have a potential for significantly mixing surface water partial pressure of CO2 (pCO2). Their effect on estimates of air–sea CO2 flux, especially in the coastal ocean, has not been adequately assessed. Here we show the response of surface water pCO2 and CO2 fluxes during high bora wind in the Northern Adriatic for a range of conditions including: stratified and oversaturated with respect to atmospheric CO2, stratified and undersaturated, and non-stratified and undersaturated. Three representative bora cases of 1.5–2day duration with wind speeds over 10ms−1 indicate that in all three studied cases, regardless of pre-bora conditions, pCO2 in the surface water increases by 30–50μatm and CO2 flux magnitudes peak up to 4 folds (−22.6 and −24.1mmolm−2day−1 day in the winter cases and 29mmolm−2day−1 in the summer case) over the magnitude of the mean annual value. Oceanic data measured simultaneously to surface pCO2 measurements suggest that the most likely responsible mechanisms for the observed pCO2 increases were oceanic vertical mixing and/or oceanic horizontal advection. Our study contributes to a very limited set of observations currently available on the biogeochemical response to episodic high wind events in coastal areas and their role in CO2 exchange. In such coastal environments the presence of shallow depths and short horizontal spatial scales of variation facilitate the exchange of pCO2 both vertically within ocean layers and horizontally across ocean basins, which can then alter air-sea pCO2 difference across the ocean surface during high wind events and affect gas exchange.

Methods Used For the 2006 Radiance Lights

The Operational Linescan System (OLS) flown on the Defense Meteorological Satellite Program (DMSP) satellites, has a unique capability to record low light imaging data at night worldwide. These data are archived at the National Oceanic and Atmospheric Administration (NOAA) National Geophysical Data Center (NGDC). The useful data record stretches back to 1992 and is ongoing. The OLS visible band detector observes radiances about one million times dimmer than most other Earth observing satellites. The sensor is typically operated in a high gain setting to enable the detection of moonlit clouds. However, with six bit quantization and limited dynamic range, the recorded data are saturated in the bright cores of urban centers. A limited set of observations have been obtained at low lunar illumination were obtained where the gain of the detector was set significantly lower than its typical operational setting (sometimes by a factor of 100). By combining these sparse data acquired at low gain settings with the operational data acquired at high gain settings, we have produced a global nighttime lights product for 2006 with no sensor saturation. This product can be related to radiances based on the pre-flights sensor calibration.

Can 4D‐Var use dynamical information from targeted observations of a baroclinic structure?

AbstractTargeted observations are generally taken in regions of high baroclinicity, but often show little impact. One plausible explanation is that important dynamical information, such as upshear tilt, is not extracted from the targeted observations by the data assimilation scheme and used to correct initial condition error. This is investigated by generating pseudo targeted observations which contain a singular vector (SV) structure that is not present in the background field or routine observations, i.e. assuming that the background has an initial condition error with tilted growing structure. Experiments were performed for a single case‐study with varying numbers of pseudo targeted observations. These were assimilated by the Met Office four‐dimensional variational (4D‐Var) data assimilation scheme, which uses a 6 h window for observations and background‐error covariances calculated using the National Meteorological Centre (NMC) method. The forecasts were run using the operational Met Office Unified Model on a 24 km grid. The results presented clearly demonstrate that a 6 h window 4D‐Var system is capable of extracting baroclinic information from a limited set of observations and using it to correct initial condition error. To capture the SV structure well (projection of 0.72 in total energy), 50 sondes over an area of 1×106 km2 were required. When the SV was represented by only eight sondes along an example targeting flight track covering a smaller area, the projection onto the SV structure was lower; the resulting forecast perturbations showed an SV structure with increased tilt and reduced initial energy. The total energy contained in the perturbations decreased as the SV structure was less well described by the set of observations (i.e. as fewer pseudo observations were assimilated). The assimilated perturbation had lower energy than the SV unless the pseudo observations were assimilated with the dropsonde observation errors halved from operational values. Copyright © 2010 Royal Meteorological Society

Neutron Research in High Magnetic Fields at the Helmholtz-Zentrum Berlin

While neutron diffraction and scattering prove to be indispensable techniques in many areas of scientific research, one of their most outstanding usages is the determination of magnetic structures and their related spin dynamics, possibly combined with extreme applied conditions. Due to the necessity of applying magnetic fields and/or pressures along a particular direction with respect to the crystal structure, it can be that sometimes only a very limited set of observables can be determined. Fortunately, neutrons can penetrate various materials enabling the design of complex apparatus that combine several extreme conditions at once. Combination of magnetic fields, low temperatures and high hydrostatic or uniaxial pressures are possible. However, compromises must be made between the angular range, the strength and the direction of the magnetic field, the value and the type of pressure, the lowest temperature and the size of studied samples. These combine to make magnetism under extreme conditions a challenging, but scientifically rewarding field of research. In this contribution we review a few of the experiments which combine neutron techniques with magnetic fields at low temperatures performed at HZB and the future outlook.

Rotation of sea/land breezes along the northeastern Adriatic coast

Abstract. The diurnal evolution of the sea/land breeze hodographs over the northeastern Adriatic coast has been examined for several episodes, each lasting a few days. A limited set of observations, as well as the results of a three-dimensional nonhydrostatic mesoscale model are studied by applying a rotary-component method. This revealed a spatial distribution of the clockwise versus anti-clockwise rotation of the wind vectors for the sea/land breeze events. An application of the rotary-component method to the results of additional numerical sensitivity tests showed that the coastal topography height considerably influences both the shape of the wind hodographs and the sense of wind rotation. The method also displayed which areas are under a strong influence of the 24-h topographic forcing and which areas show a large wind consistency. A further analysis of the 24-h modeled wind hodographs at several selected stations has been performed, thus revealing the hodograph shapes and the reasons for them.

Wind-Induced Circulation in Semienclosed Homogeneous, Rotating Basins

Abstract The wind-induced circulation over laterally varying bathymetry was investigated in homogeneous systems using the three-dimensional Regional Ocean Model System (ROMS). The investigation focused on the influence of the earth’s rotation on the lateral distribution of the flow, with particular emphasis on the transverse circulation. Along-basin wind stress with no rotation caused a circulation dominated by an axially symmetric transverse structure consisting of downwind flow over the shoals and upwind flow in the channel along the whole domain. Transverse circulation was important only at the head of the system where the water sank and reversed direction to move toward the mouth. The wind-induced flow pattern under the effects of the earth’s rotation depended on the ratio of the maximum basin’s depth h to the Ekman depth d. The solution tended to that described in a nonrotating system as h/d remained equal to or below 1. For higher values of h/d, the longitudinal flow was axially asymmetric. Maximum downwind flow was located over the right shoal (in the Northern Hemisphere, looking downwind). The transverse component of velocity described three gyres. The main gyre was clockwise (looking downwind) and occupied the entire basin cross section, as expected from the earth’s rotation and the presence of channel walls. The other two gyres were small and localized and were linked to the lateral distribution of the along-channel velocity component, which in turn was dictated by bathymetry. These results compared favorably with a limited set of observations and are expected to motivate future measurements.

The Unusual Dynamics of Northern Dark Spots on Neptune

Hubble Space Telescope (HST) and ground-based observations of Neptune from 1991 to 2000 show that Neptune's northern Great Dark Spots (NGDS) remained remarkably stable in latitude and longitudinal drift rate, in marked contrast to the 1989 southern Great Dark Spot (GDS), which moved continuously equatorward during 1989 and dissipated unseen during 1990. NGDS-32, discovered in October 1994 HST images, (H. B. Hammel et al., 1995, Science 268, 1740–1742), stayed at ∼32°N from 1994 through at least 1996, and possibly through 2000. The second northern GDS (NGDS-15), discovered in August 1996 HST images, (L. A. Sromovsky et al. 2001, Icarus 146, 459–488), appears to have existed as early as 8 March 1996 and remained near 15°N for the 16 months over which it was observed. NGDS-32 had a very uniform longitudinal drift rate averaging −36.28±0.04°/day from 10 October 1994 to 2 November 1995, and −35.84±0.02°/day from 1 September 1995 through 24 November 1995. A single circulation feature certainly exists during each of the first two periods, though it is not certain that it is the same feature. It is probable, but less certain, that only a single circulation feature was tracked during the 1996–1998 period, during which positions are consistent with a modulated drift rate averaging −35.401±0.001°/day, but with a peak-to-peak modulation of 1.5°/day with an ∼760-day period. If NDS-32 varied its drift rate in accord with the local latitudinal shear in the zonal wind, then all its drift-rate changes might be due to only ∼0.4° of latitudinal motion. The movement of NGDS-15 is also not consistent with a uniform longitudinal drift rate, but the nature of its variation cannot be estimated from the limited set of observations. The relatively stable latitudinal positions of both northern dark spots are not consistent with current numerical model calculations treating them as anticyclonic vortices in a region of uniform potential vorticity gradient (R. P. Lebeau and T. E. Dowling 1998, Icarus 132, 239–265). Possible explanations include unresolved latitudinal structure in the zonal wind background or unaccounted-for variations in vertical stability structure.

Radar surface rainfall estimates using a typical shape function approach to correct for the variations in the vertical profile of reflectivity

A new approach is presented to the problem of correcting radar estimates of surface rainfall for errors resulting from the changes in reflectivity between the surface and the height at which the radar measures reflectivity. In this approach, a set of five typical shape functions (TSF) of a sample of 89 000 vertical profiles was found. These vertical profiles were formed from volumes scan information, interpolated onto 10 levels, at 250 m spacing, with level 6 being set to the height of the top of the bright band. The TSF class for each vertical profile was determined from a limited set of observations of reflectivity aloft using Bayesian discriminant functions. Regression equations were developed for each TSF class to estimate the lowest interpolated level reflectivity (level 1) from these observations aloft. Application of the discriminant functions shows that the 62% of the dependent sample could be correctly classified into its TSF class for data at heights greater than 500 m below the bright band. In four of the five TSF classes, there was significant skill in estimating the surface reflectivity, explaining 80% of the variation of the level 1 reflectivity. The fifth class explained 49% of the level 1 variation. On average, using this approach of determining the TSF for each vertical profile rather than using a single profile for each volume scan increased the variation of the surface reflectivity explained by observations aloft from 59.5% to 77.4%. Information on the skill of estimating the surface reflectivity was also produced, using the posterior probability and the explained variance of the regression equations.

Spectral Interferences in Light Element Analysis

Interferences (overlaps) occurring when lines of other elements affect either peak or background measurements can cause errors in quantitative WD analysis, but may be minimised by suitable choices of analysis conditions such as spectrometer crystal, background offsets, and pulse-height analyser settings. Computer spectrum-simulation is much more effective than reference to wavelength tables for investigating interferences. The ‘Virtual WDS’ simulation program developed by the present authors, hitherto applied only to ‘ordinary’ elements (Z ≥ 11), has been extended to light elements for which evaporated multilayers are used in place of true crystals. ‘Virtual WDS’ utilises experimentally recorded light-element K spectra and L and M spectra of heavier elements in the same wavelength range. It is impractical to record all high-order peaks, so computed line profiles are used, with widths and intensities interpolated from a limited set of observations. The relative positions of first and higher order peaks are affected significantly by the refractive index of the multilayer, requiring modification of the Bragg equation. Suppression of high orders by pulse-height analysis is less effective than for ‘normal’ wavelengths, owing to the breadth of the pulse-height distribution for low X-ray energies. Simulation using a Gaussian expression aids optimisation of threshold and window-width settings.

The asteroid ephemerides program at the U.S. Naval Observatory

The U.S. Naval Observatory has begun a program of ephemeris improvement and reference frame determination from the main belt asteroids. The program is, currently, starting out with a limited set of observations of the larger asteroids to determine the equator and equinox corrections for the USNO W1J00 transit circle observations catalog, and, if possible, improve the orbits of these asteroids based on this limited set of observations. For this project, transit circle observations of the Sun and the planets Mercury through Jupiter, are also being used to determine the equator, equinox, and ephemeris corrections, the next goal is to improve the orbits of the larger asteroids in the optical reference frame using observation series that cover a much longer period of time. This will allow the exploration of the differences between the dynamical reference frame based on radar observations of main belt asteroids and its relation with the optical reference frame. Other goals include the exploration of the mass distribution in the main asteroid belt from high precision observations, and the effect of this mass on the ephemerides of the major planets.

Spatial and Temporal Variations of Photosynthetic Parameters in Relation to Environmental Conditions in Coastal Waters of the Northern Gulf of Mexico

On a series of eight cruises conducted in the northern Gulf of Mexico, efforts were made to characterize temporal and spatial variability in parameters of the photosynthesis-irradiance saturation curve (P:,.,., a 8 , I.) and to relate the observed variations to environmental conditions. Experiments to examine the importance of diel variation in upper mixed layer populations were conducted in July-August 1990 and March 1991. During July-August 1990, p:,_ and 1. showed significant increases and a 8 decreased during the photoperiod in both river plume and shelf-slope populations. During March 1991, no consistent covariance of P-1 parameters with local time was found, although highest values of a 8 in the river plume were observed in early morning. Seasonal variation in pa ~ and a 8 were correlated with temperature. Spatial variations of photosynthetic parameters in the upper mixed layer ranged from twofold to threefold within any given cruise. Variations of photosynthetic parameters in the upper mixed layer were related to principal components derived from environmental variables, including temperature, salinity, nutrients, mixed layer depth, attenuation coeffi­ cient, and daily photosynthetically available radiation (PAR). Greater than 70% of the variation in the environmental variables could be accounted for by two principal components; the majority of this variation was associated with the first principal component, which was generally strongly correlated with salinity, nutrients, mixed layer depth, and attenuation coefficient. Correlations of P:..,., a 8 , and Iwith the first principal component were found to be significant in some cases, an indication that spatial variability in P-1 parameters was related to river outflow. Variation of P-1 parameters in relation to depth and PAR were evaluated by regressions with principal components derived from depth, temperature, . mean daily PAR. For most cruises, p:,_ and Iwere negatively correlated with the first principal component, which was strongly positively correlated with depth and negatively correlated with daily PAR. This was consistent with a decreaSe in both p:,_ and I. with depth that could be related to decreasing daily PAR. Positive correlations of a 8 with the first principal component for two cruises, March 1991 and April 1992, indicated an increasing trend with depth. In conclusion, rela­ tionships between P-1 parameters and environmental variables in the region of study were significant in some cases, but variation between cruises made it difficult to generalize. We attributed this variation to the physically dynamic charac­ teristics of the region and the possible effects of variables that were not included in the analysis such as species com­ position. Our findings do support the view that a limited set of observations may be adequate to characterize P-1 parameter distributions in a given region within a restricted period of time.