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Spectroscopic orbital elements and/or related parameters have been determined for eight binary systems, using radial-velocity measurements that have a typical precision of about 15 ms⁻¹. The orbital periods of these systems range from about 10 days to 26 years, with a median of about 6 years. Orbital solutions were determined for the seven systems with shorter periods. The measurement of the mass ratio of the longest-period system, HD217166, demonstrates that this important astrophysical quantity can be estimated in a model-free manner with less than 10% of the orbital cycle observed spectroscopically.\\ Single-lined orbital solutions have been derived for five of the binaries. Two of these systems are astrometric binaries: β Ret and ν Oct. The other SB1 systems were 94 Aqr A, θ Ant, and the 10-day system, HD159656. The preliminary spectroscopic solution for θ Ant (P~18 years), is the first one derived for this system. The improvement to the precision achieved for the elements of the other four systems was typically between 1--2 orders of magnitude. The very high precision with which the spectroscopic solution for HD159656 has been measured should allow an investigation into possible apsidal motion in the near future. In addition to the variable radial velocity owing to its orbital motion, the K-giant, ν Oct, has been found to have an additional long-term irregular periodicity, attributed, for the time being, to the rotation of a large surface feature.\\ Double-lined solutions were obtained for HD206804 (K7V+K7V), which previously had two competing astrometric solutions but no spectroscopic solution, and a newly discovered seventh-magnitude system, HD181958 (F6V+F7V). This latter system has the distinction of having components and orbital characteristics whose study should be possible with present ground-based interferometers. All eight of the binary systems have had their mass ratio and the masses of their components estimated.\\ The following comments summarize the motivation for getting these results, and the manner in which the research was carried out. \\ The majority of stars exist in binary systems rather than singly as does the Sun. These systems provide astronomers with the most reliable and proven means to determine many of the fundamental properties of stars. One of these properties is the stellar mass, which is regarded as being the most important of all, since most other stellar characteristics are very sensitive to the mass. Therefore, empirical masses, combined with measurements of other stellar properties, such as radii and luminosities, are an excellent test for competing models of stellar structure and evolution.\\ Binary stars also provide opportunities to observe and investigate many extraordinary astrophysical processes that do not occur in isolated stars. These processes often arise as a result of direct and indirect interactions between the components, when they are sufficiently close to each other. Some of the interactions are relatively passive, such as the circularization of the mutual orbits, whilst others result from much more active processes, such as mass exchange leading to intense radiation emissions. \\ A complete understanding of a binary system's orbital characteristics, as well as the measurement of the all-important stellar masses, is almost always only achieved after the binary system has been studied using two or more complementary observing techniques. Two of the suitable techniques are astrometry and spectroscopy. In favourable circumstances, astrometry can deduce the angular dimensions of the orbit, the total mass of the system, and sometimes, its distance from us. Spectroscopy, on the other hand, can determine the linear scale of the orbit and the ratio of the stellar masses, based on the changing radial velocities of both stars. When a resolved astrometric orbital solution is also available, the velocities of both stars can allow the binary system's parallax to be determined, and the velocities of one star can provide a measure of the system mass ratio.\\ Unfortunately, relatively few binary systems are suited to these complementary studies. Underlying this difficulty are the facts that, typically, astrometrically-determined orbits favour those with periods of years or decades, whereas spectroscopic orbital solutions are more often measured for systems with periods of days to months. With the development of high-resolution astrometric and spectroscopic techniques in recent years, it is hoped that many more binary systems will be amenable to these complementary strategies.\\ Several months after this thesis began, a high-resolution spectrograph, HERCULES, commenced operations at the Mt John University Observatory, to be used in conjuction with the 1-metre McLellan telescope. For late-type stars, the anticipated velocity precision was ≲10 ms⁻¹. The primary goals of this thesis were: 1.~to assess the performance of HERCULES and the related reduction software that subsequently followed, 2.~to carry out an observational programme of 20 or so binary systems, and 3.~to determine the orbital and stellar parameters which characterize some of these systems. The particular focus was on those binaries that have resolved or unresolved astrometric orbital solutions, which therefore may be suited to complementary investigations.\\ HERCULES was used to acquire spectra of the programme stars, usually every few weeks, over a timespan of about three years. High-resolution spectra were acquired for the purpose of measuring precise radial velocities of the stars. When possible, orbital solutions were derived from these velocities, using the method of differential corrections.

La recherche et caractérisation de planètes extrasolaires en transit (i.e., qui passent devant leur étoile, vue depuis la Terre) est un domaine important de la planétologie car ces planètes permettent de contraindre les processus de formation, d'évolution et de migration des systèmes planétaires. Les missions spatiales CoRoT et Kepler ont permis, ces dernières années, de découvrir plusieurs milliers de candidats-planètes en transit. Cependant, ces candidats-planètes doivent être confirmés afin d'exclure tout scénario de faux-positifs pouvant imiter un transit d'une exo-planète. Pour cela, l'une des méthodes possible consiste à mener des observations complémentaires de vitesse radiale permettant de mesurer la masse et les paramètres orbitaux de l'objet qui transite et ainsi de pouvoir déterminer la nature des candidats-planètes. Au cours de ma thèse, je me suis attaché à résoudre la nature des candidats-planètes en transit issues des missions spatiales CoRoT et Kepler en menant des observations avec les spectrographes SOPHIE et HARPS, ce qui m'a permis d'identifier plusieurs nouvelles planètes extrasolaires en transit. J'ai également pu mesurer le taux de faux-positif de la mission Kepler, égal à 35% pour les candidats planètes-géantes à courte période orbitale, contredisant les précédentes estimations, beaucoup plus optimistes. J'ai également participé au développement d'un nouveau logiciel, "PASTIS", qui permet de valider statistiquement des planètes extrasolaires de faible masse, trop petites pour être caractérisées grâce aux spectrographes actuels. Ce logiciel permettra, à terme, de valider des dizaines de planètes de faible masse issues des missions CoRoT et Kepler. / The search and characterization of transiting extrasolar planets (i.e. that pass in front of their host star, as seen from the Earth) is an important domain of planetology since these planets constrain the formation, evolution and migration process of planetary systems. The CoRoT (CNES) and Kepler (NASA) space missions permit, these last years, to discover several thousand of transiting-planet candidates. However, these planet candidates need to be confirmed in order to exclude all false positive scenario that can mimic a planetary transit. For that, one of the method consist on performing radial velocity follow-up observations to measure the transiting object's mass and orbital parameters and thus, to determine the nature of planet candidates.During my PhD thesis, I tried to resolve the nature of transiting planet candidates from the CoRoT and Kepler space missions. For that, I performed follow-up observations with the SOPHIE (OHP) and HARPS (ESO) spectrographs that were used to discover several new transiting extrasolar planets. I also measured the Kepler false-positive rate, equal to 35% for giant close-in exoplanet candidates, contradicting previous estimations, much more optimistic.I also participate to the development of a new software, called "PASTIS", which objective is to validate statistically low-mass transiting exoplanets out of reach for current spectrographs. This new tool will, in a near future, validate tens of low-mass planets from the CoRoT and Kepler space missions.

I present the results of a comprehensive assessment of companions to 454 solar-type stars within 25 pc. New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy (CHARA) Array, (2) close companions with speckle interferometry, and (3) wide proper motion companions identified by blinking multi-epoch archival images. I have also obtained and included unpublished results from extensive radial velocity monitoring programs. The many sources utilized enable a thorough evaluation of stellar and brown dwarf companions. The results presented here include eight new companion discoveries, four of which are wide common proper motion pairs discovered by blinking archival images, and four more are from the spectroscopic data. The overall observed fractions of single, double, triple, and higher order systems are 57%±3%, 33%±2%, 8%±1%, and 3%±1%, respectively, counting all stellar and brown dwarf companions. The incompleteness analysis indicates that only a few undiscovered companions remain in this well-studied sample, showing that a majority of the solar-type stars are single. Bluer, more massive stars are more likely to have companions than redder, less massive ones. I confirm earlier expectations that more active stars are more likely to have companions. A preliminary, but important indication is that brown dwarfs, like planets, prefer stars with higher metallicity, tentatively suggesting that brown dwarfs may form like planets when they are companions to stars. The period distribution is unimodal and roughly Gaussian with peak and median values of about 300 years. The period-eccentricity relation shows a roughly flat distribution beyond the circularization limit of about 12 days. The mass-ratio distribution shows a clear discontinuity near a value of one, indicating a preference for twins, which are not confined to short orbital periods, suggesting that stars form by multiple formation mechanisms. The ratio of planet hosts among single, binary, and multiple systems are statistically indistinguishable, suggesting that planets are as likely to form around single stars as they are around components of binary or multiple systems at sufficiently wide separations.

Signal acquisition, signal reconstruction and analysis of spectrum of the signal are the three most important steps in signal processing and they are found in almost all of the modern day hardware. In most of the signal processing hardware, the signal of interest is sampled at uniform intervals satisfying some conditions like Nyquist rate. However, in some cases the privilege of having uniformly sampled data is lost due to some constraints on the hardware resources. In this thesis an important problem of signal reconstruction and spectral analysis from nonuniformly sampled data is addressed and a variety of methods are presented. The proposed methods are tested via numerical experiments on both artificial and real-life data sets. The thesis starts with a brief review of methods available in the literature for signal reconstruction and spectral analysis from non uniformly sampled data. The methods discussed in the thesis are classified into two broad categories - dense and sparse methods, the classification is based on the kind of spectra for which they are applicable. Under dense spectral methods the main contribution of the thesis is a non-parametric approach named LIMES, which recovers the smooth spectrum from non uniformly sampled data. Apart from recovering the spectrum, LIMES also gives an estimate of the covariance matrix. Under sparse methods the two main contributions are methods named SPICE and LIKES - both of them are user parameter free sparse estimation methods applicable for line spectral estimation. The other important contributions are extensions of SPICE and LIKES to multivariate time series and array processing models, and a solution to the grid selection problem in sparse estimation of spectral-line parameters. The third and final part of the thesis contains applications of the methods discussed in the thesis to the problem of radial velocity data analysis for exoplanet detection. Apart from the exoplanet application, an application based on Sudoku, which is related to sparse parameter estimation, is also discussed.

Spectroscopic orbital elements and/or related parameters have been determined for eight binary systems, using radial-velocity measurements that have a typical precision of about 15 ms⁻¹. The orbital periods of these systems range from about 10 days to 26 years, with a median of about 6 years. Orbital solutions were determined for the seven systems with shorter periods. The measurement of the mass ratio of the longest-period system, HD217166, demonstrates that this important astrophysical quantity can be estimated in a model-free manner with less than 10% of the orbital cycle observed spectroscopically.\\ Single-lined orbital solutions have been derived for five of the binaries. Two of these systems are astrometric binaries: β Ret and ν Oct. The other SB1 systems were 94 Aqr A, θ Ant, and the 10-day system, HD159656. The preliminary spectroscopic solution for θ Ant (P~18 years), is the first one derived for this system. The improvement to the precision achieved for the elements of the other four systems was typically between 1--2 orders of magnitude. The very high precision with which the spectroscopic solution for HD159656 has been measured should allow an investigation into possible apsidal motion in the near future. In addition to the variable radial velocity owing to its orbital motion, the K-giant, ν Oct, has been found to have an additional long-term irregular periodicity, attributed, for the time being, to the rotation of a large surface feature.\\ Double-lined solutions were obtained for HD206804 (K7V+K7V), which previously had two competing astrometric solutions but no spectroscopic solution, and a newly discovered seventh-magnitude system, HD181958 (F6V+F7V). This latter system has the distinction of having components and orbital characteristics whose study should be possible with present ground-based interferometers. All eight of the binary systems have had their mass ratio and the masses of their components estimated.\\ The following comments summarize the motivation for getting these results, and the manner in which the research was carried out. \\ The majority of stars exist in binary systems rather than singly as does the Sun. These systems provide astronomers with the most reliable and proven means to determine many of the fundamental properties of stars. One of these properties is the stellar mass, which is regarded as being the most important of all, since most other stellar characteristics are very sensitive to the mass. Therefore, empirical masses, combined with measurements of other stellar properties, such as radii and luminosities, are an excellent test for competing models of stellar structure and evolution.\\ Binary stars also provide opportunities to observe and investigate many extraordinary astrophysical processes that do not occur in isolated stars. These processes often arise as a result of direct and indirect interactions between the components, when they are sufficiently close to each other. Some of the interactions are relatively passive, such as the circularization of the mutual orbits, whilst others result from much more active processes, such as mass exchange leading to intense radiation emissions. \\ A complete understanding of a binary system's orbital characteristics, as well as the measurement of the all-important stellar masses, is almost always only achieved after the binary system has been studied using two or more complementary observing techniques. Two of the suitable techniques are astrometry and spectroscopy. In favourable circumstances, astrometry can deduce the angular dimensions of the orbit, the total mass of the system, and sometimes, its distance from us. Spectroscopy, on the other hand, can determine the linear scale of the orbit and the ratio of the stellar masses, based on the changing radial velocities of both stars. When a resolved astrometric orbital solution is also available, the velocities of both stars can allow the binary system's parallax to be determined, and the velocities of one star can provide a measure of the system mass ratio.\\ Unfortunately, relatively few binary systems are suited to these complementary studies. Underlying this difficulty are the facts that, typically, astrometrically-determined orbits favour those with periods of years or decades, whereas spectroscopic orbital solutions are more often measured for systems with periods of days to months. With the development of high-resolution astrometric and spectroscopic techniques in recent years, it is hoped that many more binary systems will be amenable to these complementary strategies.\\ Several months after this thesis began, a high-resolution spectrograph, HERCULES, commenced operations at the Mt John University Observatory, to be used in conjuction with the 1-metre McLellan telescope. For late-type stars, the anticipated velocity precision was ≲10 ms⁻¹. The primary goals of this thesis were: 1.~to assess the performance of HERCULES and the related reduction software that subsequently followed, 2.~to carry out an observational programme of 20 or so binary systems, and 3.~to determine the orbital and stellar parameters which characterize some of these systems. The particular focus was on those binaries that have resolved or unresolved astrometric orbital solutions, which therefore may be suited to complementary investigations.\\ HERCULES was used to acquire spectra of the programme stars, usually every few weeks, over a timespan of about three years. High-resolution spectra were acquired for the purpose of measuring precise radial velocities of the stars. When possible, orbital solutions were derived from these velocities, using the method of differential corrections.

La recherche des exoplanètes traverse aujourd'hui une période décisive. D'un côté, notre connaissance des planètes géantes gazeuses s'est considérablement développée, et l'objectif de la recherche est maintenant de caractériser leurs propriétés physiques et de mieux comprendre leurs mécanismes de formation et d'évolution. D'un autre côté, la précision et la stabilité des instruments ont atteint un niveau qui rend techniquement possible la détection de planètes telluriques situées dans la zone habitable de leur étoile. Cependant, les perturbations du signal dues à l'étoile elle-même constituent un obstacle important à cette avancée. Mon travail de thèse se situe à la rencontre de ces problématiques. Il a consisté d'une part en l'analyse de deux relevés de vitesses radiales visant des étoiles relativement exotiques pour la recherche d'exoplanètes: les étoiles naines de type AF massives. Ce travail a donné lieu à la première caractérisation de la population de planètes géantes autour de ces étoiles et a montré que les mécanismes de migration planétaire étaient au moins partiellement inhibés autour de ces étoiles par rapport aux étoiles de type FGKM. Dans un second temps, j'ai conduit les observations et l'analyse des premiers résultats de deux grands relevés de vitesses radiales débutés pendant ma thèse et visant à détecter des planètes géantes en orbite autour d'étoiles jeunes et proches. Ces étoiles jeunes sont les seules sources pour lesquelles une exploration complète des planètes géantes à toutes les séparations devient possible, par combinaison des techniques de vitesses radiales et de l'imagerie. Cette combinaison permettra de tester de manière unique les modèles de formation et d'évolution planétaire. Les résultats provisoires de ces relevés indiquent une absence de planètes géantes à très courte séparation (Jupiters chauds) autour de nos cibles. Un autre résultat intéressant est la découverte d'une binaire spectroscopique eccentrique au centre d'un système planétaire imagé à grande séparation. Pour compléter cette approche observationnelle et mieux évaluer la détectabilité des exoplanètes semblables à la Terre, j'ai étalonné et caractérisé un modèle entièrement paramétré de l'activité d'une étoile semblable au Soleil et de son impact sur les vitesses radiales. Je l'ai dans un premier temps étalonné en comparant ses résultats à ceux obtenus à partir d'observations des zones actives du Soleil, puis je l'ai utilisé pour caractériser l'impact de l'inclinaison de l'étoile sur le signal induit par l'activité. Ce modèle paramétré ouvre de très nombreuses possibilités, étant en effet potentiellement adaptable à des types d'étoiles et d'activité différents. Il permettrait ainsi de caractériser les perturbations en vitesses radiales attendues pour chaque cas testé, et donc à la fois de déterminer quelles étoiles et quels types d'activité sont les plus favorables pour la détection de planètes de masse terrestre dans la zone habitable. En explorant ces trois problématiques en apparence très diverses mais complémentaires, j'y ai retrouvé un motif commun, celui de l'importance des étoiles elles-mêmes et de la physique stellaire pour la recherche d'exoplanètes. / The search for exoplanets has reached a decisive moment. On the one hand, our knowledge of giant gaseous planets has significantly developed, and the aim of the research is now to characterize their physical properties and to better understand the formation and evolution processes. On the other hand, the instrumental precision and stability have reached a level that makes it technically possible to detect telluric planets in the habitable zone of their host star. However, the signal alterations induced by the star itself definitely challenge this breakthrough. My PhD stands at the crossroads of these problems. It consisted first in the analysis of two radial velocity surveys dedicated to stars somewhat exotic to exoplanet searches: the massive AF dwarf stars. This work has led to the first characterization of the giant planet population found around these stars and has showed that the planetary migration mechanisms were at least partially inhibited around these stars compared to FGKM stars. I then made the observations and the first analysis of two radial velocity surveys dedicated to the search for giant planets around young, nearby stars. Young stars are the only sources for which a full exploration of the giant planets at all separations can be reached, through the combination of radial velocities techniques and direct imaging. Such a combination will allow to test uniquely the planetary formation and evolution processes. The first results of these surveys show an absence of giant planets at very short separations (Hot Jupiters) around our targets. Another interesting result is the detection of an eccentric spectroscopic binary at the center of a planetary system imaged at a wide separation. To complete this observational approach and better estimate the detectability of Earth-like planets, I calibrated and characterized a fully parameterized model of the activity pattern of a Sun-like star and its impact on the radial velocities. I first calibrated it by comparing it to the results obtained with observations of the solar active structures, and then characterized the impact of stellar inclination on the activity-induced signal. Such a fully parameterized model is potentially adaptable to different types of stars and of activity and would thus allow to characterize the expected radial velocity jitter for each tested case, and then allow both to determine which types of stars and of activity patterns are the most favorable for detecting Earth-like planets in the habitable zone. While investigating these three seemingly different but complementary topics, I found that they shared a basic feature, namely the importance of the stars themselves and of stellar physics in exoplanet searches.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In order to determine distances of Southern Galactic HII regions, we carried out spectroscopic and photometric observations of the stellar content of a set of these objects. We have chosen objects only visible in the South hemisphere, with no published or uncertain distances. In this work, we present spectral classification based on intermediate dispersion spectra with a very high signal to noise ratio and on stellar UBV photometry, so that the distances have been determined using the usual method, the spectroscopic parallax. We picked up the 2MASS infrared photometry and assessed the reddening individually for each star, using the color-difference method. This way, we have estimated the totalto-selective extinction ratio for the most of the classified stars, and so, we have found a mean value 21% higher than the mean value of RV calculated on the whole directions of the Galaxy. As a result, we have found distances in general smaller than those already published on the literature, although confirming several spectral classifications. Besides that, large fluctuations around the values normally adopted were also observed, which would result in larger discrepancies between the stellar distances. At last, we have also extracted nebulae spectra in order to estimate the kinematics distances, so that we could compare the distance measurement results by different methods. In general, we have found reasonably compatible distances. However, in some cases large differences was found, suggesting that some objects present deviations of the circular motion. / Com o objetivo de determinar distâncias de regiões HII Galácticas observáveis no Hemisfério Sul, realizamos observações espectroscópicas e fotométricas do conteúdo estelar de um conjunto desses objetos. Demos preferência para aqueles objetos cuja observação só é possível no Hemisfério Sul, sem publicações de distância encontrada ou com grande dispersão entre os valores publicados. Neste trabalho, apresentamos classificação espectral baseada em espectros de dispersão intermediária, com elevada razão sinal / ruído e, também, classificação espectral via fotometria UBV , ambas com o objetivo de determinar as distâncias das regiões HII via paralaxe espectroscópica de suas estrelas ionizantes. Nós também extraímos as magnitudes dessas estrelas no infravermelho próximo diretamente do catálogo 2MASS e calculamos o avermelhamento individualmente para cada estrela usando o método das diferenças de cores. Assim, a razão entre a extinção total e a seletiva a banda V (RV ) foi estimada para a maior parte das estrelas, de forma que encontramos um valor médio 21% maior que o valor médio de RV calculado sobre todas as direções da Galáxia e, por este motivo, nós encontramos distâncias heliocêntricas, em geral, menores do que aquelas encontradas na literatura, mesmo confirmando a maior parte das classificações espectrais dadas por esses autores. Além disso, grandes flutuações em torno do valor médio foram encontradas, o que acarretaria maiores discrepâncias entre as distâncias estelares. Por fim, extraímos espectros nebulares dos objetos, com o objetivo de estimar suas distâncias cinemáticas e comparar os resultados obtidos com diferentes métodos. Em geral, encontramos distâncias razoavelmente compatíveis. Contudo, em alguns casos, grandes diferenças foram encontradas, sugerindo que alguns objetos como RCW 88 e NGC 3503 apresentam desvios do movimento circular.

Considérant une série temporelle affectée par un bruit coloré dont les propriétés statistiques sont inconnues, la difficulté pour la détection de signaux périodiques est de contrôler le degré de confiance avec lequel les tests de détection rejettent l'hypothèse nulle en faveur de l'hypothèse alternative. L'objectif de cette thèse est de développer une nouvelle méthode utilisant des séries temporelles simulées du bruit pour améliorer ce contrôle. Dans le cas d'un échantillonnage régulier, nous avons analysé les performances de différents tests de détection appliqués à un périodogramme standardisé par le spectre simulé du bruit. La standardisation proposée entraîne, dans la majorité des cas, des tests de détection puissants dont les taux de fausses alarmes sont constants. Grâce au développement des distributions asymptotiques de ce périodogramme, nous avons déterminé des expressions analytiques pour les probabilités de fausses alarmes (PFA) et de détections de différents tests. Dans le cas d'un échantillonnage irrégulier, nous montrons qu'il est possible de combiner la standardisation proposée du périodogramme avec des techniques de bootstrap pour contrôler la PFA de manière fiable. La procédure peut être optimisée en utilisant les valeurs extrêmes généralisées. Cette étude a été appliquée au cas de la détection de planètes extrasolaires par la méthode des vitesses radiales dont l'une des principales barrières pour détecter des planètes de masse terrestre vient de l'activité de l'étoile hôte, notamment la convection de surface. Le travail effectué dans cette thèse a porté sur la contribution de simulations hydrodynamiques du bruit convectif dans le processus de détection. / Considering a time series affected by a colored noise of unknown statistics, a difficulty for periodic signal detection is to control the true significance level at which the detection tests are conducted. The objective of this thesis is to develop a new method using training datasets of the noise to improve this control. For the case of regularly sampled observations, we analyze the performances of various detectors applied to periodograms standardized using the noise training datasets. The proposed standardization leads, in some cases, to powerful constant false alarm rate tests. Thanks to the development of the asymptotical distribution of the standardized periodogram, we derive analytical expressions for the false alarm and detection rates of several tests. In the case of irregular sampling, we show that it is possible to combine the proposed periodogram standardization and bootstrap techniques to consistently estimate the false alarm rate. We also show that the procedure can be improved by using generalized extreme value distributions. This study has been applied to the case of extrasolar planet detection in radial velocity (RV) data. The main barrier to detect Earth-mass planets comes from the host star activity, as the convection at the stellar surface. This work investigates the possibility of using hydrodynamic simulations of the stellar convection in the detection process to control exoplanet detection claims.

This study examines the efficacy of Sentinel-1 Radial Velocity (RVL) imagery at determining the position of ocean current front features, using the Gulf Stream (GS) and Agulhas Current (AC) as case studies. Fronts derived from RVL imagery are compared to fronts derived from Sea Surface Temperature (SST) imagery, specifically Multi-scale Ultra-high Resolution Sea Surface Temperature Analysis (MURSST) data. In the case of the GS, front locations from the Naval Oceanographic Office (NAVOCEANO) were also used for comparison. Only the northern walls of ocean current features are considered in this study, which is broken into three main steps: Preprocessing, front extraction, and front comparison. First, RVL imagery is selected from Sentinel-1 ocean products, preprocessed to remove antenna mispointing artifacts, and all products from the same orbit are combined into a single swath. Second, front features are extracted from both the RVL and MURSST imagery using a ridge detection algorithm, the main ocean current is chosen from all ridge features using a ranking algorithm, and the northern wall of this current is extracted. Third, the RVL, SST, and in the case of the GS, NAVOCEANO GS locations, features are compared using a symmetric Hausdorff Distance (HD) measure, and Mean Hausdorff Distance (MHD). In some cases, the automatic front extraction failed by either misclassifying an eddy or similar ocean feature as the ocean current in either the RVL or SST image or failed to extract the entire length of the front visible within the image. All the SST and RVL fronts were classified manually to determine the success rate of the automatic front extraction and to exclude failed front extractions from the analysis, as they are not accurate representations of the SST and RVL data’s ability to detect fronts. In special cases, the RVL image itself does not detect the entire ocean current, such that there are noticeable gaps in the ocean current. Similarly, in special cases the MURSST does not detect the entire ocean current. The automatic front extraction succeeded 65% of the time, including the special cases. The results demonstrated that RVL products were effective at determining the location of ocean fronts where the angle of the front's normal vector is within approximately 40° of the sensor’s azimuthal heading. A mean HD of 31.9 km and a mean MHD of 13.2 km was calculated for all front pairs over all study areas. The RVL fronts appeared consistently to the north of the SST fronts, with an average offset of 25.4 km between the centroids of the SST and RVL fronts. Positive correlations were noted between cloud coverage and MURSST error in both study regions. Several RVL images detected ocean currents in regions of high MURSST error where the MURSST did not detect the ocean currents, suggesting that RVL may provide more accuracy than SST-based products in clouded regions where there is no auxiliary data.