Academic literature on the topic 'High frequency DGPS surveys'

Detailed geophysical surveys are required in both deep and shallow water to avoid potential hazards and to provide for the installation and safety of fiber optic telecommunication cables. Unfortunately, data obtained in potential burial zones with existing technology are slow and often data accuracy may be questionable. Towing cabled or tethered survey systems, from a project perspective, is time consuming and provides marginally adequate data. Additionally, a launch is usually required to survey between the surf and the safe working limits of the survey ship. This requires additional equipment that is weather sensitive and subject to failure.To address this problem, C & C Technologies, Inc. of Lafayette, Louisiana, USA has contracted with Kongsberg Simrad for the construction of a Hugin 3000 autonomous underwater vehicle (AUV). C & C Technologies’ Hugin 3000 AUV, which is to be delivered in July of 2000, will be integrated with a variety of sensors including high frequency multibeam swath bathymetry and imagery. Other survey sensors include chirp side scan sonar, chirp sub-bottom profiler, and magnetometer. Vehicle positioning will be provided by a USBL acoustic positioning system, integrated with Doppler speed log, an inertial navigation system, and for surface operations, DGPS. AUV power will be delivered by aluminum oxygen fuel cells.This paper will address AUV operations, platform performance, sensor specifications and integration, project milestones, and system economics with regards to cable route surveys.

This study investigates the accuracy of an online Precise Point Positioning (PPP) service operated by the Geodetic Survey Division of Natural Resources Canada (NRCan), Canadian Spatial Reference System (CSRS)-PPP, by using single/dual-frequency Global Positioning System (GPS) data collected by dual-frequency geodetic-grade and Original Equipment Manufacturer (OEM) board type single-frequency GPS receivers. In this work, a kinematic test was carried out in Halic Bay (Golden Horn), Istanbul, Turkey, to assess the performance of the PPP method in a dynamic environment. Based on this study, it can be concluded that the coordinates estimated from the online CSRS-PPP service have a potential of about metre-level accuracy by processing single frequency data collected by an OEM receiver and about a decimetre to a few centimetres level accuracy by processing dual frequency data collected by a geodetic-grade receiver. In general, results show that the PPP technique has become a significant alternative to the conventional relative (differential) positioning techniques (i.e., Differential GPS (DGPS), Real-time Kinematic (RTK)). The technique does not suffer from the drawbacks of the DGPS technique and has potential to provide the same position accuracy without the requirement for a reference station. Consequently, it has been concluded that the PPP technique may be effectively used in marine applications due to its ease of use and provision of high accuracy, as well as being able to offer reduced field operational costs.

Cliff collapse poses a serious hazard to infrastructure and passers-by. Obtaining information such as magnitude-frequency relationship for a specific site is of great help to adapt appropriate mitigation measures. While it is possible to monitor hundreds-of-meter-long cliff sites with ground based techniques (e.g. lidar or photogrammetry), it is both time consuming and scientifically limiting to focus on short cliff sections. In the project SUAVE, we sought to investigate whether an octocopter UAV photogrammetric survey would perform sufficiently well in order to repeatedly survey cliff face geometry and derive rock fall inventories amenable to probabilistic rock fall hazard computation. An experiment was therefore run on a well-studied site of the chalk coast of Normandy, in Mesnil Val, along the English Channel (Northern France). Two campaigns were organized in January and June 2015 which surveyed about 60 ha of coastline, including the 80-m-high cliff face, the chalk platform at its foot, and the hinterland in a matter of 4 hours from start to finish. To conform with UAV regulations, the flight was flown in 3 legs for a total of about 30 minutes in the air. A total of 868 and 1106 photos were respectively shot with a Sony NEX 7 with fixed focal 16mm. Three lines of sight were combined: horizontal shots for cliff face imaging, 45°-oblique views to tie plateau/platform photos with cliff face images, and regular vertical shots. Photogrammetrically derived dense point clouds were produced with Agisoft Photoscan at ultra-high density (median density is 1 point every 1.7cm). Point cloud density proved a critical parameter to reproduce faithfully the chalk face’s geometry. Tuning down the density parameter to “high” or “medium”, though efficient from a computational point of view, generated artefacts along chalk bed edges (i.e. smoothing the sharp gradient) and ultimately creating ghost volumes when computing cloud to cloud differences. Yet, from a hazard point of view, this is where small rock fall will most likely occur. Absolute orientation of both point clouds proved unsufficient despite the 30 black and white quadrants ground control point DGPS surveyed. Additional ICP was necessary to reach centimeter-level accuracy and segment rock fall scars corresponding to the expected average daily rock fall volume (ca. 0.013 m3).

Cliff collapse poses a serious hazard to infrastructure and passers-by. Obtaining information such as magnitude-frequency relationship for a specific site is of great help to adapt appropriate mitigation measures. While it is possible to monitor hundreds-of-meter-long cliff sites with ground based techniques (e.g. lidar or photogrammetry), it is both time consuming and scientifically limiting to focus on short cliff sections. In the project SUAVE, we sought to investigate whether an octocopter UAV photogrammetric survey would perform sufficiently well in order to repeatedly survey cliff face geometry and derive rock fall inventories amenable to probabilistic rock fall hazard computation. An experiment was therefore run on a well-studied site of the chalk coast of Normandy, in Mesnil Val, along the English Channel (Northern France). Two campaigns were organized in January and June 2015 which surveyed about 60 ha of coastline, including the 80-m-high cliff face, the chalk platform at its foot, and the hinterland in a matter of 4 hours from start to finish. To conform with UAV regulations, the flight was flown in 3 legs for a total of about 30 minutes in the air. A total of 868 and 1106 photos were respectively shot with a Sony NEX 7 with fixed focal 16mm. Three lines of sight were combined: horizontal shots for cliff face imaging, 45°-oblique views to tie plateau/platform photos with cliff face images, and regular vertical shots. Photogrammetrically derived dense point clouds were produced with Agisoft Photoscan at ultra-high density (median density is 1 point every 1.7cm). Point cloud density proved a critical parameter to reproduce faithfully the chalk face’s geometry. Tuning down the density parameter to “high” or “medium”, though efficient from a computational point of view, generated artefacts along chalk bed edges (i.e. smoothing the sharp gradient) and ultimately creating ghost volumes when computing cloud to cloud differences. Yet, from a hazard point of view, this is where small rock fall will most likely occur. Absolute orientation of both point clouds proved unsufficient despite the 30 black and white quadrants ground control point DGPS surveyed. Additional ICP was necessary to reach centimeter-level accuracy and segment rock fall scars corresponding to the expected average daily rock fall volume (ca. 0.013 m3).

Abstract High-resolution Multibeam Echosounder shallow water surveys should not be performed with DGPS (Differential Global Positioning System), especially where feature detection is a priority. Despite the fact that International Hydrographic Organization most demanding Special Order Specification allows for 2 meters horizontal positioning level, it poorly interacts with horizontal centimetric level nadir footprint, causing degradation of bathy-metric data.

This paper describes an advanced method, and the corresponding algorithms, which could provide a high precision Wide Area Differential GPS (WADGPS). The service would be suitable for single or dual frequency users, and could be introduced with very few reference stations. The two main components of the service are a precise, near real-time orbit determination of the GPS satellites, and an accurate estimation and modelling of ionospheric and tropospheric effects. Broad principles of the processing algorithms and results of both simulation and real data tests are described. User positioning accuracies of better than 2·5 m (r.m.s.) in plan and 3·0 m (r.m.s.) in height are achieved by both single and dual frequency scenarios.Wide Area Differential GPS (WADGPS) is being developed to overcome the main drawbacks of conventional or Local Area Differential GPS (LADGPS), where positional accuracy of a user degrades as the reference-to-user separation increases. The spatial decorrelation of the error sources, notably the atmospheric propagation and satellite orbital errors inherent in GPS, are the main causes of this accuracy degradation. Several organizations are involved in WADGPS research, and different conceptual approaches have been suggested. The proposed methods all share a common basic assumption: that the error sources which affect the system are broken down into individual error components and are modelled separately. The variance between the different techniques comes from the way in which the different error components are modelled.

The objective of the present study is to achieve a better understanding of the possible rotation of embayed beaches using shoreline position data from two beaches on the central Tyrrhenian Sea (Italy) during a 64-year period. With this aim, this study tests the utility of Differential Global Positioning System (DGPS) and GPS RTK (Real Time Kinematic) dual-frequency navigation system for the in situ surveys, low-altitude aerial imagery collected by Unmanned Aerial Vehicle (UAV), and satellite polarimetric Synthetic Aperture Radar (SAR) measurements. The dataset consists of aerial photographs and orthophotos, DGPS, and remote surveys performed by UAV and SAR platform in 2018 along with wave data coming from the Ponza buoy. The results of the field data analysis explained a part of the beach variations in terms of coastline rotation around a virtual pivotal point. This rotation has been correlated with the wave directional shift in the recent period. The results of the comparison between the different techniques gave the possibility to investigate the limitations of remote survey methods for the identification of shoreline rotation.

The 11-year solar sunspot cycle is approaching a maximum in 2000. The sunspot activity causes an increase in the solar flux, charged particles and electromagnetic rays emitted from the Sun. This solar flux affects the ionosphere, thus influencing the transmission of radio waves through the ionosphere. The GPS satellite navigation system is affected in that the transit time of the signals varies, introducing position errors. Also GPS equipment may experience degraded performance in tracking of the GPS satellites due to scintillations, rapidly varying amplitude and phase of the GPS signal. The equatorial and high latitude regions are most severely affected by this increased ionospheric activity. Experience has shown that, in equatorial regions, errors of 10–20 m may be introduced in Differential GPS services, even on distances down to a few hundred kilometres from the reference station. During the peak of the solar cycle, for the next 3–4 years, this situation will rather be the rule than the exception in the affected areas. Fugro has introduced an enhanced real-time DGPS service utilising dual frequency GPS called Starfix-Plus in selected areas. This service removes ionospheric delay errors by calculating the delay using dual frequency GPS receivers on the reference stations and the mobiles. The resulting accuracy is down to a few metres, even using reference stations up to 2000 km away. This increases the availability and redundancy of usable reference stations in a region, increasing the probability that the required accuracy is available, even if individual stations are not available due to scintillations or for other reasons.

The integration of the Global Positioning System (DGPS) with an Inertial Navigation System (INS) has been implemented for several years. In an integrated INS/DGPS system, the DGPS provides positions while the INS provides attitudes. In case of DGPS outages (signal blockages), the INS is used for positioning until the DGPS signals are available again. One of the major issues that limit the INS accuracy, as a stand-alone navigation system, is the level of sensor noise. The problem with inertial data is that the required signal is buried into a large window of high frequency noise. If such noise component could be removed, the overall inertial navigation accuracy is expected to improve considerably. The INS sensor outputs contain actual vehicle motion and sensor noise. Therefore, the resulting position errors are proportional to the existing sensor noise and vehicle vibrations. In this paper, wavelet techniques are applied for de-noising the inertial measurements to minimize the undesirable effects of sensor noise and other disturbances. To test the efficiency of inertial data de-noising, two road vehicle INS/DGPS data sets are utilized. Compared to the obtained position errors using the original inertial measurements, the results showed that the positioning performance using de-noised data improves by 34%–63%.

Cette thèse présente une étude de la dynamique des plages sableuses ouvertes dominées par la houle, au travers d’une base de données originale, couvrant une période de 29 mois, et composée de 150 levés DGPS couvrant 750m de linéaire côtier, donnant accès à la morphodynamique du site de Biscarrosse à différentes échelles de temps. Dans un premier temps, l’analyse du jeu de données à l’échelle des événements (tempêtes et successions de tempêtes appelées clusters) nous a permis de montrer que la réponse des plages sableuses aux clusters ne résulte pas de la somme des impacts induits par chaque tempête d’un cluster. Ainsi, l’effet cumulé des clusters, rapporté sur d'autres sites dans la littérature, n’est ici pas vérifié. L'impact de l’enchainement des tempêtes a également été étudié et il en résulte que lors d’un cluster, un changement des conditions hydrodynamique, à savoir, une augmentation des hauteurs de vagues et/ou du niveau d’eau, est nécessaire pour que la tempête suivante ait un impact érosif significatif sur le système. Dans un second temps, nous avons étudié la dynamique saisonnière du système plage/dune, que ce soit la saison hivernale ou estivale, dans le but de mettre en relief les principaux processus impliqués à cette échelle. Nos travaux montrent que la réponse hivernale de la plage ne dépend pas uniquement des conditions énergétiques et du profil pré-hivernal de la plage, mais également du séquençage des événements, comme lors d'un cluster. Mes travaux confirment également la nécessité de prendre en compte de nombreux paramètres dans l’étude de la dynamique hivernale des littoraux sableux : les conditions hydrodynamiques, le séquençage des évènements érosifs mais également reconstructifs, en particulier le ré-engraissement post-évènement, les transports sédimentaires cross-shore et longshore, ainsi que la position de la barre interne et des courants d’arrachements. La saison estivale est, quant-à-elle, marquée par la reconstruction de berme. Elle semble être liée à la fois aux conditions hydrodynamiques et aux caractéristiques des barres sableuses. L’étude de deux étés et deux hivers successifs a ainsi permis d’identifier les interactions entre les saisons et l’impact de la saison hivernale sur l’estivale, et l’influence de la dynamique événementielle sur la dynamique saisonnière. Elle a aussi permis de mettre en relief l’impact de l’urbanisme et des stratégies d’aménagement dans la réponse du système, à différentes échelles de temps
This thesis presents a study of an open sandy beach wave-dominated, based on an original dataset, covering 29 months and composed by 150 DGPS surveys recorded along 750m of sandy shore, giving an access to the morphodynamic of Biscarrosse beach at different timescales. In a first time, event scale analysis showed that sandy beach response to clusters is not the result of the sum of the impact generated by each storm of a cluster on the system. Thus, the cumulated effect of clusters, described in the literature is not verified here. The storm sequencing has also been studied: during a cluster, changes in hydrodynamics conditions (rising of the water level and/or wave height) are necessary to provoke a significant erosion of the system by the second storm. In a second time, we studied the seasonal scale dynamic of the beach/dune system (winter and summer seasons) with the purpose to highlight dominant processes involved at this timescale. Beach response to winter seasons not only depends on hydrodynamic conditions and previous beach profile, but also on erosion/recovery event sequencing, post-storm recovery, cross-shore and longshore sediment transport, the barline characteristics and RIP current positions. Summer seasons are here defined by the berm reconstruction. Recovery periods are both linked to hydrodynamic conditions and barline characteristics (e.g. position and shape).The study of successive winters and summers allowed us to identify interactions between seasons, and the influence of short-scale dynamics on the seasonal one. It also emphasizes the impact of urbanism and coastal management strategies on the system’s response, at different timescales

This hydrogeophysical field experiment evaluated the ability of high frequency (450 & 900 MHz) ground penetrating radar (GPR) to characterize the release of gasoline over an annual cycle of in situ conditions. In August 2008, 200 liters of E10 gasoline were released into the unconfined sand aquifer at CFB Borden. The 900 MHz profiling clearly shows the development of shallow (i.e., above 10 ns) high reflectivity in the vicinity of the trench immediately after the release. Additional lateral extension of high reflectivity zone was observed over the following 20 days until the seasonal water table low stand occurred, after which no further lateral movement was observed. Throughout the remainder of the monitoring, the 900 MHz profiling observed a long-term dimming of reflectivity at the periphery of the impacted zone. While direct imaging of the shallow impacted zone by the 450 MHz antennas was significantly obscured by the superposition with the direct air-ground wave arrival; its improved depth of penetration allowed the measurement of a velocity “pull-up” of an underlying stratigraphic interface resulting from the displacement of low velocity water by high velocity gasoline. The maximum pull-up was observed during the water table low stand. The ongoing changes in the pull-up magnitude during the remainder of the observation period suggest the continued redistribution of fluids in the impacted zone. Because of the shallow depth of the gasoline impacted zone, the effects of freezing during the winter period were observed in the GPR imaging. The presence of the gasoline impacted zone appears to have affected the depth of freezing, causing a depression of the frozen soil base. The dimming of the direct air-ground wave complex indicates that the contaminant phase brought to the surface by the water table fluctuations have impacted the nature of the near-surface freezing.

<em>Abstract.-</em>Declines in recreational fishing participation, under representation of women and nonwhites among the angling population, and increased urban immigration and urban sprawl have prompted the development of urban fishing programs throughout the United States. The Arkansas Game and Fish Commission initiated their urban fishing program, the Family and Community Fishing Program (FCFP), in 2001. The FCFP stocks channel catfish <em>Ictalurus punctatus </em>biweekly from April to August and rainbow trout <em>Oncorhynchus mykiss </em>biweekly from December to March. In this study, the effects of stocking frequency on fishing quality and angler satisfaction were determined for biweekly and monthly stocking regimes. Stocking frequencies were randomly assigned to ponds in the first year, and reversed in the second year of the study. Roving creel surveys were used to collect angler effort, catch, harvest, and satisfaction data. Response rates of the 1,533 catfish and 512 trout angler parties approached were 96% and 98%, respectively. There were no significant differences between the two stocking frequencies for effort, catch, harvest, or angler satisfaction ratings during catfish or trout seasons. Satisfaction ratings were much lower for fishing satisfaction (26-38% excellent or good rating) than overall trip satisfaction (61-74% excellent or good rating), and appeared to be closely associated with catch rates. These findings suggest that the FCFP can reduce stocking frequency without causing detrimental effects to fishing quality, as long as the same monthly allocations of fish are stocked. Biweekly stocking has high transportation and personnel costs, thus reducing stocking frequency could potentially decrease costs and better allocate funds and labor.

Introduction: The study aimed to determine gender differences in the prevalence and dynamics of affective states over a long period, i.e., 23 years, and to establish their effect on the risk of cardiovascular diseases (CVD), i.e., arterial hypertension (AH), myocardial infarction (MI), and stroke among the population aged 25–64 in Russia / Siberia. Methods: Between 1994 and 2017, we conducted 4 screening surveys of representative samples (totalling 4,815 people) under the international programs MONICA and HAPIEE in Russia / Siberia. To determine the sex differences in cardiovascular risk from 1994 to 2010, we observed cohorts formed from the screened individuals without CVD and diabetes mellitus (DM). Results: High levels of affective states in the period from 1994 to 2003, especially in women, were replaced by a downward trend in 2013. At the same time, there was a reduction in the gender gap in terms of frequency of depression lower 1%, and men in the younger age groups reported higher levels of personal anxiety (49.3% vs 46.1% in adults aged 35-44y) and vital exhaustion (16.9% vs 15.6%) than women in 2017. We found that men with unfavourable levels of affective states have a 3–5 fold higher risk of hypertension and stroke, while women have a higher risk of myocardial infarction (p for all < 0.05). Hostility in men is associated with a negative risk of myocardial infarction and stroke (HR=0.3 and HR=0.29, respectively; p for all < 0.05). However, this was levelled out by unfavourable social characteristics. Conclusions: The downward trends in prevalence of psychosocial factors were unstable and associated with reduced gender gap for affective states. It had a significant impact on the gender magnitude of cardiovascular risk.

Vegetation is the plant cover of a region, which usually refers to the potential natural vegetation prior to any intensive human disturbance. The description of vegetation for an extensive area involves the recognition and characterization of units called formations, which are named with reference to composition (e.g., coniferous), aspect of habit (deciduous), distribution (western North America), and climate, either directly (tropical) or indirectly (tundra). Further subdivisions are termed associations or series, such as the beech-maple association or series within the deciduous forest formation. Formations and associations constitute a convenient organizational framework for considering the development of vegetation through Late Cretaceous and Cenozoic time. For this purpose seven extant plant formations are recognized for North America: (1) tundra, (2) coniferous forest, (3) deciduous forest, (4) grassland, (5) shrubland/chaparral- woodland- savanna, (6) desert, and (7) elements of a tropical formation. Several summaries are available for the modern vegetation of North America, including Barbour and Billings (1988), Barbour and Christensen, Kuchler (1964), and Vankat (1979). The following discussions are based primarily on these surveys. Tundra (Fig. 1.2) is a treeless vegetation dominated by shrubs and herbs, and it is characteristic of the cold climates of polar regions (Arctic tundra) and high-altitude regions (alpine tundra). In the Arctic tundra a few isolated trees or small stands may occur locally, such as Picea glauca (white spruce), but these are always in protected habitats. The Arctic region experiences nearly continuous darkness in midwinter, and nearly continuous daylight in midsummer. There is a short growing season of only 6-24 weeks; this accounts, in part, for the fact that 98% of all Arctic tundra plants are perennials (Vankat, 1979). Strong winds are another feature of the Arctic landscape, often exceeding 65 km/h for 24 h or more. They likely account for the frequency of rosettes, persistent dead leaves, and the cushion growth form, in the center of which wind velocities may be reduced by 90%. The harsh growing conditions also result in leaves of the microphyllous size class being comparable to those of desert plants. Vegetative reproduction and self-pollination is common, and phenotypic plasticity is high among Arctic tundra plants.

This chapter emphasizes the linear optical properties of solids as a function of frequency and temperature. Such information is basic to understanding the performance of optical fibers, lenses, dielectric and metallic mirrors, window materials, thin films, and solid-state photonic devices in general. Optical properties are comprehensively covered in terms of mathematical models of the complex index of refraction based on those discussed in Chapters 4 and 5. Parameters for these models are listed in Appendix 4. A general review of solid-state properties precedes this development because the choice of an optical material requires consideration of thermal, mechanical, chemical, and physical properties as well. This section introduces the classification of optical materials and surveys other material properties that must be considered as part of total optical system design involving solidstate optics. Solid-state materials can be classified in several ways. The following are relevant to optical materials. Three general classes of solids are insulators, semiconductors, and metals. Insulators and semiconductors are used in a variety of ways, such as lenses, windows materials, fibers, and thin films. Semiconductors are used in electrooptic devices and optical detectors. Metals are used as reflectors and high-pass filters in the ultraviolet. This type of classification is a function of the material’s electronic bandgap. Materials with a large room-temperature bandgap (Eg > 3eV) are insulators. Materials with bandgaps between 0 and 3 eV are semiconductors. Metals have no observable bandgap because the conduction and valence bands overlap. Optical properties change drastically from below the bandgap, where the medium is transparent, to above the bandgap, where the medium is highly reflective and opaque. Thus, knowledge of its location is important. Appendix 4 lists the bandgaps of a wide variety of optical materials. To characterize a medium within the region of transparency requires an understanding of the mechanisms of low-level absorption and scattering. These mechanisms are classified as intrinsic or extrinsic. Intrinsic properties are the fundamental properties of a perfect material, caused by lattice vibrations, electronic transitions, and so on, of the atoms composing the material.

<strong><em>Abstract. </em></strong>Historical distributions (<em>n </em>= 32<em>y</em>) of age-1 juvenile haddock <em>Melanogrammus aeglefinus </em>from the eastern Scotian Shelf population varied linearly with year-class strength, indicating a dependence on demersal habitats. Distributions of haddock ages 2–5 were weakly density dependent, indicating weaker associations with benthic habitats. The preferred areas (≥75%) of occurrence for age-1 haddock changed with the spatial scale of analysis. As bin size was reduced from 1,342 km² (400 nm²) to 755 km² (225 nm²) to 336 km² (100 nm²) to 84 km² (25 nm²), the boundaries of preferred areas shifted in location and the total area increased in size. As the spatial scale of bin size was reduced, the frequency of missing data increased, making it difficult to determine the true nature and extent of high-preference areas. The historical data indicated that preferred areas occur at the smallest scale analyzed of approximately 100 km². Therefore, preferred areas (≥75% occurrence) and nonpreferred (≤25% occurrence) areas 10 km by 10 km were selected on three banks of differing size for directed studies. Acoustic surveys were carried out in the selected study areas using a normal incidence echosounder to determine fine-scale (16–18 m) bathymetric structure. These areas ranged in mean depths from 42 to 84 m. Bathymetric relief (m/km) was always greater in preferred areas within each bank. Spatial auto-correlation of bathymetric relief had smaller decorrelation scales for preferred areas within banks. Preferred areas for age-1 haddock were always more rugged at finer spatial scales than nonpreferred areas, indicating that preferred habitats may be more complex. There was a bank-scale dependency in surface structure where smaller banks were less rugged at finer spatial scales. We hypothesize that there may be a bank-dependent scaling of habitats where larger banks have a greater variety of habitats that span a greater range of spatial scales.

<em>Abstract</em>.—Introduced blue catfish <em>Ictalurus furcatus</em> populations in tidal rivers of the Atlantic slope support important recreational and commercial fisheries, with the James River trophy fishery being nationally recognized. During the period 2001–2008, low-frequency (15 pulses/s) pulsed DC electrofishing was used to sample blue catfish in tidal fresh-oligohaline sections of the James, Mattaponi, Pamunkey, and Rappahannock River systems; 54,174 blue catfish were collected, and 4,660 of these were aged using otoliths. Mean catch per unit effort (CPUE) was generally high (ranging from 223 to 6,106 fish per hour). Trends of increasing CPUE through time occurred in the James (839–4,449 fish per hour) and Rappahannock (1,400–6,106 fish per hour) rivers, and differences in CPUE were detected among rivers. Temporal shifts in growth (mean length at age) were observed, with growth slowing for all ages in the Pamunkey River and slowing for older ages in the Mattaponi (ages 9–13) and Rappahannock (ages 8–12 and age 14) rivers. In the Pamunkey and Rappahannock rivers, a negative relationship existed between growth (mean length at age 10) and density (CPUE). Although density increased dramatically in the James River, growth remained stable. Growth varied among rivers; by the end of the study, mean total length at age 10 ranged from 416 mm in the Rappahannock River to 675 mm in the James River. Growth through age 15 fi t linear models, as opposed to the von Bertalanffy nonlinear curve. In three of the four populations, the maximum age sampled increased in each succeeding survey year, and the maturing of all four populations was reflected in concurrent increases in size distributions. Recruitment was variable, with coincident strong and weak year-classes occurring in all four populations—an implication that landscape-level environmental variables play a role in determining recruitment success. In three of the four populations, patterns in year-class strength persisted, with correlation of catch-curve residuals from surveys separated by time. Approximately 35 years poststocking in the James and Rappahannock rivers and 25 years poststocking in the Mattaponi River, these populations had not yet reached equilibrium. It is unknown what the dynamics of blue catfish abundance, growth, and survival will be in the long-term in these rivers, leaving uncertainty regarding the future of the fisheries the populations support, as well as unanswered questions related to potential effects on other species.

The author has developed a small and powerful high frequency cam-type vibrator using roller thrust bearings with uneven races. The diameter of the vibrator is nearly the same as the outer diameter of the thrust bearing, and it is very small compared with other vibrators. This vibrator can be installed at the bottom end of a drill string as a high frequency vibro-hammering gear. Although the amplitude of the axial displacement is fixed, combination of two vibrators of this type can make the amplitude variable by superimposition. This variable superimposition can also be used as an On-Off switch of the vibration. The underwater sound used for seismic survey is usually a short pulse with a duration of several to several tens of milliseconds. The vibrator described in this paper is capable of generating such short sound pulses owing to the variable superimposition. Present sound generators for seismic survey are usually big and heavy and generate sound pulses with a wide frequency spectrum, centered around 100Hz. The cam-type vibrator described in this research is much smaller and lighter than present systems, making the deployment near the seafloor easy for even at great depths, which in return leads to more detailed results in stratum surveys. The emitted sound is a pure tone whose frequency can be anywhere between 100 and 1000Hz. The author has tried to develop this type of sound generator under the support of JOGMEC (Japan Oil, Gas and Metals National Corporation). In this paper, the principle of the vibration, the design of the sound generator and the result of the experiment shall be discussed.

Recently Nalcor announced the discovery of three newly defined hydrocarbon basins located primarily in deep water in the Labrador Sea, off the east coast of Newfoundland and Labrador, Canada. The basins are Henley, Chidley and Holton Basins and expanded the extent of the Hawke Basin. On behalf of Nalcor Energy, C-CORE recently completed the Offshore Newfoundland and Labrador Metocean Study which summarizes environmental conditions of these regions to support offshore petroleum exploration and development in the Labrador Sea and to outline the resource potential to the global oil and gas industry. Defining iceberg densities was one of the required tasks for the study. Among various environmental conditions, iceberg density is one of the most challenging parameter to define accurately both spatially and temporally. Aerial iceberg reconnaissance flight surveys provided by IIP (International Ice Patrol) and CIS (Canadian Ice Service) were studied, classified and analyzed to compute iceberg density (number of icebergs per square km). Only open water icebergs were considered for analysis because of the difficulty associated with reliably identifying icebergs in pack ice, which may lead to an underestimation of iceberg occurrence. Therefore, aerial reconnaissance data were compared with CIS pack ice charts to eliminate any possibility of iceberg sightings in pack ice being included in the analysis. Satellite radar data acquired using Envisat wide swath mode (WSM) imagery was also used for iceberg detections in order to provide full coverage of the study area. Again, sea ice was outlined in the imagery to ensure no targets in sea ice were counted. The WSM imagery provided a 400 km wide swath with an approximate radar resolution of 150 m, meaning smaller targets were not detected. In order to combine satellite radar data with aerial reconnaissance surveys a non-detection factor was calculated using a comparison of concurrent Envisat and aerial coverage to compensate for missed targets due to the coarser radar resolution. The resulting map of open water iceberg densities will provide a baseline for the region which shall be further refined through an on-going program using high-resolution Sentinel satellite data. Detailed descriptions of the analysis, procedures and results are presented in this paper. Areal density results of the newly defined basins are compared to the other frontier regions, where iceberg risks are higher.

Abstract High-fidelity trajectory estimation combined with dual-probe Measurement-While-Drilling (MWD) directional instrumentation provides a solution to minimum curvature’s known inefficiencies in modeling the true wellbore position and definition (Stockhausen & Lesso, 2003). While it may not be cost efficient to increase survey frequency from the industry standard of 30ft-200ft, it is possible using the techniques defined in this research to maintain current survey intervals and increase wellbore placement accuracy while reducing positional uncertainty by up to 45% over the most advanced commercially available magnetic survey correction algorithms. Taking advantage of modern MWD tool platforms enables the installation of an additional (30-inch) survey measurement probe in the existing tool string with a fixed and known offset to the primary survey probe. Directional surveys from both survey probes are telemetered to surface at traditional course length survey intervals in real-time. The two surveys along with the known steering and non-steering intervals are processed through a high-fidelity trajectory estimation algorithm to quantify the wellbore behavior between survey stations. The result is a highly accurate and dense survey listing with modeled trajectory waypoints between traditional surveys to reduce the course length between directional measurement datapoints and better capture the true well path. Through extensive lab modeling, it was determined that the use of the dual-probe MWD package in combination with the high-fidelity trajectory estimation algorithm could result in a reduction in the Ellipse of Uncertainty (EOU) by 20% in the horizontal (semi-major) plane and 45% in the vertical (semi-minor) plane when compared to Multi-Station Analysis (MSA) and BHA Sag survey correction techniques. In addition to proof-of-concept modeling, the system has been deployed and used in real-time application on three separate pads, totaling nine wells. The results were able to validate and exceed baseline goals by exhibiting, on average, a reduction of the EOU by 21% in the horizontal plane and 58% in the vertical plane. Further, True Vertical Depth (TVD) error at well Total Depth (TD) in excess of 10ft was observed on three out of nine wells (33%) in this limited real-time application study. This difference was relative to separate, concurrent processing of the surveys via Multi-Station Analysis (MSA) and BHA sag corrections. This level of increased TVD accuracy is significant in many applications, depending on zone thickness and difficulty of geological interpretation. Increased accuracy and reduced uncertainty result from a better understanding of the true well path between traditional course length surveys. The trajectory estimation algorithm quantifies the rotational build/drop and walk rates in real-time and is reinforced by the dual-probe directional survey measurements. These tendencies can be used to better project forward to the bit as the well is drilled. Improved projection to the bit allows for enhanced recognition of deviation from the well plan and better-informed steering decisions.

Boundary layer separation has been studied on a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes. Experiments were done under low (0.6%) and high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Wakes were produced from moving rods upstream of the cascade. Flow coefficients were varied from 0.35 to 1.4 and wake spacing was varied from 1 to 2 blade spacings, resulting in dimensionless wake passing frequencies F = fLj-te/Uave (f is the frequency, Lj-te is the length of the adverse pressure gradient region on the suction surface of the airfoils, and Uave is the average freestream velocity) ranging from 0.14 to 0.56. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer and downstream of the cascade. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. In cases without wakes, the boundary layer separated and did not reattach. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. At lower frequencies the boundary layer separated between wakes. Background freestream turbulence had some effect on separation, but its role was secondary to the wake effect.

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. Jet pulsing frequency, duty cycle, and blowing ratio were all varied. Computational results from a large eddy simulation of one case showed reattachment in agreement with the experiment. In cases without flow control, the boundary layer separated and did not reattach. With the VGJs, separation control was possible even at the lowest Reynolds number. Pulsed VGJs were more effective than steady jets. At sufficiently high pulsing frequencies, separation control was possible even with low jet velocities and low duty cycles. At lower frequencies, higher jet velocity was required, particularly at low Reynolds numbers. Effective separation control resulted in an increase in lift and a reduction in total pressure losses. Phase averaged velocity profiles and wavelet spectra of the velocity show the VGJ disturbance causes the boundary layer to reattach, but that it can re-separate between disturbances. When the disturbances occur at high enough frequency, the time available for separation is reduced, and the separation bubble remains closed at all times.

Boundary layer separation control with pulsed vortex generator jets (VGJs) has been studied on a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes. Experiments were done under low (0.6%) and high (4%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000 and 50,000. Wakes were produced from moving rods upstream of the cascade with flow coefficient 1.13 and rod spacing equal 2 blade pitches, resulting in a dimensionless wake passing frequency F = fLj-te/Uave = 0.14, where f is the frequency, Lj-te is the length of the adverse pressure gradient region on the suction surface, and Uave is the average freestream velocity. The VGJs were injected at the beginning of the adverse pressure gradient region on the suction surface with maximum jet velocity in each pulse equal to the local freestream velocity and a jet duty cycle of 10%. Several different timings of the VGJs with respect to the wakes were considered. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in the suction surface boundary layer and downstream of the cascade. In cases without VGJs, the boundary layer momentarily reattached in response to the wake passing, but separated between wakes. The VGJs also caused reattachment, and if the VGJ pulsing frequency was sufficiently high, separation was largely suppressed for the full wake passing cycle. The timing of the VGJs with respect to the wakes was not very important. The jet pulsing frequency needed for separation control was about the same as found previously in cases without wakes. The background freestream turbulence effect was negligible in the presence of the larger wake and VGJ disturbances.

The development of the unsteady suction side boundary layer of a highly loaded LP turbine blade has been investigated in a rectilinear cascade experiment. Upstream rotor wakes were simulated with a moving-bar wake generator. A variety of cases with different wake-passing frequencies, different wake strength and different Reynolds-numbers were tested. Boundary layer surveys have been obtained with a single hot-wire probe. Wall shear stress has been investigated with surface-mounted hot-film gauges. Losses have been measured. The suction surface boundary layer development of a modern highly loaded LP turbine blade is shown to be dominated by effects associated with unsteady wake-passing. Whereas without wakes the boundary layer features a large separation bubble at a typical cruise Reynolds-number, the bubble was largely suppressed if subjected to unsteady wake-passing at a typical frequency and wake strength. Transitional patches and becalmed regions, induced by the wake, dominated the boundary layer development. The becalmed regions inhibited transition and separation and are shown to reduce the loss of the wake-affected boundary layer. An optimum wake-passing frequency exists at cruise Reynolds-numbers. For a selected wake-passing frequency and wake-strength, the profile loss is almost independent of Reynolds-number. This demonstrates a potential to design highly loaded LP turbine profiles without suffering large losses at low Reynolds-numbers.

An experimental study was conducted to improve the performance of an aft-loaded ultra-high-lift low-pressure turbine blade known as U2 at low Reynolds numbers. This was achieved by manipulation of the laminar-turbulent transition process on the suction surface. The U2 profile was designed to meet the targets of reduced cost, weight and fuel burn of aircraft engines. The studies were conducted on both low-speed and high-speed experimental facilities under the unsteady flow conditions with upstream passing wakes. The current paper presents the low-speed investigation results. On the smooth suction surface, the incoming wakes are not strong enough to suppress the separation bubble due to the strong adverse pressure gradient on the suction surface and the low wake passing frequency, which allows the separation between the wakes more time to re-establish. Therefore, the profile losses of this ultra-high-lift blade are not as low as conventional or high-lift blades at low Reynolds numbers even in unsteady flows. Two different types of passive separation control devices, i.e. surface trips and air jets, were investigated to further improve the blade performance. The measurement results show that the profile losses can be further reduced to the levels similar to those of the high-lift and conventional blades due to the aft-loaded nature of this ultra-high-lift blade. Detailed surveys of the blade surface boundary layer developments showed that the loss reduction was due to the suppression of the separation underneath the wakes, the effect of the strengthened calmed region and the smaller separation bubble between wakes.

Geophysical surveys, both land-based and water-borne, were conducted at the Old River Control Complex‒Low Sill, Concordia Parish, LA. The purpose of the surveys was to assess the condition of the grout within the scour region resulting from the 1973 flood event, including identification of potential voids within the grout. Information from the ground studies will also be used for calibration of subsequent marine geophysical data and used in stability analysis studies. The water-borne survey consisted of towed low frequency (16-80 MHz) ground penetrating radar (GPR), whereas the land-based surveys used electrical resistivity and seismic refraction. The GPR survey was conducted in the Old River Channel on the upstream side of the Low Sill structure. The high electrical conductivity of the water (~50 mS/m) precluded penetration of the GPR signal; thus, no useful data were obtained. The land-based surveys were performed on both northeast and southeast sides of the Low Sill structure. Both resistivity and seismic surveys identify a layered subsurface stratigraphy that corresponds, in general, with available borehole data and constructed geologic profiles. In addition, an anomalous area on the southeast side was identified that warrants future investigation and monitoring.

Managers are challenged with the impact of problematic plants, including exotic, invasive, and pest plant species. Information on the cover and frequency of these plants is essential for developing risk-based approaches to managing these species. Based on surveys conducted in 2008, 2011, 2015, and 2019, Heartland Network staff and contractors identified a cumulative total of 51 potentially problematic plant species in Hopewell Culture National Historical Park. Of the 37 species found in 2019, we characterized 7 as very low frequency, 9 as low frequency, 17 as medium frequency, and 4 as high frequency. Of these, midpoint cover estimates of 2 medium frequency and 2 high frequency species exceeded the 10-acre threshold. Because of the number, extent, and cover of problematic plants in the park and the small park size, control efforts should focus on treating high priority species across the entire park. High priority species may include plant species capable of rapid spread, species at low population levels, and species which can effectively be controlled.

Managers are challenged with the impact of problematic plants, including exotic, invasive, and pest plant species. Information on the cover, distribution, and location of these plants is essential for developing risk-based approaches to managing these species. Based on surveys conducted in 2006, 2011, 2015, and 2019, Heartland Network staff and contractors identified a cumulative total of 45 potentially problematic plant taxa in Lincoln Boyhood National Memorial. Of the 34 species found in 2019, we characterized 4 as very low frequency, 14 as low frequency, 9 as medium frequency, and 7 as high frequency. A single species exceeded a 10-acre threshold based on a mid-point estimate. Because of the number of problematic plant taxa, as well as the extent and cover of problematic plants in the park and the small park size, control efforts should focus on treating high priority species across the entire park. High priority species may include plant species capable of rapid spread, species at low population levels, and species which can effectively be controlled.

Managers are challenged with the impact of problematic plants, including exotic, invasive, and pest plant species. Information on the cover, distribution, and location of these plants is essential for developing risk-based approaches to managing these species. Based on surveys conducted in 2006, 2011, 2015, and 2019, Heartland Network staff and contractors identified a cumulative total of 28 potentially problematic plant taxa in Arkansas Post National Memorial. Of the 23 species found in 2019, we characterized 9 as very low frequency, 7 as low frequency, 5 as medium frequency, and 2 as high frequency. Cover of all species was low with a single species slightly exceeding a 1-acre threshold based on a midpoint estimate. Efforts to control the woody invasive black locust, Chinese privet, and hardy orange appear to have successfully reduced the cover of these plants across the Memorial Unit. Japanese stiltgrass may have been increasing as recently as 2015, but a combination of recent flooding and control efforts may have stemmed the spread of this invasive grass. Efforts to control localized patches of Chinaberry tree also appear to have reduced the cover of this species. Outside of the problematic species currently subject

Invasive exotic plant (IEP) species are a significant threat to natural ecosystem integrity and biodiversity, and controlling them is a high priority for the National Park Service. The North-ern Colorado Plateau Network (NCPN) selected the early detection of IEPs as one of 11 monitoring protocols to be implemented as part of its long-term monitoring program. From May 30 to June 1, 2019, network staff conducted surveys for priority IEP species along the Scenic Drive and Cathedral Valley Road monitoring routes at Capitol Reef National Park. We detected 119 patches of six priority IEP species along 34 kilometers of the two monitor-ing routes. There were more patches of IEPs, and a higher percentage of large patches, than in previous years. This indicates that previously identified infestations have expanded and grown. The most common (47.1%) patch size among priority species was 1,000–2,000 m2 (0.25–0.5 acre). The vast majority (93.2%) of priority patches ranked either low (58.8%) or very low (34.4%) on the patch management index scale. Tamarisk (Tamarix sp., 72 patches) was the most prevalent priority IEP species. African mustard (Malcolmia africana, 32 patch-es), field bindweed (Convolvulus arvensis, 9 patches), and Russian olive (Elaeagnus angusti-folia, 3 patches) occurred less commonly. Together, these four species represented 97.5% of all patches recorded in 2019. Four IEP species were found on the monitored routes for the first time: Russian olive (Elaeagnus angustifolia), quackgrass (Elymus repens), Siberian elm (Ulmus pumila), and African mustard (Malcolmia africana, not on the priority species list before 2019). Cathedral Valley Road had higher IEP priority patches per kilometer (5.68) than the Scenic Drive (2.05). IEP species were found on 37.9% (25 of 66) of monitored transects. Almost all these detections were Russian thistle (Salsola sp.). Russian thistle was widespread, present in 33.3% of transects, with an estimated cover of 0.2% across all transects sampled. Across routes monitored in all three rotations (2012, 2015, and 2019), Russian thistle has increased in frequency. However, its frequency remained about the same from 2015 to 2019, and percent cover remains low. Tamarisk and field bindweed have both increased in preva-lence since monitoring began, with tamarisk showing a dramatic increase in the number and size of patches. Immediate control of tamarisk and these other species is recommended to reduce their numbers on these routes. The NCPN plans to Capitol Reef in 2020 to monitor Oak and Pleasant creeks, completing the third rotation of invasive plant monitoring.

This research sought to understand the impact of probation inspection on probation policy, practice and practitioners. This important but neglected area of study has significant ramifications because the Her Majesty’s Inspectorate of Probation has considerable power to influence policy through its inspection regime and research activities. The study utilised a mixed methodological approach comprising observations of inspections and interviews with people who work in probation, the Inspectorate and external stakeholders. In total, 77 people were interviewed or took part in focus groups. Probation practitioners, managers and leaders were interviewed in the weeks after an inspection to find out how they experienced the process of inspection. Staff at HMI Probation were interviewed to understand what inspection is for and how it works. External stakeholders representing people from the voluntary sector, politics and other non-departmental bodies were interviewed to find out how they used the work of inspection in their own roles. Finally, leaders within the National Probation Service and Her Majesty’s Prisons and Probation Service were interviewed to see how inspection impacts on policy more broadly. The data were analysed thematically with five key themes being identified. Overall, participants were positive about the way inspection is carried out in the field of probation. The main findings are: 1. Inspection places a burden on practitioners and organisations. Practitioners talked about the anxiety that a looming inspection created and how management teams created additional pressures which were hard to cope with on top of already high workloads. Staff responsible for managing the inspection and with leadership positions talked about the amount of time the process of inspection took up. Importantly, inspection was seen to take people away from their day jobs and meant other priorities were side-lined, even if temporarily. However, the case interviews that practitioners take part in were seen as incredibly valuable exercises which gave staff the opportunity to reflect on their practice and receive positive feedback and validation for their work. 2. Providers said that the findings and conclusions from inspections were often accurate and, to some extent, unsurprising. However, they sometimes find it difficult to implement recommendations due to reports failing to take context into account. Negative reports have a serious impact on staff morale, especially for CRCs and there was concern about the impact of negative findings on a provider’s reputation. 3. External stakeholders value the work of the Inspectorate. The Inspectorate is seen to generate highly valid and meaningful data which stakeholders can use in their own roles. This can include pushing for policy reform or holding government to account from different perspectives. In particular, thematic inspections were seen to be useful here. 4. The regulatory landscape in probation is complex with an array of actors working to hold providers to account. When compared to other forms of regulation such as audit or contract management the Inspectorate was perceived positively due to its methodological approach as well as the way it reflects the values of probation itself. 5. Overall, the inspectorate appears to garner considerable legitimacy from those it inspects. This should, in theory, support the way it can impact on policy and practice. There are some areas for development here though such as more engagement with service users. While recognising that the Inspectorate has made a concerted effort to do this in the last two years participants all felt that more needs to be done to increase that trust between the inspectorate and service users. Overall, the Inspectorate was seen to be independent and 3 impartial although this belief was less prevalent amongst people in CRCs who argued that the Inspectorate has been biased towards supporting its own arguments around reversing the now failed policy of Transforming Rehabilitation. There was some debate amongst participants about how the Inspectorate could, or should, enforce compliance with its recommendations although most people were happy with the primarily relational way of encouraging compliance with sanctions for non-compliance being considered relatively unnecessary. To conclude, the work of the Inspectorate has a significant impact on probation policy, practice and practitioners. The majority of participants were positive about the process of inspection and the Inspectorate more broadly, notwithstanding some of the issues raised in the findings. There are some developments which the Inspectorate could consider to reduce the burden inspection places on providers and practitioners and enhance its impact such as amending the frequency of inspection, improving the feedback given to practitioners and providing more localised feedback, and working to reduce or limit perceptions of bias amongst people in CRCs. The Inspectorate could also do more to capture the impact it has on providers and practitioners – both positive and negative - through existing procedures that are in place such as post-case interview surveys and tracking the implementation of recommendations.

1.1 Macroeconomic summary Economic recovery has consistently outperformed the technical staff’s expectations following a steep decline in activity in the second quarter of 2020. At the same time, total and core inflation rates have fallen and remain at low levels, suggesting that a significant element of the reactivation of Colombia’s economy has been related to recovery in potential GDP. This would support the technical staff’s diagnosis of weak aggregate demand and ample excess capacity. The most recently available data on 2020 growth suggests a contraction in economic activity of 6.8%, lower than estimates from January’s Monetary Policy Report (-7.2%). High-frequency indicators suggest that economic performance was significantly more dynamic than expected in January, despite mobility restrictions and quarantine measures. This has also come amid declines in total and core inflation, the latter of which was below January projections if controlling for certain relative price changes. This suggests that the unexpected strength of recent growth contains elements of demand, and that excess capacity, while significant, could be lower than previously estimated. Nevertheless, uncertainty over the measurement of excess capacity continues to be unusually high and marked both by variations in the way different economic sectors and spending components have been affected by the pandemic, and by uneven price behavior. The size of excess capacity, and in particular the evolution of the pandemic in forthcoming quarters, constitute substantial risks to the macroeconomic forecast presented in this report. Despite the unexpected strength of the recovery, the technical staff continues to project ample excess capacity that is expected to remain on the forecast horizon, alongside core inflation that will likely remain below the target. Domestic demand remains below 2019 levels amid unusually significant uncertainty over the size of excess capacity in the economy. High national unemployment (14.6% for February 2021) reflects a loose labor market, while observed total and core inflation continue to be below 2%. Inflationary pressures from the exchange rate are expected to continue to be low, with relatively little pass-through on inflation. This would be compatible with a negative output gap. Excess productive capacity and the expectation of core inflation below the 3% target on the forecast horizon provide a basis for an expansive monetary policy posture. The technical staff’s assessment of certain shocks and their expected effects on the economy, as well as the presence of several sources of uncertainty and related assumptions about their potential macroeconomic impacts, remain a feature of this report. The coronavirus pandemic, in particular, continues to affect the public health environment, and the reopening of Colombia’s economy remains incomplete. The technical staff’s assessment is that the COVID-19 shock has affected both aggregate demand and supply, but that the impact on demand has been deeper and more persistent. Given this persistence, the central forecast accounts for a gradual tightening of the output gap in the absence of new waves of contagion, and as vaccination campaigns progress. The central forecast continues to include an expected increase of total and core inflation rates in the second quarter of 2021, alongside the lapse of the temporary price relief measures put in place in 2020. Additional COVID-19 outbreaks (of uncertain duration and intensity) represent a significant risk factor that could affect these projections. Additionally, the forecast continues to include an upward trend in sovereign risk premiums, reflected by higher levels of public debt that in the wake of the pandemic are likely to persist on the forecast horizon, even in the context of a fiscal adjustment. At the same time, the projection accounts for the shortterm effects on private domestic demand from a fiscal adjustment along the lines of the one currently being proposed by the national government. This would be compatible with a gradual recovery of private domestic demand in 2022. The size and characteristics of the fiscal adjustment that is ultimately implemented, as well as the corresponding market response, represent another source of forecast uncertainty. Newly available information offers evidence of the potential for significant changes to the macroeconomic scenario, though without altering the general diagnosis described above. The most recent data on inflation, growth, fiscal policy, and international financial conditions suggests a more dynamic economy than previously expected. However, a third wave of the pandemic has delayed the re-opening of Colombia’s economy and brought with it a deceleration in economic activity. Detailed descriptions of these considerations and subsequent changes to the macroeconomic forecast are presented below. The expected annual decline in GDP (-0.3%) in the first quarter of 2021 appears to have been less pronounced than projected in January (-4.8%). Partial closures in January to address a second wave of COVID-19 appear to have had a less significant negative impact on the economy than previously estimated. This is reflected in figures related to mobility, energy demand, industry and retail sales, foreign trade, commercial transactions from selected banks, and the national statistics agency’s (DANE) economic tracking indicator (ISE). Output is now expected to have declined annually in the first quarter by 0.3%. Private consumption likely continued to recover, registering levels somewhat above those from the previous year, while public consumption likely increased significantly. While a recovery in investment in both housing and in other buildings and structures is expected, overall investment levels in this case likely continued to be low, and gross fixed capital formation is expected to continue to show significant annual declines. Imports likely recovered to again outpace exports, though both are expected to register significant annual declines. Economic activity that outpaced projections, an increase in oil prices and other export products, and an expected increase in public spending this year account for the upward revision to the 2021 growth forecast (from 4.6% with a range between 2% and 6% in January, to 6.0% with a range between 3% and 7% in April). As a result, the output gap is expected to be smaller and to tighten more rapidly than projected in the previous report, though it is still expected to remain in negative territory on the forecast horizon. Wide forecast intervals reflect the fact that the future evolution of the COVID-19 pandemic remains a significant source of uncertainty on these projections. The delay in the recovery of economic activity as a result of the resurgence of COVID-19 in the first quarter appears to have been less significant than projected in the January report. The central forecast scenario expects this improved performance to continue in 2021 alongside increased consumer and business confidence. Low real interest rates and an active credit supply would also support this dynamic, and the overall conditions would be expected to spur a recovery in consumption and investment. Increased growth in public spending and public works based on the national government’s spending plan (Plan Financiero del Gobierno) are other factors to consider. Additionally, an expected recovery in global demand and higher projected prices for oil and coffee would further contribute to improved external revenues and would favor investment, in particular in the oil sector. Given the above, the technical staff’s 2021 growth forecast has been revised upward from 4.6% in January (range from 2% to 6%) to 6.0% in April (range from 3% to 7%). These projections account for the potential for the third wave of COVID-19 to have a larger and more persistent effect on the economy than the previous wave, while also supposing that there will not be any additional significant waves of the pandemic and that mobility restrictions will be relaxed as a result. Economic growth in 2022 is expected to be 3%, with a range between 1% and 5%. This figure would be lower than projected in the January report (3.6% with a range between 2% and 6%), due to a higher base of comparison given the upward revision to expected GDP in 2021. This forecast also takes into account the likely effects on private demand of a fiscal adjustment of the size currently being proposed by the national government, and which would come into effect in 2022. Excess in productive capacity is now expected to be lower than estimated in January but continues to be significant and affected by high levels of uncertainty, as reflected in the wide forecast intervals. The possibility of new waves of the virus (of uncertain intensity and duration) represents a significant downward risk to projected GDP growth, and is signaled by the lower limits of the ranges provided in this report. Inflation (1.51%) and inflation excluding food and regulated items (0.94%) declined in March compared to December, continuing below the 3% target. The decline in inflation in this period was below projections, explained in large part by unanticipated increases in the costs of certain foods (3.92%) and regulated items (1.52%). An increase in international food and shipping prices, increased foreign demand for beef, and specific upward pressures on perishable food supplies appear to explain a lower-than-expected deceleration in the consumer price index (CPI) for foods. An unexpected increase in regulated items prices came amid unanticipated increases in international fuel prices, on some utilities rates, and for regulated education prices. The decline in annual inflation excluding food and regulated items between December and March was in line with projections from January, though this included downward pressure from a significant reduction in telecommunications rates due to the imminent entry of a new operator. When controlling for the effects of this relative price change, inflation excluding food and regulated items exceeds levels forecast in the previous report. Within this indicator of core inflation, the CPI for goods (1.05%) accelerated due to a reversion of the effects of the VAT-free day in November, which was largely accounted for in February, and possibly by the transmission of a recent depreciation of the peso on domestic prices for certain items (electric and household appliances). For their part, services prices decelerated and showed the lowest rate of annual growth (0.89%) among the large consumer baskets in the CPI. Within the services basket, the annual change in rental prices continued to decline, while those services that continue to experience the most significant restrictions on returning to normal operations (tourism, cinemas, nightlife, etc.) continued to register significant price declines. As previously mentioned, telephone rates also fell significantly due to increased competition in the market. Total inflation is expected to continue to be affected by ample excesses in productive capacity for the remainder of 2021 and 2022, though less so than projected in January. As a result, convergence to the inflation target is now expected to be somewhat faster than estimated in the previous report, assuming the absence of significant additional outbreaks of COVID-19. The technical staff’s year-end inflation projections for 2021 and 2022 have increased, suggesting figures around 3% due largely to variation in food and regulated items prices. The projection for inflation excluding food and regulated items also increased, but remains below 3%. Price relief measures on indirect taxes implemented in 2020 are expected to lapse in the second quarter of 2021, generating a one-off effect on prices and temporarily affecting inflation excluding food and regulated items. However, indexation to low levels of past inflation, weak demand, and ample excess productive capacity are expected to keep core inflation below the target, near 2.3% at the end of 2021 (previously 2.1%). The reversion in 2021 of the effects of some price relief measures on utility rates from 2020 should lead to an increase in the CPI for regulated items in the second half of this year. Annual price changes are now expected to be higher than estimated in the January report due to an increased expected path for fuel prices and unanticipated increases in regulated education prices. The projection for the CPI for foods has increased compared to the previous report, taking into account certain factors that were not anticipated in January (a less favorable agricultural cycle, increased pressure from international prices, and transport costs). Given the above, year-end annual inflation for 2021 and 2022 is now expected to be 3% and 2.8%, respectively, which would be above projections from January (2.3% and 2,7%). For its part, expected inflation based on analyst surveys suggests year-end inflation in 2021 and 2022 of 2.8% and 3.1%, respectively. There remains significant uncertainty surrounding the inflation forecasts included in this report due to several factors: 1) the evolution of the pandemic; 2) the difficulty in evaluating the size and persistence of excess productive capacity; 3) the timing and manner in which price relief measures will lapse; and 4) the future behavior of food prices. Projected 2021 growth in foreign demand (4.4% to 5.2%) and the supposed average oil price (USD 53 to USD 61 per Brent benchmark barrel) were both revised upward. An increase in long-term international interest rates has been reflected in a depreciation of the peso and could result in relatively tighter external financial conditions for emerging market economies, including Colombia. Average growth among Colombia’s trade partners was greater than expected in the fourth quarter of 2020. This, together with a sizable fiscal stimulus approved in the United States and the onset of a massive global vaccination campaign, largely explains the projected increase in foreign demand growth in 2021. The resilience of the goods market in the face of global crisis and an expected normalization in international trade are additional factors. These considerations and the expected continuation of a gradual reduction of mobility restrictions abroad suggest that Colombia’s trade partners could grow on average by 5.2% in 2021 and around 3.4% in 2022. The improved prospects for global economic growth have led to an increase in current and expected oil prices. Production interruptions due to a heavy winter, reduced inventories, and increased supply restrictions instituted by producing countries have also contributed to the increase. Meanwhile, market forecasts and recent Federal Reserve pronouncements suggest that the benchmark interest rate in the U.S. will remain stable for the next two years. Nevertheless, a significant increase in public spending in the country has fostered expectations for greater growth and inflation, as well as increased uncertainty over the moment in which a normalization of monetary policy might begin. This has been reflected in an increase in long-term interest rates. In this context, emerging market economies in the region, including Colombia, have registered increases in sovereign risk premiums and long-term domestic interest rates, and a depreciation of local currencies against the dollar. Recent outbreaks of COVID-19 in several of these economies; limits on vaccine supply and the slow pace of immunization campaigns in some countries; a significant increase in public debt; and tensions between the United States and China, among other factors, all add to a high level of uncertainty surrounding interest rate spreads, external financing conditions, and the future performance of risk premiums. The impact that this environment could have on the exchange rate and on domestic financing conditions represent risks to the macroeconomic and monetary policy forecasts. Domestic financial conditions continue to favor recovery in economic activity. The transmission of reductions to the policy interest rate on credit rates has been significant. The banking portfolio continues to recover amid circumstances that have affected both the supply and demand for loans, and in which some credit risks have materialized. Preferential and ordinary commercial interest rates have fallen to a similar degree as the benchmark interest rate. As is generally the case, this transmission has come at a slower pace for consumer credit rates, and has been further delayed in the case of mortgage rates. Commercial credit levels stabilized above pre-pandemic levels in March, following an increase resulting from significant liquidity requirements for businesses in the second quarter of 2020. The consumer credit portfolio continued to recover and has now surpassed February 2020 levels, though overall growth in the portfolio remains low. At the same time, portfolio projections and default indicators have increased, and credit establishment earnings have come down. Despite this, credit disbursements continue to recover and solvency indicators remain well above regulatory minimums. 1.2 Monetary policy decision In its meetings in March and April the BDBR left the benchmark interest rate unchanged at 1.75%.