Shipboard Radar Research Articles

An overview of frequency synthesizers for radars

The authors present an overview of frequency synthesizer techniques suitable for radar systems. Various synthesizer architectures and key synthesizer components are considered along with a discussion of advantages and disadvantages. Some architectures are hardware intensive and, because of their physical size, are more suitable for stationary or shipboard radars. Architectures requiring smaller volume are more suitable for airborne applications. Direct, phase-locked, and frequency-locked architectures are covered, including key building blocks and performance limitations. The direct digital synthesizer (DDS) architecture is considered briefly, as it is not yet widely used in radar systems. Finally, projections are made of advances in components that have a direct effect on frequency synthesis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Recent Results from Oil Spill Response Research

ABSTRACT Recent large oil spills from tankers have reaffirmed the need for continuing technology assessment and research to improve oil-spill response capabilities. The Minerals Management Service (MMS) remains a lead agency in conducting these studies. This paper discusses MMS concerns, as reinforced by the acceleration of its research program in 1990. It briefly assesses the current state-of-the-art technology for major aspects of spill response, including remote sensing, open-ocean containment, recovery, in-situ burning, chemical treating agents, beach-line cleanup, and oil behavior. The paper reports on specific research projects that have begun to yield information that will improve detection and at-sea equipment performance. The first detection project, for which MMS has patent pending, involves the use of shipboard navigational radar to track slicks at relatively long range. The second project involves the use of conventional containment and cleanup in a downwind mode, which is contrary to the traditional procedures. The paper also discusses current research projects, including the development of an airborne, laser-assisted fluorosensor that can determine whether apparent slicks contain oil. Additional projects involve the development of improved strategies for responding to oil in broken-ice conditions, for gaining an improved understanding of the fate and behavior of spilled oil as it affects response strategies, and for reopening and operating the oil and hazardous materials simulated environmental test tank (OHMSETT) facility in Leonardo, New Jersey. Recent progress on the development of safe and environmentally acceptable strategies to burn spilled oil in-situ is also discussed. The OHMSETT facility is necessary for testing prospective improvements in chemical treating agents and to develop standard procedures for testing and evaluating response equipment.

The beam filling error in the Nimbus 5 electronically scanning microwave radiometer observations of Global Atlantic Tropical Experiment rainfall

A comparison of rain rates retrieved from the Nimbus 5 electronically scanning microwave radiometer (ESMR 5) brightness temperatures and observed from shipboard radars during the Global Atlantic Tropical Experiment (GATE) phase I shows that the beam filling error is the major source of discrepancy between the two. When averaged over a large scene (the GATE radar array, 400 km in diameter), the beam filling error is quite stable, being 50% of the observed rain rate. This suggests the simple procedure of multiplying retrieved rain rates by 2 (correction factor). A statistical model of the beam filling error is developed by envisioning an idealized instrument field‐of‐view that encompasses an entire gamma distribution of rain rates. A modeled correction factor near 2 is found for rain rate and temperature characteristics consistent with GATE conditions. The statistical model also suggests that (1) the correction factor varies from 1.5 to 2.5 for suppressed to enhanced tropical convective regimes and (2) decreases to 1.5 as the freezing level and average depth of the rain column decreases to 2.5 km.

Open ocean bird migration

A large body of indirect evidence suggests that migrant birds may constitute a significant proportion of the coherent airborne radar echoes detected at sea. Shipboard and island-based radars frequently detect large numbers of small cross-section targets moving at angles to the wind. Calculated airspeeds of these echoes are between 25 and 100 km/h (7-28 ms/sup -1/). Radar ornithologists have concluded that these echoes are due to migrant birds as the peak density occurs during fall and spring migration seasons. Land birds which make energetically advantageous crossings between continents are the most numerous migrants detected on radar. The occurrence, speed, and direction of the migrations are dependent not only upon location but also on the season of the year and weather conditions prevailing at the continental point of departure. Avian radar echoes over the open oceans can usually be identified as waterfowl, shorebirds, passerines or seabirds. The first three groups, which are all land birds, are most dense near continental margins, but significant migrations have been detected by radar more than 3000 km from land. Seabirds have not been extensively studied with radar but are known to migrate at least in small numbers over all the oceans of the world.

Timely prediction of low-altitude radar performance in operational environments using in situ atmospheric refractivity data

A shipboard radar decision aid that may be used to predict current low-altitude radar performance and assist the radar operator in maximising system capabilities in the existing propagation environment is discussed. The system, developed for use aboard US Navy AEGIS-class ships, uses expendable rocketborne radiosondes to make high-resolution measurements of the atmo sphere. A version of the Johns Hopkins University Applied Physics Laboratory&apos;s electromagnetic parabolic equation (EMPE) propagation model is used to calculate the effects of the measured refractivity environment on the propagation of energy radiated by the radar. A radar modeluses these data in predictions of the system&apos;s current low-altitude target detection capabilities. A colour display indicates the size of targets that may be detected through contour shading of a range-height display. The effects of many radar operator controllable options on target detectability may be evaluated in the current propagation environment with this system. A significant portion of the data acquisition-to-display process has been automated. Design and implementation of this system and results of recent at-sea testing are discussed.

SHIPBOARD NAVIGATIONAL RADAR AS AN OIL SPILL TRACKING TOOL1

ABSTRACT The utility of shipboard navigational radar as an oil spill tracking tool was evaluated in a wide range of sea states during an intentional oil spill exercise off Nova Scotia in September 1987. Specially tuned ship's radar onboard the Canadian Coast Guard Cutter Mary Hitchens was able to detect slicks of five barrels of spilled crude oil during periods of fog, rain, and darkness. Slicks were detectable in winds ranging from less than 10 knots up to more than 30 knots. There appeared to be a correlation between slick thickness and the capability for radar detection. This paper explores the observed limits of radar for detection during the exercise.

Development of the F/A-18A automatic carrier landing system

The F/A-18A Automatic Carrier Landing System integrates the aircraft flight control system, throttle control system, inertial navigation sensors, and shipboard SPN-42 tracking radar and computer system to achieve fully automatic approach control to the carrier deck in all weather conditions. Accurate touchdown position and sink rate must be achieved under varying conditions of visibility, deck motion, air turbulence, and ship air wake downdraft. Design analysis of this integrated digital control system is described, including digital synthesis methods used and projected performance under wind and deck motion conditions, two shipboard trials have verified the high touchdown accuracy potential of the system, resulting in along-deck touchdown dispersion of only 19 ft for 91 automatic landings.

FIBER OPTICS FOR SHIPBOARD RADAR DATA TRANSMISSION

ABSTRACTOptional Fiber Optic Data Links have been installed on four different types of Shipboard Radars and an IFF System at a Navy landbased test site. These data links carry all of the signals both directions between the Radars and the Combat Information Center. The use of fiber optics solved some very real problems at the site and, at the same time, provided an excellent opportunity to evaluate the performance and reliability of the data transmission systems prior to making commitments for shipboard installations. Subsequently, detailed specifications were generated for shipboard hardware, and qualification test programs are underway. All elements of the data links must pass qualification testing or be approved as non‐standard parts before they can be installed in an operational shipboard system. This paper will describe the fiberoptic systems that are operational at the landbased test site, and will detail some of the tradeoffs that have been made for shipboard installations.

Data Processing in Ship Relative Position Estimation

Shipboard radar is used to estimate the relative position and velocity of nearby ships for potential use in collision-avoidance. The noise in the radar data, and the small perturbations in the ship motion both have an influence on the steady-state error or uncertainty in these estimates. Optimal filtering is modelled with a range of these parameters, and the variation of position uncertainty is found with respect to both of these noise sources, and with respect to the sample interval.

Electronic Search Beam Stabilization

Compensating for ship's motion (roll and pitch) is a problem fundamental to shipboard radars. The more traditional aproach has been to mechanically stabilize the antenna structure. The alternative approach of stabilizing only the antenna beam is far from being new conceptually, but is more realizable with today's technology. The basic elements are a planar array with an elevation scan capability that rotates continuously in azimuth combined with a high speed digital processor. Electronic stabilization of such an antenna is inherently more challenging than that of a two-axis phase-scanned array. An algorithm is derived for surveillance beam positioning as the antenna rotates. The implementation of this algorithm provides hemispheric search beam stabilization.

Early Shipboard Search Radars of the U. S. Navy

Evolutionary charts and brief descriptive notes are presented on over one hundred types of shipboard search radars developed in the United States between 1936 and 1970.

The Structure and Evolution of Convection in a Tropical Cloud Cluster

Abstract A large cloud cluster which occurred over the data network of the Global Atmospheric Research Program's Atlantic Tropical Experiment (GATE) on 5 September 1974 is examined. Data from four quantitative shipboard weather radars show that virtually all of the precipitation in the tropical cloud cluster was associated with six mesoscale precipitation features. A prototype for the structure and life cycle of these features is presented which is sufficiently general to describe all six precipitation features, one of which was a tropical squall-line system. These mesoscale features appear to he the primary entitles within which deep tropical convection occurs. In their formative stage, mesoscale precipitation features consist of a line of isolated cumulonimbus cells oriented perpendicular to the low-level wind flow. In the intensifying stage, the rain areas of the individual cells merge when new convective cells develop between and ahead of the existing cells, where the outflow from convective-scale dow...

AZ-RRelationship for the GATE B-Scale Array

Abstract A better understanding of how the precipitation budget operates in tropical convective systems is a prime objective of the GATE research effort. Measurement of rainfall rate with shipboard radar is the principal method by which precipitation from tropical clouds that develop within the GATE B-scale array will be determined. Knowledge of the relationship between radar reflectivity (Z) and rainfall rate (R) is essential for an accurate interpretation of precipitation data derived through the use of radar technology. The Z-R relationship is determined through application of a least-squares linear regression to data points derived by appropriate integration of the third and sixth moments of a series of raindrop size spectra. Drop spectra measurements were obtained during GATE by means of a foil impactor operated at cloud-base level on board the NOAA DC-6 aircraft. A total of 107 Z-R data points are available, representing showers occurring on 12 days. The best-fit Z-R relationship for the cloud-base ...

Radar Navigation Trainer, Device 15F12

The device is a digital landmass and target simulator for surface search radar sets. It is used to train bridge personnel and navigation teams in the techniques of shipboard radar navigation and collision avoidance. The trainer provides simulated radar video for landmass and target returns coordinated with depth indicator readings and a dead reckoning plot. The landmass region simulated by the device is a 64 x 64 nautical mile square. The Norfolk-Hampton Roads area was the first such area to be simulated. Ownership and 12 surface ship targets can be maneuvered, within a 164 square nautical mile area centered on the landmass region, by the device operator from helm and engine orders or the ship tracks can be part of a preprogrammed exercise. The simulated radar can be adjusted over a very broad range of antenna, receiver and transmitter characteristics. These characteristics are programmable and can be varied by the device operator to simulate almost any surface search radar set. The radar video simulation includes sea return as well as returns from targets, land, cultural features, and navigation aids. The digital data base includes bathymetry for depth indicator simulation. One of the unique features of Device 15F12 is its ability to operate directly from a digitized topographical map. Any port or harbor area for which digitized charts exist can be simulated by the device. Changes to navigation aids, shorelines, etc. can be readily incorporated into the data base. For comparison and examination the data base can be plotted to reproduce a topographical map of the area. Only a few special rules are required in the digitizing process to insure that the data base is suitable for Device 15F12.

WAVE MEASUREMENTS IN OPEN OCEAN

The ability to measure the wave spectra in the open ocean from a moving vessel has met with varying degrees of success. Each sensor to date has suffered in its performance due to environmental conditions or due to its physical placement aboard the vessel for measuring the unperturbed sea. This paper will discuss the utilization of a microwave sensor on a moving vessel for measuring the open ocean wave spectra. Employing microwaves, some of the limitations of other sensors are not experienced. Tucker [1] developed the Tuckermeter for measuring the wave spectra from a moving ship by sensing changes in water pressure due to surface wave conditions. The Tuckermeter is placed below the water line and thus requires calibration for each wave frequency, ship speed, and depth. Since the sensor operates on pressure, it performs as a low pass filter and will not sense the higher frequencies. A microwave shipboard wave height radar sensor for measuring the ocean wave spectra was developed by the Naval Research Laboratory (NRL) and was installed on the S.S. McLean in February 1975 and its performance, design, and analysis of data for one data run will be discussed.

One-Man Navigation for Seagoing Vessels

Spacious commanding-bridges of seagoing vessels hamper navigation. A vast supply of personnel (lookout, helmsman, officer of the watch and captain) does not ease the situation but brings up new risks.The situation on the bridge of a number of seagoing vessels involved in collisions was examined. More than 40% of the analyzed collisions were caused by the fact that at least one of the vessels was navigated by a team or that the bridge installations were arranged for “team-navigation”. This system of “team-navigation” hampers the passing and processing of information on the bridge of the vessel.Except for the seagoing ship all other transport vehicles are controlled by the system of “one-man-control”. One man has access to all navigational information, and this one man commands the vehicle controls directly.Particularly towboats on the Rhine river serve as working examples of the principle of one-man bridge control of ships. Up to 11.000 tons of cargo are carried in a rigid array of barges pushed in front of the towboat. In the wheelhouse, which is perfectly equipped for “one-man-control”, the navigator has access to all sources of information, such as optical view and radar, and in addition, he is in touch with the vessel’s controls, such as helm and engine telegraph.The system of “one-man-navigation” helped to keep the collision rate on the Rhine river on a constant level in spite of growing traffic density. “Continuous navigation” around the clock was introduced using shipboard radar. The reduced crew size is just an added benefit of this system of “one-man-navigation”.