Real-time Stations Research Articles

Earth observation by the adaptive wavelength optical image sensor

An AOTF (Acousto-Optic Tunable Filter) and a LCTF (Liquid Crystal Tunable Filter) are bandpass filters with a capability of adapting observation wavelength as desired almost instantaneously and with high spectral resolution. When a sensor with these filters is used for the earth observation, a user can change the observation wavelength according to the demand. The change can be made manually during the observation from an air plane. If the observation is from a satellite then the change can be made by the command from the ground station in real time. Thus the very useful data for observation purpose can be obtained through use of a sensor with these filters. Furthermore, these filters are suitable for polarization observation which can provide another valuable information to the multi-spectral observation data. In this paper, the comparison of these adaptive sensors with a conventional ones and the problems for loading such an adaptive sensor are described.

Fluid Level Sensor‐Controlled, Fully Automatic Spectrophotometry System

This study deals with a new, relatively economical, and fully automatic spectrophotometer. The most difficult part when working with automatic spectrophotometers is that the same quantities of sample to be analyzed and reagent have to be prepared for each measurement to maintain the reproducibility and accuracy of the measurements. This generally requires the use of very expensive systems (pumps, selection valves, etc.). In the system proposed here, the flow is gravitational and quantities of sample and reagent are kept constant using level sensors. Simple electrical solenoid valves are used for these processes. The PIC 16F877 microcontroller serves to control the solenoid valves and to save the analytical results. These results are saved on an EEPROM on the electronic card, and may be read directly on an LCD or saved on a PC from the EEPROM. In order to obtain data from remote stations in real time, the results are transmitted as SMS via GSM operators. The system analyzes the Fe(II) ions in the rainwater. By small modifications, it may be used to measure other parameters.

Flight Tests of the KSR-III: The Enhanced Onboard Electronics System

The third-generation Korean sounding rocket, KSR-III, was successfully launched on Nov. 28, 2002 from the western coastal area of the Korean Peninsula. The previous KSR-I and -II series had employed a solid propulsion system whereas the KSR-III utilizes Korea’s first liquid propulsion system. The prime objective of the mission was to evaluate the performance of the liquid propulsion system. The onboard electronics system of the KSR-III is an enhanced version of the ones used in the previous series. The system has extended data channels and has adopted a distributed data processing system using the RS-485 bus network. The rocket has various sensors to measure physical characteristics such as temperature, pressure, strain, acceleration, etc., and has scientific instruments including an ozone detector and two magnetometers. The flight data is transmitted to the ground station in real time by the onboard telemetry system. The onboard electronics system of the KSR-III mainly consists of telemetry, an RF subsystem, a tele-command system, a power supply system, and scientific payloads. Herein, we present an overview of the enhanced electronics system of the KSR-III and representative flight test results analyses including scientific data are discussed.

Real-time transient simulation of multimachine power system networks in the phase domain

This paper details implementation of the mathematical model of a synchronous generator in the direct time phase domain suitable for transient analysis in a real-time simulation environment. The network model, which is a full multimachine model in the phase domain, has been implemented on a multipurpose real time station (RTS). A solution method for solving the direct time phase domain model of the generator in the multimachine environment, where transmission imbalances are fully taken into account, has also been proposed. The method is based on discretisation of the state equations for the generator and the interconnecting network. The proposed model and solution method is compared with an industry standard power system package, PSCAD/EMTDC™. The model enables a unified approach to be adopted in the study of both symmetrical and asymmetrical operating conditions. A thorough analysis is performed to evaluate the model performance in real-time, where the frame time of simulation is a subject of study.

Real-time traffic over the IEEE 802.11 medium access control layer

This paper proposes multiple access procedures to transport real-time traffic over IEEE 802.11 wireless local area networks (LANs). As currently defined, the IEEE 802.11 standard supports real-time traffic by switching from its normal, distributed access mode — carrier sense multiple access/collision avoidance (CSMA/CA) — to a centralized one. The centralized mode severely constrains the operation of wireless LANs and provides inadequate performance. Our proposed procedures, on the other hand, are totally distributed and can be overlaid on CSMA/CA. They use the carrier sense capabilities of the network interfaces and require only the ability to jam the channel with pulses of energy of specified duration. The resulting scheme guarantees priority to real-time traffic and provides round-robin service and bounded access delays to real-time stations. This paper examines the behavior of the new access techniques to derive conditions under which they can be considered stable. In addition, it presents simulation results that assess the impact of these access procedures on the average delay of data packets. The simulations are also used to provide estimates of the number of real-time stations that can be supported under various network operating conditions.

A CSMA/CD compatible MAC for real-time transmissions based on varying collision intervals

This paper suggests a CSMA/CD compatible MAC protocol for real-time transmissions in a shared Home or Small Office Local Area Network. The new MAC is based on the distributed assignment of special TAG numbers to the stations transmitting real-time traffic. These TAG numbers determine a Round Robin order of transmissions among the real-time stations. They also help in resolving collisions among real time stations by setting the length of the Jam signal, transmitted in case of a collision, to be a function of the TAG number. In a collision the station with the highest TAG number, and so with the longest Jam, is persisting with its Jam transmission for the longest until all the other stations defer. Thus, the collision terminates and the longest persisting station can transmit its packet successfully. The new protocol enables stations implementing the IEEE 802.3 MAC standard to transmit on the same network with stations implementing the new protocol. After introducing the protocol, we compute an upper bound on the access delay that the protocol guarantees and prove the correctness of the distributed TAG assignment procedure. Finally, we simulate the protocol in a network consisting stations implementing the new protocol together with stations implementing the standard IEEE 802.3 MAC. We show that the access delays of the stations transmitting real-time traffic are indeed bounded as predicted.

Measurement of middle atmospheric ozone density profile by rocket-borne radiometer onboard KSR-II

KSR-II, a two-stage sounding rocket of KARI was launched successfully at the Korean Peninsula on June 11, 1998. The apogee of the rocket was 137 km. For the ozone measurement, 8-channel UV and visible radiometers were onboard the rocket. The rocket measured an in situ stratospheric and mesospheric ozone density profile over Korea during its ascending phase using the radiometer and transmitted the data to ground station in real time. The maximum ozone density occurs near 25 km. Retrieved profile has a random error (1σ) of approximately 15% for altitude below 20km, 7% between 20-50 km and 10% greater than 50 km. The retrieved data were compared with Dobson spectrophotometer, ozonesonde, and HALOE onboard the UARS. Our results are in reasonable agreements with others.

A bandwidth allocation/sharing/extension protocol for multimedia over IEEE 802.11 ad hoc wireless LANs

We propose a novel bandwidth allocation/sharing/extension (DBASE) protocol to support both asynchronous traffic and multimedia traffic with the characteristics of variable bit rate (VBR) and constant bit rate (CBR) over IEEE 802.11 ad hoc wireless local area networks. The overall quality of service (QoS) will be guaranteed by DBASE. The designed DBASE protocol will reserve bandwidth for real-time stations based on a fair and efficient allocation. Besides, the proposed DBASE is still compliant with the IEEE 802.11 standard. The performance of DBASE is evaluated by analysis and simulations. Simulations show that the DBASE is able to provide almost 90% channel utilization and low packet loss due to delay expiry for real-time multimedia services.

Design and development of a radioactive gas monitoring system in the positron emission tomography center.

This paper presents experiences in developing a simple, inexpensive radioactive gas monitoring system that proved to be practical and useful at a clinical and research Positron Emission Tomography (PET) Center. The system is described from four key aspects: (1) design of radiation detectors and calibrations; (2) use of an existing PC-based hospital-wide facility management network; (3) placement and oversight of real-time PC monitor stations; and (4) modification of a ventilation system in the PET center. The radiation safety oversight efficacy of a real-time PC-based radioactive gas monitoring system in the academic PET center also is discussed.

Mobile Station Positioning Using GSM Cellular Phone and Artificial Neural Networks

In this paper, we describe a novel approach to mobile station positioning using a GSM mobile phone. The approach is based on the use of an inherent feature of the GSM cellular system (the mobile phone continuously measures radio signal strengths from a number of the nearest base stations (antennas)) and on the use of this information to estimate the phone's location. The current values of the signal strengths are processed by a trained artificial neural network executed at the computer attached to the mobile phone to estimate the position of the mobile station in real time. The neural network configuration is obtained by using a genetic algorithm that searches the space of specific neural network types and determines which one provides the best location estimation results. Two general methods are explored: the first is based on using a neural network for classification and the second uses function approximation. The experimental results are reported and discussed.

Daily streamflow conditions map now online

A new daily streamflow conditions map for the United States is now available online from the U.S. Geological Survey (USGS). The map depicts streamflow as a percentile of its longterm value for each day Located at http://water.usgs.gov/public/dwc/national_map.html, it is updated every 3 hours.The flows are grouped into seven color‐coded percentile categories. More than 2000 realtime stations from the USGS stream gaging network, each having at least 30 years of continuous records, are represented. Changes in daily streamflow over the past several weeks can be viewed in an animated sequence.

A smart gas sensor for monitoring environmental changes in closed systems: results from the MIR space station

The European Space Agency promotes the development of instrumentation for monitoring vital safety functions within manned spacecraft environments. A smart gas sensor based on conducting polymer gas sensors and quartz microbalance sensors was constructed and tested extensively. The system was launched as part of the EuroMir '95 mission, was successfully operated for six months, and was again reactivated as part of the DARA Mir mission 1997. It was capable of monitoring the changes in the air quality of the space station in real time as the cosmonauts carried out their daily duties. It successfully monitored deliberate atmospheric contamination, as well as leakage, spillage and combustion events within the missions.

Real‐Time Vehicle Systems Monitoring

The use of computer‐based systems to monitor and display vehicle location is currently an area of strong interest, and a number of organizations have developed such systems. Real‐time vehicle systems monitoring, which can fit hand‐inglove with location monitoring, is less well developed. Our requirement for vehicle data acquisition systems (DAS) was to monitor and store data on driving cycle, temperatures, pressures, engine stoichiometry, etc. In the course of working with fleets, it became clear that if vehicle systems data could be transmitted to a base station in real time, could be interpreted by base station software to provide a diagnostic capability, and could be combined with a map location display capability, then it would be of interest to a large number of fleets. The system, which has recently been developed, consists of enboard vehicle microprocessor monitoring, data reduction and transmission components, a VHF or satellite communications link, a base station signal modem, and an AT‐type microcomputer for data analysis and display. This paper traces the evolution of the microcomputer‐based systems monitoring of vehicles and provides some insight into the capabilities of such systems.

A computer system for HREM image processing and simulation

A facility for electron microscope image analysis and interpretation has been established at the National Center for Electron Microscopy (NCEM) as a support for the electron microscopes. The main component of the facility is a computer system designed to assist the experimenter in both “real time” and post-recording image analysis. Real-time includes operator-controlled enhancement of the video-rate TV signal coming from the microscope, and the presentation of diffractograms as required by the microscope operator. Post-recording analysis includes post-processing of the experimental image as well as image simulation from model structures. Our chosen system is based on two host computers (Fig. 1): one host controls the post-recording workstations and the other runs the real-time stations. MicroVAX II minicomputers running the VMS operating system were chosen for both the main and real time hosts because the VMS system is multi-user and has virtual memory capability; in addition, it is the operating system most familiar to outside users of the facility.

SAR images updated

A new camera system using lasers and charge‐coupled devices and which can obtain data by radar at any time or under any weather conditions has been designed by the California Institute of Technology as part of a NASA continuing program. The system is intended to improve the imaging functions of synthetic operative radar (SAR) units. SAR units have been carried on earth‐orbiting spacecraft such as the Seasat satellite and the space shuttle Columbia. In the past, imaging was achieved as the result of a complex process from film. The new system transmits radar imaging data directly to an earth station in real time, the result being an instantaneously synthesized replication.

Estimation of the Mean Velocity of Acoustic Signal Propagation for Sea Operations

A representative velocity profile and a priori bathymetric information about possible undersea device depths are the only data required to generate coefficients for a three-dimensional quadric polynomial surface which then expresses an accurate estimate of the mean velocity of acoustic signal propagation as a function of measured travel time and receiver depth. The resultant polynomial estimator is easily implemented in real-time navigating, station keeping, and undersea device tracking software to account for the variable refraction effects on mean velocities encountered in raypath trajectories that extend from the vertical out to and including the limiting direct raypaths.

Automatic analysis of microearthquake network data

The microearthquake data collected by the dense network of seismographs in California may contain a wealth of information about the tectonic process, structure and properties of the earth's crust. However, before this data can be fully exploited for the purposes of earthquake prediction research, a relatively automatic, accurate, and uniform procedure for the analysis of seismic data is needed. A simple algorithm which identifies earthquakes and times first arrivals using data from an array of single component seismometers is being studied. The algorithm is simple enough that it could easily be implemented on a microprocessor monitoring a single station in real time. A unique aspect of the algorithm is that it not only picks arrivals but also objectively determines arrival time accuracy. Earthquakes are located by an iterative method. First, the most accurate arrivals are used to locate the event. Then arrivals which do not agree with this location are repicked using a more sensitive algorithm. This process is repeated until a stable location is obtained. For clear, unambiguous arrivals, the arrival times determined by the algorithm agree to within a few hundredths of a second of arrival times determined by an analyst. For weaker, more ambiguous arrivals, computer picks and hand picks are always within the accuracy prescribed by the algorithm. Using such an algorithm in routine processing of seismic data could require as little as 2 percent of the human effort now required by manual processing, and would provide for the first time, an accurate objective data base for earthquake prediction research. Syntactic structural analysis (a formal method of symbolic description) of seismic wave-forms is being investigated as a tool to improve the descriptive capability of the algorithm and as a formalism in which other picking algorithms can be expressed easily and compared. Using syntactic procedures to automatically provide descriptions of the first-arrival waveform is proposed as way of providing useful information about the earth that is not presently available on a routine basis.

Statistically-Optimum Dynamic Server Assignment in Systems with Interfering Servers

Cellular mobile radio systems have been proposed that use many base stations to provide radio service over a large geographical area. In such systems, a stored-program processor assigns radio channels to base stations in real time, under certain interference constraints. The capacity and the queueing characteristics of the overall system are strongly dependent on the processor algorithms that are used. This paper presents three algorithms which are in a certain minimax sense statistically optimum. The procedures are quite general, and may be applied to any system that employs many servers, the use of some combinations of which is not allowed. The first algorithm provides for the preferential assignment of a channel. If all standard channels are busy, a channel is selected in such a manner that the probability of blocking is minimized in that interferable facility most likely to suffer blocking. The second algorithm provides for the transfer of service from nonstandard to standard channels whenever standard channels become free. The choice of the particular nonstandard channel to be freed is again made in a manner which minimizes the maximum probability of future blockage. The third algorithm provides for the rearrangement of channel assignments in those instances when all assignable channels, both standard and nonstandard, are busy. Such rearrangement can cause channels to become available under certain circumstances. If more than one rearrangement is possible, again the choice of what particular action should be taken is governed by the goal of minimizing the maximum probability of future blockage. All three algorithms attain short-term optimality by enumeration; that is, each candidate for assignment is considered in turn. Under the condition that the given candidate is selected, the conditional probability of future blocking in each of the server groups is calculated, and the maximum of these probabilities is associated with the candidate. After all candidates have been considered, that candidate which has the minimum associated probability is assigned. These algorithms produce, by definition, an instantaneous system state which is always optimum in the above minimax sense. In systems with large numbers of servers, the system changes state rapidly; thus, occasional short-term errors disappear rapidly, and short-term optimization tends to lead to peak performance in the long term as well.

Statistically-optimum dynamic server assignment in systems with interfering servers

Cellular mobile radio systems have been proposed that use many base stations to provide radio service over a large geographical area. In such systems, a stored-program processor assigns radio channels to base stations in real time, under certain interference constraints. The capacity and the queueing characteristics of the overall system are strongly dependent on the processor algorithms that are used. This paper presents three algorithms which are in a certain minimax sense statistically optimum. The procedures are quite general, and may be applied to any system that employs many servers, the use of some combinations of which is not allowed. The first algorithm provides for the preferential assignment of a channel. If all standard channels are busy, a channel is selected in such a manner that the probability of blocking is minimized in that interferable facility most likely to suffer blocking. The second algorithm provides for the transfer of service from non-standard to standard channels whenever standard channels become free. The choice of the particular nonstandard channel to be freed is again made in a manner which minimizes the maximum probability of future blockage. The third algorithm provides for the rearrangement of channel assignments in those instances when all assignable channels, both standard and nonstandard, are busy. Such rearrangement can cause channels to become available under certain circumstances. If more than one rearrangement is possible, again the choice of what particular action should be taken is governed by the goal of minimizing the maximum probability of future blockage. All three algorithms attain short-term optimality by enumeration; that is, each candidate for assignment is considered in turn. Under the condition that the given candidate is selected, the conditional probability of future blocking in each of the server groups is calculated, and the maximum of these probabilities is associated with the candidate. After all candidates have been considered, that candidate which has the minimum associated probability is assigned. These algorithms produce, by definition, an instantaneous system state which is always optimum in the above minimax sense. In systems with large numbers of servers, the system changes state rapidly; thus, occasional short-term errors disappear rapidly, and short-term optimization tends to lead to peak performance in the long term as well.