Integration of GPS and dead reckoning for real-time vehicle performance and emissions monitoring     

Washington Ochieng  J. Polak  R. Noland  J.-Y. Park  L. Zhao  D. Briggs  J. Gulliver  A. Crookell  R. Evans  M. Walker  W. Randolph 《GPS Solutions》2003,6(4):229-241

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The ACPI Climate Change Simulations     

Aiguo Dai  W. M. Washington  G. A. Meehl  T. W. Bettge  W. G. Strand 《Climatic change》2004,62(1-3):29-43

The Parallel Climate Model (PCM) has been used in the Accelerated ClimatePrediction Initiative (ACPI) Program to simulate the global climateresponse to projected CO₂, sulfate, and other greenhouse gasforcingunder a business-as-usual emissions scenario during the 21st century. In these runs, the oceans were initialized to 1995 conditions by a group from the Scripps Institution of Oceanography and other institutions. An ensemble of three model runs was then carried out to the year 2099 using the projected forcing. Atmospheric data fromthese runs were saved at 6-hourly intervals (hourly for certain criticalfields) to support the ACPI objective of accurately modeling hydrologicalcycles over the western U.S. It is shown that the initialization to1995 conditions partly removes the un-forced oceanic temperature and salinity drifts that occurred in the standard 20th century integration. The ACPI runs show a global surface temperature increase of 3–8 °C over northern high-latitudes by the end of the 21st century, and 1–2 °C over the oceans. This is generally within ±0.1°Cof model runs without the 1995 ocean initialization. The exception is in theAntarctic circumpolar ocean where surface air temperature is cooler in theACPI run; however the ensemble scatter is large in this region. Althoughthe difference in climate at the end of the 21st century is minimalbetween the ACPI runs and traditionally spun up runs, it might be largerfor CGCMs with higher climate sensitivity or larger ocean drifts. Ourresults suggest that the effect of small errors in the oceans (such asthose associated with climate drifts) on CGCM-simulated climate changesfor the next 50–100 years may be negligible.  相似文献   

The Effects of Climate Change on Water Resources in the West: Introduction and Overview     

Tim Barnett  Robert Malone  William Pennell  Detlet Stammer  Bert Semtner  Warren Washington 《Climatic change》2004,62(1-3):1-11

The results of an experimental `end to end' assessment of the effects of climate change on water resources in the western United States are described. The assessment focuses on the potential effects of climate change over the first half of the 21st century on the Columbia, Sacramento/San Joaquin, and Colorado river basins. The paper describes the methodology used for the assessment, and it summarizes the principal findings of the study. The strengths and weaknesses of this study are discussed, and suggestions are made for improving future climate change assessments.  相似文献   

Analysis of anomalies in ADS-B and its GPS data     

Busyairah Syd Ali  Wolfgang Schuster  Washington Ochieng  Arnab Majumdar 《GPS Solutions》2016,20(3):429-438

Traditionally, the surveillance component of the air traffic management system has been based on radar, which consists of two separate systems: primary radar and secondary radar, which both enable the measurement of the aircraft range and bearing to the radar station. Primary radar is based on signals emitted by a ground station simply being reflected off an object and detected by a ground-based receiver. Secondary radar also emits signals, but relies upon a transponder onboard the aircraft to emit a signal itself, modulated among others by a four-digit aircraft identity (Mode A), aircraft altitude (Mode C) and/or 24-bit unique address (Mode S). Typical accuracies of secondary radar are of the order of 0.03 NM in range and 0.07° in azimuth. However, no position integrity report is provided. Air traffic density is expected to significantly increase in the future. In order to maintain or enhance air travel efficiency, while maintaining safety, more accurate surveillance systems, with the required integrity, will be required. Automatic dependent surveillance–broadcast (ADS-B) is a new aviation surveillance system, envisioned to overcome the limitations of radar and to enhance surveillance performance and thereby increase airspace capacity. However, its high dependence on external systems such as onboard navigation and communication systems also increases the number of potential points of failure. It is important to understand and mitigate these failure modes before the system can reliably be implemented. The present study emerged as an exploratory research as part of a safety assessment framework development for the ADS-B system. It reviews the ADS-B failure modes, data collection and analysis of ADS-B and its corresponding onboard GPS data. The study identifies a set of failures common to certain aircraft models, with consistent error patterns. A key failure mode was found to be associated with the navigation data from the onboard GPS. We discuss the identified failure modes and investigate the nature and causes of these failures. The findings highlight some of the deficiencies of the current ADS-B system, which will need to be addressed before the ADS-B system can reliably be implemented.  相似文献   

New signals and systems: extending the applications of GNSS     

Washington Y. Ochieng 《地球空间信息科学学报》2013,16(3):139-140

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Greenhouse sensitivity experiments with penetrative cumulus convection and tropical cirrus albedo effects     

Warren M Washington  Gerald A Meehl 《Climate Dynamics》1993,8(5):211-223

Results are presented from two versions of a global R15 atmospheric general circulation model (GCM) coupled to a nondynamic, 50-m deep, slab ocean. Both versions include a penetrative convection scheme that has the effect of pumping more moisture higher into the troposphere. One also includes a simple prescribed functional dependence of cloud albedo in areas of high sea-surface temperature (SST) and deep convection. Previous analysis of observations has shown that in regions of high SST and deep convection, the upper-level cloud albedos increase as a result of the greater optical depth associated with increased moisture content. Based on these observations, we prescribe increased middle- and upper-level cloud albedos in regions of SST greater than 303 K where deep convection occurs. This crudely accounts for a type of cloud optical property feedback, but is well short of a computed cloud-optical property scheme. Since great uncertainty accompanies the formulation and tuning of such schemes, the prescribed albedo feedback is an intermediate step to examine basic feedbacks and sensitivities. We compare the two model versions (with earlier results from the same model with convective adjustment) to a model from the Canadian Climate Centre (CCC) having convective adjustment and a computed cloud optical properties feedback scheme and to several other GCMs. The addition of penetrative convection increases tropospheric moisture, cloud amount, and planetary albedo and decreases net solar input at the surface. However, the competing effect of increased downward infrared flux (from increased tropospheric moisture) causes a warmer surface and increased latent heat flux. Adding the prescribed cirrus albedo feedback decreases net solar input at the surface in the tropics, since the cloud albedos increase in regions of high SST and deep convection. Downward infrared radiation (from increased moisture) also increases, but this effect is overpowered by the reduced solar input in the tropics. Therefore, the surface is somewhat cooler in the tropics, latent heat flux decreases, and global average sensitivity to a doubling of CO₂ with regard to temperature and precipitation/evaporation feedback is reduced. Similar processes, evident in the CCC model with convective adjustment and a computed cloud optical properties feedback scheme, occur over a somewhat expanded latitudinal range. The addition of penetrative convection produces global effects, as does the prescribed cirrus albedo feedback, although the strongest local effects of the latter occur in the tropics.Portions of this study are supported by the Office of Health and Environmental Research of the U.S. Department of Energy as part of its Carbon Dioxide Research Program, and by the Electric Power Research Institute as part of its Model Evaluation Consortium for Climate Assessment ProjectThe National Center for Atmospheric Research is sponsored by the National Science Foundation  相似文献   

Seasonal Forecasting for Climate Hazards: Prospects and Responses     

Murphy  Sarah J.  Washington  Richard  Downing  Thomas E.  Martin  Randall V.  Ziervogel  Gina  Preston  Anthony  Todd  Martin  Butterfield  Ruth  Briden  Jim 《Natural Hazards》2001,23(2-3):171-196

One of the most promising developments for early warning of climate hazards is seasonal climate forecasting. Already forecasts are operational in many parts of the tropics and sub-tropics, particularly for droughts and floods associated with ENSO events. Prospects for further development of seasonal forecasting for a range of climatichazards are reviewed, illustrated with case studies in Africa, Australia, the U.S.A. and Europe. A critical evaluation of the utility of seasonal forecasts centres on vulnerability, communicationchannels, and effective responses. In contrast to short-term prediction, seasonal forecasts raise new issues of preparedness and the use of information.  相似文献   

MARS:A TUTORIAL     

SONJASEKULIC  BRUCER.KOWALSKI 《地理学报(英文版)》1992,(4)

This tutorial paper presents a simplified view of one of the more recently published multivariatecalibration methods particularly suited to dealing with non-linear data sets.The method is referred toas MARS and stands for multivariate adaptive regression splines.Simple examples are provided toexplain the workings of the method.  相似文献   

African Easterly Jet South: control,maintenance mechanisms and link with Southern subtropical waves     

Giresse Kuete  Wilfried Pokam Mba  Richard Washington 《Climate Dynamics》2020,54(3):1539-1552

The African Easterly Jet South (AEJ-S) is an important feature of the central African mid tropospheric circulation and has been identified as a key contributor to convection over the region. This study uses 21-year (1983–2003) Reanalysis data sets of ERA-Interim, NCEP2 and MERRA2 to establish mechanisms related to AEJ-S dynamics. Results demonstrate that AEJ-S is dominated by rotational circulation and is maintained by a mid-level high that forms over the Kalahari region during September to November. Because of the role played by this high pressure system in the AEJ-S dynamics, an effort is made to understand how this anticyclone develops. We show that this mid-tropospheric high over the Kalahari region is established in response to lower tropospheric dry convection over the region from September to November. At the core of this high, anticyclonic circulation is induced and maintains AEJ-S located at the northern flank of the high. A link between AEJ-S dynamics and southern subtropical westerly waves is also revealed. It is shown that, when waves amplify over the southern subtropics, they modify lower tropospheric heating. Depending on the phase of the wave, this modifies the cross latitude temperature gradient throughout equatorial regions, therefore modulating the intensity of the jet. By clarifying the mechanisms that govern the AEJ-S, this research work contributes to insight into central Africa climate mechanisms and also suggests a link between central Africa and Southern Africa climate systems. This research work also improves the foundation of new mechanisms that help to identify suitable metrics for the evaluation of Global models over the Central Africa region.  相似文献   

Performance of rate detector algorithms for an integrated GPS/INS system in the presence of slowly growing error     

Umar I. Bhatti  Washington Y. Ochieng  Shaojun Feng 《GPS Solutions》2012,16(3):293-301

In the Global Positioning System, there is no provision for real-time integrity information within the Standard Positioning Service, by design. However, in safety critical sectors like aviation, stringent integrity performance requirements must be met. This can be achieved using the special augmentation systems or RAIM (Receiver Autonomous Integrity Monitoring) or both. RAIM, the most cost-effective method relies on data consistency, and therefore requires redundant measurements for its operation. An external aid to provide this redundancy can be in the form of an Inertial Navigation system. This should enable continued performance even when no redundant satellite measurements are available. An algorithm presented in previous papers by the authors detects the rate of slowly growing errors. The algorithm was shown to be effective for early detection of slowly growing errors that belong to the class of most difficult to detect errors. Firstly, rate detector is tested for varying faults. Secondly, real data are used to validate the rate detector algorithm. The data are extensively analyzed to ascertain whether it is suitable for integrity and fault diagnostics. A modification to the original rate detector algorithm is suggested by addition of a bias state to the dynamic model. The performance is then compared with the existing techniques and substantial improvement is shown.  相似文献