GPS Modeling for Designing Aerospace Vehicle Navigation Systems

The complexity of the design of a Global Positioning System (GPS) user segment, as well as the performance demanded of the components, depends on user requirements such as total navigation accuracy. Other factors, for instance the expected satellite/vehicle geometry or the accuracy of an accompanying inertial navigation system can also affect the user segment design. Models of GPS measurements are used to predict user segment performance at various levels. Design curves are developed which illustrate the relationship between user requirements, the user segment design, and component performance

GPS Modeling for Designing Aerospace Vehicle Navigation Systems

The complexity of the design of a Global Positioning System (GPS) user segment, as well as the performance demanded of the components, depends on user requirements such as total navigation accuracy. Other factors, for instance the expected satellite/vehicle geometry or the accuracy of an accompanying inertial navigation system can also affect the user segment design. Models of GPS measurements are used to predict user segment performance at various levels. Design curves are developed which illustrate the relationship between user requirements, the user segment design, and component performance

A Design Approach for a GPS User Segment for Aerospace Vehicles

As new applications for the use of the Global Positioning System (GPS) on aerospace vehicles emerge, more attention is being paid to the design of the user segment, which comprises the hardware and software employed by the user to obtain navigation information from GPS. The complexity of the design of the user segment, as well as the performance demanded of the components (such as the antenna), depends on user requirements such as total navigation accuracy. Other factors, for instance the expected satellite/vehicle geometry or the accuracy of an accompanying inertial navigation system, can also affect the user segment design. The interaction between these effects, the user requirements, and the user segment design is studied. Design curves are developed which allow quick trade studies to be performed

A Design Approach for a GPS User Segment for Aerospace Vehicles

As new applications for the use of the Global Positioning System (GPS) on aerospace vehicles emerge, more attention is being paid to the design of the user segment, which comprises the hardware and software employed by the user to obtain navigation information from GPS. The complexity of the design of the user segment, as well as the performance demanded of the components (such as the antenna), depends on user requirements such as total navigation accuracy. Other factors, for instance the expected satellite/vehicle geometry or the accuracy of an accompanying inertial navigation system, can also affect the user segment design. The interaction between these effects, the user requirements, and the user segment design is studied. Design curves are developed which allow quick trade studies to be performed

An objective approach to dry eye disease severity. Invest Ophthalmol Vis Sci

PURPOSE. A prospective, multisite clinical study (10 sites in the European Union and the United States) evaluated the clinical utility of commonly used tests and tear osmolarity for assessing dry eye disease severity. METHODS. Three hundred fourteen consecutive subjects between the ages of 18 and 82 years were recruited from the general patient population, 299 of which qualified with complete datasets. Osmolarity testing, Schirmer test without anesthesia, tear film breakup time (TBUT), corneal staining, meibomian dysfunction assessment, and conjunctival staining were performed bilaterally. A symptom questionnaire, the Ocular Surface Disease Index (OSDI), was also administered to each patient. Distributions of clinical signs and symptoms against a continuous composite severity index were evaluated. RESULTS. Osmolarity was found to have the highest correlation coefficient to disease severity (r 2 ϭ 0.55), followed by conjunctival staining (r 2 ϭ 0.47), corneal staining (r 2 ϭ 0.43), OSDI (r 2 ϭ 0.41), meibomian score (r 2 ϭ 0.37), TBUT (r 2 ϭ 0.30), and Schirmer result (r 2 ϭ 0.17). A comparison of standard threshold-based classification with the composite severity index revealed significant overlap between the disease severities of prospectively defined normal and dry eye groups. Fully 63% of the subjects were found to be poorly classified by combinations of clinical thresholds. CONCLUSIONS. Tear film osmolarity was found to be the single best marker of disease severity across normal, mild/moderate, and severe categories. Other tests were found to be informative in the more severe forms of disease; thus, clinical judgment remains an important element in the clinical assessment of dry eye severity. The results also indicate that the initiation and progression of dry eye is multifactorial and supports the rationale for redefining severity on the basis of a continuum of clinical signs. (ClinicalTrials.gov number, NCT00848198.) (Invest Ophthalmol Vis Sci. 2010;51:6125-6130