(nondifferential) GPS receivers can be used to track radiosondes making simple wind measurements, their level of accuracy is not sufficient for measuring boundary-layer vertical velocities from aircraft. This application also requires rugged and compact GPS devices that are low in cost.

In a final paper and videotape presentation, Paul Montgomery demonstrated the success of using differential GPS for the navigation of a small (12-foot) autonomously piloted aircraft. Carrier phase-based differential techniques were used to determine the aircraft's position, velocity, attitude, and angular velocity relative to the ground in real time. Additional data related to air velocity were gathered using on-board sensors. The real-time combination of this information made automated flight from takeoff to landing possible.

WORKING GROUP DISCUSSIONS

GPS was designed with military and civilian dynamic positioning and navigation applications in mind and has been used in this capacity for a number of years. Nevertheless, the first issue addressed by the working group on dynamic positioning and navigation was to define a “dynamic application” in contrast to a “static application.” There was broad agreement that dynamic applications involve vehicles or platforms designed to move on or above the Earth's surface on human time scales. Platforms include satellites, aircraft, trucks, cars, trains, boats, ships, buoys, drifters, dropsondes, and, potentially, autonomous underwater vehicles.

Earth, oceanic, and atmospheric applications using these vehicles or platforms include the measurement and mapping of gravity, magnetics, topography, radiometry, meteorology, and fluid dynamics. Dynamic applications often require real-time measurements of position and attitude to support remote sensors or closed-loop control systems. Real-time augmentation of the basic GPS and high sampling rates are usually required as well.

The great diversity of requirements for this broad range of applications, generated considerable discussion about spatial and temporal accuracy and sampling rates. The spatial resolution requirements discussed were within a range of 1 centimeter to 5 meters for most applications, and temporal resolution requirements were within a range of 0.1 seconds to 5 seconds. However, certain applications have much more stringent requirements. For example, airborne gravimetrics could benefit from spatial resolutions of less than 1 centimeter to derive aircraft accelerations, and sampling rates for some mapping applications could exceed 10 Hz. These requirements are shown in Table 4-1 and Table 4-2.

TABLE 4-1 Spatial Resolution Requirements for Dynamic Applications a

Resolution

Application

<1 centimeter

Gravimetry (acceleration)

1–10 centimeters

Mapping

10–100 centimeters

Mapping, ocean sciences

1–5 meters

Ship navigation/dynamic positioning; satellite radiometry/remote sensing

>5 meters

Some atmospheric/meteorological applications; magnetometry

a The quantitative requirements listed in this table were determined by the remote sensing working group. They do not represent requirements defined by an internationally recognized standardization committee or government agency.



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