Journal of Surveying Engineering

The NAVSTAR Global Positioning System (GPS) Program began a decade ago when the United States Air Force, Army, Marine Corps, Navy, and the Defense Mapping Agency (DMA) combined their technical resources to develop a highly‐accurate, space‐based navigation system. The GPS concept is the outgrowth of extensive studies, analysis, tests, and operational demonstrations which validated system performance and feasibility. The GPS will provide extremely accurate three‐dimensional position, velocity, and timing information to an unlimited number of suitably equipped users and do so on a continuous basis. Currently the GPS program is in the Full‐Scale Engineering Development (FSED) Phase. In this phase, the operational effectiveness of the GPS concept for both military and civilian users will be verified.

Although the Global Positioning System (GPS) was designed primarily for real‐time navigation and positioning applications at the dekameter (10‐m, or 33‐ft) level of accuracy, the GPS has been used to determine the relative position coordinates of fixed points with centimeter‐level accuracy, when the distance between the points has been of the order of 10 km. All three position coordinates are determined with this accuracy. For inter‐site distances less than 1 km the uncertainty is about 3 mm, and for distances greater than 10 km the uncertainty in each coordinate is about 1–2 parts per million (ppm) of the distance. These results have been obtained with commercially available production equipment (MACROMETER model V‐1000 Interferometric Surveyors) operated by regular surveying personnel under real field conditions, not just by university scientists under ideal laboratory conditions. However, at MIT techniques that promise to reduce the uncertainty to 1 part in ${10}^7$ for distances greater than 10 km are being developed.

A new field positioning capability is now available for engineering surveys using the TRANSIT satellite transmissions and the JMR‐2000 Global Surveyor. Three dimensional position transfers over “one‐hop” distances of 500 km or more and accomplished in the field with a precision of 20 to 50 cm. The complete field instrument including battery is contained within one briefcasesized package. Operation of the system is automatic allowing one person to perform an entire survey. The positioning power of the JMR‐2000 is used in a wide range of surveying applications, including geodetic point positioning, three‐dimensional position transfer over long baseline nonline‐of‐sight distances, simultaneous multiple site positioning and adjustment, and low‐accuracy reconnaissance surveys. Because of the system's currently available accuracy and the cost effective Versatility of the JMR‐2000, use of the system in civil engineering applications has become particularly advantageous.

The Airborne Laser Ranging System (ALRS) is a proposed multibeam subnanosecond pulse laser ranging system on board an aircraft. It simultaneously measures the distances between the aircraft and six laser retroreflectors (targets) deployed on the Earth's surface with $\pm 1\mathrm{cm}$ precision. Depending on the host aircraft and terrain characteristics, the system can interrogate hundreds of small targets distributed over an area as large as $6\times {10}^4$ sq kilometers in a matter of hours. Potentially, a total of 1.3 million individual range measurements can be made in one six hour flight. Trilateration techniques are used to derive the intersite vectors between laser ground targets with precisions as high as one part in 107. Since all data is initiated, received, collected and processed in the aircraft via totally passive ground targets, there is no need for complex ground instrumentation or skilled personnel in the field. The high precision, speed, and large area coverage of the ALRS make it an attractive and highly cost effective instrument for a variety of geophysics studies and large scale surveying, engineering and land management applications, especially when combined with photogrammetric instrumentation.

The historical background of the development of inertial survey systems and the basic principles of inertial navigation systems are presented. Inertial survey systems and their operation are described. Some of the operational results in the use of inertial survey systems and the accuracy of inertial positioning systems are examined. Recent work accomplished at the U.S. Army Engineer Topographic Laboratories is also described.

Since 1974, the U.S. Geological Survey (USGS) has been developing the Aerial Profiling of Terrain System (APTS) for measuring stream‐valley cross sections and profiles, older map reliability testing, and producing control for topographic maps. The system, which has completed laboratory testing at the Charles Stark Draper Laboratory in Cambridge, Mass., consists of an inertial measuring unit (IMU), a laser tracker, a laser profiler, a video imaging system, supporting electronics, and a computer. The equipment has been installed in a modified Twin‐Otter aircraft based at Hanscom Field, Mass.