Journal of Surveying Engineering

National satellite control points, or any fixed points determined relative to a known control point, can serve as monitoring stations when equipped with dual-frequency global positioning system (GPS) receivers. The available monitoring station coordinates are used to advantage to derive time-varying ionospheric and tropospheric path delays from the observed carrier phase data. Distinguishing atmospheric parameters from geometric positions is necessary in many cases because the relative tropospheric zenith delays are strongly correlated with the interstation height differences. In addition, GPS users may work with the single-frequency receivers that track satellite signals for only a few minutes at a time. The algorithm in this paper is based on the cosine functions of double-difference carrier phase measurements. After removing the first-order temporal and spatial ionospheric effects, the relative tropospheric delays are found to have correlation coefficients of up to 0.85, with the Saastamoinen model delays using some standard values for atmospheric pressure, temperature, and humidity. When comparing the 19 GPS-derived orthometric heights with the independently leveled heights, in a 5.5 × 4.0 km² area, the use of GPS-monitored atmospheric path delays led to an improved root-mean-square height error of ±1.48 cm.

A hydrographic surveying system has been designed and tested to acquire nearshore beach profile data. Traditional vessel-mounted echosounder surveying instrumentation was placed in watertight containers and configured for a personal watercraft for measurements of subaqueous nearshore beach profiles. The system is able to withstand the harsh environment of the nearshore and acquire beach profile information across the surf zone. This paper describes the system and results of a comparison in Myrtle Beach, S.C., between surveys collected over a 3-day period by the personal watercraft system and by a similar system mounted aboard a traditional coastal survey vessel. The bathymetric measurements for the personal watercraft-mounted echosounder surveying system display mean repetitive differences of 6 cm.

A new method of leveling, suitable for high-precision industrial applications, is described. The observation procedure involves only minor modifications to the standard observation procedure for precise leveling. The analysis procedure is based on a simple linear least-squares adjustment model. Two applications of the method are given, one in which the usual type of precise leveling equipment is used and one in which modern electronic digital leveling equipment is used. Standard deviations of point elevations in these applications are on the order of 0.1 mm or greater.