Understanding of the raised beach and other interglacial sequences in the southern part of the British Isles has been improved through use of the amino acid racemization technique. This method has permitted correlation of these isolated and fragmentary marine deposits1,2 which, except for the Portland site, are located around the shores of the Bristol Channel1. By applying this technique with the U-series method, we have obtained a geochronometric date from the ‘8-m’ raised beach of the Belle Hougue Cave, Jersey, Channel Islands. Our results suggest that the 8-m raised beach of the Channel should be correlated with isotope stage 5, and that raised beaches above this altitude in the area may pre-date this stage, and thus also the Ipswichian interglacial which forms part of it.

U series and amino acid dates from Jersey

The Transit Navigation System was widely used by the U.S. Navy and the civilian community as an all-weather global navigation system. The Applied Physics Laboratory designed all aspects of Transit, including the spacecraft, user equipment, and ground control system. Several experimental satellites were launched to test key features of the design, after which a series of operational satellites were launched. Transit was continuously improved during its years of operation, resulting in an extremely reliable and accurate navigation system. (

An Overview of Transit Development

Since 1967, when the U.S. Navy Navigation System was released to the general public, the accuracy of geodetic and geodynamic satellite Doppler positioning using satellite Doppler has improved steadily. This improvement is due mainly to refinements in hardware, refraction, and orbital modeling. Point positioning, using a minimum of 30 passes and the U.S. Defense Mapping Agency (DMA) precise ephemeris, has reached submeter accuracy. Relative positioning among several simultaneously observing stations separated by distances up to 250 km and using a minimum of 30 passes has a typical accuracy below 0.5 m (1σ). Current hardware design and errors in modeling of delays in the wet portion of the troposphere limit the achievable accuracy in relative positioning at the 0.1- to 0.5-m (1σ) level, unless errors in receiver phase and tropospheric refraction delays are continuously measured (calibrated). Also, a crystal oscillator of lower short-term stability (≥ 5 × 10−12/100 s) increases the Doppler data noise and causes a positive correlation persisting over several minutes. Geodetic and geodynamic Doppler data reductions usually involve meticulous modeling for instrumental, atmospheric, and orbital errors as well as careful Doppler data editing. A short-arc orbit computation employed in such satellite Doppler reductions requires a gravitational potential expanded to at least degree and order 10 if the orbit shape accuracy is to be comparable to DMA precise ephemeris. Satellite Doppler positioning has had a significant impact on geodetic datum definition and the establishment of national and continental networks of unprecedented accuracy. Satellite Doppler methods, apart from providing one of the most accurate continuous methods of polar motion monitoring, have also been found useful in other geodynamical and ice motion studies. This review concentrates mainly on system performance, models, and computational methods.

A review of geodetic and geodynamic satellite Doppler positioning

The Many Faces of Transit

Low Earth orbit (LEO) constellations have potentialities to augment global navigation satellite systems for better service performance. The prerequisite is to provide the broadcast ephemerides that meet the accuracy requirement for navigation and positioning. In this study, the Kepler ephemeris model is chosen as the basis of LEO broadcast ephemeris design for backward compatibility and simplicity. To eliminate the singularity caused by the smaller eccentricity of LEO satellites compared to MEO satellites, non-singular elements are introduced for curve fitting of parameters and then transformed to Kepler elements to assure the algorithm of ephemeris computation remains unchanged for the user. We analyze the variation characteristics of LEO orbital elements and establish suitable broadcast ephemeris models considering fit accuracy, number of parameters, fit interval, and orbital altitude. The results of the fit accuracy for different fit intervals and orbital altitudes suggest that the optimal parameter selections are $$(Crs3,Crc3)$$
 , $$(Crs3,Crc3, \, \dot{a},\dot{n})$$
 and $$\left( {Crs3,Crc3, \, \dot{a},\dot{n}, \, \ddot{i},\ddot{a}} \right)$$
 , i.e., adding two, four or six parameters to the GPS 16-parameter ephemeris. When adding four parameters, the fit accuracy can be improved by about one order of magnitude compared to the GPS 16-parameter ephemeris model, and fit errors of less than 10 cm can be achieved with 20-min fit interval for a 400–1400 km orbital altitude. In addition, the effects of the number of parameters, fit interval, and orbit altitude on fit accuracy are discussed in detail. The validation with four LEO satellites in orbit also confirms the effectiveness of proposed models.

Design and validation of broadcast ephemeris for low Earth orbit satellites

Removal of the pole wander (Chandler wobble) as a source of bias in the Transit Navigation System has improved the precision available to a stationary user (surveyor). The precision associated with the mean of several (say 20) combined passes should be less than 5 meters. The dominant items in the error budget will remain (for a land-based user) uncertainty in the satellite position and instrumentation errors.



For an at-sea, non-stationary user; the errors are much larger and (still) dominated by uncertainties in the user's motion; typically 400 meters/knot of navigator's velocity error. The changes discussed here will not alter this situation in any way.



We discuss, herein, just how the polar motion is accounted for in the system. No changes are required of any user's hardware or computer programs. The benefits accrue to him (or her) automatically via an improved precision ephemeris in the satellite which now contains the polar motion implicitly. The improvement will be implemented on Dec. 15, 1973.



The Transit Coordinate System is reviewed and the recent performance (accuracy) of the system described.

H. D. Black

Papers

Recent (1973) improvements in the navy navigation satellite system

Comments on the prime meridian