ALBERT

Description: The National Geodetic Survey (NGS) in cooperation with a number of federal agencies, state and local groups and universities is establishing GPS networks in the United States, east of the Rocky Mountains, which can be used to monitor strain and vertical deformation. These GPS networks are tied to a framework of some 14 fixed and mobile VLBI sites. In cooperation with the Nuclear Regulatory Commission (NRC), NGS established a 45 station GPS regional network in Nov.–Dec. 1987 which is tied to the VLBI framework. This network is scheduled for reobservation in 1989 and funds permitting, at regular intervals thereafter. A number of additional, more dense networks have been or are in the process of being established. The Tennessee Department of Transportation has established a 60 station statewide network to act as a reference network for surveying in conjunction with road construction. This network is expected to have an accuracy of a few parts in 107. NGS in cooperation with the NRC and the University of Maine established in 1986 a high accuracy GPS network in southeast Maine. In 1987 NGS in support of the Federal Aviation Administration (FAA) has established approximately 100 stations throughout Ohio with an accuracy in the 1:106 to 1:107 range. Toward the end of 1988, NGS, working in conjunction with several state agencies and the University of Florida, will establish a statewide network of about 140 stations with an accuracy in the 1:106 to 1:107 range. NGS, in cooperation with the Department of Energy, has also established a high accuracy to 1:107 to 1:108 GPS traverse from Florida to Maine connecting stations at tide gauge sites. The State of Texas is establishing a number of permanent GPS stations in support of highway surveying. These stations will allow strain monitoring across Texas at the 1:108 level. Additional networks are in the planning stage. It is clear that large numbers of high accuracy GPS networks are being established throughout the eastern United States. Many of these networks are being established for other than geophysical purposes. In many cases the state highway departments and others are interested only in 1:106 accuracy. As a practical matter this means that to assure 1:106 accuracy a few parts in 107 accuracy (1 to 3 cm over 100 kms) is often attained, but this is by no means certain. Also there are normally no plans for systematic resurveys, only replacement of destroyed monuments. A challenge to the geophysical community is to interact with the groups undertaking the high accuracy surveys to assure that, at points of geophysical interest, satisfactory accuracies are achieved during initial epoch measurements. This means that a satisfactory number of observations are obtained and high accuracy reduction methods are used in obtaining differential positions from the data. The geophysical community must also develop plans for resurvey of geophysically interesting network components on a systematic basis.

Description: National Geodetic Survey activities towards the development of operational geodetic survey systems based on radio interferometry are reviewed. Information about the field procedures, data reduction and analysis, and the results obtained to date is presented.

Description: A series of lunar gravity analyses were carried out using unified S-band tracking network data obtained from Apollos 8, 10, 11, 12, 14, and 15. The progress obtained to date is summarized as it relates to the estimation of lunar mass distributions and their geologic interpretation. The analyses reported are of two distinct types. The first type consists of data obtained at two ranges of altitude to estimate the total mass associated with various lunar features employing a point mass assumption. The second type consists of detailed analyses of Apollo 14 tracking data.

Description: Development of gravimetric geoid for US from satellite derived gravity data and local gravimetric measurements

Description: A detailed gravimetric geoid was computed for the United States using a combination of satellite-derived spherical harmonic coefficients and 1 by 1 deg mean gravity values from surface gravimetry. Comparisons of this geoid with astrogeodetic geoid data indicate that a precision of plus or minus 2 meters has been obtained. Translations only were used to convert the NAD astrogeodetic geoid heights to geocentric astrogeodetic heights. On the basis of the agreement between the geocentric astrogeodetic geoid heights and the gravimetric geoid heights, no evidence is found for rotation in the North American datum. The value of the zero-order undulation can vary by 10 to 20 meters, depending on which investigator's station positions are used to establish it.

Description: A comparison is presented of sets of satellite tracking station coordinate values published in the past few years by a number of investigators, i.e. Goddard Space Flight Center, Smithsonian Astrophysical Observatory, Ohio State University, The Naval Weapons Laboratory, Air Force Cambridge Research Laboratories, and Wallops Island. The comparisons have been made in terms of latitude, longitude and height. The results of the various solutions have been compared directly and also with external standards such as local survey data and gravimetrically derived geoid heights. After taking into account systematic rotations, latitude and longitude agreement on a global basis is generally 15 meters or better, on the North American Datum agreement is generally better than 10 meters. Allowing for scale differences (of the order of 2 ppm) radial agreement is generally of the order of 10 meters.

Description: A detailed gravimetric geoid of the United States, North Atlantic, and Eurasia, which was computed from a combination of satellite derived and surface gravity data, is presented. The precision of this detailed geoid is + or - 2 to + or - 3 m in the continents but may be in the range of 5 to 7 m in those areas where data is sparse. Comparisons of the detailed gravimetric geoid with results of Rapp, Fischer, and Rice for the United States, Bomford in Europe, and Heiskanen and Fischer in India are presented. Comparisons are also presented with geoid heights from satellite solutions for geocentric station coordinates in North America, the Caribbean, and Europe.

Description: A detailed gravimetric geoid of North America, the North Atlantic, Eurasia, and Australia computed from a combination of satellite-derived and surface 1 x 1 gravity data, is presented. Using a consistent set of parameters, this geoid is referenced to an absolute datum. The precision of this detailed geoid is + or - 2 meters in the continents but may be in the range of 5 to 7 meters in those areas where data was sparse. Comparisons of the detailed gravimetric geoid with results of Rice for the United States, Bomford and Fischer in Eurasia, and Mather in Australia are presented. Comparisons are also presented with geoid heights from satellite solutions for geocentric station coordinates in North America, the Caribbean, Europe, and Australia.

Description: Resonant satellites requirements for gravimetric satellite geodesy, discussing earth gravitational field spherical harmonic extension and tesseral harmonics from satellite perturbations