An analysis of tide-gauge and atmospheric data reveals that a transient, unusual sea-level drop occurred in mid-April 1997 along coasts of the Nisyros island volcano, SE Aegean Sea. This event had an ...amplitude several times larger than the average tidal range (∼6 cm) and caused a transient shift of coastal biological zones and a biological anomaly, the signs of which survived for at least one year. This proves first, that the observed sea-level low was an effect of meteorological origin, not related to a clustering of seismicity which affected Nisyros and the wider area. Second, that the coastal biological zoning and the Biological Mean Sea Level (BMSL) are stable and characteristic in each site, and do not depend on short-wavelength fluctuations of the sea level. And third, that biological observations can be used to identify the detailed history of recent sea-level changes caused by tectonic, volcanic or even meteorological effects; the amplitude of such changes may be as low as a few tens of centimeters. An implication of the above is that in rocky, nearly tideless and low-energy coasts, BMSL (which generally corresponds to the Mean Low Waters during spring tides) approximates Mean Sea Level (MSL) with an accuracy similar to that obtained from ∼1 year long tide-gauge records, and therefore can define a geodetic datum suitable for all engineering projects.
The technical aspects of delimiting, depicting, and recovering international maritime boundaries are addressed. Potential sources of error in the delimitation, depiction, and recovery of boundaries ...are exposed, and recommendations are made for avoiding errors in the future. Recent technological advances in the field of international maritime boundary making are discussed. The technical information provided in international maritime boundary treaties signed between 1940 and 1991 is analyzed.
This paper analyses the problem of conversion of space coordinates into coordinate system of planes and vice versa. It also examines the issue of conversion of geodetic coordinates of standard ...ellipsoids used in our country and the countries in the region. Basic assumptions and problems related to the conversion and the methods of projecting the coordinates to a plane are presented. The second part gives an outline of a newly developed software module which provides a high- precision conversion of coordinates. This software module is primarily intended to be used in the RF spectrum planning, GPS positioning, etc.
This paper recounts the conventional geodetic accomplishments of the Defense Mapping Agency (DMA) and its predecessor organizations in Africa, beginning with the 30th Meridian Arc in the early 1950's ...and continuing through the 12th Parallel Survey, which was completed in 1970. Additionally, it identifies the modernization resulting from the many Doppler geodetic positions, referenced to DMA's precise Navy Navigation Satellite ephemerides, established to date throughout the continent. Further it provides a conceptual plan for accomplishing, through bilateral agreements with the countries involved unification of the African datum by means of future efforts of Doppler data acquisition and reduction/adjustments of geodetic control.
This paper proposes a new method of deriving 9-parameter affine 3D datum transformations by ordinary least-squares. Unlike previous methods, it covers all versions of the transformation. Initially, ...an 'average' scale factor is computed by distance analysis. Removing the scaling effect, the 'RIGOPT' subroutine is applied to optimise the rigid transformation that consists of 3 translations and 3 rotations. Using an equivalent enlargement hypothesis, the number of scale factors is increased to 3 by a short series of single-search-direction optimisations. The minimisation of residuals is verified by enclosing-interval analysis. The case studies cover datasets in Western Australia, Great Britain and Sweden.
Using geodetic and oceanographic data, we show that the apparent north‐south slope between the Australian Height Datum (AHD) and the geoid is caused almost completely by the ocean's time‐mean dynamic ...topography (MDT). This is because the AHD was constrained to zero height at local mean sea level at multiple tide gauges around the Australian continent. Using MDT models and corrected leveling data, almost all of the apparent north‐south slope can be removed from the AHD. An auxiliary observation is that a satellite‐only MDT model based on only around one year of GOCE data generates results commensurate with geodetic, oceanographic and combined MDT models.
Key Points
MDT explains north‐south tilt in AHD
The apparent sea level slope problem in Australia is solved
GOCE‐based MDT models show promise
This paper proposes a new method of deriving rigorously-conformal 7-parameter 3D coordinate transformations between geodetic datums. The problem of linearisation is reduced by distance analysis which ...provides an estimate of scale-change. The resulting 6-parameter transformation is linearised to enable an initial least-squares estimate of the rotation parameters. The 6-parameter transformation is then re-linearised to obtain a least-squares estimate of the corrections to the rotations. The validity of the scale-change estimate can be tested and is verified in almost all cases. The exception is transformations covering very small areas where short distances maximise the impact of measurement errors in the control data. Even there, the method can be adapted to optimise the transformation. The method can also be used to obtain pseudo-optimal conformal transformations that provide a closest fit to published Bursa-Wolf transformations.
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