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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

On least squares collocation

It is shown that the least squares collocation approach to estimating geodetic parameters is identical to conventional minimum variance estimation. Hence, the least squares collocation estimator can be derived either by minimizing the usual least squares quadratic loss function or by computing a conditional expectation by means of the regression equation. When a deterministic functional relationship between the data and the parameters to be estimated is available, one can implement a least squares solution using the functional relation to obtain an equation of condition. It is proved the solution so obtained is identical to what is obtained through least squares collocation. The implications of this equivalance for the estimation of mean gravity anomalies are discussed.

Argentiero, P. D.↗
NASA NTRS1978

Research in support of the EODAP validation program and solid earth geophysics

A validation program to verify that geodetic space techniques can measure intersite distances of several hundred to several thousand kilometers and polar motion, both with a precision of about 5 cm is described. Laser data were analyzed using a new analytical approach "scalar translocation." It was found that this approach can give geodynamic information and that the method is promising and can be used on a variety of satellites with data of different accuracy.

Gaposchkin, E. M.↗
NASA NTRS1977

Two hundred years of flight in America: A bicentennial survey

The first recorded balloon ascension in America took place on June 19, 1784, when an unmanned balloon was raised in a public demonstration at Bladensburg, Maryland. On June 24, 1784, a thirteen-year-old boy ascended in the same balloon. The history of actual flight during the nineteenth century was entirely concerned with balloons except for several gliders and models leading to the coming of the airship and the aircraft. The history of practical flight in America begins in the twentieth century. The described developments related to aerostatics are concerned with balloons, rigid airships, and blimps. In a review of the evolution of aeronautics, attention is given to general aviation and its search for a market, trends in military aeronautics, and commercial aviation. It is pointed out that American air transport had its birth on New Year's Day, 1914, at Tampa Bay, Florida. The evolution of astronautics during the period from 1957 to 1976 is also examined, taking into account scientific satellites, the Apollo project, the exploration of the planets with the aid of unmanned spacecraft, strategic reconnaissance satellites, missile alarm satellites, instrumental satellites for detecting nuclear and thermonuclear explosions, weather satellites, communications satellites, and earth resource survey and geodetic satellites.

Emme, E. M.↗
NASA NTRS1978

A picosecond resolution Time Digitizer for laser ranging

The Time Digitizer capable of covering a range of 0.34 sec in 9.76 psec increments is described. The time interval between a pair of start-stop pulses is digitized coarsely in 20 nsec periods by a very accurate 50 MHz reference clock. The residual fractions of a clock period at the start and the stop end of the measured interval are stretched in two interpolators and digitized in 9.76 psec increments. An equivalent digitizing frequency of 102.4 GHz is thus achieved. The digitizer is built in a minicrate and communicates via a standard crate controller. It is intended for use in the laser ranging between ground stations and the Laser Geodetic Satellite (LAGEOS). It is shown that the distribution in any two adjacent 9.76 psec channels of a small number of identical test time intervals is essentially binomial. The performance of the digitizer and test results are given.

Turko, B.↗
NASA NTRS1978

The behavior of a convergent plate boundary - Crustal deformation in the South Kanto district, Japan

The northwesternmost part of the Sagami trough, a part of the Philippine Sea-Eurasian plate boundary, was ruptured during the great South Kanto earthquake in 1923. Very extensive and frequent geodetic measurements of crustal deformation have been made in the South Kanto district since the 1890's, and these constitute the most complete data set on crustal movements in the world. These data were reanalyzed and interpreted and according to our interpretation indicate the following sequence of events. The coseismic movements were due to oblique thrust and right lateral slip of about 8 m on a fault outcropping at the base of the Sagami trough. This was followed by postseismic deformation resulting from reversed afterslip of 20-60 cm that occurred at an exponentially decaying rate in time. The interseismic deformation is produced by steady subduction at a rate of about 1.8 cm/yr. During subduction the top 10-15 km of the plate boundary is apparently locked, while deeper parts slip aseismically at an irregular rate. No significant precursory deformation was observed. The recurrence time for 1923 type earthquakes is 200-300 years. The Boso and Miura peninsulas are broken into a series of fault-bound blocks that move semi-independently of the surrounding region. The subduction zone itself, where it is exposed on land, is shown to be a wide zone encompassing several faults that are active at different times.

Scholz, C. H.↗
NASA NTRS1977

On the definition of the Listing-geoid taking into consideration different height systems

An attempt is made to define the geoid on the basis of geodetic height systems determined from sea-surface topographic data. Existing height systems are corrected using sea-surface data. An equipotential surface is then chosen in such a way as to minimize the sum of the squares of the deviations from the corrected height systems. This equipotential surface is defined as the geoid. A least squares procedure is used to realize this definition.

Lelgemann, D.↗
NASA NTRS1977

Precision gravity detection - Gradiometry and/or radiometry

Current knowledge concerning the earth's gravity field is limited to about 1500-2000 km resolution. However, the resolution of gravity anomalies having a spatial extent of 100-1000 km over the entire globe is needed for important geophysical and geodetic applications. In the near future satellite altimetry will be used to determine the ocean geoid at the 10 cm - 1 m level. In order to provide a similar level of resolutions over the land regions, there exists a need for utilizing new promising techniques such as gravity gradiometry and new radiometric measurements, viz., satellite-to-satellite tracking. Satellite-to-satellite tracking techniques have shown potential for improving the medium wavelength component of the gravity field. The gravity gradiometer has not yet been tested on board a satellite. The reported analysis includes a simplified theoretical model to compare the effectiveness of the gradiometer measurements and radiometric measurements for high resolution gravity field determination, and the direct estimation of local gravity anomalies represented by point masses using a simulated gravity gradiometer and satellite-to-satellite tracking data.

Ananda, M.↗
NASA NTRS1978

Microwave radiometer measurement of water vapor path delay: Data reduction techniques

Data reduction techniques are developed to compensate for water vapor path delay, a limiting error source in geodetic measurements made with very long baseline interferometry and in radio ranging to spacecraft. It is shown that water vapor path delay is proportional to a linear combination of saturation-corrected sky brightness temperatures, measured on and off the water vapor line. The effects of emission from liquid water droplets in clouds as well as most of the oxygen emission are removed by the off-line channel. Sky brightness temperatures are saturation-corrected or 'linearized' using estimates of effective sky temperatures made from surface temperature. Tipping curves are used to remove instrumental error. Coefficients are found by two methods: from a regression analysis of measured brightness temperatures versus radiosonde measured delay, and from a regression analysis of theoretical brightness temperatures versus radiosonde measured delay. In each case the coefficients are adjusted for differing climatic conditions by measurements of surface temperature, pressure, and relative humidity. Regression solutions are constrained to remove liquid water contributions and to give the correct slope for radiometer versus radiosonde path delay.

Claflin, E. S.↗
NASA NTRS1978

High-precision gravimetric survey in support of lunar laser ranging at Haleakala, Maui, 1976 - 1978

The planning, observations and adjustment of high-precision gravity survey networks established on the islands of Maui and Oahu as part of the geodetic-geophysical program in support of lunar laser ranging at Haleakala, Maui, Hawaii are described. The gravity survey networks include 43 independently measured gravity differences along the gravity calibration line from Kahului Airport to the summit of Mt. Haleakala, together with some key points close to tidal gauges on Maui, and 40 gravity differences within metropolitan Honolulu. The results of the 1976-1978 survey are compared with surveys made in 1961 and in 1964-1965. All final gravity values are given in the system of the international gravity standardization net 1971 (IGSN 71); values are obtained by subtracting 14.57 mgal from the Potsdam value at the gravity base station at the Hickam Air Force Base, Honolulu.

Schenck, B. E.↗
NASA NTRS1978

Applications of Geodesy to Geodynamics, an International Symposium

Geodetic techniques in detecting and monitoring geodynamic phenomena are reviewed. Specific areas covered include: rotation of the earth and polar motion; tectonic plate movements and crustal deformations (space techniques); horizontal crustal movements (terrestrial techniques); vertical crustal movements (terrestrial techniques); gravity field, geoid, and ocean surface by space techniques; surface gravity and new techniques for the geophysical interpretation of gravity and geoid undulation; and earth tides and geodesy.

Mueller, I. I.↗
NASA NTRS1978

Principles of very-long-baseline interferometry

The basic principles of very-long-baseline interferometry as related to its use in the determination of vector baselines, polar motion, and earth rotation are presented. Aspects relevant to geodetic applications that involve observations of extragalactic radio sources are covered. The instrumentation used in these observations and the basic observables and their simplest interpretation are described. Complications of the interpretation due to the various geophysical 'signals' and nongeophysical 'noise' that affect the observables are considered.

Shapiro, I. I.↗
NASA NTRS1978

Detection of horizontal crustal movements by photogrammetric methods

The photogrammetric methods can be applied only if the horizontal displacements of the ground are of the order of several centimeters, because the standard error of the points so determined cannot, at the present time, be smaller than two centimeters. The procedure to be adopted, which has already been applied with satisfactory results for the densification of geodetic nets, is the aerial analytical triangulation. The taking can be executed with wide-angle cameras (f = 15 cm), or normal-angle cameras (f = 30 cm) and format 23 x 23 cm. Since the average scale of photos must be chosen in relation with the desired accuracy and then is independent of the principal distance of the cameras, the number of photos is constant, whereas the flying height varies according to the focal length.

Solaini, L.↗
NASA NTRS1978

Sea level data and techniques for detecting vertical crustal movements

An attempt is made to survey problems, requirements, and the outlook for the future in the study of sea level time series so as to determine the relative movement of land and sea levels. The basic aim is to eliminate from the record the contributions from whatever marine dynamic phenomena respond to treatment, allowing the secular element to be identified with optimum clarity. Nevertheless the concept of sea level perturbation varies according to regional experience. The recent work of the Permanent Service for Mean Sea Level helps to eliminate geodetic noise from the series and makes it possible, perhaps, to treat the global mean sea level data bank so as to define eustatic changes in ocean volume which, in the present context, may be regarded as the final goal, allowing the identification of vertical crustal motion itself.

Lennon, G. W.↗
NASA NTRS1978

World gravity standards

In order to use gravity anomalies in geodetic computations and geophysical interpretations, the observed gravity values from which anomalies are derived should be referred to one consistent world wide system. The International Gravity Standardization Net 1971 was adapted by the International Union of Geodesy and Geophysics at Moscow in 1971, the network was result of extensive cooperation by many organizations and individuals around the world. The network contains more than 1800 stations around the world. The data used in the adjustment included more than 25,000 gravimetry, pendulum and absolute measurements.

Uotila, U. A.↗
NASA NTRS1978

The influence of earth tides on earth's coordinates

The importance of the Earth's tides on Earth coordinates were examined for the following reasons: (1) the precision for obtaining the Earth's coordinates shows that the effects of Earth tides appear on the values obtained for the coordinates; (2) the possibility of determining the values of the Earth tides; and (3) the consideration of theoretical models that can compute the values of Earth tides. The astronomical and geodetic coordinates of a point at the Earth's surface are described.

Vincente, R. O.↗
NASA NTRS1979

Multiple scene attitude estimator performance for LANDSAT-1

Initial results are presented to demonstrate the performance of a linear sequential estimator (Kalman Filter) used to estimate a LANDSAT 1 spacecraft attitude time series defined for four scenes. With the revised estimator a GCP poor scene - a scene with no usable geodetic control points (GCPs) - can be rectified to higher accuracies than otherwise based on the use of GCPs in adjacent scenes. Attitude estimation errors was determined by the use of GCPs located in the GCP-poor test scene, but which are not used to update the Kalman filter. Initial results achieved indicate that errors of 500m (rms) can be attained for the GCP-poor scenes. Operational factors are related to various scenarios.

Rifman, S. S.↗
NASA NTRS1979

Tectonic motion site survey of the National Radio Astronomy Observatory, Green Bank, West Virginia

A geological and geophysical site survey was made of the area around the National Radio Astronomy Observatory (NRAO) to determine whether there are at present local tectonic movements that could introduce significant errors to Very Long Baseline Interferometry (VLBI) geodetic measurements. The site survey consisted of a literature search, photogeologic mapping with Landsat and Skylab photographs, a field reconnaissance, and installation of a seismometer at the NRAO. It is concluded that local tectonic movement will not contribute significantly to VLBI errors. It is recommended that similar site surveys be made of all locations used for VLBI or laser ranging.

Webster, W. J., Jr.↗